Quantum Entanglement in Open Systems
Isar, Aurelian
2008-01-24
In the framework of the theory of open systems based on completely positive quantum dynamical semigroups, the master equation for two independent harmonic oscillators interacting with an environment is solved in the asymptotic long-time regime. Using the Peres-Simon necessary and sufficient condition for separability of two-mode Gaussian states, we show that the two non-interacting systems become asymptotically entangled for certain environments, so that in the long-time regime they manifest non-local quantum correlations. We calculate also the logarithmic negativity characterizing the degree of entanglement of the asymptotic state.
Perturbative approach to Markovian open quantum systems
Li, Andy C. Y.; Petruccione, F.; Koch, Jens
2014-01-01
The exact treatment of Markovian open quantum systems, when based on numerical diagonalization of the Liouville super-operator or averaging over quantum trajectories, is severely limited by Hilbert space size. Perturbation theory, standard in the investigation of closed quantum systems, has remained much less developed for open quantum systems where a direct application to the Lindblad master equation is desirable. We present such a perturbative treatment which will be useful for an analytical understanding of open quantum systems and for numerical calculation of system observables which would otherwise be impractical. PMID:24811607
Repeated interactions in open quantum systems
Bruneau, Laurent; Joye, Alain; Merkli, Marco
2014-07-15
Analyzing the dynamics of open quantum systems has a long history in mathematics and physics. Depending on the system at hand, basic physical phenomena that one would like to explain are, for example, convergence to equilibrium, the dynamics of quantum coherences (decoherence) and quantum correlations (entanglement), or the emergence of heat and particle fluxes in non-equilibrium situations. From the mathematical physics perspective, one of the main challenges is to derive the irreversible dynamics of the open system, starting from a unitary dynamics of the system and its environment. The repeated interactions systems considered in these notes are models of non-equilibrium quantum statistical mechanics. They are relevant in quantum optics, and more generally, serve as a relatively well treatable approximation of a more difficult quantum dynamics. In particular, the repeated interaction models allow to determine the large time (stationary) asymptotics of quantum systems out of equilibrium.
Mechanism for quantum speedup in open quantum systems
NASA Astrophysics Data System (ADS)
Liu, Hai-Bin; Yang, W. L.; An, Jun-Hong; Xu, Zhen-Yu
2016-02-01
The quantum speed limit (QSL) time for open system characterizes the most efficient response of the system to the environmental influences. Previous results showed that the non-Markovianity governs the quantum speedup. Via studying the dynamics of a dissipative two-level system, we reveal that the non-Markovian effect is only the dynamical way of the quantum speedup, while the formation of the system-environment bound states is the essential reason for the quantum speedup. Our attribution of the quantum speedup to the energy-spectrum character can supply another vital path for experiments when the quantum speedup shows up without any dynamical calculations. The potential experimental observation of our quantum speedup mechanism in the circuit QED system is discussed. Our results may be of both theoretical and experimental interest in exploring the ultimate QSL in realistic environments, and may open new perspectives for devising active quantum speedup devices.
Quantum Simulation for Open-System Dynamics
NASA Astrophysics Data System (ADS)
Wang, Dong-Sheng; de Oliveira, Marcos Cesar; Berry, Dominic; Sanders, Barry
2013-03-01
Simulations are essential for predicting and explaining properties of physical and mathematical systems yet so far have been restricted to classical and closed quantum systems. Although forays have been made into open-system quantum simulation, the strict algorithmic aspect has not been explored yet is necessary to account fully for resource consumption to deliver bounded-error answers to computational questions. An open-system quantum simulator would encompass classical and closed-system simulation and also solve outstanding problems concerning, e.g. dynamical phase transitions in non-equilibrium systems, establishing long-range order via dissipation, verifying the simulatability of open-system dynamics on a quantum Turing machine. We construct an efficient autonomous algorithm for designing an efficient quantum circuit to simulate many-body open-system dynamics described by a local Hamiltonian plus decoherence due to separate baths for each particle. The execution time and number of gates for the quantum simulator both scale polynomially with the system size. DSW funded by USARO. MCO funded by AITF and Brazilian agencies CNPq and FAPESP through Instituto Nacional de Ciencia e Tecnologia-Informacao Quantica (INCT-IQ). DWB funded by ARC Future Fellowship (FT100100761). BCS funded by AITF, CIFAR, NSERC and USARO.
Zeno dynamics in quantum open systems.
Zhang, Yu-Ran; Fan, Heng
2015-01-01
Quantum Zeno effect shows that frequent observations can slow down or even stop the unitary time evolution of an unstable quantum system. This effect can also be regarded as a physical consequence of the statistical indistinguishability of neighboring quantum states. The accessibility of quantum Zeno dynamics under unitary time evolution can be quantitatively estimated by quantum Zeno time in terms of Fisher information. In this work, we investigate the accessibility of quantum Zeno dynamics in quantum open systems by calculating noisy Fisher information when a trace preserving and completely positive map is assumed. We firstly study the consequences of non-Markovian noise on quantum Zeno effect and give the exact forms of the dissipative Fisher information and the quantum Zeno time. Then, for the operator-sum representation, an achievable upper bound of the quantum Zeno time is given with the help of the results in noisy quantum metrology. It is of significance that the noise reducing the accuracy in the entanglement-enhanced parameter estimation can conversely be favorable for the accessibility of quantum Zeno dynamics of entangled states. PMID:26099840
Zeno dynamics in quantum open systems
NASA Astrophysics Data System (ADS)
Zhang, Yu-Ran; Fan, Heng
2015-06-01
Quantum Zeno effect shows that frequent observations can slow down or even stop the unitary time evolution of an unstable quantum system. This effect can also be regarded as a physical consequence of the statistical indistinguishability of neighboring quantum states. The accessibility of quantum Zeno dynamics under unitary time evolution can be quantitatively estimated by quantum Zeno time in terms of Fisher information. In this work, we investigate the accessibility of quantum Zeno dynamics in quantum open systems by calculating noisy Fisher information when a trace preserving and completely positive map is assumed. We firstly study the consequences of non-Markovian noise on quantum Zeno effect and give the exact forms of the dissipative Fisher information and the quantum Zeno time. Then, for the operator-sum representation, an achievable upper bound of the quantum Zeno time is given with the help of the results in noisy quantum metrology. It is of significance that the noise reducing the accuracy in the entanglement-enhanced parameter estimation can conversely be favorable for the accessibility of quantum Zeno dynamics of entangled states.
Zeno dynamics in quantum open systems
Zhang, Yu-Ran; Fan, Heng
2015-01-01
Quantum Zeno effect shows that frequent observations can slow down or even stop the unitary time evolution of an unstable quantum system. This effect can also be regarded as a physical consequence of the statistical indistinguishability of neighboring quantum states. The accessibility of quantum Zeno dynamics under unitary time evolution can be quantitatively estimated by quantum Zeno time in terms of Fisher information. In this work, we investigate the accessibility of quantum Zeno dynamics in quantum open systems by calculating noisy Fisher information when a trace preserving and completely positive map is assumed. We firstly study the consequences of non-Markovian noise on quantum Zeno effect and give the exact forms of the dissipative Fisher information and the quantum Zeno time. Then, for the operator-sum representation, an achievable upper bound of the quantum Zeno time is given with the help of the results in noisy quantum metrology. It is of significance that the noise reducing the accuracy in the entanglement-enhanced parameter estimation can conversely be favorable for the accessibility of quantum Zeno dynamics of entangled states. PMID:26099840
Controlling open quantum systems: Tools, achievements, limitations
NASA Astrophysics Data System (ADS)
Koch, Christiane
2015-03-01
Quantum control is an important prerequisite for quantum devices. A major obstacle is the fact that a quantum system can never completely be isolated from its environment. The interaction with the environment causes decoherence. Optimal control theory is a tool that can be used to identify control strategies in the presence of decoherence. I will show how to adapt optimal control theory to quantum information tasks for open quantum systems and present examples for cold atoms and superconducting qubits. In particular, I will discuss how non-Markovianity of the open system time evolution can be exploited for control. The perspective on decoherence only as the adversary of quantum control is nevertheless too narrow. There exist a number of control tasks, such as cooling and measurement, that can only be achieved by an interplay of control and dissipation. I will show how to utilize optimal control theory to derive efficient cooling strategies when the timescales of coherent dynamics and dissipation are very different. Our approach can be generalized to quantum reservoir engineering, opening up new avenues for control.
Quantum Entanglement and Quantum Discord in Gaussian Open Systems
Isar, Aurelian
2011-10-03
In the framework of the theory of open systems based on completely positive quantum dynamical semigroups, we give a description of the continuous-variable quantum entanglement and quantum discord for a system consisting of two noninteracting modes embedded in a thermal environment. Entanglement and discord are used to quantify the quantum correlations of the system. For all values of the temperature of the thermal reservoir, an initial separable Gaussian state remains separable for all times. In the case of an entangled initial Gaussian state, entanglement suppression (entanglement sudden death) takes place for non-zero temperatures of the environment. Only for a zero temperature of the thermal bath the initial entangled state remains entangled for finite times. We analyze the time evolution of the Gaussian quantum discord, which is a measure of all quantum correlations in the bipartite state, including entanglement, and show that quantum discord decays asymptotically in time under the effect of the thermal bath.
From Classical to Quantum Theory of Open Systems
NASA Astrophysics Data System (ADS)
Klimontovich, Yu. L.
The paper consists of a short survey of some results concerning the physical interpretation the basic equations for quantum open systems. The concept of a continuous medium for quantum systems is introduced. From this point of view the question of completeness description and the hidden parameters (scales) for quantum open systems is considered. The Heisenberg uncertainty principle in the physics of open quantum systems is represented. The question: Is the concept of “pure ensemble” justified in quantum mechanics is also discussed.
Open quantum systems and random matrix theory
Mulhall, Declan
2014-10-15
A simple model for open quantum systems is analyzed with RMT. The system is coupled to the continuum in a minimal way. In this paper we see the effect of opening the system on the level statistics, in particular the level spacing, width distribution and Î”{sub 3}(L) statistic are examined as a function of the strength of this coupling. The usual super-radiant state is observed, and it is seen that as it is formed, the level spacing and Î”{sub 3}(L) statistic exhibit the signatures of missed levels.
Current in open quantum systems.
Gebauer, Ralph; Car, Roberto
2004-10-15
We show that a dissipative current component is present in the dynamics generated by a Liouville-master equation, in addition to the usual component associated with Hamiltonian evolution. The dissipative component originates from coarse graining in time, implicit in a master equation, and needs to be included to preserve current continuity. We derive an explicit expression for the dissipative current in the context of the Markov approximation. Finally, we illustrate our approach with a simple numerical example, in which a quantum particle is coupled to a harmonic phonon bath and dissipation is described by the Pauli master equation. PMID:15524960
Relativistic Quantum Metrology in Open System Dynamics
Tian, Zehua; Wang, Jieci; Fan, Heng; Jing, Jiliang
2015-01-01
Quantum metrology studies the ultimate limit of precision in estimating a physical quantity if quantum strategies are exploited. Here we investigate the evolution of a two-level atom as a detector which interacts with a massless scalar field using the master equation approach for open quantum system. We employ local quantum estimation theory to estimate the Unruh temperature when probed by a uniformly accelerated detector in the Minkowski vacuum. In particular, we evaluate the Fisher information (FI) for population measurement, maximize its value over all possible detector preparations and evolution times, and compare its behavior with that of the quantum Fisher information (QFI). We find that the optimal precision of estimation is achieved when the detector evolves for a long enough time. Furthermore, we find that in this case the FI for population measurement is independent of initial preparations of the detector and is exactly equal to the QFI, which means that population measurement is optimal. This result demonstrates that the achievement of the ultimate bound of precision imposed by quantum mechanics is possible. Finally, we note that the same configuration is also available to the maximum of the QFI itself. PMID:25609187
Relativistic quantum metrology in open system dynamics.
Tian, Zehua; Wang, Jieci; Fan, Heng; Jing, Jiliang
2015-01-01
Quantum metrology studies the ultimate limit of precision in estimating a physical quantity if quantum strategies are exploited. Here we investigate the evolution of a two-level atom as a detector which interacts with a massless scalar field using the master equation approach for open quantum system. We employ local quantum estimation theory to estimate the Unruh temperature when probed by a uniformly accelerated detector in the Minkowski vacuum. In particular, we evaluate the Fisher information (FI) for population measurement, maximize its value over all possible detector preparations and evolution times, and compare its behavior with that of the quantum Fisher information (QFI). We find that the optimal precision of estimation is achieved when the detector evolves for a long enough time. Furthermore, we find that in this case the FI for population measurement is independent of initial preparations of the detector and is exactly equal to the QFI, which means that population measurement is optimal. This result demonstrates that the achievement of the ultimate bound of precision imposed by quantum mechanics is possible. Finally, we note that the same configuration is also available to the maximum of the QFI itself. PMID:25609187
Evolution of Quantum Entanglement in Open Systems
Isar, A.
2010-08-04
In the framework of the theory of open systems based on completely positive quantum dynamical semigroups, we give a description of the continuous-variable entanglement for a system consisting of two uncoupled harmonic oscillators interacting with a thermal environment. Using Peres-Simon necessary sufficient criterion for separability of two-mode Gaussian states, we show that for some values of diffusion coefficient, dissipation constant and temperature of the environment, the state keeps for all times its initial type: separable or entangled. In other cases, entanglement generation, entanglement sudden death or a periodic collapse revival of entanglement take place.
Quantum arrival time for open systems
Yearsley, J. M.
2010-07-15
We extend previous work on the arrival time problem in quantum mechanics, in the framework of decoherent histories, to the case of a particle coupled to an environment. The usual arrival time probabilities are related to the probability current, so we explore the properties of the current for general open systems that can be written in terms of a master equation of the Lindblad form. We specialize to the case of quantum Brownian motion, and show that after a time of order the localization time of the current becomes positive. We show that the arrival time probabilities can then be written in terms of a positive operator-valued measure (POVM), which we compute. We perform a decoherent histories analysis including the effects of the environment and show that time-of-arrival probabilities are decoherent for a generic state after a time much greater than the localization time, but that there is a fundamental limitation on the accuracy {delta}t, with which they can be specified which obeys E{delta}t>>({h_bar}/2{pi}). We confirm that the arrival time probabilities computed in this way agree with those computed via the current, provided there is decoherence. We thus find that the decoherent histories formulation of quantum mechanics provides a consistent explanation for the emergence of the probability current as the classical arrival time distribution, and a systematic rule for deciding when probabilities may be assigned.
Identification of open quantum systems from observable time traces
Zhang, Jun; Sarovar, Mohan
2015-05-27
Estimating the parameters that dictate the dynamics of a quantum system is an important task for quantum information processing and quantum metrology, as well as fundamental physics. In our paper we develop a method for parameter estimation for Markovian open quantum systems using a temporal record of measurements on the system. Furthermore, the method is based on system realization theory and is a generalization of our previous work on identification of Hamiltonian parameters.
Quantum coherence and noise in open quantum systems
NASA Astrophysics Data System (ADS)
Nazir, Ahsan
2013-03-01
Recent experiments demonstrating signatures of quantum coherence in the excitonic energy transfer dynamics of a variety of systems have sparked renewed interest in the theoretical modelling of energy transfer processes within a dissipative environment. A major challenge remains the development of techniques that allow one to probe the diverse parameter regimes relevant to such systems. Master equation methods provide useful tools with which to efficiently analyse energy transfer dynamics in open quantum systems. However, they are often valid only in rather restrictive parameter regimes, limiting their applicability in the present context. Here, I shall present a versatile variational master equation approach to the non-equilibrium dynamics of dissipative excitonic quantum systems, which allows for the exploration of a wide range of parameter regimes within a single formalism. Derived through the combination of a variationally optimised unitary transformation and the time-local projection operator technique, the master equation can be applied to a range of bath spectral densities, temperatures, and system-bath coupling strengths, and accounts for both non-Markovian and non-equilibrium environmental effects. Applying the formalism in the case of excitonic energy transfer, I shall show that while it correctly reproduces Redfield, polaron, and Foerster dynamics in the appropriate limits, it can also be used in intermediate regimes where none of these theories may be applicable. I shall also discuss the extension of the theory to many-site energy transfer systems Variational master equations thus represent a promising avenue for the exploration of (essentially non-perturbative) dissipative dynamics in a variety of physical systems.
Conserved current in Markovian open-quantum systems
Bodor, Andras; Diosi, Lajos
2006-06-15
We reexamine the Markovian approximation of local current in open quantum systems, discussed recently by Gebauer and Car. Our derivation is more transparent; the proof of the current conservation becomes explicit and easy.
Identification of open quantum systems from observable time traces
NASA Astrophysics Data System (ADS)
Zhang, Jun; Sarovar, Mohan
2015-05-01
Estimating the parameters that dictate the dynamics of a quantum system is an important task for quantum information processing and quantum metrology, as well as fundamental physics. In this paper we develop a method for parameter estimation for Markovian open quantum systems using a temporal record of measurements on the system. The method is based on system realization theory and is a generalization of our previous work on identification of Hamiltonian parameters [Phys. Rev. Lett. 113, 080401 (2014), 10.1103/PhysRevLett.113.080401].
Dynamics of open bosonic quantum systems in coherent state representation
Dalvit, D. A. R.; Berman, G. P.; Vishik, M.
2006-01-15
We consider the problem of decoherence and relaxation of open bosonic quantum systems from a perspective alternative to the standard master equation or quantum trajectories approaches. Our method is based on the dynamics of expectation values of observables evaluated in a coherent state representation. We examine a model of a quantum nonlinear oscillator with a density-density interaction with a collection of environmental oscillators at finite temperature. We derive the exact solution for dynamics of observables and demonstrate a consistent perturbation approach.
Driven harmonic oscillator as a quantum simulator for open systems
Piilo, Jyrki; Maniscalco, Sabrina
2006-09-15
We show theoretically how a driven harmonic oscillator can be used as a quantum simulator for the non-Markovian damped harmonic oscillator. In the general framework, our results demonstrate the possibility to use a closed system as a simulator for open quantum systems. The quantum simulator is based on sets of controlled drives of the closed harmonic oscillator with appropriately tailored electric field pulses. The non-Markovian dynamics of the damped harmonic oscillator is obtained by using the information about the spectral density of the open system when averaging over the drives of the closed oscillator. We consider single trapped ions as a specific physical implementation of the simulator, and we show how the simulator approach reveals physical insight into the open system dynamics, e.g., the characteristic quantum mechanical non-Markovian oscillatory behavior of the energy of the damped oscillator, usually obtained by the non-Lindblad-type master equation, can have a simple semiclassical interpretation.
Investigating non-Markovian dynamics of quantum open systems
NASA Astrophysics Data System (ADS)
Chen, Yusui
Quantum open system coupled to a non-Markovian environment has recently attracted widespread interest for its important applications in quantum information processing and quantum dissipative systems. New phenomena induced by the non-Markovian environment have been discovered in variety of research areas ranging from quantum optics, quantum decoherence to condensed matter physics. However, the study of the non-Markovian quantum open system is known a difficult problem due to its technical complexity in deriving the fundamental equation of motion and elusive conceptual issues involving non-equilibrium dynamics for a strong coupled environment. The main purpose of this thesis is to introduce several new techniques of solving the quantum open systems including a systematic approach to dealing with non-Markovian master equations from a generic quantum-state diffusion (QSD) equation. In the first part of this thesis, we briefly introduce the non-Markovian quantum-state diffusion approach, and illustrate some pronounced non-Markovian quantum effects through numerical investigation on a cavity-QED model. Then we extend the non-Markovian QSD theory to an interesting model where the environment has a hierarchical structure, and find out the exact non-Markovian QSD equation of this model system. We observe the generation of quantum entanglement due to the interplay between the non-Markovian environment and the cavity. In the second part, we show an innovative method to obtain the exact non-Markovian master equations for a set of generic quantum open systems based on the corresponding non-Markovian QSD equations. Multiple-qubit systems and multilevel systems are discussed in details as two typical examples. Particularly, we derive the exact master equation for a model consisting of a three-level atom coupled to an optical cavity and controlled by an external laser field. Additionally, we discuss in more general context the mathematical similarity between the multiple-qubit systems and multilevel systems. Based on our systematic method, we also show how to solve different types of models. In the last part, we use Heisenberg equations of motion and quantum trajectory approach to obtain the exact master equation for a quantum harmonic oscillator chains coupled to two finite temperature environments. The derived exact non-Markovian master equation is useful for exploration of quantum transport and quantum coherence dynamics.
Geometric phase for open quantum systems and stochastic unravelings
Bassi, Angelo; Ippoliti, Emiliano
2006-06-15
We analyze the geometric phase for an open quantum system when computed by resorting to a stochastic unraveling of the reduced density matrix (quantum jump approach or stochastic Schroedinger equations). We show that the resulting phase strongly depends on the type of unraveling used for the calculations: as such, this phase is not a geometric object since it depends on nonphysical parameters, which are not related to the path followed by the density matrix during the evolution of the system.
Quantum Information Biology: From Theory of Open Quantum Systems to Adaptive Dynamics
NASA Astrophysics Data System (ADS)
Asano, Masanari; Basieva, Irina; Khrennikov, Andrei; Ohya, Masanori; Tanaka, Yoshiharu; Yamato, Ichiro
This chapter reviews quantum(-like) information biology (QIB). Here biology is treated widely as even covering cognition and its derivatives: psychology and decision making, sociology, and behavioral economics and finances. QIB provides an integrative description of information processing by bio-systems at all scales of life: from proteins and cells to cognition, ecological and social systems. Mathematically QIB is based on the theory of adaptive quantum systems (which covers also open quantum systems). Ideologically QIB is based on the quantum-like (QL) paradigm: complex bio-systems process information in accordance with the laws of quantum information and probability. This paradigm is supported by plenty of statistical bio-data collected at all bio-scales. QIB re ects the two fundamental principles: a) adaptivity; and, b) openness (bio-systems are fundamentally open). In addition, quantum adaptive dynamics provides the most generally possible mathematical representation of these principles.
Nonlocal Memory Effects in the Dynamics of Open Quantum Systems
NASA Astrophysics Data System (ADS)
Laine, Elsi-Mari; Breuer, Heinz-Peter; Piilo, Jyrki; Li, Chuan-Feng; Guo, Guang-Can
2012-05-01
We explore the possibility to generate nonlocal dynamical maps of an open quantum system through local system-environment interactions. Employing a generic decoherence process induced by a local interaction Hamiltonian, we show that initial correlations in a composite environment can lead to nonlocal open system dynamics which exhibit strong memory effects, although the local dynamics is Markovian. In a model of two entangled photons interacting with two dephasing environments, we find a direct connection between the degree of memory effects and the amount of correlation in the initial environmental state. The results demonstrate that, contrary to conventional wisdom, enlarging an open system can change the dynamics from Markovian to non-Markovian.
Quasiprobability distributions in open quantum systems: Spin-qubit systems
NASA Astrophysics Data System (ADS)
Thapliyal, Kishore; Banerjee, Subhashish; Pathak, Anirban; Omkar, S.; Ravishankar, V.
2015-11-01
We study nonclassical features in a number of spin-qubit systems including single, two and three qubit states, as well as an N qubit Dicke model and a spin-1 system, of importance in the fields of quantum optics and information. This is done by analyzing the behavior of the well known Wigner, P, and Q quasiprobability distributions on them. We also discuss the not so well known F function and specify its relation to the Wigner function. Here we provide a comprehensive analysis of quasiprobability distributions for spin-qubit systems under general open system effects, including both pure dephasing as well as dissipation. This makes it relevant from the perspective of experimental implementation.
Eigenvalue problem of the Liouvillian of open quantum systems
Hatano, Naomichi; Petrosky, Tomio
2015-03-10
It is argued that the Liouvillian that appears in the Liouville-von Neumann equation for open quantum systems can have complex eigenvalues. Attention is paid to the question whether the Liouvillian has an eigenvalue that are not given by the difference of the two Hamiltonian eigenvalues.
Coherently tracking the covariance matrix of an open quantum system
NASA Astrophysics Data System (ADS)
Miao, Zibo; Hush, Michael R.; James, Matthew R.
2015-07-01
Coherent feedback control of quantum systems has demonstrable advantages over measurement-based control, but so far there has been little work done on coherent estimators and more specifically coherent observers. Coherent observers are input the coherent output of a specified quantum plant and are designed such that some subset of the observer's and plant's expectation values converge in the asymptotic limit. We previously developed a class of mean tracking (MT) observers for open harmonic oscillators that only converged in mean position and momentum; here we develop a class of covariance matrix tracking (CMT) coherent observers that track both the mean and the covariance matrix of a quantum plant. We derive necessary and sufficient conditions for the existence of a CMT observer and find that there are more restrictions on a CMT observer than there are on a MT observer. We give examples where we demonstrate how to design a CMT observer and show that it can be used to track properties like the entanglement of a plant. As the CMT observer provides more quantum information than a MT observer, we expect it will have greater application in future coherent feedback schemes mediated by coherent observers. Investigation of coherent quantum estimators and observers is important in the ongoing discussion of quantum measurement because they provide an estimation of a system's quantum state without explicit use of the measurement postulate in their derivation.
Time evolution of open quantum many-body systems
NASA Astrophysics Data System (ADS)
Overbeck, Vincent R.; Weimer, Hendrik
2016-01-01
We establish a generic method to analyze the time evolution of open quantum many-body systems. Our approach is based on a variational integration of the quantum master equation describing the dynamics and naturally connects to a variational principle for its nonequilibrium steady state. We successfully apply our variational method to study dissipative Rydberg gases, finding very good quantitative agreement with small-scale simulations of the full quantum master equation. We observe that correlations related to non-Markovian behavior play a significant role during the relaxation dynamics towards the steady state. We further quantify this non-Markovianity and find it to be closely connected to an information-theoretical measure of quantum and classical correlations.
Control landscapes for observable preparation with open quantum systems
Wu Rebing; Pechen, Alexander; Rabitz, Herschel; Hsieh, Michael; Tsou, Benjamin
2008-02-15
A quantum control landscape is defined as the observable as a function(al) of the system control variables. Such landscapes were introduced to provide a basis to understand the increasing number of successful experiments controlling quantum dynamics phenomena. This paper extends the concept to encompass the broader context of the environment having an influence. For the case that the open system dynamics are fully controllable, it is shown that the control landscape for open systems can be lifted to the analysis of an equivalent auxiliary landscape of a closed composite system that contains the environmental interactions. This inherent connection can be analyzed to provide relevant information about the topology of the original open system landscape. Application to the optimization of an observable expectation value reveals the same landscape simplicity observed in former studies on closed systems. In particular, no false suboptimal traps exist in the system control landscape when seeking to optimize an observable, even in the presence of complex environments. Moreover, a quantitative study of the control landscape of a system interacting with a thermal environment shows that the enhanced controllability attainable with open dynamics significantly broadens the range of the achievable observable values over the control landscape.
The Kitaev-Feynman clock for open quantum systems
NASA Astrophysics Data System (ADS)
Tempel, David G.; Aspuru-Guzik, Alán
2014-11-01
We show that Kitaev's construction of Feynman's clock, in which the time-evolution of a closed quantum system is encoded as a ground state problem, can be extended to open quantum systems. In our formalism, the ground states of an ensemble of non-Hermitian Kitaev-Feynman clock Hamiltonians yield stochastic trajectories, which unravel the evolution of a Lindblad master equation. In this way, one can use the Kitaev-Feynman clock not only to simulate the evolution of a quantum system, but also its interaction with an environment such as a heat bath or measuring apparatus. A simple numerical example of a two-level atom undergoing spontaneous emission is presented and analyzed.
Hierarchy of Stochastic Pure States for Open Quantum System Dynamics
NASA Astrophysics Data System (ADS)
Suess, D.; Eisfeld, A.; Strunz, W. T.
2014-10-01
We derive a hierarchy of stochastic evolution equations for pure states (quantum trajectories) for open quantum system dynamics with non-Markovian structured environments. This hierarchy of pure states (HOPS) is generally applicable and provides the exact reduced density operator as an ensemble average over normalized states. The corresponding nonlinear equations are presented. We demonstrate that HOPS provides an efficient theoretical tool and apply it to the spin-boson model, the calculation of absorption spectra of molecular aggregates, and energy transfer in a photosynthetic pigment-protein complex.
Ab-Initio Coupled Cluster Theory for Open Quantum Systems
NASA Astrophysics Data System (ADS)
Hagen, G.; Dean, D. J.; Papenbrock, T.; Hjorth-Jensen, M.
2008-04-01
We discuss peculiarities of open-quantum systems, as compared to closed quantum systems. We emphasize the importance of taking continuum degrees of freedom into account when dealing with systems with a tendency to decay through emission of fragments. In this context we introduce the Coupled-Cluster theory, and argue that this method allows for an accurate description of such systems starting from nucleon-nucleon degrees of freedom. We present Ab-initio Coupled Cluster calculations with singles and doubles excitations (CCSD) for the ground states of the helium isotopes 3-10He. The calculated masses and decay widths are in semi-quantitative agreement with experiment. The discrepancy with experiment is suspected to be attributed to the three-nucleon force (3NF) which is not included at this point.
Stochastic theory of non-Markovian open quantum system
NASA Astrophysics Data System (ADS)
Zhao, Xinyu
In this thesis, a stochastic approach to solving non-Markovian open quantum system called "non-Markovian quantum state diffusion" (NMQSD) approach is discussed in details. The NMQSD approach can serve as an analytical and numerical tool to study the dynamics of the open quantum systems. We explore three main topics of the NMQSD approach. First, we extend the NMQSD approach to many-body open systems such as two-qubit system and coupled N-cavity system. Based on the exact NMQSD equations and the corresponding master equations, we investigate several interesting non-Markovian features due to the memory effect of the environment such as the entanglement generation in two-qubit system and the coherence and entanglement transfer between cavities. Second, we extend the original NMQSD approach to the case that system is coupled to a fermionic bath or a spin bath. By introducing the anti-commutative Grassmann noise and the fermionic coherent state, we derive a fermionic NMQSD equation and the corresponding master equation. The fermionic NMQSD is illustrated by several examples. In a single qubit dissipative example, we have explicitly demonstrated that the NMQSD approach and the ordinary quantum mechanics give rise to the exactly same results. We also show the difference between fermionic bath and bosonic bath. Third, we combine the bosonic and fermionic NMQSD approach to develop a unified NMQSD approach to study the case that an open system is coupled to a bosonic bath and a fermionic bath simultaneously. For all practical purposes, we develop a set of useful computer programs (NMQSD Toolbox) to implement the NMQSD equation in realistic computations. In particular, we develop an algorithm to calculate the exact O operator involved in the NMQSD equation. The NMQSD toolbox is designed to be user friendly, so it will be especially valuable for a non-expert who has interest to employ the NMQSD equation to solve a practical problem. Apart from the central topics on the NMQSD approach, we also study the environment-assisted error correction (EAEC) scheme. We have proposed two new schemes beyond the original EAEC scheme. Our schemes can be used to recover an unknown entangled initial state for a dephasing channel and recover an arbitrary unknown initial state for a dissipative channel using a generalized quantum measurement.
Partly invariant steady state of two interacting open quantum systems
NASA Astrophysics Data System (ADS)
Bernád, József Zsolt; Torres, Juan Mauricio
2015-12-01
We investigate two interacting open quantum systems whose time evolutions are governed by Markovian master equations. We show a class of coupled systems whose interaction leaves invariant the steady state of one of the systems, i.e., only one of the reduced steady states is sensitive to the interactions. A detailed proof with the help of the Trotter product formula is presented. We apply this general statement to a few models, one of which is the optomechanical coupling model where an optical cavity is coupled to a small mechanical oscillator.
Dynamical invariants and nonadiabatic geometric phases in open quantum systems
Sarandy, M. S.; Duzzioni, E. I.; Moussa, M. H. Y.
2007-11-15
We introduce an operational framework to analyze nonadiabatic Abelian and non-Abelian, cyclic and noncyclic, geometric phases in open quantum systems. In order to remove the adiabaticity condition, we generalize the theory of dynamical invariants to the context of open systems evolving under arbitrary convolutionless master equations. Geometric phases are then defined through the Jordan canonical form of the dynamical invariant associated with the superoperator that governs the master equation. As a by-product, we provide a sufficient condition for the robustness of the phase against a given decohering process. We illustrate our results by considering a two-level system in a Markovian interaction with the environment, where we show that the nonadiabatic geometric phase acquired by the system can be constructed in such a way that it is robust against both dephasing and spontaneous emission.
Boundary driven open quantum many-body systems
Prosen, TomaÅ¾
2014-01-08
In this lecture course I outline a simple paradigm of non-eqjuilibrium quantum statistical physics, namely we shall study quantum lattice systems with local, Hamiltonian (conservative) interactions which are coupled to the environment via incoherent processes only at the system's boundaries. This is arguably the simplest nontrivial context where one can study far from equilibrium steady states and their transport properties. We shall formulate the problem in terms of a many-body Markovian master equation (the so-called Lindblad equation, and some of its extensions, e.g. the Redfield eqaution). The lecture course consists of two main parts: Firstly, and most extensively we shall present canonical Liouville-space many-body formalism, the so-called 'third quantization' and show how it can be implemented to solve bi-linear open many-particle problems, the key peradigmatic examples being the XY spin 1/2 chains or quasi-free bosonic (or harmonic) chains. Secondly, we shall outline several recent approaches on how to approach exactly solvable open quantum interacting many-body problems, such as anisotropic Heisenberg ((XXZ) spin chain or fermionic Hubbard chain.
Nontrivial Eigenvalues of the Liouvillian of an Open Quantum System
NASA Astrophysics Data System (ADS)
Nakano, Ruri; Hatano, Naomichi; Petrosky, Tomio
2011-04-01
We present methods of finding complex eigenvalues of the Liouvillian of an open quantum system. The goal is to find eigenvalues that cannot be predicted from the eigenvalues of the corresponding Hamiltonian. Our model is a T-type quantum dot with an infinitely long lead. We suggest the existence of the non-trivial eigenvalues of the Liouvillian in two ways: one way is to show that the original problem reduces to the problem of a two-particle Hamiltonian with a two-body interaction and the other way is to show that diagram expansion of the Green's function has correlation between the bra state and the ket state. We also introduce the integral equations equivalent to the original eigenvalue problem.
NASA Astrophysics Data System (ADS)
Mostame, Sarah; Rebentrost, Patrick; Eisfeld, Alexander; Kerman, Andrew J.; Tsomokos, Dimitris I.; Aspuru-Guzik, Alán
2012-10-01
Open quantum system approaches are widely used in the description of physical, chemical and biological systems. A famous example is electronic excitation transfer in the initial stage of photosynthesis, where harvested energy is transferred with remarkably high efficiency to a reaction center. This transport is affected by the motion of a structured vibrational environment, which makes simulations on a classical computer very demanding. Here we propose an analog quantum simulator of complex open system dynamics with a precisely engineered quantum environment. Our setup is based on superconducting circuits, a well established technology. As an example, we demonstrate that it is feasible to simulate exciton transport in the Fenna-Matthews-Olson photosynthetic complex. Our approach allows for a controllable single-molecule simulation and the investigation of energy transfer pathways as well as non-Markovian noise-correlation effects.
Tomograms for open quantum systems: In(finite) dimensional optical and spin systems
NASA Astrophysics Data System (ADS)
Thapliyal, Kishore; Banerjee, Subhashish; Pathak, Anirban
2016-03-01
Tomograms are obtained as probability distributions and are used to reconstruct a quantum state from experimentally measured values. We study the evolution of tomograms for different quantum systems, both finite and infinite dimensional. In realistic experimental conditions, quantum states are exposed to the ambient environment and hence subject to effects like decoherence and dissipation, which are dealt with here, consistently, using the formalism of open quantum systems. This is extremely relevant from the perspective of experimental implementation and issues related to state reconstruction in quantum computation and communication. These considerations are also expected to affect the quasiprobability distribution obtained from experimentally generated tomograms and nonclassicality observed from them.
Dynamics of incompatibility of quantum measurements in open systems
NASA Astrophysics Data System (ADS)
Addis, Carole; Heinosaari, Teiko; Kiukas, Jukka; Laine, Elsi-Mari; Maniscalco, Sabrina
2016-02-01
The nonclassical nature of quantum states, often illustrated using entanglement measures or quantum discord, constitutes a resource for quantum information protocols. However, the nonclassicality of a quantum system cannot be seen as a property of the state alone, as the set of available measurements used to extract information on the system is typically restricted. In this work we study how the nonclassicality of quantum measurements, quantified via their incompatibility, is influenced by quantum noise and how a non-Markovian environment can be useful for maintaining the measurement resources.
Landauer's Principle in Multipartite Open Quantum System Dynamics.
Lorenzo, S; McCloskey, R; Ciccarello, F; Paternostro, M; Palma, G M
2015-09-18
We investigate the link between information and thermodynamics embodied by Landauer's principle in the open dynamics of a multipartite quantum system. Such irreversible dynamics is described in terms of a collisional model with a finite temperature reservoir. We demonstrate that Landauer's principle holds, for such a configuration, in a form that involves the flow of heat dissipated into the environment and the rate of change of the entropy of the system. Quite remarkably, such a principle for heat and entropy power can be explicitly linked to the rate of creation of correlations among the elements of the multipartite system and, in turn, the non-Markovian nature of their reduced evolution. Such features are illustrated in two exemplary cases. PMID:26430974
Landauer's Principle in Multipartite Open Quantum System Dynamics
NASA Astrophysics Data System (ADS)
Lorenzo, S.; McCloskey, R.; Ciccarello, F.; Paternostro, M.; Palma, G. M.
2015-09-01
We investigate the link between information and thermodynamics embodied by Landauer's principle in the open dynamics of a multipartite quantum system. Such irreversible dynamics is described in terms of a collisional model with a finite temperature reservoir. We demonstrate that Landauer's principle holds, for such a configuration, in a form that involves the flow of heat dissipated into the environment and the rate of change of the entropy of the system. Quite remarkably, such a principle for heat and entropy power can be explicitly linked to the rate of creation of correlations among the elements of the multipartite system and, in turn, the non-Markovian nature of their reduced evolution. Such features are illustrated in two exemplary cases.
Time-dependent density functional theory for open quantum systems
NASA Astrophysics Data System (ADS)
Tempel, David; Aspuru-Guzik, Alan
2012-02-01
We present the extension of time-dependent density functional theory (TDDFT) to the realm of open quantum systems (OQS). OQS-TDDFT allows a first principles description of electronic systems undergoing non-unitary dynamics due to coupling with a bath, such as that arising from molecular vibrations, solvent degrees of freedom or photon modes of the electromagnetic field. We first prove extensions of the Runge-Gross and van Leeuwen theorems to OQS-TDDFT, which rigorously establish it as a formally exact theory. We then discuss development of approximate OQS-TDDFT functionals, exact conditions on these functionals, as well as future challenges. Finally, we will discuss the application of OQS-TDDFT in obtaining broadened absorption spectra.
Non-Markovian dynamics of open quantum systems
NASA Astrophysics Data System (ADS)
Fleming, Chris H.
An open quantum system is a quantum system that interacts with some environment whose degrees of freedom have been coarse grained away. This model describes non-equilibrium processes more general than scattering-matrix formulations. Furthermore, the microscopically-derived environment provides a model of noise, dissipation and decoherence far more general than Markovian (white noise) models. The latter are fully characterized by Lindblad equations and can be motivated phenomenologically. Non-Markovian processes consistently account for backreaction with the environment and can incorporate effects such as finite temperature and spatial correlations. We consider linear systems with bilinear coupling to the environment, or quantum Brownian motion, and nonlinear systems with weak coupling to the environment. For linear systems we provide exact solutions with analytical results for a variety of spectral densities. Furthermore, we point out an important mathematical subtlety which led to incorrect master-equation coefficients in earlier derivations, given nonlocal dissipation. For nonlinear systems we provide perturbative solutions by translating the formalism of canonical perturbation theory into the context of master equations. It is shown that unavoidable degeneracy causes an unfortunate reduction in accuracy between perturbative master equations and their solutions. We also extend the famous theorem of Lindblad, Gorini, Kossakowski and Sudarshan on completely positivity to non-Markovian master equations. Our application is primarily to model atoms interacting via a common electromagnetic field. The electromagnetic field contains correlations in both space and time, which are related to its relativistic (photon-mediated) nature. As such, atoms residing in the same field experience different environmental effects depending upon their relative position and orientation. Our more accurate solutions were necessary to assess sudden death of entanglement at zero temperature. In contrast to previous claims, we found that all initial states of two-level atoms undergo finite-time disentanglement. We were also able to access regimes which cannot be described by Lindblad equations and other simpler methods, such as near resonance. Finally we revisit the infamous Abraham-Lorentz force, wherein a single particle in motion experiences backreaction from the electromagnetic field. This leads to a number of well-known problems including pre-acceleration and runaway solutions. We found a more a more-suitable open-system treatment of the nonrelativistic particle to be perfectly causal and dissipative without any extraneous requirements for finite size of the particle, weak coupling to the field, etc..
Minimal evolution time and quantum speed limit of non-Markovian open systems
Meng, Xiangyi; Wu, Chengjun; Guo, Hong
2015-01-01
We derive a sharp bound as the quantum speed limit (QSL) for the minimal evolution time of quantum open systems in the non-Markovian strong-coupling regime with initial mixed states by considering the effects of both renormalized Hamiltonian and dissipator. For a non-Markovian quantum open system, the possible evolution time between two arbitrary states is not unique, among the set of which we find that the minimal one and its QSL can decrease more steeply by adjusting the coupling strength of the dissipator, which thus provides potential improvements of efficiency in many quantum physics and quantum information areas. PMID:26565062
Minimal evolution time and quantum speed limit of non-Markovian open systems
NASA Astrophysics Data System (ADS)
Meng, Xiangyi; Wu, Chengjun; Guo, Hong
2015-11-01
We derive a sharp bound as the quantum speed limit (QSL) for the minimal evolution time of quantum open systems in the non-Markovian strong-coupling regime with initial mixed states by considering the effects of both renormalized Hamiltonian and dissipator. For a non-Markovian quantum open system, the possible evolution time between two arbitrary states is not unique, among the set of which we find that the minimal one and its QSL can decrease more steeply by adjusting the coupling strength of the dissipator, which thus provides potential improvements of efficiency in many quantum physics and quantum information areas.
Minimal evolution time and quantum speed limit of non-Markovian open systems.
Meng, Xiangyi; Wu, Chengjun; Guo, Hong
2015-01-01
We derive a sharp bound as the quantum speed limit (QSL) for the minimal evolution time of quantum open systems in the non-Markovian strong-coupling regime with initial mixed states by considering the effects of both renormalized Hamiltonian and dissipator. For a non-Markovian quantum open system, the possible evolution time between two arbitrary states is not unique, among the set of which we find that the minimal one and its QSL can decrease more steeply by adjusting the coupling strength of the dissipator, which thus provides potential improvements of efficiency in many quantum physics and quantum information areas. PMID:26565062
NASA Astrophysics Data System (ADS)
Perdomo, Alejandro
The 20th century saw the first revolution of quantum mechanics, setting the rules for our understanding of light, matter, and their interaction. The 21st century is focused on using these quantum mechanical laws to develop technologies which allows us to solve challenging practical problems. One of the directions is the use quantum devices which promise to surpass the best computers and best known classical algorithms for solving certain tasks. Crucial to the design of realistic devices and technologies is to account for the open nature of quantum systems and to cope with their interactions with the environment. In the first part of this dissertation, we show how to tackle classical optimization problems of interest in the physical sciences within one of these quantum computing paradigms, known as quantum annealing (QA). We present the largest implementation of QA on a biophysical problem (six different experiments with up to 81 superconducting quantum bits). Although the cases presented here can be solved on a classical computer, we present the first implementation of lattice protein folding on a quantum device under the Miyazawa-Jernigan model. This is the first step towards studying optimization problems in biophysics and statistical mechanics using quantum devices. In the second part of this dissertation, we focus on the problem of excitonic energy transfer. We provide an intuitive platform for engineering exciton transfer dynamics and we show that careful consideration of the properties of the environment leads to opportunities to engineer the transfer of an exciton. Since excitons in nanostructures are proposed for use in quantum information processing and artificial photosynthetic designs, our approach paves the way for engineering a wide range of desired exciton dynamics. Finally, we develop the theory for a two-dimensional electronic spectroscopic technique based on fluorescence (2DFS) and challenge previous theoretical results claiming its equivalence to the two-dimensional photon echo (2DPE) technique which is based on polarization. Experimental realization of this technique confirms our theoretical predictions. The new technique is more sensitive than 2DPE as a tool for conformational determination of excitonically coupled chromophores and offers the possibility of applying two-dimensional electronic spectroscopy to single-molecules.
Spectral properties and classical decays in quantum open systems.
García-Mata, Ignacio; Saraceno, Marcos
2004-05-01
We study the relationship between the spectral properties of diffusive open quantum maps and the classical spectrum of Ruelle-Pollicott resonances. The leading resonances determine the asymptotic time regime for several quantities of interest--the linear entropy, the Loschmidt echo, and the correlations of the initial state. A numerical method that allows an efficient calculation of the leading spectrum is developed using a truncated basis adapted to the dynamics. PMID:15244908
NASA Astrophysics Data System (ADS)
Chitambar, Eric; Abu-Nada, Ali; Ceballos, Russell; Byrd, Mark
2015-11-01
The dynamics of an open quantum system is often modeled by introducing a bath initially in a product state with the system, letting the system and bath evolve unitarily together, and then tracing over the bath. However, often this model may not accurately reflect a particular experimental situation. Here, we provide some restrictions on one's ability to model an open quantum system using an initial product state when some information about the system-bath interaction is known. For instance, when certain symmetries exist in the system-bath interaction, we compute limitations on how much the system's purity can be increased if the bath is initially uncorrelated white noise. Furthermore, when the system and bath are qubits, we find that effectively only swap and product unitaries always generate system dynamics capable of being modeled using an initial product state. Finally, we show how any initial correlations between the system and environment are detectable, in principle, by observing the system transformation alone during certain joint evolutions. Our results have application in experimental quantum control and quantum computing where the system and environment are often assumed to be initially uncorrelated.
Exceptional points for parameter estimation in open quantum systems: analysis of the Bloch equations
NASA Astrophysics Data System (ADS)
Am-Shallem, Morag; Kosloff, Ronnie; Moiseyev, Nimrod
2015-11-01
We suggest to employ the dissipative nature of open quantum systems for the purpose of parameter estimation: the dynamics of open quantum systems is typically described by a quantum dynamical semigroup generator {L}. The eigenvalues of {L} are complex, reflecting unitary as well as dissipative dynamics. For certain values of parameters defining {L}, non-Hermitian degeneracies emerge, i.e. exceptional points (EP). The dynamical signature of these EPs corresponds to a unique time evolution. This unique feature can be employed experimentally to locate the EPs and thereby to determine the intrinsic system parameters with a high accuracy. This way we turn the disadvantage of the dissipation into an advantage. We demonstrate this method in the open system dynamics of a two-level system described by the Bloch equation, which has become the paradigm of diverse fields in physics, from NMR to quantum information and elementary particles.
Dissipative quantum computing with open quantum walks
Sinayskiy, Ilya; Petruccione, Francesco
2014-12-04
An open quantum walk approach to the implementation of a dissipative quantum computing scheme is presented. The formalism is demonstrated for the example of an open quantum walk implementation of a 3 qubit quantum circuit consisting of 10 gates.
Nature of heat in strongly coupled open quantum systems
NASA Astrophysics Data System (ADS)
Esposito, Massimiliano; Ochoa, Maicol A.; Galperin, Michael
2015-12-01
We show that any heat definition expressed as an energy change in the reservoir energy plus any fraction of the system-reservoir interaction is not an exact differential when evaluated along reversible isothermal transformations, except when that fraction is zero. Even in that latter case the reversible heat divided by temperature, namely entropy, does not satisfy the third law of thermodynamics and diverges in the low temperature limit. These results are found within the framework of nonequilibrium Green functions (NEGF) using a single level quantum dot strongly coupled to fermionic reservoirs and subjected to a time-dependent protocol modulating the dot energy as well as the dot-reservoir coupling strength.
Rise and fall of quantum and classical correlations in open-system dynamics
Khasin, Michael; Kosloff, Ronnie
2007-07-15
Interacting quantum systems evolving from an uncorrelated composite initial state generically develop quantum correlations--entanglement. As a consequence, a local description of interacting quantum systems is impossible as a rule. A unitarily evolving (isolated) quantum system generically develops extensive entanglement: the magnitude of the generated entanglement will increase without bounds with the effective Hilbert space dimension of the system. It is conceivable that coupling of the interacting subsystems to local dephasing environments will restrict the generation of entanglement to such extent that the evolving composite system may be considered as approximately disentangled. This conjecture is addressed in the context of some common models of a bipartite system with linear and nonlinear interactions and local coupling to dephasing environments. Analytical and numerical results obtained imply that the conjecture is generally false. Open dynamics of the quantum correlations is compared to the corresponding evolution of the classical correlations and a qualitative difference is found.
NASA Astrophysics Data System (ADS)
Chen, Chien-Chang; Goan, Hsi-Sheng
2016-03-01
We investigate the preparation of a target initial state for a two-level (qubit) system from a system-environment equilibrium or correlated state by an external field. The system-environment equilibrium or correlated state results from the inevitable interaction of the system with its environment. An efficient method in an extended auxiliary Liouville space is introduced to describe the dynamics of the non-Markovian open quantum system in the presence of a strong field and an initial system-environment correlation. By using the time evolutions of the population difference, the state trajectory in the Bloch sphere representation, and the trace distance between two reduced system states of the open quantum system, the effect of initial system-environment correlations on the preparation of a system state is studied. We introduce an upper bound and a lower bound for the trace distance within our perturbation formalism to describe the diverse behaviors of the dynamics of the trace distance between various correlated states after the system state preparation. These bounds, that are much more computable than similar bounds in the literature, give a sufficient condition and a necessary condition for the increase of the trace distance and are related to the witnesses of non-Markovianity and initial system-bath correlation.
Dynamics of super-quantum discord and direct control with weak measurement in open quantum system
NASA Astrophysics Data System (ADS)
Ji, Ying-Hua
2015-12-01
Super-quantum discord (SQD) with weak measurement is regarded as a kind of quantum correlation in quantum information processing. We compare and analyze the dynamical evolutions of SQD, quantum discord (QD), and quantum entanglement (QE) between two qubits in the correlated dephasing environmental model. The results indicate that (i) owing to the much smaller influence of weak measurement on the coherence of the system than that of von Neumann projection measurement, SQD with weak measurement is larger than QD, and (ii) dynamical evolution of QD or QE monotonically goes to zero with time, while SQD monotonically tends to a stable value and a freezing phenomenon occurs. The stable value after freezing mainly depends on the measurement strength and the purity of the initial quantum state. Project supported by the National Natural Science Foundation of China (Grant No. 11264015).
Geometric phase for an adiabatically evolving open quantum system
Kamleitner, Ingo; Cresser, James D.; Sanders, Barry C.
2004-10-01
We derive a solution for a two-level system evolving adiabatically under the influence of a driving field, which includes open system effects. This solution, which is obtained by working in the representation corresponding to the eigenstates of the time-dependent Hermitian Hamiltonian, enables the dynamic and geometric phases of the evolving density matrix to be separated. The dynamic phase can be canceled in the limit of weak coupling to the environment, thereby allowing the geometric phase to be readily extracted both mathematically and operationally.
Canonical versus noncanonical equilibration dynamics of open quantum systems.
Yang, Chun-Jie; An, Jun-Hong; Luo, Hong-Gang; Li, Yading; Oh, C H
2014-08-01
In statistical mechanics, any quantum system in equilibrium with its weakly coupled reservoir is described by a canonical state at the same temperature as the reservoir. Here, by studying the equilibration dynamics of a harmonic oscillator interacting with a reservoir, we evaluate microscopically the condition under which the equilibration to a canonical state is valid. It is revealed that the non-Markovian effect and the availability of a stationary state of the total system play a profound role in the equilibration. In the Markovian limit, the conventional canonical state can be recovered. In the non-Markovian regime, when the stationary state is absent, the system equilibrates to a generalized canonical state at an effective temperature; whenever the stationary state is present, the equilibrium state of the system cannot be described by any canonical state anymore. Our finding of the physical condition on such noncanonical equilibration might have significant impact on statistical physics. A physical scheme based on circuit QED is proposed to test our results. PMID:25215704
Equivalence of matrix product ensembles of trajectories in open quantum systems.
Kiukas, Jukka; Gu??, M?d?lin; Lesanovsky, Igor; Garrahan, Juan P
2015-07-01
The equivalence of thermodynamic ensembles is at the heart of statistical mechanics and central to our understanding of equilibrium states of matter. Recently, a formal connection has been established between the dynamics of open quantum systems and statistical mechanics in an extra dimension: an open system dynamics generates a matrix product state (MPS) encoding all possible quantum jump trajectories which allows to construct generating functions akin to partition functions. For dynamics generated by a Lindblad master equation, the corresponding MPS is a so-called continuous MPS which encodes the set of continuous measurement records terminated at some fixed total observation time. Here, we show that if one instead terminates trajectories after a fixed total number of quantum jumps, e.g., emission events into the environment, the associated MPS is discrete. The continuous and discrete MPS correspond to different ensembles of quantum trajectories, one characterized by total time, the other by total number of quantum jumps. Hence, they give rise to quantum versions of different thermodynamic ensembles, akin to "grand canonical" and "isobaric," but for trajectories. Here, we prove that these trajectory ensembles are equivalent in a suitable limit of long time or large number of jumps. This is in direct analogy to equilibrium statistical mechanics where equivalence between ensembles is only strictly established in the thermodynamic limit. An intrinsic quantum feature is that the equivalence holds only for all observables that commute with the number of quantum jumps. PMID:26274149
Equivalence of matrix product ensembles of trajectories in open quantum systems
NASA Astrophysics Data System (ADS)
Kiukas, Jukka; GuÃ…Â£ÇŽ, MÇŽdÇŽlin; Lesanovsky, Igor; Garrahan, Juan P.
2015-07-01
The equivalence of thermodynamic ensembles is at the heart of statistical mechanics and central to our understanding of equilibrium states of matter. Recently, a formal connection has been established between the dynamics of open quantum systems and statistical mechanics in an extra dimension: an open system dynamics generates a matrix product state (MPS) encoding all possible quantum jump trajectories which allows to construct generating functions akin to partition functions. For dynamics generated by a Lindblad master equation, the corresponding MPS is a so-called continuous MPS which encodes the set of continuous measurement records terminated at some fixed total observation time. Here, we show that if one instead terminates trajectories after a fixed total number of quantum jumps, e.g., emission events into the environment, the associated MPS is discrete. The continuous and discrete MPS correspond to different ensembles of quantum trajectories, one characterized by total time, the other by total number of quantum jumps. Hence, they give rise to quantum versions of different thermodynamic ensembles, akin to "grand canonical" and "isobaric," but for trajectories. Here, we prove that these trajectory ensembles are equivalent in a suitable limit of long time or large number of jumps. This is in direct analogy to equilibrium statistical mechanics where equivalence between ensembles is only strictly established in the thermodynamic limit. An intrinsic quantum feature is that the equivalence holds only for all observables that commute with the number of quantum jumps.
Quantum and classical fluctuation theorems from a decoherent histories, open-system analysis.
Suba??, Y; Hu, B L
2012-01-01
In this paper we present a first-principles analysis of the nonequilibrium work distribution and the free energy difference of a quantum system interacting with a general environment (with arbitrary spectral density and for all temperatures) based on a well-understood microphysics (quantum Brownian motion) model under the conditions stipulated by the Jarzynski equality [Jarzynski, Phys. Rev. Lett. 78, 2690 (1997)] and Crooks' fluctuation theorem [Crooks, Phys. Rev. E 60, 2721 (1999)] (in short, fluctuation theorems, FTs). We use the decoherent histories conceptual framework to explain how the notion of trajectories in a quantum system can be made viable and use the environment-induced decoherence scheme to assess the strength of noise that could provide sufficient decoherence to warrant the use of trajectories to define work in open quantum systems. From the solutions to the Langevin equation governing the stochastic dynamics of such systems we were able to produce formal expressions for these quantities entering in the FTs and from them prove explicitly the validity of the FTs at the high temperature limit. At low temperatures our general results would enable one to identify the range of parameters where FTs may not hold or need be expressed differently. We explain the relation between classical and quantum FTs and the advantage of this microphysics open-system approach over the phenomenological modeling and energy-level calculations for substitute closed quantum systems. PMID:22400517
Solving non-Markovian open quantum systems with multi-channel reservoir coupling
NASA Astrophysics Data System (ADS)
Broadbent, Curtis J.; Jing, Jun; Yu, Ting; Eberly, Joseph H.
2012-08-01
We extend the non-Markovian quantum state diffusion (QSD) equation to open quantum systems which exhibit multi-channel coupling to a harmonic oscillator reservoir. Open quantum systems which have multi-channel reservoir coupling are those in which canonical transformation of reservoir modes cannot reduce the number of reservoir operators appearing in the interaction Hamiltonian to one. We show that the non-Markovian QSD equation for multi-channel reservoir coupling can, in some cases, lead to an exact master equation which we derive. We then derive the exact master equation for the three-level system in a vee-type configuration which has multi-channel reservoir coupling and give the analytical solution. Finally, we examine the evolution of the three-level vee-type system with generalized Ornstein-Uhlenbeck reservoir correlations numerically.
Lyapunov control on quantum open systems in decoherence-free subspaces
Wang, W.; Wang, L. C.; Yi, X. X.
2010-09-15
A scheme to drive and manipulate a finite-dimensional quantum system in decoherence-free subspaces (DFSs) by Lyapunov control is proposed. Control fields are established by the Lyapunov function. This proposal can drive the open quantum system into DFSs and manipulate it to any desired eigenstate of the free Hamiltonian. An example which consists of a four-level system with three long-lived states driven by two lasers is presented to demonstrate the scheme. We have performed numerical simulations of the dynamics of the four-level system, which show that the scheme works well.
Simulation of single-qubit open quantum systems
NASA Astrophysics Data System (ADS)
Sweke, Ryan; Sinayskiy, Ilya; Petruccione, Francesco
2014-08-01
A quantum algorithm is presented for the simulation of arbitrary Markovian dynamics of a qubit, described by a semigroup of single-qubit quantum channels {Tt} specified by a generator L. This algorithm requires only single-qubit and controlled-not gates and approximates the channel Tt=etL up to the chosen accuracy ?, with a slightly superlinear cost O((?L?(1?1)t)1+1/2k/?1/2k) for any integer k. Inspired by developments in Hamiltonian simulation, a decomposition and recombination technique is utilized which allows for the exploitation of recently developed methods for the approximation of arbitrary single-qubit channels. In particular, as a result of these methods the algorithm requires only a single ancilla qubit, the minimal possible dilation for a nonunitary single-qubit quantum channel.
Chain representations of Open Quantum Systems and Lieb-Robinson like bounds for the dynamics
NASA Astrophysics Data System (ADS)
Woods, Mischa
2013-03-01
This talk is concerned with the mapping of the Hamiltonian of open quantum systems onto chain representations, which forms the basis for a rigorous theory of the interaction of a system with its environment. This mapping progresses as an interaction which gives rise to a sequence of residual spectral densities of the system. The rigorous mathematical properties of this mapping have been unknown so far. Here we develop the theory of secondary measures to derive an analytic, expression for the sequence solely in terms of the initial measure and its associated orthogonal polynomials of the first and second kind. These mappings can be thought of as taking a highly nonlocal Hamiltonian to a local Hamiltonian. In the latter, a Lieb-Robinson like bound for the dynamics of the open quantum system makes sense. We develop analytical bounds on the error to observables of the system as a function of time when the semi-infinite chain in truncated at some finite length. The fact that this is possible shows that there is a finite ``Speed of sound'' in these chain representations. This has many implications of the simulatability of open quantum systems of this type and demonstrates that a truncated chain can faithfully reproduce the dynamics at shorter times. These results make a significant and mathematically rigorous contribution to the understanding of the theory of open quantum systems; and pave the way towards the efficient simulation of these systems, which within the standard methods, is often an intractable problem. EPSRC CDT in Controlled Quantum Dynamics, EU STREP project and Alexander von Humboldt Foundation
General response formula and application to topological insulator in quantum open system.
Shen, H Z; Qin, M; Shao, X Q; Yi, X X
2015-11-01
It is well-known that the quantum linear response theory is based on the first-order perturbation theory for a system in thermal equilibrium. Hence, this theory breaks down when the system is in a steady state far from thermal equilibrium and the response up to higher order in perturbation is not negligible. In this paper, we develop a nonlinear response theory for such quantum open system. We first formulate this theory in terms of general susceptibility, after which we apply it to the derivation of Hall conductance for open system at finite temperature. As an example, the Hall conductance of the two-band model is derived. Then we calculate the Hall conductance for a two-dimensional ferromagnetic electron gas and a two-dimensional lattice model. The calculations show that the transition points of topological phase are robust against the environment. Our results provide a promising platform for the coherent manipulation of the nonlinear response in quantum open system, which has potential applications for quantum information processing and statistical physics. PMID:26651662
General response formula and application to topological insulator in quantum open system
NASA Astrophysics Data System (ADS)
Shen, H. Z.; Qin, M.; Shao, X. Q.; Yi, X. X.
2015-11-01
It is well-known that the quantum linear response theory is based on the first-order perturbation theory for a system in thermal equilibrium. Hence, this theory breaks down when the system is in a steady state far from thermal equilibrium and the response up to higher order in perturbation is not negligible. In this paper, we develop a nonlinear response theory for such quantum open system. We first formulate this theory in terms of general susceptibility, after which we apply it to the derivation of Hall conductance for open system at finite temperature. As an example, the Hall conductance of the two-band model is derived. Then we calculate the Hall conductance for a two-dimensional ferromagnetic electron gas and a two-dimensional lattice model. The calculations show that the transition points of topological phase are robust against the environment. Our results provide a promising platform for the coherent manipulation of the nonlinear response in quantum open system, which has potential applications for quantum information processing and statistical physics.
QuTiP: An open-source Python framework for the dynamics of open quantum systems
NASA Astrophysics Data System (ADS)
Johansson, J. R.; Nation, P. D.; Nori, Franco
2012-08-01
We present an object-oriented open-source framework for solving the dynamics of open quantum systems written in Python. Arbitrary Hamiltonians, including time-dependent systems, may be built up from operators and states defined by a quantum object class, and then passed on to a choice of master equation or Monte Carlo solvers. We give an overview of the basic structure for the framework before detailing the numerical simulation of open system dynamics. Several examples are given to illustrate the build up to a complete calculation. Finally, we measure the performance of our library against that of current implementations. The framework described here is particularly well suited to the fields of quantum optics, superconducting circuit devices, nanomechanics, and trapped ions, while also being ideal for use in classroom instruction. Catalogue identifier: AEMB_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEMB_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public License, version 3 No. of lines in distributed program, including test data, etc.: 16 482 No. of bytes in distributed program, including test data, etc.: 213 438 Distribution format: tar.gz Programming language: Python Computer: i386, x86-64 Operating system: Linux, Mac OSX, Windows RAM: 2+ Gigabytes Classification: 7 External routines: NumPy (http://numpy.scipy.org/), SciPy (http://www.scipy.org/), Matplotlib (http://matplotlib.sourceforge.net/) Nature of problem: Dynamics of open quantum systems. Solution method: Numerical solutions to Lindblad master equation or Monte Carlo wave function method. Restrictions: Problems must meet the criteria for using the master equation in Lindblad form. Running time: A few seconds up to several tens of minutes, depending on size of underlying Hilbert space.
Demonstration of open-quantum-system optimal control in dynamic nuclear polarization
NASA Astrophysics Data System (ADS)
Sheldon, S.; Cory, D. G.
2015-10-01
Dynamic nuclear polarization (DNP) is used in nuclear magnetic resonance to transfer polarization from electron spins to nuclear spins. The resulting nuclear polarization enhancement can, in theory, be two or three orders of magnitude depending on the sample. In solid-state systems, however, there are competing mechanisms of DNP, which, when occurring simultaneously, reduce the net polarization enhancement of the nuclear spin. We present a simple quantum description of DNP and apply optimal control theory (OCT) with an open-quantum-system framework to design pulses that select one DNP process and suppress the others. We demonstrate experimentally an order of magnitude improvement in the DNP enhancement using OCT pulses.
Superradiance, disorder, and the non-Hermitian Hamiltonian in open quantum systems
Celardo, G. L.; Biella, A.; Giusteri, G. G.; Mattiotti, F.; Zhang, Y.; Kaplan, L.
2014-10-15
We first briefly review the non-Hermitian effective Hamiltonian approach to open quantum systems and the associated phenomenon of superradiance. We next discuss the superradiance crossover in the presence of disorder and the relationship between superradiance and the localization transition. Finally, we investigate the regime of validity of the energy-independent effective Hamiltonian approximation and show that the results obtained by these methods are applicable to realistic physical systems.
Solving non-Markovian open quantum systems with multi-channel reservoir coupling
Broadbent, Curtis J.; Jing, Jun; Yu, Ting; Eberly, Joseph H.
2012-08-15
We extend the non-Markovian quantum state diffusion (QSD) equation to open quantum systems which exhibit multi-channel coupling to a harmonic oscillator reservoir. Open quantum systems which have multi-channel reservoir coupling are those in which canonical transformation of reservoir modes cannot reduce the number of reservoir operators appearing in the interaction Hamiltonian to one. We show that the non-Markovian QSD equation for multi-channel reservoir coupling can, in some cases, lead to an exact master equation which we derive. We then derive the exact master equation for the three-level system in a vee-type configuration which has multi-channel reservoir coupling and give the analytical solution. Finally, we examine the evolution of the three-level vee-type system with generalized Ornstein-Uhlenbeck reservoir correlations numerically. - Highlights: Black-Right-Pointing-Pointer The concept of multi-channel vs. single-channel reservoir coupling is rigorously defined. Black-Right-Pointing-Pointer The non-Markovian quantum state diffusion equation for arbitrary multi-channel reservoir coupling is derived. Black-Right-Pointing-Pointer An exact time-local master equation is derived under certain conditions. Black-Right-Pointing-Pointer The analytical solution to the three-level system in a vee-type configuration is found. Black-Right-Pointing-Pointer The evolution of the three-level system under generalized Ornstein-Uhlenbeck noise is plotted for many parameter regimes.
NASA Astrophysics Data System (ADS)
Hsiang, J.-T.; Hu, B. L.
2015-11-01
The existence and uniqueness of a steady state for nonequilibrium systems (NESS) is a fundamental subject and a main theme of research in statistical mechanics for decades. For Gaussian systems, such as a chain of classical harmonic oscillators connected at each end to a heat bath, and for classical anharmonic oscillators under specified conditions, definitive answers exist in the form of proven theorems. Answering this question for quantum many-body systems poses a challenge for the present. In this work we address this issue by deriving the stochastic equations for the reduced system with self-consistent backaction from the two baths, calculating the energy flow from one bath to the chain to the other bath, and exhibiting a power balance relation in the total (chain + baths) system which testifies to the existence of a NESS in this system at late times. Its insensitivity to the initial conditions of the chain corroborates to its uniqueness. The functional method we adopt here entails the use of the influence functional, the coarse-grained and stochastic effective actions, from which one can derive the stochastic equations and calculate the average values of physical variables in open quantum systems. This involves both taking the expectation values of quantum operators of the system and the distributional averages of stochastic variables stemming from the coarse-grained environment. This method though formal in appearance is compact and complete. It can also easily accommodate perturbative techniques and diagrammatic methods from field theory. Taken all together it provides a solid platform for carrying out systematic investigations into the nonequilibrium dynamics of open quantum systems and quantum thermodynamics.
Probability-current analysis of energy transport in open quantum systems
NASA Astrophysics Data System (ADS)
Roden, Jan J. J.; Whaley, K. Birgitta
2016-01-01
We introduce a probability-current analysis of excitation energy transfer between states of an open quantum system. Expressing the energy transfer through currents of excitation probability between the states in a site representation enables us to gain key insights into the energy transfer dynamics. In particular, the analysis yields direct identification of the pathways of energy transport in large networks of sites and quantifies their relative weights, as well as the respective contributions of unitary dynamics, coherence, dephasing, and relaxation and dissipation processes to the energy transfer. It thus provides much more information than studying only excitation probabilities of the states as a function of time. Our analysis is general and can be readily applied to a broad range of dynamical descriptions of open quantum system dynamics with coupling to non-Markovian or Markovian environments.
Enhancing quantum correlation in open-system dynamics by reliable quantum operations
NASA Astrophysics Data System (ADS)
Shi, Jia Dong; Wang, Dong; Ma, Wen Chao; Ye, Liu
2015-09-01
We investigate the decoherence to generate quantum discord between two separable qubits of an unentangled mixed state and propose a series of feasible schemes to enhance quantum discord by means of reliable quantum operations. By combing our schemes with the previous proposal, one can note that the generated quantum discord can be greatly enhanced. Moreover, our success probability entirely depends on the quantum measurement strength.
Resonant-state Expansion of the Green's Function of Open Quantum Systems
NASA Astrophysics Data System (ADS)
Hatano, Naomichi; Ordonez, Gonzalo
2011-04-01
Our series of recent work on the transmission coefficient of open quantum systems in one dimension will be reviewed. The transmission coefficient is equivalent to the conductance of a quantum dot connected to leads of quantum wires. We will show that the transmission coefficient is given by a sum over all discrete eigenstates of the Hamiltonian, without a background integral. An apparent "background" is in fact not a background but generated by tails of various resonance peaks. By using the expression, we will show that the Fano asymmetry of a resonance peak is caused by the interference between various discrete eigenstates. In particular, a broad resonance can strongly skew the peak of a nearby sharp resonance.
Efficient method to generate time evolution of the Wigner function for open quantum systems
NASA Astrophysics Data System (ADS)
Cabrera, Renan; Bondar, Denys I.; Jacobs, Kurt; Rabitz, Herschel A.
2015-10-01
The Wigner function is a useful tool for exploring the transition between quantum and classical dynamics, as well as the behavior of quantum chaotic systems. Evolving the Wigner function for open systems has proved challenging, however; a variety of methods have been devised but suffer from being cumbersome and resource intensive. Here we present an efficient fast-Fourier method for evolving the Wigner function that has a complexity of O (N logN ) where N is the size of the array storing the Wigner function. The efficiency, stability, and simplicity of this method allows us to simulate open-system dynamics previously thought to be prohibitively expensive. As a demonstration we simulate the dynamics of both one-particle and two-particle systems under various environmental interactions. For a single particle we also compare the resulting evolution with that of the classical Fokker-Planck and Koopman-von Neumann equations and show that the environmental interactions induce the quantum-to-classical transition as expected. In the case of two interacting particles we show that an environment interacting with one of the particles leads to the loss of coherence of the other.
Rushai, Vladimir D; Lobanov, Yuri Yu
2005-06-01
Representation of propagator for open quantum systems in the form of a double functional integral with respect to conditional Wiener measure is proposed. It allows one to apply the approximate formulas exact for functional polynomials of a certain power to calculation of such integrals. Within this deterministic approach the problem is reduced to evaluation of usual (Riemann) integrals of low multiplicity. The formulas are in fact the basis of a numerical method of studying time evolution of the systems. The features of the method are discussed and some examples of calculations are given. PMID:16089912
Renormalization approach to non-Markovian open-quantum-system dynamics
NASA Astrophysics Data System (ADS)
Gualdi, Giulia; Koch, Christiane P.
2013-08-01
We show that time induces a dynamical renormalization of the system-environment coupling in open-quantum-system dynamics. The renormalizability condition, of the interactions being either local, or, alternatively, defined on a finite continuum support, is generally fulfilled for both discrete and continuous environments. As a consequence, we find a generalized Lieb-Robinson bound to hold for local and, surprisingly, also for nonlocal interactions. This unified picture allows us to devise a controllable approximation for arbitrary non-Markovian dynamics with an a priori estimate of the worst-case computational cost.
Lei, Chan U; Zhang Weimin
2011-11-15
In this paper, we provide a mechanism of decoherence suppression for open quantum systems in general and that for a ''Schroedinger cat-like'' state in particular, through strong couplings to non-Markovian reservoirs. Different from the usual strategies in the literature of suppressing decoherence by decoupling the system from the environment, here the decoherence suppression employs a strong back-reaction from non-Markovian reservoirs. The mechanism relies on the existence of the singularities (bound states) of the nonequilibrium retarded Green function, which completely determines the dissipation and decoherence dynamics of open systems. As an application, we examine the decoherence dynamics of a photonic crystal nanocavity that is coupled to a waveguide. The strong non-Markovian suppression of decoherence for the ''optical cat'' state is attained.
Creation of Two-Particle Entanglement in Open Macroscopic Quantum Systems
Merkli, M.; Berman, G. P.; Borgonovi, F.; Tsifrinovich, V. I.
2012-01-01
We considermoreÂ Â» an open quantum system of N not directly interacting spins (qubits) in contact with both local and collective thermal environments. The qubit-environment interactions are energy conserving. We trace out the variables of the thermal environments and N âˆ’ 2 qubits to obtain the time-dependent reduced density matrix for two arbitrary qubits. We numerically simulate the reduced dynamics and the creation of entanglement (concurrence) as a function of the parameters of the thermal environments and the number of qubits, N . Our results demonstrate that the two-qubit entanglement generally decreases as N increases. We show analytically that, in the limit N â†’ âˆž , no entanglement can be created. This indicates that collective thermal environments cannot create two-qubit entanglement when many qubits are located within a region of the size of the environment coherence length. We discuss possible relevance of our consideration to recent quantum information devices and biosystems.Â«Â less
Thermofield-based chain-mapping approach for open quantum systems
NASA Astrophysics Data System (ADS)
de Vega, Inés; Bañuls, Mari-Carmen
2015-11-01
We consider a thermofield approach to analyze the evolution of an open quantum system coupled to an environment at finite temperature. In this approach, the finite-temperature environment is exactly mapped onto two virtual environments at zero temperature. These two environments are then unitarily transformed into two different chains of oscillators, leading to a one-dimensional structure that can be numerically studied using tensor network techniques. Compared to previous approaches using a single chain mapping, our strategy offers the advantage of an exact description of the initial state at arbitrary temperatures, which results in a gain in computational efficiency and a reduced truncation error.
Bound states, scattering states, and resonant states in PT -symmetric open quantum systems
NASA Astrophysics Data System (ADS)
Garmon, Savannah; Gianfreda, Mariagiovanna; Hatano, Naomichi
2015-08-01
We study a simple open quantum system with a PT -symmetric defect potential as a prototype in order to illustrate a number of general features of PT -symmetric open quantum systems; however, the potential itself could be mimicked by a number of PT systems that have been experimentally studied quite recently. One key feature is the resonance in continuum (RIC), which appears in both the discrete spectrum and the scattering spectrum of such systems. The RIC wave function forms a standing wave extending throughout the spatial extent of the system and in this sense represents a resonance between the open environment associated with the leads of our model and the central PT -symmetric potential. We also illustrate that as one deforms the system parameters, the RIC may exit the continuum by splitting into a bound state and a virtual bound state at the band edge, a process which should be experimentally observable. We also study the exceptional points appearing in the discrete spectrum at which two eigenvalues coalesce; we categorize these as either EP2As, at which two real-valued solutions coalesce before becoming complex-valued, and EP2Bs, for which the two solutions are complex on either side of the exceptional point. The EP2As are associated with PT -symmetry breaking; we argue that these are more stable against parameter perturbation than the EP2Bs. We also study complex-valued solutions of the discrete spectrum for which the wave function is nevertheless spatially localized, something that is not allowed in traditional open quantum systems; we illustrate that these may form quasibound states in continuum under some circumstances. We also study the scattering properties of the system, including states that support invisible propagation and some general features of perfect transmission states. We finally use our model as a prototype for the construction of scattering states that satisfy PT -symmetric boundary conditions; while these states do not conserve the traditional probability current, we introduce the PT current which is preserved. The perfect transmission states appear as a special case of the PT -symmetric scattering states.
General Formalism of Decision Making Based on Theory of Open Quantum Systems
NASA Astrophysics Data System (ADS)
Asano, M.; Ohya, M.; Basieva, I.; Khrennikov, A.
2013-01-01
We present the general formalism of decision making which is based on the theory of open quantum systems. A person (decision maker), say Alice, is considered as a quantum-like system, i.e., a system which information processing follows the laws of quantum information theory. To make decision, Alice interacts with a huge mental bath. Depending on context of decision making this bath can include her social environment, mass media (TV, newspapers, INTERNET), and memory. Dynamics of an ensemble of such Alices is described by Gorini-Kossakowski-Sudarshan-Lindblad (GKSL) equation. We speculate that in the processes of evolution biosystems (especially human beings) designed such "mental Hamiltonians" and GKSL-operators that any solution of the corresponding GKSL-equation stabilizes to a diagonal density operator (In the basis of decision making.) This limiting density operator describes population in which all superpositions of possible decisions has already been resolved. In principle, this approach can be used for the prediction of the distribution of possible decisions in human populations.
NASA Astrophysics Data System (ADS)
Fleming, C. H.; Hu, B. L.
2012-04-01
We treat several key stochastic equations for non-Markovian open quantum system dynamics and present a formalism for finding solutions to them via canonical perturbation theory, without making the Born-Markov or rotating wave approximations (RWA). This includes master equations of the (asymptotically) stationary, periodic, and time-nonlocal type. We provide proofs on the validity and meaningfulness of the late-time perturbative master equation and on the preservation of complete positivity despite a general lack of Lindblad form. More specifically, we show how the algebraic generators satisfy the theorem of Lindblad and Gorini, Kossakowski and Sudarshan, even though the dynamical generators do not. These proofs ensure the mathematical viability and physical soundness of solutions to non-Markovian processes. Within the same formalism we also expand upon known results for non-Markovian corrections to the quantum regression theorem. Several directions where these results can be usefully applied to are also described, including the analysis of near-resonant systems where the RWA is inapplicable and the calculation of the reduced equilibrium state of open systems.
Ultracold Mixtures of Rubidium and Ytterbium for Open Quantum System Engineering
NASA Astrophysics Data System (ADS)
Herold, Creston David
Exquisite experimental control of quantum systems has led to sharp growth of basic quantum research in recent years. Controlling dissipation has been crucial in producing ultracold, trapped atomic samples. Recent theoretical work has suggested dissipation can be a useful tool for quantum state preparation. Controlling not only how a system interacts with a reservoir, but the ability to engineer the reservoir itself would be a powerful platform for open quantum system research. Toward this end, we have constructed an apparatus to study ultracold mixtures of rubidium (Rb) and ytterbium (Yb). We have developed a Rb-blind optical lattice at 423.018(7) nm, which will enable us to immerse a lattice of Yb atoms (the system) into a Rb BEC (superfluid reservoir). We have produced Bose-Einstein condensates of 170Yb and 174Yb, two of the five bosonic isotopes of Yb, which also has two fermionic isotopes. Flexible optical trapping of Rb and Yb was achieved with a two-color dipole trap of 532 and 1064 nm, and we observed thermalization in ultracold mixtures of Rb and Yb. Using the Rb-blind optical lattice, we measured very small light shifts of 87Rb BECs near the light shift zero-wavelengths adjacent the 6p electronic states, through a coherent series of lattice pulses. The positions of the zero-wavelengths are sensitive to the electric dipole matrix elements between the 5s and 6p states, and we made the first experimental measurement of their strength. By measuring a light shift, we were not sensitive to excited state branching ratios, and we achieved a precision better than 0.3%.
Multifractal fluctuations in the survival probability of an open quantum system
NASA Astrophysics Data System (ADS)
Facchini, Angelo; Wimberger, Sandro; Tomadin, Andrea
2007-03-01
We predict a multifractal behavior of transport in the deep quantum regime for the opened ?-kicked rotor model. Our analysis focuses on intermediate and large scale correlations in the transport signal and generalizes previously found parametric mono-fractal fluctuations in the quantum survival probability on small scales.
Neutral kaons as an open quantum system in a second quantization approach
NASA Astrophysics Data System (ADS)
Smoli?ski, Kordian Andrzej
2015-09-01
We have shown that it is possible to formulate the consistent and probability-preserving description of the CP -symmetry-violating evolution of a system of decaying particles. This has been done within the framework of quantum mechanics of open systems. This approach allows the description of both the exponential decay and flavor oscillations. We have solved explicitly the Kossakowski-Lindblad master equation for a system of particles with violated CP symmetry and found the evolution of any observable bilinear in creation and annihilation operators. The choice of a concrete observable can be done by the proper choice of initial conditions for the system of differential equations. We have calculated the evolution as well as mean values of the observables most interesting from the physical point of view, and we have found their lowest order difference with the CP -preserved values.
Critical exponent of a quantum-noise-driven phase transition: The open-system Dicke model
Nagy, D.; Szirmai, G.; Domokos, P.
2011-10-15
The quantum phase transition of the Dicke model has been observed recently in a system formed by motional excitations of a laser-driven Bose-Einstein condensate coupled to an optical cavity [Baumann et al., Nature (London) 464, 1301 (2010)]. The cavity-based system is intrinsically open: photons leak out of the cavity where they are detected. Even at zero temperature, the continuous weak measurement of the photon number leads to an irreversible dynamics toward a steady state. In the framework of a generalized Bogoliubov theory, we show that the steady state exhibits a dynamical quantum phase transition. We find that the critical point and the mean field are only slightly modified with respect to the phase transition in the ground state. However, the critical exponents of the singular quantum correlations are significantly different in the two cases. There is also a drastic modification of the atom-field entanglement, since the divergence of the logarithmic negativity of the ground state at the critical point is suppressed and a finite entanglement is found in the steady state.
Critical exponent of a quantum-noise-driven phase transition: The open-system Dicke model
NASA Astrophysics Data System (ADS)
Nagy, D.; Szirmai, G.; Domokos, P.
2011-10-01
The quantum phase transition of the Dicke model has been observed recently in a system formed by motional excitations of a laser-driven Bose-Einstein condensate coupled to an optical cavity [Baumann , Nature (London)NATUAS0028-083610.1038/nature09009 464, 1301 (2010)]. The cavity-based system is intrinsically open: photons leak out of the cavity where they are detected. Even at zero temperature, the continuous weak measurement of the photon number leads to an irreversible dynamics toward a steady state. In the framework of a generalized Bogoliubov theory, we show that the steady state exhibits a dynamical quantum phase transition. We find that the critical point and the mean field are only slightly modified with respect to the phase transition in the ground state. However, the critical exponents of the singular quantum correlations are significantly different in the two cases. There is also a drastic modification of the atom-field entanglement, since the divergence of the logarithmic negativity of the ground state at the critical point is suppressed and a finite entanglement is found in the steady state.
Problem-free time-dependent variational principle for open quantum systems.
Joubert-Doriol, Loïc; Izmaylov, Artur F
2015-04-01
Methods of quantum nuclear wave-function dynamics have become very efficient in simulating large isolated systems using the time-dependent variational principle (TDVP). However, a straightforward extension of the TDVP to the density matrix framework gives rise to methods that do not conserve the energy in the isolated system limit and the total system population for open systems where only energy exchange with environment is allowed. These problems arise when the system density is in a mixed state and is simulated using an incomplete basis. Thus, the basis set incompleteness, which is inevitable in practical calculations, creates artificial channels for energy and population dissipation. To overcome this unphysical behavior, we have introduced a constrained Lagrangian formulation of TDVP applied to a non-stochastic open system Schrödinger equation [L. Joubert-Doriol, I. G. Ryabinkin, and A. F. Izmaylov, J. Chem. Phys. 141, 234112 (2014)]. While our formulation can be applied to any variational ansatz for the system density matrix, derivation of working equations and numerical assessment is done within the variational multiconfiguration Gaussian approach for a two-dimensional linear vibronic coupling model system interacting with a harmonic bath. PMID:25854228
Problem-free time-dependent variational principle for open quantum systems
NASA Astrophysics Data System (ADS)
Joubert-Doriol, Loïc; Izmaylov, Artur F.
2015-04-01
Methods of quantum nuclear wave-function dynamics have become very efficient in simulating large isolated systems using the time-dependent variational principle (TDVP). However, a straightforward extension of the TDVP to the density matrix framework gives rise to methods that do not conserve the energy in the isolated system limit and the total system population for open systems where only energy exchange with environment is allowed. These problems arise when the system density is in a mixed state and is simulated using an incomplete basis. Thus, the basis set incompleteness, which is inevitable in practical calculations, creates artificial channels for energy and population dissipation. To overcome this unphysical behavior, we have introduced a constrained Lagrangian formulation of TDVP applied to a non-stochastic open system Schrödinger equation [L. Joubert-Doriol, I. G. Ryabinkin, and A. F. Izmaylov, J. Chem. Phys. 141, 234112 (2014)]. While our formulation can be applied to any variational ansatz for the system density matrix, derivation of working equations and numerical assessment is done within the variational multiconfiguration Gaussian approach for a two-dimensional linear vibronic coupling model system interacting with a harmonic bath.
Problem-free time-dependent variational principle for open quantum systems
Joubert-Doriol, LoÃ¯c; Izmaylov, Artur F.
2015-04-07
Methods of quantum nuclear wave-function dynamics have become very efficient in simulating large isolated systems using the time-dependent variational principle (TDVP). However, a straightforward extension of the TDVP to the density matrix framework gives rise to methods that do not conserve the energy in the isolated system limit and the total system population for open systems where only energy exchange with environment is allowed. These problems arise when the system density is in a mixed state and is simulated using an incomplete basis. Thus, the basis set incompleteness, which is inevitable in practical calculations, creates artificial channels for energy and population dissipation. To overcome this unphysical behavior, we have introduced a constrained Lagrangian formulation of TDVP applied to a non-stochastic open system SchrÃ¶dinger equation [L. Joubert-Doriol, I. G. Ryabinkin, and A. F. Izmaylov, J. Chem. Phys. 141, 234112 (2014)]. While our formulation can be applied to any variational ansatz for the system density matrix, derivation of working equations and numerical assessment is done within the variational multiconfiguration Gaussian approach for a two-dimensional linear vibronic coupling model system interacting with a harmonic bath.
A review of progress in the physics of open quantum systems: theory and experiment.
Rotter, I; Bird, J P
2015-11-01
This report on progress explores recent advances in our theoretical and experimental understanding of the physics of open quantum systems (OQSs). The study of such systems represents a core problem in modern physics that has evolved to assume an unprecedented interdisciplinary character. OQSs consist of some localized, microscopic, region that is coupled to an external environment by means of an appropriate interaction. Examples of such systems may be found in numerous areas of physics, including atomic and nuclear physics, photonics, biophysics, and mesoscopic physics. It is the latter area that provides the main focus of this review, an emphasis that is driven by the capacity that exists to subject mesoscopic devices to unprecedented control. We thus provide a detailed discussion of the behavior of mesoscopic devices (and other OQSs) in terms of the projection-operator formalism, according to which the system under study is considered to be comprised of a localized region (Q), embedded into a well-defined environment (P) of scattering wavefunctions (with Qâ€‰â€‰â€‰+â€‰â€‰â€‰Pâ€‰â€‰â€‰=â€‰â€‰â€‰1). The Q subspace must be treated using the concepts of non-Hermitian physics, and of particular interest here is: the capacity of the environment to mediate a coupling between the different states of Q; the role played by the presence of exceptional points (EPs) in the spectra of OQSs; the influence of EPs on the rigidity of the wavefunction phases, and; the ability of EPs to initiate a dynamical phase transition (DPT). EPs are singular points in the continuum, at which two resonance states coalesce, that is where they exhibit a non-avoided crossing. DPTs occur when the quantum dynamics of the open system causes transitions between non-analytically connected states, as a function of some external control parameter. Much like conventional phase transitions, the behavior of the system on one side of the DPT does not serve as a reliable indicator of that on the other. In addition to discussing experiments on mesoscopic quantum point contacts that provide evidence of the environmentally-mediated coupling of quantum states, we also review manifestations of DPTs in mesoscopic devices and other systems. These experiments include observations of resonance-trapping behavior in microwave cavities and open quantum dots, phase lapses in tunneling through single-electron transistors, and spin swapping in atomic ensembles. Other possible manifestations of this phenomenon are presented, including various superradiant phenomena in low-dimensional semiconductors. From these discussions a generic picture of OQSs emerges in which the environmentally-mediated coupling between different quantum states plays a critical role in governing the system behavior. The ability to control or manipulate this interaction may even lead to new applications in photonics and electronics. PMID:26510115
A review of progress in the physics of open quantum systems: theory and experiment
NASA Astrophysics Data System (ADS)
Rotter, I.; Bird, J. P.
2015-11-01
This report on progress explores recent advances in our theoretical and experimental understanding of the physics of open quantum systems (OQSs). The study of such systems represents a core problem in modern physics that has evolved to assume an unprecedented interdisciplinary character. OQSs consist of some localized, microscopic, region that is coupled to an external environment by means of an appropriate interaction. Examples of such systems may be found in numerous areas of physics, including atomic and nuclear physics, photonics, biophysics, and mesoscopic physics. It is the latter area that provides the main focus of this review, an emphasis that is driven by the capacity that exists to subject mesoscopic devices to unprecedented control. We thus provide a detailed discussion of the behavior of mesoscopic devices (and other OQSs) in terms of the projection-operator formalism, according to which the system under study is considered to be comprised of a localized region (Q), embedded into a well-defined environment (P) of scattering wavefunctions (with Qâ€‰â€‰â€‰+â€‰â€‰â€‰Pâ€‰â€‰â€‰=â€‰â€‰â€‰1). The Q subspace must be treated using the concepts of non-Hermitian physics, and of particular interest here is: the capacity of the environment to mediate a coupling between the different states of Q; the role played by the presence of exceptional points (EPs) in the spectra of OQSs; the influence of EPs on the rigidity of the wavefunction phases, and; the ability of EPs to initiate a dynamical phase transition (DPT). EPs are singular points in the continuum, at which two resonance states coalesce, that is where they exhibit a non-avoided crossing. DPTs occur when the quantum dynamics of the open system causes transitions between non-analytically connected states, as a function of some external control parameter. Much like conventional phase transitions, the behavior of the system on one side of the DPT does not serve as a reliable indicator of that on the other. In addition to discussing experiments on mesoscopic quantum point contacts that provide evidence of the environmentally-mediated coupling of quantum states, we also review manifestations of DPTs in mesoscopic devices and other systems. These experiments include observations of resonance-trapping behavior in microwave cavities and open quantum dots, phase lapses in tunneling through single-electron transistors, and spin swapping in atomic ensembles. Other possible manifestations of this phenomenon are presented, including various superradiant phenomena in low-dimensional semiconductors. From these discussions a generic picture of OQSs emerges in which the environmentally-mediated coupling between different quantum states plays a critical role in governing the system behavior. The ability to control or manipulate this interaction may even lead to new applications in photonics and electronics.
NASA Astrophysics Data System (ADS)
Chen, Xin
2014-04-01
Understanding the roles of the temporary and spatial structures of quantum functional noise in open multilevel quantum molecular systems attracts a lot of theoretical interests. I want to establish a rigorous and general framework for functional quantum noises from the constructive and computational perspectives, i.e., how to generate the random trajectories to reproduce the kernel and path ordering of the influence functional with effective Monte Carlo methods for arbitrary spectral densities. This construction approach aims to unify the existing stochastic models to rigorously describe the temporary and spatial structure of Gaussian quantum noises. In this paper, I review the Euclidean imaginary time influence functional and propose the stochastic matrix multiplication scheme to calculate reduced equilibrium density matrices (REDM). In addition, I review and discuss the Feynman-Vernon influence functional according to the Gaussian quadratic integral, particularly its imaginary part which is critical to the rigorous description of the quantum detailed balance. As a result, I establish the conditions under which the influence functional can be interpreted as the average of exponential functional operator over real-valued Gaussian processes for open multilevel quantum systems. I also show the difference between the local and nonlocal phonons within this framework. With the stochastic matrix multiplication scheme, I compare the normalized REDM with the Boltzmann equilibrium distribution for open multilevel quantum systems.
Chen, Xin
2014-04-21
Understanding the roles of the temporary and spatial structures of quantum functional noise in open multilevel quantum molecular systems attracts a lot of theoretical interests. I want to establish a rigorous and general framework for functional quantum noises from the constructive and computational perspectives, i.e., how to generate the random trajectories to reproduce the kernel and path ordering of the influence functional with effective Monte Carlo methods for arbitrary spectral densities. This construction approach aims to unify the existing stochastic models to rigorously describe the temporary and spatial structure of Gaussian quantum noises. In this paper, I review the Euclidean imaginary time influence functional and propose the stochastic matrix multiplication scheme to calculate reduced equilibrium density matrices (REDM). In addition, I review and discuss the Feynman-Vernon influence functional according to the Gaussian quadratic integral, particularly its imaginary part which is critical to the rigorous description of the quantum detailed balance. As a result, I establish the conditions under which the influence functional can be interpreted as the average of exponential functional operator over real-valued Gaussian processes for open multilevel quantum systems. I also show the difference between the local and nonlocal phonons within this framework. With the stochastic matrix multiplication scheme, I compare the normalized REDM with the Boltzmann equilibrium distribution for open multilevel quantum systems.
Lyapunov control on quantum systems
NASA Astrophysics Data System (ADS)
Wang, L. C.; Yi, X. X.
2014-12-01
We review the scheme of quantum Lyapunov control and its applications into quantum systems. After a brief review on the general method of quantum Lyapunov control in closed and open quantum systems, we apply it into controlling quantum states and quantum operations. The control of a spin-1/2 quantum system, driving an open quantum system into its decoherence free subspace (DFS), constructing single qubit and two-qubit logic gates are taken to illustrate the scheme. The optimalization of the Lyapunov control is also reviewed in this article.
Tracking an open quantum system using a finite state machine: Stability analysis
Karasik, R. I.; Wiseman, H. M.
2011-11-15
A finite-dimensional Markovian open quantum system will undergo quantum jumps between pure states, if we can monitor the bath to which it is coupled with sufficient precision. In general these jumps, plus the between-jump evolution, create a trajectory which passes through infinitely many different pure states, even for ergodic systems. However, as shown recently by us [Phys. Rev. Lett. 106, 020406 (2011)], it is possible to construct adaptive monitorings which restrict the system to jumping between a finite number of states. That is, it is possible to track the system using a finite state machine as the apparatus. In this paper we consider the question of the stability of these monitoring schemes. Restricting to cyclic jumps for a qubit, we give a strong analytical argument that these schemes are always stable and supporting analytical and numerical evidence for the example of resonance fluorescence. This example also enables us to explore a range of behaviors in the evolution of individual trajectories, for several different monitoring schemes.
Asplund, Erik; Kluener, Thorsten
2012-03-28
In this paper, control of open quantum systems with emphasis on the control of surface photochemical reactions is presented. A quantum system in a condensed phase undergoes strong dissipative processes. From a theoretical viewpoint, it is important to model such processes in a rigorous way. In this work, the description of open quantum systems is realized within the surrogate Hamiltonian approach [R. Baer and R. Kosloff, J. Chem. Phys. 106, 8862 (1997)]. An efficient and accurate method to find control fields is optimal control theory (OCT) [W. Zhu, J. Botina, and H. Rabitz, J. Chem. Phys. 108, 1953 (1998); Y. Ohtsuki, G. Turinici, and H. Rabitz, J. Chem. Phys. 120, 5509 (2004)]. To gain control of open quantum systems, the surrogate Hamiltonian approach and OCT, with time-dependent targets, are combined. Three open quantum systems are investigated by the combined method, a harmonic oscillator immersed in an ohmic bath, CO adsorbed on a platinum surface, and NO adsorbed on a nickel oxide surface. Throughout this paper, atomic units, i.e., ({Dirac_h}/2{pi})=m{sub e}=e=a{sub 0}= 1, have been used unless otherwise stated.
Basharov, A. M.
2012-09-15
It is shown that the effective Hamiltonian representation, as it is formulated in author's papers, serves as a basis for distinguishing, in a broadband environment of an open quantum system, independent noise sources that determine, in terms of the stationary quantum Wiener and Poisson processes in the Markov approximation, the effective Hamiltonian and the equation for the evolution operator of the open system and its environment. General stochastic differential equations of generalized Langevin (non-Wiener) type for the evolution operator and the kinetic equation for the density matrix of an open system are obtained, which allow one to analyze the dynamics of a wide class of localized open systems in the Markov approximation. The main distinctive features of the dynamics of open quantum systems described in this way are the stabilization of excited states with respect to collective processes and an additional frequency shift of the spectrum of the open system. As an illustration of the general approach developed, the photon dynamics in a single-mode cavity without losses on the mirrors is considered, which contains identical intracavity atoms coupled to the external vacuum electromagnetic field. For some atomic densities, the photons of the cavity mode are 'locked' inside the cavity, thus exhibiting a new phenomenon of radiation trapping and non-Wiener dynamics.
Real-time dynamics of open quantum spin systems driven by dissipative processes
NASA Astrophysics Data System (ADS)
Hebenstreit, F.; Banerjee, D.; Hornung, M.; Jiang, F.-J.; Schranz, F.; Wiese, U.-J.
2015-07-01
We study the real-time evolution of large open quantum spin systems in two spatial dimensions, whose dynamics is entirely driven by a dissipative coupling to the environment. We consider different dissipative processes and investigate the real-time evolution from an ordered phase of the Heisenberg or XY model towards a disordered phase at late times, disregarding unitary Hamiltonian dynamics. The corresponding Kossakowski-Lindblad equation is solved via an efficient cluster algorithm. We find that the symmetry of the dissipative process determines the time scales, which govern the approach towards a new equilibrium phase at late times. Most notably, we find a slow equilibration if the dissipative process conserves any of the magnetization Fourier modes. In these cases, the dynamics can be interpreted as a diffusion process of the conserved quantity.
Limits in the characteristic-function description of non-Lindblad-type open quantum systems
Maniscalco, Sabrina
2005-08-15
In this paper I investigate the usability of the characteristic functions for the description of the dynamics of open quantum systems focussing on non-Lindblad-type master equations. I consider, as an example, a non-Markovian generalized master equation containing a memory kernel which may lead to nonphysical time evolutions characterized by negative values of the density matrix diagonal elements [S. M. Barnett and S. Stenholm, Phys. Rev. A 64, 033808 (2001)]. The main result of the paper is to demonstrate that there exist situations in which the symmetrically ordered characteristic function is perfectly well-defined while the corresponding density matrix loses positivity. Therefore, nonphysical situations may not show up in the characteristic function. As a consequence, the characteristic function cannot be considered an alternative complete description of the non-Lindblad dynamics.
Casimir force for absorbing media in an open quantum system framework: Scalar model
Lombardo, Fernando C.; Rubio Lopez, Adrian E.; Mazzitelli, Francisco D.
2011-11-15
In this article we compute the Casimir force between two finite-width mirrors at finite temperature, working in a simplified model in 1+1 dimensions. The mirrors, considered as dissipative media, are modeled by a continuous set of harmonic oscillators which in turn are coupled to an external environment at thermal equilibrium. The calculation of the Casimir force is performed in the framework of the theory of open quantum systems. It is shown that the Casimir interaction has two different contributions: the usual radiation pressure from the vacuum, which is obtained for ideal mirrors without dissipation or losses, and a Langevin force associated with the noise induced by the interaction between dielectric atoms in the slabs and the thermal bath. Both contributions to the Casimir force are needed in order to reproduce the analogous Lifshitz formula in 1+1 dimensions. We also discuss the relationship between the electromagnetic properties of the mirrors and the spectral density of the environment.
Larsen, Ask Hjorth; De Giovannini, Umberto; Rubio, Angel
2016-01-01
We present a review of different computational methods to describe time-dependent phenomena in open quantum systems and their extension to a density-functional framework. We focus the discussion on electron emission processes in atoms and molecules addressing excited-state lifetimes and dissipative processes. Initially we analyze the concept of an electronic resonance, a central concept in spectroscopy associated with a metastable state from which an electron eventually escapes (electronic lifetime). Resonances play a fundamental role in many time-dependent molecular phenomena but can be rationalized from a time-independent context in terms of scattering states. We introduce the method of complex scaling, which is used to capture resonant states as localized states in the spirit of usual bound-state methods, and work on its extension to static and time-dependent density-functional theory. In a time-dependent setting, complex scaling can be used to describe excitations in the continuum as well as wave packet dynamics leading to electron emission. This process can also be treated by using open boundary conditions which allow time-dependent simulations of emission processes without artificial reflections at the boundaries (i.e., borders of the simulation box). We compare in detail different schemes to implement open boundaries, namely transparent boundaries using Green functions, and absorbing boundaries in the form of complex absorbing potentials and mask functions. The last two are regularly used together with time-dependent density-functional theory to describe the electron emission dynamics of atoms and molecules. Finally, we discuss approaches to the calculation of energy and angle-resolved time-dependent pump-probe photoelectron spectroscopy of molecular systems. PMID:25860253
Time-reversal symmetric resolution of unity without background integrals in open quantum systems
Hatano, Naomichi; Ordonez, Gonzalo
2014-12-15
We present a new complete set of states for a class of open quantum systems, to be used in expansion of the Green’s function and the time-evolution operator. A remarkable feature of the complete set is that it observes time-reversal symmetry in the sense that it contains decaying states (resonant states) and growing states (anti-resonant states) parallelly. We can thereby pinpoint the occurrence of the breaking of time-reversal symmetry at the choice of whether we solve Schrödinger equation as an initial-condition problem or a terminal-condition problem. Another feature of the complete set is that in the subspace of the central scattering area of the system, it consists of contributions of all states with point spectra but does not contain any background integrals. In computing the time evolution, we can clearly see contribution of which point spectrum produces which time dependence. In the whole infinite state space, the complete set does contain an integral but it is over unperturbed eigenstates of the environmental area of the system and hence can be calculated analytically. We demonstrate the usefulness of the complete set by computing explicitly the survival probability and the escaping probability as well as the dynamics of wave packets. The origin of each term of matrix elements is clear in our formulation, particularly, the exponential decays due to the resonance poles.
Resonant purification of mixed states for closed and open quantum systems
Romano, Raffaele
2007-02-15
Pure states are fundamental for the implementation of quantum technologies, and several methods for the purification of the state of a quantum system S have been developed in the past years. In this work we describe a mechanism leading to purification of mixed states, based on the interaction of S with an auxiliary system P. Considering two-level systems and assuming a particular interaction between them, we study how the dynamical parameters of the system P affect the purification of S. By using analytical and numerical tools, we show that the purification process exhibits a resonant behavior in both the cases of system isolated from the external environment or not.
QuTiP 2: A Python framework for the dynamics of open quantum systems
NASA Astrophysics Data System (ADS)
Johansson, J. R.; Nation, P. D.; Nori, Franco
2013-04-01
We present version 2 of QuTiP, the Quantum Toolbox in Python. Compared to the preceding version [J.R. Johansson, P.D. Nation, F. Nori, Comput. Phys. Commun. 183 (2012) 1760.], we have introduced numerous new features, enhanced performance, and made changes in the Application Programming Interface (API) for improved functionality and consistency within the package, as well as increased compatibility with existing conventions used in other scientific software packages for Python. The most significant new features include efficient solvers for arbitrary time-dependent Hamiltonians and collapse operators, support for the Floquet formalism, and new solvers for Bloch-Redfield and Floquet-Markov master equations. Here we introduce these new features, demonstrate their use, and give a summary of the important backward-incompatible API changes introduced in this version. Catalog identifier: AEMB_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEMB_v2_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: GNU General Public License, version 3 No. of lines in distributed program, including test data, etc.: 33625 No. of bytes in distributed program, including test data, etc.: 410064 Distribution format: tar.gz Programming language: Python. Computer: i386, x86-64. Operating system: Linux, Mac OSX. RAM: 2+ Gigabytes Classification: 7. External routines: NumPy, SciPy, Matplotlib, Cython Catalog identifier of previous version: AEMB_v1_0 Journal reference of previous version: Comput. Phys. Comm. 183 (2012) 1760 Does the new version supercede the previous version?: Yes Nature of problem: Dynamics of open quantum systems Solution method: Numerical solutions to Lindblad, Floquet-Markov, and Bloch-Redfield master equations, as well as the Monte Carlo wave function method. Reasons for new version: Compared to the preceding version we have introduced numerous new features, enhanced performance, and made changes in the Application Programming Interface (API) for improved functionality and consistency within the package, as well as increased compatibility with existing conventions used in other scientific software packages for Python. The most significant new features include efficient solvers for arbitrary time-dependent Hamiltonians and collapse operators, support for the Floquet formalism, and new solvers for Bloch-Redfield and Floquet-Markov master equations. Restrictions: Problems must meet the criteria for using the master equation in Lindblad, Floquet-Markov, or Bloch-Redfield form. Running time: A few seconds up to several tens of hours, depending on size of the underlying Hilbert space.
Connecting two jumplike unravelings for non-Markovian open quantum systems
Luoma, Kimmo; Suominen, Kalle-Antti; Piilo, Jyrki
2011-09-15
The development and use of Monte Carlo algorithms plays a visible role in the study of non-Markovian quantum dynamics due to the provided insight and powerful numerical methods for solving the system dynamics. In the Markovian case, the connections between the various types of methods are fairly well understood while, for the non-Markovian case, there has so far been only a few studies. We focus here on two jumplike unravelings of non-Markovian dynamics: the non-Markovian quantum jump (NMQJ) method and the property state method by Gambetta, Askerud, and Wiseman (GAW). The results for simple quantum optical systems illustrate the connections between the realizations of the two methods and also highlight how the probability currents between the system and environment, or between the property states of the total system, are associated with the decay rates of time-local master equations and, consequently, with the jump rates of the NMQJ method.
Optical signatures of non-Markovian behavior in open quantum systems
NASA Astrophysics Data System (ADS)
McCutcheon, Dara P. S.
2016-02-01
We derive an extension to the quantum regression theorem which facilitates the calculation of two-time correlation functions and emission spectra for systems undergoing non-Markovian evolution. The derivation exploits projection operator techniques, with which we obtain explicit equations of motion for the correlation functions, making only a second-order expansion in the system-environment coupling strength and invoking the Born approximation at a fixed initial time. The results are used to investigate a driven semiconductor quantum dot coupled to an acoustic phonon bath, where we find the non-Markovian nature of the dynamics has observable signatures in the form of phonon sidebands in the resonance fluorescence emission spectrum. Furthermore, we use recently developed non-Markovianity measures to demonstrate an associated flow of information from the phonon bath back into the quantum dot exciton system.
NASA Astrophysics Data System (ADS)
Dattani, Nikesh S.
2013-12-01
This MATLAB program calculates the dynamics of the reduced density matrix of an open quantum system modeled either by the Feynman-Vernon model or the Caldeira-Leggett model. The user gives the program a Hamiltonian matrix that describes the open quantum system as if it were in isolation, a matrix of the same size that describes how that system couples to its environment, and a spectral distribution function and temperature describing the environmentâ€™s influence on it, in addition to the open quantum systemâ€™s initial density matrix and a grid of times. With this, the program returns the reduced density matrix of the open quantum system at all moments specified by that grid of times (or just the last moment specified by the grid of times if the user makes this choice). This overall calculation can be divided into two stages: the setup of the Feynman integral, and the actual calculation of the Feynman integral for time propagation of the density matrix. When this program calculates this propagation on a multi-core CPU, it is this propagation that is usually the rate-limiting step of the calculation, but when it is calculated on a GPU, the propagation is calculated so quickly that the setup of the Feynman integral can actually become the rate-limiting step. The overhead of transferring information from the CPU to the GPU and back seems to have a negligible effect on the overall runtime of the program. When the required information cannot fit on the GPU, the user can choose to run the entire program on a CPU. Catalogue identifier: AEPX_v1_0. Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEPX_v1_0.html. Program obtainable from: CPC Program Library, Queenâ€™s University, Belfast, N. Ireland. Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html. No. of lines in distributed program, including test data, etc.: 703. No. of bytes in distributed program, including test data, etc.: 11026. Distribution format: tar.gz. Programming language: MATLAB R2012a. Computer: See â€œOperating systemâ€. Operating system: Any operating system that can run MATLAB R2007a or above. Classification: 4.4. Nature of problem: Calculating the dynamics of the reduced density operator of an open quantum system. Solution method: Numerical Feynman integral. Running time: Depends on the input parameters. See the main text for examples.
Non-Markovian dynamics of an open quantum system with nonstationary coupling
Kalandarov, S. A.; Adamian, G. G.; Kanokov, Z.; Antonenko, N. V.; Scheid, W.
2011-04-15
The spectral, dissipative, and statistical properties of the damped quantum oscillator are studied in the case of non-Markovian and nonstationary system-heat bath coupling. The dissipation of collective energy is shown to be slowed down, and the decoherence rate and entropy grow with modulation frequency.
Probing the quantum-classical connection with open quantum dots
NASA Astrophysics Data System (ADS)
Ferry, D. K.; Akis, R.; Brunner, R.
2015-10-01
Open quantum dots provide a natural system in which to study both classical and quantum features of transport. From the classical point of view these dots possess a mixed phase space which yields families of closed, regular orbits as well as an expansive sea of chaos. As a closed test bed, they provide a natural system with a very rich set of eigen-states. When coupled to the environment through a pair of quantum point contacts, each of which passes several modes, the original quantum environment evolves into a set of decoherent and coherent states, which eventually couple to the classical states discussed above. The manner of this connection is governed strongly by decoherence theory. The remaining coherent states possess all the properties of pointer states. Here, we discuss the quantum-classical connection and how it appears within the experimental world.
He, Lewei; Wang, Wen-Ge
2014-02-01
We study the problem of the basis of an open quantum system, under a quantum chaotic environment, which is preferred in view of its stationary reduced density matrix (RDM), that is, the basis in which the stationary RDM is diagonal. It is shown that, under an initial condition composed of sufficiently many energy eigenstates of the total system, such a basis is given by the eigenbasis of a renormalized self-Hamiltonian of the system, in the limit of large Hilbert space of the environment. Here, the renormalized self-Hamiltonian is given by the unperturbed self-Hamiltonian plus a certain average of the interaction Hamiltonian over the environmental degrees of freedom. Numerical simulations performed in two models, both with the kicked rotor as the environment, give results consistent with the above analytical predictions. PMID:25353440
NASA Astrophysics Data System (ADS)
He, Lewei; Wang, Wen-ge
2014-02-01
We study the problem of the basis of an open quantum system, under a quantum chaotic environment, which is preferred in view of its stationary reduced density matrix (RDM), that is, the basis in which the stationary RDM is diagonal. It is shown that, under an initial condition composed of sufficiently many energy eigenstates of the total system, such a basis is given by the eigenbasis of a renormalized self-Hamiltonian of the system, in the limit of large Hilbert space of the environment. Here, the renormalized self-Hamiltonian is given by the unperturbed self-Hamiltonian plus a certain average of the interaction Hamiltonian over the environmental degrees of freedom. Numerical simulations performed in two models, both with the kicked rotor as the environment, give results consistent with the above analytical predictions.
NASA Astrophysics Data System (ADS)
Segnorile, Héctor H.; Zamar, Ricardo C.
2011-12-01
Explanation of decoherence and quasi-equilibrium in systems with few degrees of freedom demands a deep theoretical analysis that considers the observed system as an open quantum system. In this work, we study the problem of decoherence of an observed system of quantum interacting particles, coupled to a quantum lattice. Our strategy is based on treating the environment and the system-environment Hamiltonians fully quantum mechanically, which yields a representation of the time evolution operator useful for disentangling the different time scales underlying in the observed system dynamics. To describe the possible different stages of the dynamics of the observed system, we introduce quantum mechanical definitions of essentially isolated, essentially adiabatic, and thermal-contact system-environment interactions. This general approach is then applied to the study of decoherence and quasi-equilibrium in proton nuclear magnetic resonance (1H NMR) of nematic liquid crystals. A summary of the original results of this work is as follows. We calculate the decoherence function and apply it to describe the evolution of a coherent spin state, induced by the coupling with the molecular environment, in absence of spin-lattice relaxation. By assuming quantum energy conserving or non-demolition interactions, we identify an intermediate time scale, between those controlled by self-interactions and thermalization, where coherence decays irreversibly. This treatment is also adequate for explaining the buildup of quasi-equilibrium of the proton spin system, via the process we called eigen-selectivity. By analyzing a hypothetical time reversal experiment, we identify two sources of coherence loss which are of a very different nature and give rise to distinct time scales of the spin dynamics: (a) reversible or adiabatic quantum decoherence and (b) irreversible or essentially adiabatic quantum decoherence. Local irreversibility arises as a consequence of the uncertainty introduced by the coupling with an infinite quantum environment. The reversible part can be represented by a semiclassical model, similar to standard line-shape adiabatic models. By exploiting the separation existing between the time scales of the spin coherences and the irreversible decoherence, we present a novel technique to obtain the orientational molecular distribution function for a nematic liquid crystal. The procedure is based on the comparison of the observed coherence time evolution and numerical calculation under the adiabatic quantum decoherence approach. As an example, it is used the experimental free induction decay from a nematic PAAd6 sample to extract such an orientational distribution. This is the first theoretical description of the experimental liquid crystal NMR signal in the time domain. On the contrary, the irreversible decoherence is intrinsically full-quantum mechanical, as it is governed by the commutation properties of the environment and the spin-lattice Hamiltonians. Consistently, it depends on the molecular correlation in a decisive way, since it vanishes under a mean-field model for the molecular dynamics. The results of this work can contribute to the understanding of the open question of the applicability of the spin-temperature concept in spin systems with few degrees of freedom.
NASA Technical Reports Server (NTRS)
Isar, Aurelian
1995-01-01
The harmonic oscillator with dissipation is studied within the framework of the Lindblad theory for open quantum systems. By using the Wang-Uhlenbeck method, the Fokker-Planck equation, obtained from the master equation for the density operator, is solved for the Wigner distribution function, subject to either the Gaussian type or the delta-function type of initial conditions. The obtained Wigner functions are two-dimensional Gaussians with different widths. Then a closed expression for the density operator is extracted. The entropy of the system is subsequently calculated and its temporal behavior shows that this quantity relaxes to its equilibrium value.
Demonstration of Jarzynski's equality in open quantum systems using a stepwise pulling protocol.
Ngo, Van A; Haas, Stephan
2012-09-01
We present a generalization of Jarzynski's equality, applicable to quantum systems, that is related to discretized mechanical work and free-energy changes. The theory is based on a stepwise pulling protocol. We find that work distribution functions can be constructed from fluctuations of a reaction coordinate along a reaction pathway in the stepwise pulling protocol. We also propose two sets of equations to determine the two possible optimal pathways that provide the most significant contributions to free-energy changes. We find that the transitions along these most optimal pathways, satisfying both sets of equations, follow the principle of detailed balance. We then test the theory by explicitly computing the free-energy changes for a one-dimensional quantum harmonic oscillator. This approach suggests a feasible way of measuring the fluctuations to experimentally test Jarzynski's equality in many-body systems, such as Bose-Einstein condensates. PMID:23030886
Typical, finite baths as a means of exact simulation of open quantum systems
NASA Astrophysics Data System (ADS)
Silvestri, Luciano; Jacobs, Kurt; Dunjko, Vanja; Olshanii, Maxim
2014-04-01
There is presently considerable interest in accurately simulating the evolution of open systems for which Markovian master equations fail. Examples are systems that are time dependent and/or strongly damped. A number of elegant methods have now been devised to do this, but all use a bath consisting of a continuum of harmonic oscillators. While this bath is clearly appropriate for, e.g., systems coupled to the electromagnetic field, it is not so clear that it is a good model for generic many-body systems. Here we explore a different approach to exactly simulating open systems: using a finite bath chosen to have certain key properties of thermalizing many-body systems. To explore the numerical resources required by this method to approximate an open system coupled to an infinite bath, we simulate a weakly damped system and compare to the evolution given by the relevant Markovian master equation. We obtain the Markovian evolution with reasonable accuracy by using an additional averaging procedure, and elucidate how the typicality of the bath generates the correct thermal steady state via the process of "eigenstate thermalization."
Stimulated Raman adiabatic passage in an open quantum system: Master equation approach
Scala, M.; Militello, B.; Messina, A.; Vitanov, N. V.
2010-05-15
A master equation approach to the study of environmental effects in the adiabatic population transfer in three-state systems is presented. A systematic comparison with the non-Hermitian Hamiltonian approach [Vitanov and Stenholm, Phys. Rev. A 56, 1463 (1997)] shows that, in the weak-coupling limit, the two treatments lead to essentially the same results. In contrast, in the strong-damping limit the predictions are quite different: In particular, the counterintuitive sequences in the STIRAP scheme turn out to be much more efficient than expected before. This point is explained in terms of quantum Zeno dynamics.
NASA Astrophysics Data System (ADS)
Chakraborty, Romit; Mazziotti, David A.
2015-01-01
Information about the interaction of a many-electron quantum system with its environment, we show, is encoded within the one-electron density matrix (1-RDM). While the 1-RDM from an ensemble many-electron quantum system must obey the Pauli exclusion principle, the 1-RDM must obey additional constraints known as generalized Pauli conditions when it corresponds to a closed system describable by a single wave function. By examining the 1-RDM's violation of these generalized Pauli conditions, we obtain a sufficient condition at the level of a single electron for a many-electron quantum system's openness. In an application to exciton dynamics in photosynthetic light harvesting we show that the interaction of the system with the environment (quantum noise) relaxes significant constraints imposed on the exciton dynamics by the generalized Pauli conditions. This relaxation provides a geometric (kinematic) interpretation for the role of noise in enhancing exciton transport in quantum systems.
Seliger, M.
2007-03-01
We present a joint theoretical and experimental study of the time evolution of electronic states of highly charged hydrogenic ions formed by capture during transmission through solids as they undergo multiple collisions and radiative decay. For this transport problem we have developed an inhomogeneous nonunitary Lindblad master equation that allows for a description of open quantum systems with both sinks (electron loss) and source (capture) present. We apply this theoretical framework to study transient coherences created in electron capture by 13.6 MeV/amu Ar^{18+} ions transmitted through amorphous carbon foils and decoherence during subsequent interaction with the foil. In the limit of thin targets we can directly probe electron capture cross sections under single collision conditions, while for thicker targets we follow the partially coherent dynamics of the open quantum system in interaction with the solid as a function of interaction time. The calculated results are in close agreement with experimental data obtained at the LISE facility in GANIL. Photon intensities from excited argon ions were determined through high resolution x-ray spectroscopy in which individual fine structure components were resolved. Measurements were performed for a wide range of carbon foil thickness to study the time development of the excited state populations.
NASA Astrophysics Data System (ADS)
Blanchard, Philippe; Hellmich, Mario; Åugiewicz, Piotr; Olkiewicz, Robert
Quantum mechanics is the greatest revision of our conception of the character of the physical world since Newton. Consequently, David Hilbert was very interested in quantum mechanics. He and John von Neumann discussed it frequently during von Neumann's residence in GÃ¶ttingen. He published in 1932 his book Mathematical Foundations of Quantum Mechanics. In Hilbert's opinion it was the first exposition of quantum mechanics in a mathematically rigorous way. The pioneers of quantum mechanics, Heisenberg and Dirac, neither had use for rigorous mathematics nor much interest in it. Conceptually, quantum theory as developed by Bohr and Heisenberg is based on the positivism of Mach as it describes only observable quantities. It first emerged as a result of experimental data in the form of statistical observations of quantum noise, the basic concept of quantum probability.
NASA Astrophysics Data System (ADS)
SchrÃ¶der, Florian A. Y. N.; Chin, Alex W.
2016-02-01
We report the development of an efficient many-body algorithm for simulating open quantum system dynamics that utilizes a time-dependent variational principle for matrix product states to evolve large system-environment states. Capturing all system-environment correlations, we reproduce the nonperturbative, quantum-critical dynamics of the zero-temperature spin-boson model, and then exploit the many-body information to visualize the complete time-frequency spectrum of the environmental excitations. Our "environmental spectra" reveal correlated vibrational motion in polaronic modes which preserve their vibrational coherence during incoherent spin relaxation, demonstrating how environment information could yield valuable insights into complex quantum dissipative processes.
NASA Astrophysics Data System (ADS)
Nikitin, N. V.; Sotnikov, V. P.; Toms, K. S.
2015-10-01
A radically new class of Bell inequalities in Wigner's form was obtained on the basis of Kolmorov's axiomatization of probability theory and the hypothesis of locality. These inequalities take explicitly into account the dependence on time (time-dependent Bell inequalities in Wigner's form). By using these inequalities, one can propose a means for experimentally testing Bohr' complementarity principle in the relativistic region. The inequalities in question open broad possibilities for studying correlations of nonrelativistic and relativistic quantum systems in external fields. The violation of the time-dependent inequalities in quantum mechanics was studied by considering the behavior of a pair of anticorrelated spins in a constant external magnetic field and oscillations of neutral pseudoscalar mesons. The decay of a pseudoscalar particle to a fermion-antifermion pair is considered within quantum field theory. In order to test experimentally the inequalities proposed in the present study, it is not necessary to perform dedicated noninvasive measurements required in the Leggett-Garg approach, for example.
Nonequilibrium Phase Transition in a Two-Dimensional Driven Open Quantum System
NASA Astrophysics Data System (ADS)
Dagvadorj, G.; Fellows, J. M.; Matyja?kiewicz, S.; Marchetti, F. M.; Carusotto, I.; Szyma?ska, M. H.
2015-10-01
The Berezinskii-Kosterlitz-Thouless mechanism, in which a phase transition is mediated by the proliferation of topological defects, governs the critical behavior of a wide range of equilibrium two-dimensional systems with a continuous symmetry, ranging from spin systems to superconducting thin films and two-dimensional Bose fluids, such as liquid helium and ultracold atoms. We show here that this phenomenon is not restricted to thermal equilibrium, rather it survives more generally in a dissipative highly nonequilibrium system driven into a steady state. By considering a quantum fluid of polaritons of an experimentally relevant size, in the so-called optical parametric oscillator regime, we demonstrate that it indeed undergoes a phase transition associated with a vortex binding-unbinding mechanism. Yet, the exponent of the power-law decay of the first-order correlation function in the (algebraically) ordered phase can exceed the equilibrium upper limit: this shows that the ordered phase of driven-dissipative systems can sustain a higher level of collective excitations before the order is destroyed by topological defects. Our work suggests that the macroscopic coherence phenomena, observed recently in interacting two-dimensional light-matter systems, result from a nonequilibrium phase transition of the Berezinskii-Kosterlitz-Thouless rather than the Bose-Einstein condensation type.
Laguna, Humberto G; Sagar, Robin P; Tempel, David G; Aspuru-Guzik, AlÃ¡n
2016-01-01
The effects of bath coupling on an interacting two-particle quantum system are studied using tools from information theory. Shannon entropies of the one (reduced) and two-particle distribution functions in position, momentum and separable phase-space are examined. Results show that the presence of the bath leads to a delocalization of the distribution functions in position space, and a localization in momentum space. This can be interpreted as a loss of information in position space and a gain of information in momentum space. The entropy sum of the system, in the presence of a bath, is shown to be dependent on the strength of the interparticle potential and also on the strength of the coupling to the bath. The statistical correlation between the particles, and its dependence on the bath and interparticle potential, is examined using mutual information. A stronger repulsive potential between particles, in the presence of the bath, yields a smaller correlation between the particles positions, and a larger one between their momenta. PMID:26616490
A model of epigenetic evolution based on theory of open quantum systems.
Asano, Masanari; Basieva, Irina; Khrennikov, Andrei; Ohya, Masanori; Tanaka, Yoshiharu; Yamato, Ichiro
2013-12-01
We present a very general model of epigenetic evolution unifying (neo-)Darwinian and (neo-)Lamarckian viewpoints. The evolution is represented in the form of adaptive dynamics given by the quantum(-like) master equation. This equation describes development of the information state of epigenome under the pressure of an environment. We use the formalism of quantum mechanics in the purely operational framework. (Hence, our model has no direct relation to quantum physical processes inside a cell.) Thus our model is about probabilities for observations which can be done on epigenomes and it does not provide a detailed description of cellular processes. Usage of the operational approach provides a possibility to describe by one model all known types of cellular epigenetic inheritance. PMID:24432153
NASA Astrophysics Data System (ADS)
Tao, L.; Sun, K.; Cavigelli, M. A.; Gelfand, I.; Zenone, T.; Cui, M.; Miller, D. J.; Khan, M. A.; Zondlo, M. A.
2012-12-01
The ambient concentration of nitrous oxide (N2O), the fourth most abundant greenhouse gas, is rapidly increasing with emissions from both natural and anthropogenic sources [1]. Soil and aquatic areas are important sources and sinks for N2O due to complicated biogenic processes. However, N2O emissions are poorly constrained in space and time, despite its importance to global climate change and ozone depletion. We report our recent N2O emission measurements with an open-path quantum cascade laser (QCL)-based sensor for ecological systems. The newly emergent QCLs have been used to build compact, sensitive trace gas sensors in the mid-IR spectral region. A compact open-path QCL based sensor was developed to detect atmospheric N2O and CO at ~ 4.5 Î¼m using wavelength modulation spectroscopy (WMS) to achieve a sensitivity of 0.26 ppbv of N2O and 0.24 ppbv of CO in 1 s with a power consumption of ~50 W [2]. This portable sensor system has been used to perform N2O emission flux measurement both with a static flux chamber and on an eddy covariance (EC) flux tower. In the flux chamber measurements, custom chambers were used to host the laser sensor, while gas samples for gas chromatograph (GC) were collected at the same time in the same chamber for validation and comparison. Different soil treatments have been applied in different chambers to study the relationship between N2O emission and the amount of fertilizer (and water) addition. Measurements from two methods agreed with each other (95% or higher confidence interval) for emission flux results, while laser sensor gave measurements with a much high temporal resolution. We have also performed the first open-path eddy covariance N2O flux measurement at Kellogg research station, Michigan State University for a month in June, 2012. Our sensor was placed on a 4-meter tower in a corn field and powered by batteries (connected with solar panels). We have observed the diurnal cycle of N2O flux. During this deployment, an inter-comparison between our sensor and a commercial gas sensor was done to check the sensor's performance. Overall, our sensor showed a good performance with both static chamber measurement and EC flux measurement of N2O. Its open-path, compact and portable design with low power consumption provides lots of advantages for N2O emission flux measurement in the ecological systems. [1] S. A. Montzka, E. J. Dlugokencky, and J. H. Butler, "Non-CO2 greenhouse gases and climate change," Nature 476, 43-50 (2011). [2] L. Tao, K, Sun, D. J. Miller, M. A. Khan and M.A. Zondlo, "Optimizations for simultaneous detection of atmospheric N2O and CO with a quantum cascade laser," CLEO, 2012
Design of coherent quantum observers for linear quantum systems
NASA Astrophysics Data System (ADS)
Vuglar, Shanon L.; Amini, Hadis
2014-12-01
Quantum versions of control problems are often more difficult than their classical counterparts because of the additional constraints imposed by quantum dynamics. For example, the quantum LQG and quantum {{H}? } optimal control problems remain open. To make further progress, new, systematic and tractable methods need to be developed. This paper gives three algorithms for designing coherent quantum observers, i.e., quantum systems that are connected to a quantum plant and their outputs provide information about the internal state of the plant. Importantly, coherent quantum observers avoid measurements of the plant outputs. We compare our coherent quantum observers with a classical (measurement-based) observer by way of an example involving an optical cavity with thermal and vacuum noises as inputs.
Time-dependent approach to electron pumping in open quantum systems
NASA Astrophysics Data System (ADS)
Stefanucci, G.; Kurth, S.; Rubio, A.; Gross, E. K. U.
2008-02-01
We use a recently proposed time-dependent approach to investigate the motion of electrons in quantum pump device configurations. The occupied one-particle states are propagated in real time and employed to calculate the local electron density and current. The approach can also be embedded in the framework of time-dependent density functional theory to include electron-electron interactions. An advantage of the present computational scheme is that the same computational effort is required to simulate monochromatic, polychromatic, and nonperiodic drivings. Furthermore, initial-state dependence and history effects are naturally accounted for. We present results for one-dimensional devices exposed to a traveling potential wave. (i) We show that for pumping across a single potential barrier, electrons are transported in pockets and the transport mechanism resembles pumping of water with the Archimedean screw; (ii) we propose a simple model to study pumping through semiconductor nanostructures and we address the phenomenon of the current flowing in the opposite direction to the field propagation; (iii) we present the first numerical evidence of long-lived superimposed oscillations as induced by the presence of bound states and discuss the dependence of their lifetime on the frequency and amplitude of the driving field. By combining Floquet theory with nonequilibrium Green’s functions, we also obtain a general expression for the pumped current in terms of inelastic transmission probabilities. This latter result is used for benchmarking our propagation scheme in the long-time limit. Finally, we discuss the limitations of Floquet-based algorithms and suggest our approach as a possible way to go beyond them.
Measurement theory for closed quantum systems
NASA Astrophysics Data System (ADS)
Wouters, Michiel
2015-07-01
We introduce the concept of a “classical observable” as an operator with vanishingly small quantum fluctuations on a set of density matrices. Their study provides a natural starting point to analyse the quantum measurement problem. In particular, it allows to identify Schrödinger cats and the associated projection operators intrinsically, without the need to invoke an environment. We discuss how our new approach relates to the open system analysis of quantum measurements and to thermalization studies in closed quantum systems.
Generalized Open Quantum Walks on Apollonian Networks
Pawela, Åukasz; Gawron, Piotr; Miszczak, JarosÅ‚aw Adam; Sadowski, PrzemysÅ‚aw
2015-01-01
We introduce the model of generalized open quantum walks on networks using the Transition Operation Matrices formalism. We focus our analysis on the mean first passage time and the average return time in Apollonian networks. These results differ significantly from a classical walk on these networks. We show a comparison of the classical and quantum behaviour of walks on these networks. PMID:26177452
Mappings of open quantum systems onto chain representations and Markovian embeddings
Woods, M. P.; Groux, R.; Chin, A. W.; Huelga, S. F.; Plenio, M. B.
2014-03-15
We study systems coupled linearly to a bath of oscillators. In an iterative process, the bath is transformed into a chain of oscillators with nearest neighbour interactions. A systematic procedure is provided to obtain the spectral density of the residual bath in each step, and it is shown that under general conditions these data converge. That is, the asymptotic part of the chain is universal, translation invariant with semicircular spectral density. The methods are based on orthogonal polynomials, in which we also solve the outstanding so-called “sequence of secondary measures problem” and give them a physical interpretation.
Shot noise spectrum of open dissipative quantum two-level systems.
Aguado, Ramón; Brandes, Tobias
2004-05-21
We study the current noise spectrum of qubits under transport conditions in a dissipative bosonic environment. We combine (non-)Markovian master equations with correlation functions in Laplace space to derive a noise formula for both weak and strong coupling to the bath. The coherence-induced reduction of noise is diminished by weak dissipation and/or a large level separation (bias). For weak dissipation, we demonstrate that the dephasing and relaxation rates of the two-level systems can be extracted from noise. In the strong dissipation regime, the localization-delocalization transition becomes visible in the low-frequency noise. PMID:15169372
Open quantum system approach to the modeling of spin recombination reactions.
Tiersch, M; Steiner, U E; Popescu, S; Briegel, H J
2012-04-26
In theories of spin-dependent radical pair reactions, the time evolution of the radical pair, including the effect of the chemical kinetics, is described by a master equation in the Liouville formalism. For the description of the chemical kinetics, a number of possible reaction operators have been formulated in the literature. In this work, we present a framework that allows for a unified description of the various proposed mechanisms and the forms of reaction operators for the spin-selective recombination processes. On the basis of the concept that master equations can be derived from a microscopic description of the spin system interacting with external degrees of freedom, it is possible to gain insight into the underlying microscopic processes and develop a systematic approach toward determining the specific form of the reaction operator in concrete scenarios. PMID:22401141
NASA Astrophysics Data System (ADS)
Carrega, M.; Solinas, P.; Braggio, A.; Sassetti, M.; Weiss, U.
2015-04-01
We establish the path integral approach for the time-dependent heat exchange of an externally driven quantum system coupled to a thermal reservoir. We derive the relevant influence functional and present an exact formal expression for the moment generating functional which carries all statistical properties of the heat exchange process for general linear dissipation. The method is applied to the time-dependent average heat transfer in the dissipative two-state system (TSS). We show that the heat can be written as a convolution integral which involves the population and coherence correlation functions of the TSS and additional correlations due to a polarization of the reservoir. The corresponding expression can be solved in the weak-damping limit both for white noise and for quantum mechanical coloured noise. The implications of pure quantum effects are discussed. Altogether a complete description of the dynamics of the average heat transfer ranging from the classical regime down to zero temperature is achieved.
NASA Astrophysics Data System (ADS)
Cahill, Reginald T.
2002-10-01
So far proposed quantum computers use fragile and environmentally sensitive natural quantum systems. Here we explore the new notion that synthetic quantum systems suitable for quantum computation may be fabricated from smart nanostructures using topological excitations of a stochastic neural-type network that can mimic natural quantum systems. These developments are a technological application of process physics which is an information theory of reality in which space and quantum phenomena are emergent, and so indicates the deep origins of quantum phenomena. Analogous complex stochastic dynamical systems have recently been proposed within neurobiology to deal with the emergent complexity of biosystems, particularly the biodynamics of higher brain function. The reasons for analogous discoveries in fundamental physics and neurobiology are discussed.
NASA Astrophysics Data System (ADS)
Ma, Xiang-Chun; Sun, Shi-Hai; Jiang, Mu-Sheng; Liang, Lin-Mei
2013-08-01
We consider the security of practical continuous-variable quantum-key-distribution implementation with the local oscillator (LO) fluctuating in time, which opens a loophole for Eve to intercept the secret key. We show that Eve can simulate this fluctuation to hide her Gaussian collective attack by reducing the intensity of the LO. Numerical simulations demonstrate that if Bob does not monitor the LO intensity and does not scale his measurements with the instantaneous intensity values of LO, the secret key rate will be compromised severely.
NASA Astrophysics Data System (ADS)
Khrennikova, Polina; Haven, Emmanuel; Khrennikov, Andrei
2014-04-01
The Gorini-Kossakowski-Sudarshan-Lindblad equation allows us to model the process of decision making in US elections. The crucial point we attempt to make is that the voter's mental state can be represented as a superposition of two possible choices for either republicans or democrats. However, reality dictates a more complicated situation: typically a voter participates in two elections, i.e. the congress and the presidential elections. In both elections the voter has to decide between two choices. This very feature of the US election system requires that the mental state is represented by a 2-qubit state corresponding to the superposition of 4 different choices. The main issue is to describe the dynamics of the voters' mental states taking into account the mental and political environment. What is novel in this paper is that we apply the theory of open quantum systems to social science. The quantum master equation describes the resolution of uncertainty (represented in the form of superposition) to a definite choice.
Quantum coherence and correlations in quantum system
Xi, Zhengjun; Li, Yongming; Fan, Heng
2015-01-01
Criteria of measure quantifying quantum coherence, a unique property of quantum system, are proposed recently. In this paper, we first give an uncertainty-like expression relating the coherence and the entropy of quantum system. This finding allows us to discuss the relations between the entanglement and the coherence. Further, we discuss in detail the relations among the coherence, the discord and the deficit in the bipartite quantum system. We show that, the one-way quantum deficit is equal to the sum between quantum discord and the relative entropy of coherence of measured subsystem. PMID:26094795
NASA Astrophysics Data System (ADS)
Head-Marsden, Kade; Mazziotti, David A.
2015-02-01
For an open, time-dependent quantum system, Lindblad derived the most general modification of the quantum Liouville equation in the Markovian approximation that models environmental effects while preserving the non-negativity of the system's density matrix. While Lindblad's modification is correct for N-electron density matrices, solution of the Liouville equation with a Lindblad operator causes the one-electron reduced density matrix (1-RDM) to violate the Pauli exclusion principle. Consequently, after a short time, the 1-RDM is not representable by an ensemble N-electron density matrix (not ensemble N-representable). In this communication, we derive the necessary and sufficient constraints on the Lindbladian matrix within the Lindblad operator to ensure that the 1-RDM remains N-representable for all time. The theory is illustrated by considering the relaxation of an excitation in several molecules F2, N2, CO, and BeH2 subject to environmental noise.
Head-Marsden, Kade; Mazziotti, David A
2015-02-01
For an open, time-dependent quantum system, Lindblad derived the most general modification of the quantum Liouville equation in the Markovian approximation that models environmental effects while preserving the non-negativity of the system's density matrix. While Lindblad's modification is correct for N-electron density matrices, solution of the Liouville equation with a Lindblad operator causes the one-electron reduced density matrix (1-RDM) to violate the Pauli exclusion principle. Consequently, after a short time, the 1-RDM is not representable by an ensemble N-electron density matrix (not ensemble N-representable). In this communication, we derive the necessary and sufficient constraints on the Lindbladian matrix within the Lindblad operator to ensure that the 1-RDM remains N-representable for all time. The theory is illustrated by considering the relaxation of an excitation in several molecules F2, N2, CO, and BeH2 subject to environmental noise. PMID:25662627
NASA Astrophysics Data System (ADS)
Sidles, John A.; Garbini, Joseph L.; Harrell, Lee E.; Hero, Alfred O.; Jacky, Jonathan P.; Malcomb, Joseph R.; Norman, Anthony G.; Williamson, Austin M.
2009-06-01
Practical recipes are presented for simulating high-temperature and nonequilibrium quantum spin systems that are continuously measured and controlled. The notion of a spin system is broadly conceived, in order to encompass macroscopic test masses as the limiting case of large-j spins. The simulation technique has three stages: first the deliberate introduction of noise into the simulation, then the conversion of that noise into an equivalent continuous measurement and control process, and finally, projection of the trajectory onto state-space manifolds having reduced dimensionality and possessing a Kähler potential of multilinear algebraic form. These state-spaces can be regarded as ruled algebraic varieties upon which a projective quantum model order reduction (MOR) is performed. The Riemannian sectional curvature of ruled Kählerian varieties is analyzed, and proved to be non-positive upon all sections that contain a rule. These manifolds are shown to contain Slater determinants as a special case and their identity with Grassmannian varieties is demonstrated. The resulting simulation formalism is used to construct a positive P-representation for the thermal density matrix. Single-spin detection by magnetic resonance force microscopy (MRFM) is simulated, and the data statistics are shown to be those of a random telegraph signal with additive white noise. Larger-scale spin-dust models are simulated, having no spatial symmetry and no spatial ordering; the high-fidelity projection of numerically computed quantum trajectories onto low dimensionality Kähler state-space manifolds is demonstrated. The reconstruction of quantum trajectories from sparse random projections is demonstrated, the onset of Donoho-Stodden breakdown at the Candès-Tao sparsity limit is observed, a deterministic construction for sampling matrices is given and methods for quantum state optimization by Dantzig selection are given.
NASA Astrophysics Data System (ADS)
Yan, YiJing
2014-02-01
This work establishes a strongly correlated system-and-bath dynamics theory, the many-dissipaton density operators formalism. It puts forward a quasi-particle picture for environmental influences. This picture unifies the physical descriptions and algebraic treatments on three distinct classes of quantum environments, electron bath, phonon bath, and two-level spin or exciton bath, as their participating in quantum dissipation processes. Dynamical variables for theoretical description are no longer just the reduced density matrix for system, but remarkably also those for quasi-particles of bath. The present theoretical formalism offers efficient and accurate means for the study of steady-state (nonequilibrium and equilibrium) and real-time dynamical properties of both systems and hybridizing environments. It further provides universal evaluations, exact in principle, on various correlation functions, including even those of environmental degrees of freedom in coupling with systems. Induced environmental dynamics could be reflected directly in experimentally measurable quantities, such as Fano resonances and quantum transport current shot noise statistics.
Yan, YiJing
2014-02-07
This work establishes a strongly correlated system-and-bath dynamics theory, the many-dissipaton density operators formalism. It puts forward a quasi-particle picture for environmental influences. This picture unifies the physical descriptions and algebraic treatments on three distinct classes of quantum environments, electron bath, phonon bath, and two-level spin or exciton bath, as their participating in quantum dissipation processes. Dynamical variables for theoretical description are no longer just the reduced density matrix for system, but remarkably also those for quasi-particles of bath. The present theoretical formalism offers efficient and accurate means for the study of steady-state (nonequilibrium and equilibrium) and real-time dynamical properties of both systems and hybridizing environments. It further provides universal evaluations, exact in principle, on various correlation functions, including even those of environmental degrees of freedom in coupling with systems. Induced environmental dynamics could be reflected directly in experimentally measurable quantities, such as Fano resonances and quantum transport current shot noise statistics.
Open quantum reaction-diffusion dynamics: Absorbing states and relaxation.
van Horssen, Merlijn; Garrahan, Juan P
2015-03-01
We consider an extension of classical stochastic reaction-diffusion (RD) dynamics to open quantum systems. We study a class of models of hard-core particles on a one-dimensional lattice whose dynamics is generated by a quantum master operator. Particle hopping is coherent while reactions, such as pair annihilation or pair coalescence, are dissipative. These are quantum open generalizations of the A+Aâ†’âŒ€ and A+Aâ†’A classical RD models. We characterize the relaxation of the state towards the stationary regime via a decomposition of the system Hilbert space into transient and recurrent subspaces. We provide a complete classification of the structure of the recurrent subspace (and the nonequilibrium steady states) in terms of the dark states associated to the quantum master operator and its general spectral properties. We also show that, in one dimension, relaxation towards these absorbing dark states is slower than that predicted by a mean-field analysis due to fluctuation effects, in analogy with what occurs in classical RD systems. Numerical simulations of small systems suggest that the decay of the density in one dimension, in both the open quantum A+Aâ†’âŒ€ and A+Aâ†’A systems, behaves asymptotically as t-b with 1/2
Microscopic derivation of open quantum Brownian motion
NASA Astrophysics Data System (ADS)
Petruccione, Francesco; Sinayskiy, Ilya; UKZN Team
2015-03-01
Recently a model of open quantum Brownian motion (OQBM) [M. Bauer, D. Bernard, A. Tilloy, Phys. Rev. A 88 (2013) 062340] was introduced as a scaling limit of Open Quantum Walks (OQWs) [S. Attal, F. Petruccione, C. Sabot, I. Sinayskiy, J. Stat. Phys. 147 (20120 832]. OQBM is a new type of quantum Brownian motion where the dynamics of the Brownian particle not only depends on the interactions with a thermal environment, but also depends on the state of the internal degrees of freedom of the Brownian particle. Here, we present the microscopic derivation of the OQBM for a Brownian particle with two internal degrees of freedom. Examples of the dynamics for initial Gaussian and non-Gaussian distributions are presented. This work is based upon research supported by the South African Research Chair Initiative of the Department of Science and Technology and National Research Foundation.
Quantum Dynamics in Biological Systems
NASA Astrophysics Data System (ADS)
Shim, Sangwoo
In the first part of this dissertation, recent efforts to understand quantum mechanical effects in biological systems are discussed. Especially, long-lived quantum coherences observed during the electronic energy transfer process in the Fenna-Matthews-Olson complex at physiological condition are studied extensively using theories of open quantum systems. In addition to the usual master equation based approaches, the effect of the protein structure is investigated in atomistic detail through the combined application of quantum chemistry and molecular dynamics simulations. To evaluate the thermalized reduced density matrix, a path-integral Monte Carlo method with a novel importance sampling approach is developed for excitons coupled to an arbitrary phonon bath at a finite temperature. In the second part of the thesis, simulations of molecular systems and applications to vibrational spectra are discussed. First, the quantum dynamics of a molecule is simulated by combining semiclassical initial value representation and density funcitonal theory with analytic derivatives. A computationally-tractable approximation to the sum-of-states formalism of Raman spectra is subsequently discussed.
Danilov, Viatcheslav; Nagaitsev, Sergei; /Fermilab
2011-11-01
Many quantum integrable systems are obtained using an accelerator physics technique known as Ermakov (or normalized variables) transformation. This technique was used to create classical nonlinear integrable lattices for accelerators and nonlinear integrable plasma traps. Now, all classical results are carried over to a nonrelativistic quantum case. In this paper we have described an extension of the Ermakov-like transformation to the Schroedinger and Pauli equations. It is shown that these newly found transformations create a vast variety of time dependent quantum equations that can be solved in analytic functions, or, at least, can be reduced to time-independent ones.
Microscopic derivation of open quantum walks
NASA Astrophysics Data System (ADS)
Sinayskiy, Ilya; Petruccione, Francesco
2015-09-01
Open quantum walks (OQWs) are exclusively driven by dissipation and are formulated as completely positive trace-preserving (CPTP) maps on underlying graphs. The microscopic derivation of discrete and continuous-in-time OQWs is presented. It is assumed that connected nodes are weakly interacting via a common bath. The resulting reduced master equation of the quantum walker on the lattice is in the generalized master equation form. The time discretization of the generalized master equation leads to the OQW formalism. The explicit form of the transition operators establishes a connection between dynamical properties of the OQWs and thermodynamical characteristics of the environment. The derivation is demonstrated for the examples of the OQW on a circle of nodes and on a finite chain of nodes. For both examples, a transition between diffusive and ballistic quantum trajectories is observed and found to be related to the temperature of the bath.
NASA Astrophysics Data System (ADS)
Clark, John W.; Lucarelli, Dennis G.; Tarn, Tzyh-Jong
2002-12-01
A quantum system subject to external fields is said to be controllable if these fields can be adjusted to guide the state vector to a desired destination in the state space of the system. Fundamental results on controllability are reviewed against the background of recent ideas and advances in two seemingly disparate endeavours: (i) laser control of chemical reactions and (ii) quantum computation. Using Lie-algebraic methods, sufficient conditions have been derived for global controllability on a finite-dimensional manifold of an infinite-dimensional Hilbert space, in the case that the Hamiltonian and control operators, possibly unbounded, possess a common dense domain of analytic vectors. Some simple examples are presented. A synergism between quantum control and quantum computation is creating a host of exciting new opportunities for both activities. The impact of these developments on computational many-body theory could be profound.
NASA Astrophysics Data System (ADS)
Castillo, Paulo; Diaz, Adrian; Thomas, Benjamin; Gross, Barry; Moshary, Fred
2015-10-01
Methane and Nitrous Oxide are long-lived greenhouse gases in the atmosphere with significant global warming effects. We report on application of chirped-pulsed quantum cascade lasers (QCLs) to simultaneous measurements of these trace gases in both open-path fence-line and backscatter systems. The intra-pulse thermal frequency chip in a QCL can be time resolved and calibrated to allow for high resolution differential optical absorption spectroscopy over the spectral window of the chip, which for a DFB-QCL can be reach ~2cm-1 for a 500 nsec pulse. The spectral line-shape of the output from these lasers are highly stable from pulse to pulse over long period of time (> 1 day), and the system does not require frequent calibrations.
Micheli, Fiorenza de; Zanelli, Jorge
2012-10-15
A degenerate dynamical system is characterized by a symplectic structure whose rank is not constant throughout phase space. Its phase space is divided into causally disconnected, nonoverlapping regions in each of which the rank of the symplectic matrix is constant, and there are no classical orbits connecting two different regions. Here the question of whether this classical disconnectedness survives quantization is addressed. Our conclusion is that in irreducible degenerate systems-in which the degeneracy cannot be eliminated by redefining variables in the action-the disconnectedness is maintained in the quantum theory: there is no quantum tunnelling across degeneracy surfaces. This shows that the degeneracy surfaces are boundaries separating distinct physical systems, not only classically, but in the quantum realm as well. The relevance of this feature for gravitation and Chern-Simons theories in higher dimensions cannot be overstated.
Open quantum dotsâ€”probing the quantum to classical transition
NASA Astrophysics Data System (ADS)
Ferry, D. K.; Burke, A. M.; Akis, R.; Brunner, R.; Day, T. E.; Meisels, R.; Kuchar, F.; Bird, J. P.; Bennett, B. R.
2011-04-01
Quantum dots provide a natural system in which to study both quantum and classical features of transport. As a closed testbed, they provide a natural system with a very rich set of eigenstates. When coupled to the environment through a pair of quantum point contacts, each of which passes several modes, the original quantum environment evolves into a set of decoherent and coherent states, which classically would compose a mixed phase space. The manner of this breakup is governed strongly by Zurek's decoherence theory, and the remaining coherent states possess all the properties of his pointer states. These states are naturally studied via traditional magnetotransport at low temperatures. More recently, we have used scanning gate (conductance) microscopy to probe the nature of the coherent states, and have shown that families of states exist through the spectrum in a manner consistent with quantum Darwinism. In this review, we discuss the nature of the various states, how they are formed, and the signatures that appear in magnetotransport and general conductance studies.
Rapid Swept-Wavelength External Cavity Quantum Cascade Laser for Open Path Sensing
Brumfield, Brian E.; Phillips, Mark C.
2015-07-01
A rapidly tunable external cavity quantum cascade laser system is used for open path sensing. The system permits acquisition of transient absorption spectra over a 125 cm-1 tuning range in less than 0.01 s.
Scheme of thinking quantum systems
NASA Astrophysics Data System (ADS)
Yukalov, V. I.; Sornette, D.
2009-11-01
A general approach describing quantum decision procedures is developed. The approach can be applied to quantum information processing, quantum computing, creation of artificial quantum intelligence, as well as to analyzing decision processes of human decision makers. Our basic point is to consider an active quantum system possessing its own strategic state. Processing information by such a system is analogous to the cognitive processes associated to decision making by humans. The algebra of probability operators, associated with the possible options available to the decision maker, plays the role of the algebra of observables in quantum theory of measurements. A scheme is advanced for a practical realization of decision procedures by thinking quantum systems. Such thinking quantum systems can be realized by using spin lattices, systems of magnetic molecules, cold atoms trapped in optical lattices, ensembles of quantum dots, or multilevel atomic systems interacting with electromagnetic field.
Head-Marsden, Kade; Mazziotti, David A.
2015-02-07
For an open, time-dependent quantum system, Lindblad derived the most general modification of the quantum Liouville equation in the Markovian approximation that models environmental effects while preserving the non-negativity of the systemâ€™s density matrix. While Lindbladâ€™s modification is correct for N-electron density matrices, solution of the Liouville equation with a Lindblad operator causes the one-electron reduced density matrix (1-RDM) to violate the Pauli exclusion principle. Consequently, after a short time, the 1-RDM is not representable by an ensemble N-electron density matrix (not ensemble N-representable). In this communication, we derive the necessary and sufficient constraints on the Lindbladian matrix within the Lindblad operator to ensure that the 1-RDM remains N-representable for all time. The theory is illustrated by considering the relaxation of an excitation in several molecules F{sub 2}, N{sub 2}, CO, and BeH{sub 2} subject to environmental noise.
Veeraraghavan, Srikant; Mazziotti, David A.
2014-03-28
We present a density matrix approach for computing global solutions of restricted open-shell Hartree-Fock theory, based on semidefinite programming (SDP), that gives upper and lower bounds on the Hartree-Fock energy of quantum systems. While wave function approaches to Hartree-Fock theory yield an upper bound to the Hartree-Fock energy, we derive a semidefinite relaxation of Hartree-Fock theory that yields a rigorous lower bound on the Hartree-Fock energy. We also develop an upper-bound algorithm in which Hartree-Fock theory is cast as a SDP with a nonconvex constraint on the rank of the matrix variable. Equality of the upper- and lower-bound energies guarantees that the computed solution is the globally optimal solution of Hartree-Fock theory. The work extends a previously presented method for closed-shell systems [S. Veeraraghavan and D. A. Mazziotti, Phys. Rev. A 89, 010502–R (2014)]. For strongly correlated systems the SDP approach provides an alternative to the locally optimized Hartree-Fock energies and densities with a certificate of global optimality. Applications are made to the potential energy curves of C{sub 2}, CN, Cr {sub 2}, and NO {sub 2}.
Quantum game theory and open access publishing
NASA Astrophysics Data System (ADS)
Hanauske, Matthias; Bernius, Steffen; Dugall, Berndt
2007-08-01
The digital revolution of the information age and in particular the sweeping changes of scientific communication brought about by computing and novel communication technology, potentiate global, high grade scientific information for free. The arXiv, for example, is the leading scientific communication platform, mainly for mathematics and physics, where everyone in the world has free access on. While in some scientific disciplines the open access way is successfully realized, other disciplines (e.g. humanities and social sciences) dwell on the traditional path, even though many scientists belonging to these communities approve the open access principle. In this paper we try to explain these different publication patterns by using a game theoretical approach. Based on the assumption, that the main goal of scientists is the maximization of their reputation, we model different possible game settings, namely a zero sum game, the prisoners’ dilemma case and a version of the stag hunt game, that show the dilemma of scientists belonging to “non-open access communities”. From an individual perspective, they have no incentive to deviate from the Nash equilibrium of traditional publishing. By extending the model using the quantum game theory approach it can be shown, that if the strength of entanglement exceeds a certain value, the scientists will overcome the dilemma and terminate to publish only traditionally in all three settings.
Open systems storage platforms
NASA Technical Reports Server (NTRS)
Collins, Kirby
1992-01-01
The building blocks for an open storage system includes a system platform, a selection of storage devices and interfaces, system software, and storage applications CONVEX storage systems are based on the DS Series Data Server systems. These systems are a variant of the C3200 supercomputer with expanded I/O capabilities. These systems support a variety of medium and high speed interfaces to networks and peripherals. System software is provided in the form of ConvexOS, a POSIX compliant derivative of 4.3BSD UNIX. Storage applications include products such as UNITREE and EMASS. With the DS Series of storage systems, Convex has developed a set of products which provide open system solutions for storage management applications. The systems are highly modular, assembled from off the shelf components with industry standard interfaces. The C Series system architecture provides a stable base, with the performance and reliability of a general purpose platform. This combination of a proven system architecture with a variety of choices in peripherals and application software allows wide flexibility in configurations, and delivers the benefits of open systems to the mass storage world.
Quantum coherence in multipartite systems
NASA Astrophysics Data System (ADS)
Yao, Yao; Xiao, Xing; Ge, Li; Sun, C. P.
2015-08-01
Within the unified framework of exploiting the relative entropy as a distance measure of quantum correlations, we make explicit the hierarchical structure of quantum coherence, quantum discord, and quantum entanglement in multipartite systems. On this basis, we define a basis-independent measure of quantum coherence and prove that it is exactly equivalent to quantum discord. Furthermore, since the original relative entropy of coherence is a basis-dependent quantity, we investigate the local and nonlocal unitary creation of quantum coherence, focusing on the two-qubit unitary gates. Intriguingly, our results demonstrate that nonlocal unitary gates do not necessarily outperform the local unitary gates. Finally, the additivity relationship of quantum coherence in tripartite systems is discussed in detail, where the strong subadditivity of von Neumann entropy plays an essential role.
Vibhute, Pavankumar Janardan
2012-01-01
Sliding mechanics have become a popular method for space closure, with the development of preadjusted edgewise appliances. Furthermore, various space closing auxiliaries have been developed and extensively evaluated for their clinical efficiency. Their effectiveness is enhanced with optimum force magnitude and low load deflection rate/force decay. With the advent of nickel-titanium (Ni-Ti) springs in orthodontics, load deflection rates have been markedly reduced. To use Ni-Ti springs, clinicians have to depend upon prefabricated closed coil springs. The open coil traction system, or open coil retraction spring, is developed utilizing Ni-Ti open coil springs for orthodontic space closure. This article describes the fabrication and clinical application of the open coil traction system, which has a number of advantages. It sustains a low load deflection rate with optimum force magnitude, and its design is adjustable for a desired length and force level. It is fail-safe for both activation and deactivation (ie, it cannot be overactivated, and the decompression limit of the open coil is controlled by the operator). The open coil traction system can be offset from the mucosa to help reduce soft tissue impingement. PMID:22567645
Steady-State Dynamics and Effective Temperature for a Model of Quantum Criticality in an Open System
NASA Astrophysics Data System (ADS)
Ribeiro, P.; Zamani, F.; Kirchner, S.
2015-11-01
We study the thermal and nonthermal steady-state scaling functions and the steady-state dynamics of a model of local quantum criticality. The model we consider, i.e., the pseudogap Kondo model, allows us to study the concept of effective temperatures near fully interacting as well as weak-coupling fixed points. In the vicinity of each fixed point we establish the existence of an effective temperature—different at each fixed point—such that the equilibrium fluctuation-dissipation theorem is recovered. Most notably, steady-state scaling functions in terms of the effective temperatures coincide with the equilibrium scaling functions. This result extends to higher correlation functions as is explicitly demonstrated for the Kondo singlet strength. The nonlinear charge transport is also studied and analyzed in terms of the effective temperature.
Classical transients and the support of open quantum maps.
Carlo, Gabriel G; Wisniacki, D A; Ermann, Leonardo; Benito, R M; Borondo, F
2013-01-01
The basic ingredients in a semiclassical theory are the classical invariant objects serving as a support for quantization. Recent studies, mainly obtained on quantum maps, have led to the commonly accepted belief that the classical repeller-the set of nonescaping orbits in the future and past evolution-is the object that suitably plays this role in open scattering systems. In this paper we present numerical evidence warning that this may not always be the case. For this purpose we study recently introduced families of tribaker maps [L. Ermann, G. G. Carlo, J. M. Pedrosa, and M. Saraceno, Phys. Rev. E 85, 066204 (2012)], which share the same asymptotic properties but differ in their short-time behavior. We have found that although the eigenvalue distribution of the evolution operator of these maps follows the fractal Weyl law prediction, the theory of short periodic orbits for open maps fails to describe the resonance eigenfunctions of some of them. This is a strong indication that new elements must be included in the semiclassical description of open quantum systems. We provide an interpretation of the results in order to have hints about them. PMID:23410406
Open system environment procurement
NASA Technical Reports Server (NTRS)
Fisher, Gary
1994-01-01
Relationships between the request for procurement (RFP) process and open system environment (OSE) standards are described. A guide was prepared to help Federal agency personnel overcome problems in writing an adequate statement of work and developing realistic evaluation criteria when transitioning to an OSE. The guide contains appropriate decision points and transition strategies for developing applications that are affordable, scalable and interoperable across a broad range of computing environments. While useful, the guide does not eliminate the requirement that agencies posses in-depth expertise in software development, communications, and database technology in order to evaluate open systems.
DPS Quantum Key Distribution System
NASA Astrophysics Data System (ADS)
Inoue, Kyo
Differential-phase-shift (DPS) quantum key distribution (QKD) is one scheme of quantum key distribution whose security is based on the quantum nature of lightwave. This protocol features simplicity, a high key creation rate, and robustness against photon-number-splitting attacks. We describe DPS-QKD in this paper, including its setup and operation, eavesdropping against DPS-QKD, system performance, and modified systems to improve the system performance.
Martire, G.S. ); Nuttall, D.J.H. )
1993-05-01
This paper is part of a series of papers invited by the IEEE POWER CONTROL CENTER WORKING GROUP concerning the changing designs of modern control centers. Papers invited by the Working Group discuss the following issues: Benefits of Openness, Criteria for Evaluating Open EMS Systems, Hardware Design, Configuration Management, Security, Project Management, Databases, SCADA, Inter- and Intra-System Communications and Man-Machine Interfaces,'' The goal of this paper is to provide an introduction to the issues pertaining to Open Systems and Databases.'' The intent is to assist understanding of some of the underlying factors that effect choices that must be made when selecting a database system for use in a control room environment. This paper describes and compares the major database information models which are in common use for database systems and provides an overview of SQL. A case for the control center community to follow the workings of the non-formal standards bodies is presented along with possible uses and the benefits of commercially available databases within the control center. The reasons behind the emergence of industry supported standards organizations such as the Open Software Foundation (OSF) and SQL Access are presented.
NASA Astrophysics Data System (ADS)
Iqbal, A.; Toor, A. H.
2002-03-01
We investigate the role of quantum mechanical effects in the central stability concept of evolutionary game theory, i.e., an evolutionarily stable strategy (ESS). Using two and three-player symmetric quantum games we show how the presence of quantum phenomenon of entanglement can be crucial to decide the course of evolutionary dynamics in a population of interacting individuals.
Tal, J.; Lopez, A.; Edwards, J.M.
1995-04-01
In this paper, an alternative solution to the traditional CNC machine tool controller has been introduced. Software and hardware modules have been described and their incorporation in a CNC control system has been outlined. This type of CNC machine tool controller demonstrates that technology is accessible and can be readily implemented into an open architecture machine tool controller. Benefit to the user is greater controller flexibility, while being economically achievable. PC based, motion as well as non-motion features will provide flexibility through a Windows environment. Up-grading this type of controller system through software revisions will keep the machine tool in a competitive state with minimal effort. Software and hardware modules are mass produced permitting competitive procurement and incorporation. Open architecture CNC systems provide diagnostics thus enhancing maintainability, and machine tool up-time. A major concern of traditional CNC systems has been operator training time. Training time can be greatly minimized by making use of Windows environment features.
Local controllability of quantum systems
NASA Astrophysics Data System (ADS)
Pucha?a, Zbigniew
2013-01-01
We give a criterion that is sufficient for controllability of multipartite quantum systems. We generalize the graph infection criterion to the quantum systems that cannot be described with the use of a graph theory. We introduce the notation of hypergraphs and reformulate the infection property in this setting. The introduced criterion has a topological nature and therefore it is not connected to any particular experimental realization of quantum information processing.
NASA Astrophysics Data System (ADS)
Crowe, James A.
1993-08-01
The notion of a large distributed computing system in support of a program like EOSDIS, carries with it the requirement that the system provide the user with guarantees about the integrity of the data and certain assurances about the security of the network of computing systems. This paper examines the challenges of providing a `secure' open system and how these challenges may be addressed from both an architectural as well as functional viewpoint. The role of discretionary access control, mandatory access control, and detection and control of computer viruses is discussed. It has often been observed that the role of the security engineer is one of restricting access to data, whereas the role of the system architect, of an open system that is encouraging research, should make data easy to obtain and utilize. This paradox is manifest in a system such a EOSDIS where to be useful, the systems data must be easy to obtain, but to ensure the integrity of the data it must exercise some level of security. This paper address the use and role of the Security Services of the OSF Distributed Computing Environment in support of networked applications, such as those that may be used in the implementation of the EOS Science Network. It further examines the role of mandatory access control mechanisms to provide data integrity guarantees. The paper further discusses how a system like EOSDIS may prevent computer viruses using a system of automated detection mechanisms and configuration control.
Hybrid Quantum Systems of Atoms and Ions
NASA Astrophysics Data System (ADS)
Sias, Carlo; Köhl, Michael
2015-09-01
In this chapter we review the progress in experiments with hybrid systems of trapped ions and ultracold neutral atoms. We give a theoretical overview over the atom-ion interactions in the cold regime and give a summary of the most important experimental results. We conclude with an overview of remaining open challenges and possible applications in hybrid quantum systems of ions and neutral atoms.
Quantum Effects in Biological Systems
NASA Astrophysics Data System (ADS)
Roy, Sisir
2014-07-01
The debates about the trivial and non-trivial effects in biological systems have drawn much attention during the last decade or so. What might these non-trivial sorts of quantum effects be? There is no consensus so far among the physicists and biologists regarding the meaning of "non-trivial quantum effects". However, there is no doubt about the implications of the challenging research into quantum effects relevant to biology such as coherent excitations of biomolecules and photosynthesis, quantum tunneling of protons, van der Waals forces, ultrafast dynamics through conical intersections, and phonon-assisted electron tunneling as the basis for our sense of smell, environment assisted transport of ions and entanglement in ion channels, role of quantum vacuum in consciousness. Several authors have discussed the non-trivial quantum effects and classified them into four broad categories: (a) Quantum life principle; (b) Quantum computing in the brain; (c) Quantum computing in genetics; and (d) Quantum consciousness. First, I will review the above developments. I will then discuss in detail the ion transport in the ion channel and the relevance of quantum theory in brain function. The ion transport in the ion channel plays a key role in information processing by the brain.
Quantum technologies with hybrid systems.
Kurizki, Gershon; Bertet, Patrice; Kubo, Yuimaru; Mølmer, Klaus; Petrosyan, David; Rabl, Peter; Schmiedmayer, Jörg
2015-03-31
An extensively pursued current direction of research in physics aims at the development of practical technologies that exploit the effects of quantum mechanics. As part of this ongoing effort, devices for quantum information processing, secure communication, and high-precision sensing are being implemented with diverse systems, ranging from photons, atoms, and spins to mesoscopic superconducting and nanomechanical structures. Their physical properties make some of these systems better suited than others for specific tasks; thus, photons are well suited for transmitting quantum information, weakly interacting spins can serve as long-lived quantum memories, and superconducting elements can rapidly process information encoded in their quantum states. A central goal of the envisaged quantum technologies is to develop devices that can simultaneously perform several of these tasks, namely, reliably store, process, and transmit quantum information. Hybrid quantum systems composed of different physical components with complementary functionalities may provide precisely such multitasking capabilities. This article reviews some of the driving theoretical ideas and first experimental realizations of hybrid quantum systems and the opportunities and challenges they present and offers a glance at the near- and long-term perspectives of this fascinating and rapidly expanding field. PMID:25737558
Quantum technologies with hybrid systems
Kurizki, Gershon; Bertet, Patrice; Kubo, Yuimaru; MÃ¸lmer, Klaus; Petrosyan, David; Rabl, Peter; Schmiedmayer, JÃ¶rg
2015-01-01
An extensively pursued current direction of research in physics aims at the development of practical technologies that exploit the effects of quantum mechanics. As part of this ongoing effort, devices for quantum information processing, secure communication, and high-precision sensing are being implemented with diverse systems, ranging from photons, atoms, and spins to mesoscopic superconducting and nanomechanical structures. Their physical properties make some of these systems better suited than others for specific tasks; thus, photons are well suited for transmitting quantum information, weakly interacting spins can serve as long-lived quantum memories, and superconducting elements can rapidly process information encoded in their quantum states. A central goal of the envisaged quantum technologies is to develop devices that can simultaneously perform several of these tasks, namely, reliably store, process, and transmit quantum information. Hybrid quantum systems composed of different physical components with complementary functionalities may provide precisely such multitasking capabilities. This article reviews some of the driving theoretical ideas and first experimental realizations of hybrid quantum systems and the opportunities and challenges they present and offers a glance at the near- and long-term perspectives of this fascinating and rapidly expanding field. PMID:25737558
Energy Cost of Controlling Mesoscopic Quantum Systems
NASA Astrophysics Data System (ADS)
Horowitz, Jordan M.; Jacobs, Kurt
2015-09-01
We determine the minimum energy required to control the evolution of any mesoscopic quantum system in the presence of arbitrary Markovian noise processes. This result provides the mesoscopic equivalent of the fundamental cost of refrigeration, sets the minimum power consumption of mesoscopic devices that operate out of equilibrium, and allows one to calculate the efficiency of any control protocol, whether it be open-loop or feedback control. As examples, we calculate the energy cost of maintaining a qubit in the ground state and the efficiency of resolved-sideband cooling of nano-mechanical resonators, and discuss the energy cost of quantum information processing.
Energy Cost of Controlling Mesoscopic Quantum Systems.
Horowitz, Jordan M; Jacobs, Kurt
2015-09-25
We determine the minimum energy required to control the evolution of any mesoscopic quantum system in the presence of arbitrary Markovian noise processes. This result provides the mesoscopic equivalent of the fundamental cost of refrigeration, sets the minimum power consumption of mesoscopic devices that operate out of equilibrium, and allows one to calculate the efficiency of any control protocol, whether it be open-loop or feedback control. As examples, we calculate the energy cost of maintaining a qubit in the ground state and the efficiency of resolved-sideband cooling of nano-mechanical resonators, and discuss the energy cost of quantum information processing. PMID:26451540
Quantum models of classical systems
NASA Astrophysics Data System (ADS)
Hájí?ek, P.
2015-07-01
Quantum statistical methods that are commonly used for the derivation of classical thermodynamic properties are extended to classical mechanical properties. The usual assumption that every real motion of a classical mechanical system is represented by a sharp trajectory is not testable and is replaced by a class of fuzzy models, the so-called maximum entropy (ME) packets. The fuzzier are the compared classical and quantum ME packets, the better seems to be the match between their dynamical trajectories. Classical and quantum models of a stiff rod will be constructed to illustrate the resulting unified quantum theory of thermodynamic and mechanical properties.
Decoherence in infinite quantum systems
Blanchard, Philippe; Hellmich, Mario
2012-09-01
We review and discuss a notion of decoherence formulated in the algebraic framework of quantum physics. Besides presenting some sufficient conditions for the appearance of decoherence in the case of Markovian time evolutions we provide an overview over possible decoherence scenarios. The framework for decoherence we establish is sufficiently general to accommodate quantum systems with infinitely many degrees of freedom.
Naval open systems architecture
NASA Astrophysics Data System (ADS)
Guertin, Nick; Womble, Brian; Haskell, Virginia
2013-05-01
For the past 8 years, the Navy has been working on transforming the acquisition practices of the Navy and Marine Corps toward Open Systems Architectures to open up our business, gain competitive advantage, improve warfighter performance, speed innovation to the fleet and deliver superior capability to the warfighter within a shrinking budget1. Why should Industry care? They should care because we in Government want the best Industry has to offer. Industry is in the business of pushing technology to greater and greater capabilities through innovation. Examples of innovations are on full display at this conference, such as exploring the impact of difficult environmental conditions on technical performance. Industry is creating the tools which will continue to give the Navy and Marine Corps important tactical advantages over our adversaries.
NASA Astrophysics Data System (ADS)
Park, Kyungdeock; Darabad, Robabeh; Feng, Guanru; Labruyere, Stephane; Baugh, Jonathan; Laflamme, Raymond
2015-03-01
The ability to perform multiple rounds of Quantum Error Correction (QEC) is an essential task for scalable quantum information processing, but experimental realizations of it are still in their infancy. Key requirements for QEC are high control fidelity and the ability to extract entropy from ancilla qubits. Nuclear Magnetic Resonance (NMR) quantum processors have demonstrated high control fidelity with up to 12 qubits. A remaining challenge is to prepare nearly pure ancilla qubits to enable QEC. Heat Bath Algorithmic Cooling (HBAC) is an efficient tool for extracting entropy from qubits that interact with a heat bath, allowing cooling below the bath temperature. For implementing HBAC with spins, a hyperfine coupled electron-nuclear system in a single crystal is more advantageous than conventional NMR systems since the electron, with higher polarization and faster relaxation, can act as a heat bath. We characterize 3 and 5 qubit spin systems in gamma-irradiated malonic acid and present simulation and experimental results of HBAC to benchmark our quantum control. Two control schemes are compared: electron nuclear double resonance and indirect control of nuclei via the anisotropic hyperfine interaction.
Experimental test of Jarzynski equality in a quasi-open quantum using a trapped ion
NASA Astrophysics Data System (ADS)
Lu, Yao; An, Shuoming; Zhang, Xiang; Zhang, Jing-Ning; Quan, H. T.; Smith, A. M.; Jarzynski, Christopher; Kim, Kihwan
2015-05-01
We report on an experimental test of the Jarzynski equality in a quantum system consisting of a single 171Yb+ ion that undergoes dephasing. The Jarzynski equality, which relates equilibrium free energy differences to nonequilibrium work distributions, has been tested in many classical open systems and recently in isolated quantum systems. For open quantum systems, however, the definitions of work and heat are not fully settled, which hinders experimental verification. Here, we study a quantum system that interacts with an environment which causes dephasing (or decoherence) without dissipation. We observe that although the work distribution varies with the strength of dephasing, the Jarzynski equality remains valid. Our investigation constitutes the first experimental test of the quantum Jarzynski equality in an effectively open quantum system. This work was supported by the National Basic Research Program of China under Grants No. 2011CBA00300 (No. 2011CBA00301), the National Natural Science Foundation of China under Grants No. 11374178 and 11375012, and the US National Science Foundation under Grant No. DMR 1206971.
Periodic scarred States in open quantum dots as evidence of quantum Darwinism.
Burke, A M; Akis, R; Day, T E; Speyer, Gil; Ferry, D K; Bennett, B R
2010-04-30
Scanning gate microscopy (SGM) is used to image scar structures in an open quantum dot, which is created in an InAs quantum well by electron-beam lithography and wet etching. The scanned images demonstrate periodicities in magnetic field that correlate to those found in the conductance fluctuations. Simulations have shown that these magnetic transform images bear a strong resemblance to actual scars found in the dot that replicate through the modes in direct agreement with quantum Darwinism. PMID:20482124
Periodic Scarred States in Open Quantum Dots as Evidence of Quantum Darwinism
NASA Astrophysics Data System (ADS)
Burke, A. M.; Akis, R.; Day, T. E.; Speyer, Gil; Ferry, D. K.; Bennett, B. R.
2010-04-01
Scanning gate microscopy (SGM) is used to image scar structures in an open quantum dot, which is created in an InAs quantum well by electron-beam lithography and wet etching. The scanned images demonstrate periodicities in magnetic field that correlate to those found in the conductance fluctuations. Simulations have shown that these magnetic transform images bear a strong resemblance to actual scars found in the dot that replicate through the modes in direct agreement with quantum Darwinism.
Quantum measurements of coupled systems
Fedichkin, L.; Dykman, M. I.; Shapiro, M.
2009-07-15
We propose an approach to measuring coupled systems, which gives a parametrically smaller error than the conventional fast projective measurements. The measurement error is due to the excitations being not entirely localized on individual systems even where the excitation energies are different. Our approach combines spectral selectivity of the detector with temporal resolution and uses the ideas of the quantum diffusion theory. The results bear on quantum computing with perpetually coupled qubits.
Characteristics of Open Learning Systems.
ERIC Educational Resources Information Center
Wedemeyer, Charles A.
The ideal concept of open education would take the form of education permanente, although no present program includes all the features implied by this concept. Up to now the literature on open learning has focused on concern for a learner oriented system. The present focus is on the open learning system itself, with the identification of 10…
Approximation, Proof Systems, and Correlations in a Quantum World
NASA Astrophysics Data System (ADS)
Gharibian, Sevag
2013-01-01
This thesis studies three topics in quantum computation and information: The approximability of quantum problems, quantum proof systems, and non-classical correlations in quantum systems. In the first area, we demonstrate a polynomial-time (classical) approximation algorithm for dense instances of the canonical QMA-complete quantum constraint satisfaction problem, the local Hamiltonian problem. In the opposite direction, we next introduce a quantum generalization of the polynomial-time hierarchy, and define problems which we prove are not only complete for the second level of this hierarchy, but are in fact hard to approximate. In the second area, we study variants of the interesting and stubbornly open question of whether a quantum proof system with multiple unentangled quantum provers is equal in expressive power to a proof system with a single quantum prover. Our results concern classes such as BellQMA(poly), and include a novel proof of perfect parallel repetition for SepQMA(m) based on cone programming duality. In the third area, we study non-classical quantum correlations beyond entanglement, often dubbed "non-classicality". Among our results are two novel schemes for quantifying non-classicality: The first proposes the new paradigm of exploiting local unitary operations to study non-classical correlations, and the second introduces a protocol through which non-classical correlations in a starting system can be "activated" into distillable entanglement with an ancilla system. An introduction to all required linear algebra and quantum mechanics is included.
Periodic thermodynamics of isolated quantum systems.
Lazarides, Achilleas; Das, Arnab; Moessner, Roderich
2014-04-18
The nature of the behavior of an isolated many-body quantum system periodically driven in time has been an open question since the beginning of quantum mechanics. After an initial transient period, such a system is known to synchronize with the driving; in contrast to the nondriven case, no fundamental principle has been proposed for constructing the resulting nonequilibrium state. Here, we analytically show that, for a class of integrable systems, the relevant ensemble is constructed by maximizing an appropriately defined entropy subject to constraints, which we explicitly identify. This result constitutes a generalization of the concepts of equilibrium statistical mechanics to a class of far-from-equilibrium systems, up to now mainly accessible using ad hoc methods. PMID:24785013
Rapid readout of a register of qubits using open-loop quantum control
NASA Astrophysics Data System (ADS)
Combes, Joshua; Denney, Aaron; Wiseman, Howard M.
2015-02-01
Measurements are a primitive for characterizing quantum systems. Reducing the time taken to perform a measurement may be beneficial in many areas of quantum information processing. We show that permuting the eigenvalues of the state matrix in the logical basis, using open-loop control, provides an O (n ) reduction in the measurement time, where n is the number of qubits in the register. This reduction is of the same order as the (previously introduced) locally optimal feedback protocol. The advantage of the open-loop protocol is that it is far less difficult experimentally. Because the control commutes with the measured observable at all times, our rapid measurement protocol could be used for characterizing a quantum system, by state or process tomography, or to implement measurement-based quantum error correction.
Quantum hacking: attacking practical quantum key distribution systems
NASA Astrophysics Data System (ADS)
Qi, Bing; Fung, Chi-Hang Fred; Zhao, Yi; Ma, Xiongfeng; Tamaki, Kiyoshi; Chen, Christine; Lo, Hoi-Kwong
2007-09-01
Quantum key distribution (QKD) can, in principle, provide unconditional security based on the fundamental laws of physics. Unfortunately, a practical QKD system may contain overlooked imperfections and violate some of the assumptions in a security proof. Here, we report two types of eavesdropping attacks against a practical QKD system. The first one is "time-shift" attack, which is applicable to QKD systems with gated single photon detectors (SPDs). In this attack, the eavesdropper, Eve, exploits the time mismatch between the open windows of the two SPDs. She can acquire a significant amount of information on the final key by simply shifting the quantum signals forwards or backwards in time domain. Our experimental results in [9] with a commercial QKD system demonstrate that, under this attack, the original QKD system is breakable. This is the first experimental demonstration of a feasible attack against a commercial QKD system. This is a surprising result. The second one is "phase-remapping" attack [10]. Here, Eve exploits the fact that a practical phase modulator has a finite response time. In principle, Eve could change the encoded phase value by time-shifting the signal pulse relative to the reference pulse.
Optimal quantum parameter estimation in a pulsed quantum optomechanical system
NASA Astrophysics Data System (ADS)
Zheng, Qiang; Yao, Yao; Li, Yong
2016-01-01
We propose that a pulsed quantum optomechanical system can be applied to the problem of quantum parameter estimation, which targets yielding a higher precision of parameter estimation utilizing quantum resources than using classical methods. Concentrating mainly on the quantum Fisher information with respect to the mechanical frequency, we find that the corresponding precision of parameter estimation for the mechanical frequency can be enhanced by applying applicable optical resonant pulsed driving to the cavity of the optomechanical system. Further investigation shows that the mechanical squeezing resulting from the optical pulsed driving is the quantum resource used in optimal quantum estimation of the frequency.
Quantum effects in biological systems
NASA Astrophysics Data System (ADS)
Sarovar, Mohan
2010-02-01
Identification of non-trivial quantum mechanical effects in the functioning of biological systems has been a long-standing and elusive goal in the fields of physics, chemistry and biology. Recent progress in control and measurement technologies, especially in the optical spectroscopy domain, have made possible the identification of such effects. In particular, electronic coherence was recently shown to survive for relatively long times in photosynthetic light harvesting complexes despite the effects of noisy biomolecular environments. Motivated by this experimental discovery, several recent studies have combined techniques from quantum information, quantum dynamical theory and chemical physics to characterize the extent and nature of quantum dynamics in light harvesting structures. I will review these results and summarize our understanding of the subtle quantum effects in photosynthetic complexes. Then I will outline the remarkable properties of light harvesting complexes that allow quantum effects to be significant at dynamically relevant timescales, despite the decohering biomolecular environment. Finally, I will conclude by discussing the implications of quantum effects in light harvesting complexes, and in biological systems in general.
Quantum walk public-key cryptographic system
NASA Astrophysics Data System (ADS)
Vlachou, C.; Rodrigues, J.; Mateus, P.; PaunkoviÄ‡, N.; Souto, A.
2015-12-01
Quantum Cryptography is a rapidly developing field of research that benefits from the properties of Quantum Mechanics in performing cryptographic tasks. Quantum walks are a powerful model for quantum computation and very promising for quantum information processing. In this paper, we present a quantum public-key cryptographic system based on quantum walks. In particular, in the proposed protocol the public-key is given by a quantum state generated by performing a quantum walk. We show that the protocol is secure and analyze the complexity of public key generation and encryption/decryption procedures.
Classical and quantum discrete time integrable systems
NASA Astrophysics Data System (ADS)
Lipan, Ovidiu-Zeno
The standard objects of quantum integrable systems are identified with elements of classical nonlinear integrable difference equations. Functional relation for commuting quantum transfer matrices of quantum integrable models is shown to coincide with classical Hirota's bilinear difference equation. This equation is equivalent to the completely discretized classical 2D Toda lattice with open boundaries. Elliptic solutions of Hirota's equation give complete set of eigenvalues of the quantum transfer matrices. Eigenvalues of Baxter's Q-operator are solutions to the auxiliary linear problems for classical Hirota's equation. The elliptic solutions relevant to Bethe ansatz are studied. The nested Bethe ansatz equations for Ak-1-type models appear as discrete time equations of motions for zeros of classical ?- functions and Baker-Akhiezer functions. Determinant representations of the general solution to bilinear discrete Hirota's equation are analysed and a new determinant formula for eigenvalues of the quantum transfer matrices is obtained. Difference equations for eigenvalues of the Q-operators which generalize Baxter's three-term T-Q-relation are derived.
Transient features of quantum open maps.
Ermann, Leonardo; Carlo, Gabriel G; Pedrosa, Juan M; Saraceno, Marcos
2012-06-01
We study families of open chaotic maps that classically share the same asymptotic properties--forward and backward trapped sets, repeller dimensions, and escape rate--but differ in their short time behavior. When these maps are quantized we find that the fine details of the distribution of resonances and the corresponding eigenfunctions are sensitive to the initial shape and size of the openings. We study phase space localization of the resonances with respect to the repeller and find strong delocalization effects when the area of the openings is smaller than ?. PMID:23005193
Quantum energy teleportation in a quantum Hall system
Yusa, Go; Izumida, Wataru; Hotta, Masahiro
2011-09-15
We propose an experimental method for a quantum protocol termed quantum energy teleportation (QET), which allows energy transportation to a remote location without physical carriers. Using a quantum Hall system as a realistic model, we discuss the physical significance of QET and estimate the order of energy gain using reasonable experimental parameters.
The classical skeleton of open quantum chaotic maps
NASA Astrophysics Data System (ADS)
Raviola, Lisandro A.; Rivas, Alejandro M. F.; Carlo, Gabriel G.
2011-11-01
We have studied two complementary decoherence measures, purity and fidelity, for a generic diffusive noise in two different chaotic systems (the baker map and the cat map). For both quantities, we have found classical structures in quantum mechanics-the scar functions-that are specially stable when subjected to environmental perturbations. We show that these quantum states constructed on classical invariants are the most robust significant quantum distributions in generic dissipative maps.
Opening up three quantum boxes causes classically undetectable wavefunction collapse
George, Richard E.; Robledo, Lucio M.; Maroney, Owen J. E.; Blok, Machiel S.; Bernien, Hannes; Markham, Matthew L.; Twitchen, Daniel J.; Morton, John J. L.; Briggs, G. Andrew D.; Hanson, Ronald
2013-01-01
One of the most striking features of quantum mechanics is the profound effect exerted by measurements alone. Sophisticated quantum control is now available in several experimental systems, exposing discrepancies between quantum and classical mechanics whenever measurement induces disturbance of the interrogated system. In practice, such discrepancies may frequently be explained as the back-action required by quantum mechanics adding quantum noise to a classical signal. Here, we implement the “three-box” quantum game [Aharonov Y, et al. (1991) J Phys A Math Gen 24(10):2315–2328] by using state-of-the-art control and measurement of the nitrogen vacancy center in diamond. In this protocol, the back-action of quantum measurements adds no detectable disturbance to the classical description of the game. Quantum and classical mechanics then make contradictory predictions for the same experimental procedure; however, classical observers are unable to invoke measurement-induced disturbance to explain the discrepancy. We quantify the residual disturbance of our measurements and obtain data that rule out any classical model by ?7.8 standard deviations, allowing us to exclude the property of macroscopic state definiteness from our system. Our experiment is then equivalent to the test of quantum noncontextuality [Kochen S, Specker E (1967) J Math Mech 17(1):59–87] that successfully addresses the measurement detectability loophole. PMID:23412336
2015-04-17
The OpenSM Monitoring System includes a collection of diagnostic and monitoring tools for use on Infiniband networks. The information this system gathers is obtained from a service, which in turn is obtained directly from the OpenSM subnet manager.
Quantum Indeterminacy of Cosmic Systems
Hogan, Craig J.
2013-12-30
It is shown that quantum uncertainty of motion in systems controlled mainly by gravity generally grows with orbital timescale $H^{-1}$, and dominates classical motion for trajectories separated by distances less than $\\approx H^{-3/5}$ in Planck units. For example, the cosmological metric today becomes indeterminate at macroscopic separations, $H_0^{-3/5}\\approx 60$ meters. Estimates suggest that entangled non-localized quantum states of geometry and matter may significantly affect fluctuations during inflation, and connect the scale of dark energy to that of strong interactions.
On Entropy of Quantum Compound Systems
NASA Astrophysics Data System (ADS)
Watanabe, Noboru
2015-10-01
We review some notions for general quantum entropies. The entropy of the compound systems is discussed and a numerical computation of the quantum dynamical systems is carried for the noisy optical channel.
Homogeneous Open Quantum Random Walks on a Lattice
NASA Astrophysics Data System (ADS)
Carbone, Raffaella; Pautrat, Yan
2015-09-01
We study open quantum random walks (OQRWs) for which the underlying graph is a lattice, and the generators of the walk are homogeneous in space. Using the results recently obtained in Carbone and Pautrat (Ann Henri Poincaré, 2015), we study the quantum trajectory associated with the OQRW, which is described by a position process and a state process. We obtain a central limit theorem and a large deviation principle for the position process. We study in detail the case of homogeneous OQRWs on the lattice , with internal space.
Miyake, Chikahiro; Amako, Katsumi; Shiraishi, Naomasa; Sugimoto, Toshio
2009-04-01
Responses of the reduction-oxidation level of plastoquinone (PQ) in the photosynthetic electron transport (PET) system of chloroplasts to growth light intensity were evaluated in tobacco plants. Plants grown in low light (150 micromol photons m-2 s-1) (LL plants) were exposed to a high light intensity (1,100 micromol photons m-2 s-1) for 1 d. Subsequently, the plants exposed to high light (LH plants) were returned back again to the low light condition: these plants were designated as LHL plants. Both LH and LHL plants showed higher values of non-photochemical quenching of Chl fluorescence (NPQ) and the fraction of open PSII centers (qL), and lower values of the maximum quantum yield of PSII in the dark (Fv/Fm), compared with LL plants. The dependence of qL on the quantum yield of PSII [Phi(PSII)] in LH and LHL plants was higher than that in LL plants. To evaluate the effect of an increase in NPQ and decrease in Fv/Fm on qL, we derived an equation expressing qL in relation to both NPQ and Fv/Fm, according to the lake model of photoexcitation of the PSII reaction center. As a result, the heat dissipation process, shown as NPQ, did not contribute greatly to the increase in qL. On the other hand, decreased Fv/Fm did contribute to the increase in qL, i.e. the enhanced oxidation of PQ under photosynthesis-limited conditions. Thylakoid membranes isolated from LH plants, having high qL, showed a higher tolerance against photoinhibition of PSII, compared with those from LL plants. We propose a 'plastoquinone oxidation system (POS)', which keeps PQ in an oxidized state by suppressing the accumulation of electrons in the PET system in such a way as to regulate the maximum quantum yield of PSII. PMID:19251745
Classical and quantum correlative capacities of quantum systems
Li Nan; Luo Shunlong
2011-10-15
How strongly can one system be correlated with another? In the classical world, this basic question concerning correlative capacity has a very satisfying answer: The ''effective size'' of the marginal system, as quantified by the Shannon entropy, sets a tight upper bound to the correlations, as quantified by the mutual information. Although in the quantum world bipartite correlations, like their classical counterparts, are also well quantified by mutual information, the similarity ends here: The correlations in a bipartite quantum system can be twice as large as the marginal entropy. In the paradigm of quantum discord, the correlations are split into classical and quantum components, and it was conjectured that both the classical and quantum correlations are (like the classical mutual information) bounded above by each subsystem's entropy. In this work, by exploiting the interplay between entanglement of formation, mutual information, and quantum discord, we disprove that conjecture. We further indicate a scheme to restore harmony between quantum and classical correlative capacities. The results illustrate dramatically the asymmetric nature of quantum discord and highlight some subtle and unusual features of quantum correlations.
RKKY interaction in a chirally coupled double quantum dot system
Heine, A. W.; Tutuc, D.; Haug, R. J.; Zwicknagl, G.; Schuh, D.; Wegscheider, W.
2013-12-04
The competition between the Kondo effect and the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction is investigated in a double quantum dots system, coupled via a central open conducting region. A perpendicular magnetic field induces the formation of Landau Levels which in turn give rise to the so-called Kondo chessboard pattern in the transport through the quantum dots. The two quantum dots become therefore chirally coupled via the edge channels formed in the open conducting area. In regions where both quantum dots exhibit Kondo transport the presence of the RKKY exchange interaction is probed by an analysis of the temperature dependence. The thus obtained Kondo temperature of one dot shows an abrupt increase at the onset of Kondo transport in the other, independent of the magnetic field polarity, i.e. edge state chirality in the central region.
NASA Astrophysics Data System (ADS)
Cui, Ping
The thesis comprises two major themes of quantum statistical dynamics. One is the development of quantum dissipation theory (QDT). It covers the establishment of some basic relations of quantum statistical dynamics, the construction of several nonequivalent complete second-order formulations, and the development of exact QDT. Another is related to the applications of quantum statistical dynamics to a variety of research fields. In particular, unconventional but novel theories of the electron transfer in Debye solvents, quantum transport, and quantum measurement are developed on the basis of QDT formulations. The thesis is organized as follows. In Chapter 1, we present some background knowledge in relation to the aforementioned two themes of this thesis. The key quantity in QDT is the reduced density operator rho(t) â‰¡ trBrho T(t); i.e., the partial trace of the total system and bath composite rhoT(t) over the bath degrees of freedom. QDT governs the evolution of reduced density operator, where the effects of bath are treated in a quantum statistical manner. In principle, the reduced density operator contains all dynamics information of interest. However, the conventional quantum transport theory is formulated in terms of nonequilibrium Green's function. The newly emerging field of quantum measurement in relation to quantum information and quantum computing does exploit a sort of QDT formalism. Besides the background of the relevant theoretical development, some representative experiments on molecular nanojunctions are also briefly discussed. In chapter 2, we outline some basic (including new) relations that highlight several important issues on QDT. The content includes the background of nonequilibrium quantum statistical mechanics, the general description of the total composite Hamiltonian with stochastic system-bath interaction, a novel parameterization scheme for bath correlation functions, a newly developed exact theory of driven Brownian oscillator (DBO) systems, and its closely related solvation mode transformation of system-bath coupling Hamiltonian in general. The exact QDT of DBO systems is also used to clarify the validity of conventional QDT formulations that involve Markovian approximation. In Chapter 3, we develop three nonequivalent but all complete second-order QDT (CS-QDT) formulations. Two of them are of the conventional prescriptions in terms of time-local dissipation and memory kernel, respectively. The third one is called the correlated driving-dissipation equations of motion (CODDE). This novel CS-QDT combines the merits of the former two for its advantages in both the application and numerical implementation aspects. Also highlighted is the importance of correlated driving-dissipation effects on the dynamics of the reduced system. In Chapter 4, we construct an exact QDT formalism via the calculus on path integrals. The new theory aims at the efficient evaluation of non-Markovian dissipation beyond the weak system-bath interaction regime in the presence of time-dependent external field. By adopting exponential-like expansions for bath correlation function, hierarchical equations of motion formalism and continued fraction Liouville-space Green's function formalism are established. The latter will soon be used together with the Dyson equation technique for an efficient evaluation of non-perturbative reduced density matrix dynamics. The interplay between system-bath interaction strength, non-Markovian property, and the required level of hierarchy is also studied with the aid of simple spin-boson systems, together with the three proposed schemes to truncate the infinite hierarchy. In Chapter 5, we develop a nonperturbative theory of electron transfer (ET) in Debye solvents. The resulting exact and analytical rate expression is constructed on the basis of the aforementioned continued fraction Liouville-space Green's function formalism, together with the Dyson equation technique. Not only does it recover the celebrated Marcus' inversion and Kramers' turnover behaviors, the new theory also shows some distinct quantum solvation effects that can alter the ET mechanism. Moreover, the present theory predicts further for the ET reaction thermodynamics, such as equilibrium Gibbs free-energy and entropy, some interesting solvent-dependent features that are calling for experimental verification. In Chapter 6, we discuss the constructed QDTs, in terms of their unified mathematical structure that supports a linear dynamics space, and thus facilitates their applications to various physical problems. The involving details are exemplified with the CODDE form of QDT. As the linear space is concerned, we identify the Schrodinger versus Heisenberg picture and the forward versus backward propagation of the reduced, dissipative Liouville dynamics. For applications we discuss the reduced linear response theory and the optimal control problems, in which the correlated effects of non-Markovian dissipation and field driving are shown to be important. In Chapter 7, we turn to quantum transport, i.e., electric current through molecular or mesoscopic systems under finite applied voltage. By viewing the nonequilibrium transport setup as a quantum open system, we develop a reduced-density-matrix approach to quantum transport. The resulting current is explicitly expressed in terms of the molecular reduced density matrix by tracing out the degrees of freedom of the electrodes at finite bias and temperature. We propose a conditional quantum master equation theory, which is an extension of the conventional (or unconditional) QDT by tracing out the well-defined bath subsets individually, instead of the entire bath degrees of freedom. Both the current and the noise spectrum can be conveniently analyzed in terms of the conditional reduced density matrix dynamics. By far, the QDT (including the conditional one) has only been exploited in second-order form. A self-consistent Born approximation for the system-electrode coupling is further proposed to recover all existing nonlinear current-voltage behaviors including the nonequilibrium Kondo effect. Transport theory based on the exact QDT formalism will be developed in future. In Chapter 8, we study the quantum measurement of a qubit with a quantum-point-contact detector. On the basis of a unified quantum master equation (a form of QDT), we study the measurement-induced relaxation and dephasing of the qubit. Our treatment pays particular attention on the detailed-balance relation, which is a consequence of properly accounting for the energy exchange between the qubit and detector during the measurement process. We also derive a conditional quantum master equation for quantum measurement in general, and study the readout characteristics of the qubit measurement. Our theory is applicable to the quantum measurement at arbitrary voltage and temperature. A number of remarkable new features are found and highlighted in concern with their possible relevance to future experiments. In Chapter 9, we discuss the further development of QDT, aiming at an efficient evaluation of many-electron systems. This will be carried out by reducing the many-particle (Fermion or Boson) QDT to a single-particle one by exploring, e.g. the Wick's contraction theorem. It also results in a time-dependent density functional theory (TDDFT) for transport through complex large-scale (e.g. molecules) systems. Primary results of the TDDFT-QDT are reported. In Chapter 10, we summary the thesis, and comment and remark on the future work on both the theoretical and application aspects of QDT.
Optimal protocols for slowly driven quantum systems.
Zulkowski, Patrick R; DeWeese, Michael R
2015-09-01
The design of efficient quantum information processing will rely on optimal nonequilibrium transitions of driven quantum systems. Building on a recently developed geometric framework for computing optimal protocols for classical systems driven in finite time, we construct a general framework for optimizing the average information entropy for driven quantum systems. Geodesics on the parameter manifold endowed with a positive semidefinite metric correspond to protocols that minimize the average information entropy production in finite time. We use this framework to explicitly compute the optimal entropy production for a simple two-state quantum system coupled to a heat bath of bosonic oscillators, which has applications to quantum annealing. PMID:26465432
Maxwell's demons in multipartite quantum correlated systems
NASA Astrophysics Data System (ADS)
Braga, Helena C.; Rulli, Clodoaldo C.; de Oliveira, Thiago R.; Sarandy, Marcelo S.
2014-10-01
We investigate the extraction of thermodynamic work by a Maxwell's demon in a multipartite quantum correlated system. We begin by adopting the standard model of a Maxwell's demon as a Turing machine, either in a classical or quantum setup depending on its ability to implement classical or quantum conditional dynamics. Then, for an n -partite system (A1,A2,⋯,An) , we introduce a protocol of work extraction that bounds the advantage of the quantum demon over its classical counterpart through the amount of multipartite quantum correlation present in the system, as measured by a thermal version of the global quantum discord. This result is illustrated for an arbitrary n -partite pure state of qubits with Schmidt decomposition, where it is shown that the thermal global quantum discord exactly quantifies the quantum advantage. Moreover, we also consider the work extraction via mixed multipartite states, where examples of tight upper bounds can be obtained.
Localization in chaotic systems with a single-channel opening
NASA Astrophysics Data System (ADS)
Lippolis, Domenico; Ryu, Jung-Wan; Kim, Sang Wook
2015-07-01
We introduce a single-channel opening in a random Hamiltonian and a quantized chaotic map: localization on the opening occurs as a sensible deviation of the wave-function statistics from the predictions of random matrix theory, even in the semiclassical limit. Increasing the coupling to the open channel in the quantum model, we observe a similar picture to resonance trapping, made of a few fast-decaying states, whose left (right) eigenfunctions are entirely localized on the (preimage of the) opening, and plentiful long-lived states, whose probability density is instead suppressed at the opening. For the latter, we derive and test a linear relation between the wave-function intensities and the decay rates, similar to the Breit-Wigner law. We then analyze the statistics of the eigenfunctions of the corresponding (discretized) classical propagator, finding a similar behavior to the quantum system only in the weak-coupling regime.
Non-Markovian Dynamical Maps: Numerical Processing of Open Quantum Trajectories
NASA Astrophysics Data System (ADS)
Cerrillo, Javier; Cao, Jianshu
2014-03-01
The initial stages of the evolution of an open quantum system encode the key information of its underlying dynamical correlations, which in turn can predict the trajectory at later stages. We propose a general approach based on non-Markovian dynamical maps to extract this information from the initial trajectories and compress it into non-Markovian transfer tensors. Assuming time-translational invariance, the tensors can be used to accurately and efficiently propagate the state of the system to arbitrarily long time scales. The non-Markovian transfer tensor method (TTM) demonstrates the coherent-to-incoherent transition as a function of the strength of quantum dissipation and predicts the noncanonical equilibrium distribution due to the system-bath entanglement. TTM is equivalent to solving the Nakajima-Zwanzig equation and, therefore, can be used to reconstruct the dynamical operators (the system Hamiltonian and memory kernel) from quantum trajectories obtained in simulations or experiments. The concept underlying the approach can be generalized to physical observables with the goal of learning and manipulating the trajectories of an open quantum system.
Stability of Local Quantum Dissipative Systems
NASA Astrophysics Data System (ADS)
Cubitt, Toby S.; Lucia, Angelo; Michalakis, Spyridon; Perez-Garcia, David
2015-08-01
Open quantum systems weakly coupled to the environment are modeled by completely positive, trace preserving semigroups of linear maps. The generators of such evolutions are called Lindbladians. In the setting of quantum many-body systems on a lattice it is natural to consider Lindbladians that decompose into a sum of local interactions with decreasing strength with respect to the size of their support. For both practical and theoretical reasons, it is crucial to estimate the impact that perturbations in the generating Lindbladian, arising as noise or errors, can have on the evolution. These local perturbations are potentially unbounded, but constrained to respect the underlying lattice structure. We show that even for polynomially decaying errors in the Lindbladian, local observables and correlation functions are stable if the unperturbed Lindbladian has a unique fixed point and a mixing time that scales logarithmically with the system size. The proof relies on Lieb-Robinson bounds, which describe a finite group velocity for propagation of information in local systems. As a main example, we prove that classical Glauber dynamics is stable under local perturbations, including perturbations in the transition rates, which may not preserve detailed balance.
Simulation of n-qubit quantum systems. V. Quantum measurements
NASA Astrophysics Data System (ADS)
Radtke, T.; Fritzsche, S.
2010-02-01
The FEYNMAN program has been developed during the last years to support case studies on the dynamics and entanglement of n-qubit quantum registers. Apart from basic transformations and (gate) operations, it currently supports a good number of separability criteria and entanglement measures, quantum channels as well as the parametrizations of various frequently applied objects in quantum information theory, such as (pure and mixed) quantum states, hermitian and unitary matrices or classical probability distributions. With the present update of the FEYNMAN program, we provide a simple access to (the simulation of) quantum measurements. This includes not only the widely-applied projective measurements upon the eigenspaces of some given operator but also single-qubit measurements in various pre- and user-defined bases as well as the support for two-qubit Bell measurements. In addition, we help perform generalized and POVM measurements. Knowing the importance of measurements for many quantum information protocols, e.g., one-way computing, we hope that this update makes the FEYNMAN code an attractive and versatile tool for both, research and education. New version program summaryProgram title: FEYNMAN Catalogue identifier: ADWE_v5_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADWE_v5_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 27 210 No. of bytes in distributed program, including test data, etc.: 1 960 471 Distribution format: tar.gz Programming language: Maple 12 Computer: Any computer with Maple software installed Operating system: Any system that supports Maple; the program has been tested under Microsoft Windows XP and Linux Classification: 4.15 Catalogue identifier of previous version: ADWE_v4_0 Journal reference of previous version: Comput. Phys. Commun. 179 (2008) 647 Does the new version supersede the previous version?: Yes Nature of problem: During the last decade, the field of quantum information science has largely contributed to our understanding of quantum mechanics, and has provided also new and efficient protocols that are used on quantum entanglement. To further analyze the amount and transfer of entanglement in n-qubit quantum protocols, symbolic and numerical simulations need to be handled efficiently. Solution method: Using the computer algebra system Maple, we developed a set of procedures in order to support the definition, manipulation and analysis of n-qubit quantum registers. These procedures also help to deal with (unitary) logic gates and (nonunitary) quantum operations and measurements that act upon the quantum registers. All commands are organized in a hierarchical order and can be used interactively in order to simulate and analyze the evolution of n-qubit quantum systems, both in ideal and noisy quantum circuits. Reasons for new version: Until the present, the FEYNMAN program supported the basic data structures and operations of n-qubit quantum registers [1], a good number of separability and entanglement measures [2], quantum operations (noisy channels) [3] as well as the parametrizations of various frequently applied objects, such as (pure and mixed) quantum states, hermitian and unitary matrices or classical probability distributions [4]. With the current extension, we here add all necessary features to simulate quantum measurements, including the projective measurements in various single-qubit and the two-qubit Bell basis, and POVM measurements. Together with the previously implemented functionality, this greatly enhances the possibilities of analyzing quantum information protocols in which measurements play a central role, e.g., one-way computation. Running time: Most commands require ?10 seconds of processor time on a Pentium 4 processor with ?2 GHz RAM or newer, if they work with quantum registers with five or less qubits. Moreover, about 5-20 MB of working memory is typically n
A general transfer-function approach to noise filtering in open-loop quantum control
NASA Astrophysics Data System (ADS)
Viola, Lorenza
2015-03-01
Hamiltonian engineering via unitary open-loop quantum control provides a versatile and experimentally validated framework for manipulating a broad class of non-Markovian open quantum systems of interest, with applications ranging from dynamical decoupling and dynamically corrected quantum gates, to noise spectroscopy and quantum simulation. In this context, transfer-function techniques directly motivated by control engineering have proved invaluable for obtaining a transparent picture of the controlled dynamics in the frequency domain and for quantitatively analyzing performance. In this talk, I will show how to identify a computationally tractable set of ``fundamental filter functions,'' out of which arbitrary filter functions may be assembled up to arbitrary high order in principle. Besides avoiding the infinite recursive hierarchy of filter functions that arises in general control scenarios, this fundamental set suffices to characterize the error suppression capabilities of the control protocol in both the time and frequency domain. I will show, in particular, how the resulting notion of ``filtering order'' reveals conceptually distinct, albeit complementary, features of the controlled dynamics as compared to the ``cancellation order,'' traditionally defined in the Magnus sense. Implications for current quantum control experiments will be discussed. Work supported by the U.S. Army Research Office under Contract No. W911NF-14-1-0682.
Thermodynamics of Weakly Measured Quantum Systems.
Alonso, Jose Joaquin; Lutz, Eric; Romito, Alessandro
2016-02-26
We consider continuously monitored quantum systems and introduce definitions of work and heat along individual quantum trajectories that are valid for coherent superposition of energy eigenstates. We use these quantities to extend the first and second laws of stochastic thermodynamics to the quantum domain. We illustrate our results with the case of a weakly measured driven two-level system and show how to distinguish between quantum work and heat contributions. We finally employ quantum feedback control to suppress detector backaction and determine the work statistics. PMID:26967399
Quantum simulations of aqueous systems
Rossky, P.J.; Kuharski, R.A.; Schnitker, J.
1986-06-01
Discretized path-integral simulation methods have been applied to the determination of structure in two quantum mechanical aqueous systems. The first of these applications is the determination of the consequences of quantizing the rigid-body degrees of freedom of the water molecules in the many-particle pure room temperature liquid. The results provide a quantitative estimate of the significance of approximating such a system as classical and also of the size of isotope effects on the liquid structure. These features are found to have a close analogue in the structural response of the fluid to temperature. Second, we consider the structure of a hydrated excess electron. Here we treat the water classically but treat the highly quantum mechanical electron via a path-integral description, introducing a local electron-water pseudopotential for the interation. The excess electron density and solvent distribution are examined and shown to exhibit strong structural similarities to ionic solvation. However, it is found that the electronic density fluctuates sufficiently in size and shape as to nearly erase distinct features in the electron-solvent radial correlations. For both of the aqueous systems considered, comparison of results following from the simulations with experimentally accessible direct structural measures yields satisfactory agreement.
Stimulated recombination in open systems
Muoz-Cobo, J.L.; Verdu, G.; Jimenez, P.; Pea, J.
1986-09-01
In this comment we study the problem of the stimulated recombination in an open system from a stochastic point of view. We set up the bivariate master equation for the number of photons and ions inside the system. Then we perform a systematic expansion, with the system volume as an expansion parameter, and we obtain the fluctuations of the number of photons and ions around its macroscopic values in the linear noise approximation; the stationary solution is also investigated.
Relativistic quantum Darwinism in Dirac fermion and graphene systems
NASA Astrophysics Data System (ADS)
Ni, Xuan; Huang, Liang; Lai, Ying-Cheng; Pecora, Louis
2012-02-01
We solve the Dirac equation in two spatial dimensions in the setting of resonant tunneling, where the system consists of two symmetric cavities connected by a finite potential barrier. The shape of the cavities can be chosen to yield both regular and chaotic dynamics in the classical limit. We find that certain pointer states about classical periodic orbits can exist, which are signatures of relativistic quantum Darwinism (RQD). These localized states suppress quantum tunneling, and the effect becomes less severe as the underlying classical dynamics in the cavity is chaotic, leading to regularization of quantum tunneling. Qualitatively similar phenomena have been observed in graphene. A physical theory is developed to explain relativistic quantum Darwinism and its effects based on the spectrum of complex eigenenergies of the non-Hermitian Hamiltonian describing the open cavity system.
Quantum mechanics in complex systems
NASA Astrophysics Data System (ADS)
Hoehn, Ross Douglas
This document should be considered in its separation; there are three distinct topics contained within and three distinct chapters within the body of works. In a similar fashion, this abstract should be considered in three parts. Firstly, we explored the existence of multiply-charged atomic ions by having developed a new set of dimensional scaling equations as well as a series of relativistic augmentations to the standard dimensional scaling procedure and to the self-consistent field calculations. Secondly, we propose a novel method of predicting drug efficacy in hopes to facilitate the discovery of new small molecule therapeutics by modeling the agonist-protein system as being similar to the process of Inelastic Electron Tunneling Spectroscopy. Finally, we facilitate the instruction in basic quantum mechanical topics through the use of quantum games; this method of approach allows for the generation of exercises with the intent of conveying the fundamental concepts within a first year quantum mechanics classroom. Furthermore, no to be mentioned within the body of the text, yet presented in appendix form, certain works modeling the proliferation of cells types within the confines of man-made lattices for the purpose of facilitating artificial vascular transplants. In Chapter 2, we present a theoretical framework which describes multiply-charged atomic ions, their stability within super-intense laser fields, also lay corrections to the systems due to relativistic effects. Dimensional scaling calculations with relativistic corrections for systems: H, H-, H 2-, He, He-, He2-, He3- within super-intense laser fields were completed. Also completed were three-dimensional self consistent field calculations to verify the dimensionally scaled quantities. With the aforementioned methods the system's ability to stably bind 'additional' electrons through the development of multiple isolated regions of high potential energy leading to nodes of high electron density is shown. These nodes are spaced far enough from each other to minimized the electronic repulsion of the electrons, while still providing adequate enough attraction so as to bind the excess elections into orbitals. We have found that even with relativistic considerations these species are stably bound within the field. It was also found that performing the dimensional scaling calculations for systems within the confines of laser fields to be a much simpler and more cost-effective method than the supporting D=3 SCF method. The dimensional scaling method is general and can be extended to include relativistic corrections to describe the stability of simple molecular systems in super-intense laser fields. Chapter 3, we delineate the model, and aspects therein, of inelastic electron tunneling and map this model to the protein environment. G protein-coupled receptors (GPCRs) constitute a large family of receptors that sense molecules outside of a cell and activate signal transduction pathways inside the cell. Modeling how an agonist activates such a receptor is important for understanding a wide variety of physiological processes and it is of tremendous value for pharmacology and drug design. Inelastic electron tunneling spectroscopy (IETS) has been proposed as the mechanism by which olfactory GPCRs are activated by an encapsulated agonist. In this note we apply this notion to GPCRs within the mammalian nervous system using ab initio quantum chemical modeling. We found that non-endogenous agonists of the serotonin receptor share a singular IET spectral aspect both amongst each other and with the serotonin molecule: a peak that scales in intensity with the known agonist activities. We propose an experiential validation of this model by utilizing lysergic acid dimethylamide (DAM-57), an ergot derivative, and its isotopologues in which hydrogen atoms are replaced by deuterium. If validated our theory may provide new avenues for guided drug design and better in silico prediction of efficacies. Our final chapter, explores methods which may be explored to assist in the early instruction in quantum mechanics. The learning of quantum mechanics is contingent upon an understanding of the physical significance of the mathematics that one must perform. Concepts such as normalization, superposition, interference, probability amplitude and entanglement can prove challenging for the beginning student. This paper outlines several class exercises that use a non-classical version of tic-tac-toe to instruct several topics in an undergraduate quantum mechanics course. Quantum tic-tac-toe (QTTT) is a quantum analogue of classical tic-tac-toe (CTTT) benefiting from the use of superposition in movement, qualitative (and later quantitative) displays of entanglement and state collapse due to observation. QTTT can be used for the benefit of the students understanding in several other topics with the aid of proper discussion.
Topics in quantum integrable systems
NASA Astrophysics Data System (ADS)
Hikami, Kazuhiro; Wadati, Miki
2003-08-01
Recent developments in the theory of quantum integrable particle systems in one-dimension with inverse square interactions are reviewed. First the Yangian symmetry is introduced and the energy spectra of the related spin models are discussed. The character of the su(n)1 WZNW theory is shown to be closely related with the Rogers-SzegÃ¶ polynomial. Second, the infinite dimensional representation for solutions of the Yang-Baxter equation and the reflection equation is given. Based on the representation, the Dunkl operators associated with the classical root systems are constructed. The Macdonald polynomial and its generalization are discussed in connection with the eigenstates for the trigonometric case. Finally, some results on short-range interacting systems are mentioned.
Hall conductance and topological invariant for open systems
Shen, H. Z.; Wang, W.; Yi, X. X.
2014-01-01
The Hall conductivity given by the Kubo formula is a linear response of quantum transverse transport to a weak electric field. It has been intensively studied for quantum systems without decoherence, but it is barely explored for systems subject to decoherence. In this paper, we develop a formulism to deal with this issue for topological insulators. The Hall conductance of a topological insulator coupled to an environment is derived, the derivation is based on a linear response theory developed for open systems in this paper. As an application, the Hall conductance of a two-band topological insulator and a two-dimensional lattice is presented and discussed. PMID:25248375
Open-system dynamics of entanglement: a key issues review.
Aolita, Leandro; de Melo, Fernando; Davidovich, Luiz
2015-04-01
One of the greatest challenges in the fields of quantum information processing and quantum technologies is the detailed coherent control over each and every constituent of quantum systems with an ever increasing number of particles. Within this endeavor, harnessing of many-body entanglement against the detrimental effects of the environment is a major pressing issue. Besides being an important concept from a fundamental standpoint, entanglement has been recognized as a crucial resource for quantum speed-ups or performance enhancements over classical methods. Understanding and controlling many-body entanglement in open systems may have strong implications in quantum computing, quantum simulations of many-body systems, secure quantum communication or cryptography, quantum metrology, our understanding of the quantum-to-classical transition, and other important questions of quantum foundations.In this paper we present an overview of recent theoretical and experimental efforts to underpin the dynamics of entanglement under the influence of noise. Entanglement is thus taken as a dynamic quantity on its own, and we survey how it evolves due to the unavoidable interaction of the entangled system with its surroundings. We analyze several scenarios, corresponding to different families of states and environments, which render a very rich diversity of dynamical behaviors.In contrast to single-particle quantities, like populations and coherences, which typically vanish only asymptotically in time, entanglement may disappear at a finite time. In addition, important classes of entanglement display an exponential decay with the number of particles when subject to local noise, which poses yet another threat to the already-challenging scaling of quantum technologies. Other classes, however, turn out to be extremely robust against local noise. Theoretical results and recent experiments regarding the difference between local and global decoherence are summarized. Control and robustness-enhancement techniques, scaling laws, statistical and geometrical aspects of multipartite-entanglement decay are also reviewed; all in order to give a broad picture of entanglement dynamics in open quantum systems addressed to both theorists and experimentalists inside and outside the field of quantum information. PMID:25811809
Variational approach for the quantum Zakharov system
Haas, F.
2007-04-15
The quantum Zakharov system is described in terms of a Lagrangian formalism. A time-dependent Gaussian trial function approach for the envelope electric field and the low-frequency part of the density fluctuation leads to a coupled, nonlinear system of ordinary differential equations. In the semiclassical case, linear stability analysis of this dynamical system shows a destabilizing role played by quantum effects. Arbitrary values of the quantum effects are also considered, yielding the ultimate destruction of the localized, Gaussian trial solution. Numerical simulations are shown for both the semiclassical and the full quantum cases.
Superconductor-Diamond Hybrid Quantum System
NASA Astrophysics Data System (ADS)
Semba, Kouichi; Yoshihara, Fumiki; Johansson, Jan E. S.; Zhu, Xiaobo; Mizuochi, Norikazu; Munro, William J.; Saito, Shiro; Kakuyanagi, Kosuke; Matsuzaki, Yuichiro
This chapter describes recent progress on research into superconducting flux qubit, NV diamond, and superconductor-diamond hybrid quantum systems. First, we describe important physical properties of superconducting macroscopic artificial atoms i.e., the tunability of the qubit energy level spacing, the coherence property, an example of strong coupling to another quantum system such as an LC harmonic oscillator, and qubit state readout through a Josephson bifurcation amplifier. We then introduce the NV center in diamond as an intriguing candidate for quantum information processing, which offers excellent multiple accessibility via visible light, microwaves and magnetic fields. Finally, we describe the superconducting flux qubit - NV centers in a diamond hybrid quantum system.
An Open Source Simulation System
NASA Technical Reports Server (NTRS)
Slack, Thomas
2005-01-01
An investigation into the current state of the art of open source real time programming practices. This document includes what technologies are available, how easy is it to obtain, configure, and use them, and some performance measures done on the different systems. A matrix of vendors and their products is included as part of this investigation, but this is not an exhaustive list, and represents only a snapshot of time in a field that is changing rapidly. Specifically, there are three approaches investigated: 1. Completely open source on generic hardware, downloaded from the net. 2. Open source packaged by a vender and provided as free evaluation copy. 3. Proprietary hardware with pre-loaded proprietary source available software provided by the vender as for our evaluation.
Tailoring superradiance to design artificial quantum systems.
Longo, Paolo; Keitel, Christoph H; Evers, JÃ¶rg
2016-01-01
Cooperative phenomena arising due to the coupling of individual atoms via the radiation field are a cornerstone of modern quantum and optical physics. Recent experiments on x-ray quantum optics added a new twist to this line of research by exploiting superradiance in order to construct artificial quantum systems. However, so far, systematic approaches to deliberately design superradiance properties are lacking, impeding the desired implementation of more advanced quantum optical schemes. Here, we develop an analytical framework for the engineering of single-photon superradiance in extended media applicable across the entire electromagnetic spectrum, and show how it can be used to tailor the properties of an artificial quantum system. This "reverse engineering" of superradiance not only provides an avenue towards non-linear and quantum mechanical phenomena at x-ray energies, but also leads to a unified view on and a better understanding of superradiance across different physical systems. PMID:27009604
Tailoring superradiance to design artificial quantum systems
Longo, Paolo; Keitel, Christoph H.; Evers, JÃ¶rg
2016-01-01
Cooperative phenomena arising due to the coupling of individual atoms via the radiation field are a cornerstone of modern quantum and optical physics. Recent experiments on x-ray quantum optics added a new twist to this line of research by exploiting superradiance in order to construct artificial quantum systems. However, so far, systematic approaches to deliberately design superradiance properties are lacking, impeding the desired implementation of more advanced quantum optical schemes. Here, we develop an analytical framework for the engineering of single-photon superradiance in extended media applicable across the entire electromagnetic spectrum, and show how it can be used to tailor the properties of an artificial quantum system. This â€œreverse engineeringâ€ of superradiance not only provides an avenue towards non-linear and quantum mechanical phenomena at x-ray energies, but also leads to a unified view on and a better understanding of superradiance across different physical systems. PMID:27009604
Characterizing Quantum Dynamics with Initial System-Environment Correlations
NASA Astrophysics Data System (ADS)
Ringbauer, M.; Wood, C. J.; Modi, K.; Gilchrist, A.; White, A. G.; Fedrizzi, A.
2015-03-01
We fully characterize the reduced dynamics of an open quantum system initially correlated with its environment. Using a photonic qubit coupled to a simulated environment, we tomographically reconstruct a superchannel—a generalized channel that treats preparation procedures as inputs—from measurement of the system alone. We introduce novel quantitative measures for determining the strength of initial correlations, and to allow an experiment to be optimized in regard to its environment.
QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials.
Giannozzi, Paolo; Baroni, Stefano; Bonini, Nicola; Calandra, Matteo; Car, Roberto; Cavazzoni, Carlo; Ceresoli, Davide; Chiarotti, Guido L; Cococcioni, Matteo; Dabo, Ismaila; Dal Corso, Andrea; de Gironcoli, Stefano; Fabris, Stefano; Fratesi, Guido; Gebauer, Ralph; Gerstmann, Uwe; Gougoussis, Christos; Kokalj, Anton; Lazzeri, Michele; Martin-Samos, Layla; Marzari, Nicola; Mauri, Francesco; Mazzarello, Riccardo; Paolini, Stefano; Pasquarello, Alfredo; Paulatto, Lorenzo; Sbraccia, Carlo; Scandolo, Sandro; Sclauzero, Gabriele; Seitsonen, Ari P; Smogunov, Alexander; Umari, Paolo; Wentzcovitch, Renata M
2009-09-30
QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation, and Optimization. It is freely available to researchers around the world under the terms of the GNU General Public License. QUANTUM ESPRESSO builds upon newly-restructured electronic-structure codes that have been developed and tested by some of the original authors of novel electronic-structure algorithms and applied in the last twenty years by some of the leading materials modeling groups worldwide. Innovation and efficiency are still its main focus, with special attention paid to massively parallel architectures, and a great effort being devoted to user friendliness. QUANTUM ESPRESSO is evolving towards a distribution of independent and interoperable codes in the spirit of an open-source project, where researchers active in the field of electronic-structure calculations are encouraged to participate in the project by contributing their own codes or by implementing their own ideas into existing codes. PMID:21832390
QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials
NASA Astrophysics Data System (ADS)
Giannozzi, Paolo; Baroni, Stefano; Bonini, Nicola; Calandra, Matteo; Car, Roberto; Cavazzoni, Carlo; Ceresoli, Davide; Chiarotti, Guido L.; Cococcioni, Matteo; Dabo, Ismaila; Dal Corso, Andrea; de Gironcoli, Stefano; Fabris, Stefano; Fratesi, Guido; Gebauer, Ralph; Gerstmann, Uwe; Gougoussis, Christos; Kokalj, Anton; Lazzeri, Michele; Martin-Samos, Layla; Marzari, Nicola; Mauri, Francesco; Mazzarello, Riccardo; Paolini, Stefano; Pasquarello, Alfredo; Paulatto, Lorenzo; Sbraccia, Carlo; Scandolo, Sandro; Sclauzero, Gabriele; Seitsonen, Ari P.; Smogunov, Alexander; Umari, Paolo; Wentzcovitch, Renata M.
2009-09-01
QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation, and Optimization. It is freely available to researchers around the world under the terms of the GNU General Public License. QUANTUM ESPRESSO builds upon newly-restructured electronic-structure codes that have been developed and tested by some of the original authors of novel electronic-structure algorithms and applied in the last twenty years by some of the leading materials modeling groups worldwide. Innovation and efficiency are still its main focus, with special attention paid to massively parallel architectures, and a great effort being devoted to user friendliness. QUANTUM ESPRESSO is evolving towards a distribution of independent and interoperable codes in the spirit of an open-source project, where researchers active in the field of electronic-structure calculations are encouraged to participate in the project by contributing their own codes or by implementing their own ideas into existing codes.
Slightly anharmonic systems in quantum optics
NASA Technical Reports Server (NTRS)
Klimov, Andrey B.; Chumakov, Sergey M.
1995-01-01
We consider an arbitrary atomic system (n-level atom or many such atoms) interacting with a strong resonant quantum field. The approximate evolution operator for a quantum field case can be produced from the atomic evolution operator in an external classical field by a 'quantization prescription', passing the operator arguments to Wigner D-functions. Many important phenomena arising from the quantum nature of the field can be described by such a way.
Quantum Quenches in Topological Systems
NASA Astrophysics Data System (ADS)
Kells, Graham; Sen, Diptiman; Slingerland, J. K.; Vishveshwara, Smitha
2014-03-01
We study the non-equilibrium dynamics of quenching through a quantum critical point in topological systems, focusing on one of their characteristic features, namely, ground state degeneracies, and associated topological sectors. We present the notion of ``topological blocking,'' experienced by the dynamics due to the mismatch in degeneracies between two phases. We demonstrate the interplay between quenching and topology in two extensively studied systems, the transverse Ising chain and the Kitaev honeycomb model. Casting these systems in the language of fermionic spinless p-wave paired superconductors enables us to cleanly address degeneracies, subtle issues of fermion occupation and parity, and mismatches between topological sectors. We show that several features of the quench, which are related to Kibble-Zurek physics, are sensitive to the topological sector being probed. Supported by DST, India under Project No. SR/S2/JCB-44/2010, NSF under grant DMR 0644022-CAR, the Simons Foundation under Grant No.229047 and Science Foundation Ireland Awards 08/IN.1/I1961, 10/IN.1/I3013 and 12/IA/1697.
Optimized control of multistate quantum systems by composite pulse sequences
Genov, G. T.; Vitanov, N. V.; Torosov, B. T.
2011-12-15
We introduce a technique for derivation of high-fidelity composite pulse sequences for two types of multistate quantum systems: systems with the SU(2) and Morris-Shore dynamic symmetries. For the former type, we use the Majorana decomposition to reduce the dynamics to an effective two-state system, which allows us to find the propagator analytically and use the pool of available composite pulses for two-state systems. For the latter type of multistate systems, we use the Morris-Shore decomposition, which reduces the multistate dynamics to a set of two-state systems. We present examples which demonstrate that the multistate composite sequences open a variety of possibilities for coherent control of quantum systems with multiple states.
Quantum Simulation of Tunneling in Small Systems
Sornborger, Andrew T.
2012-01-01
A number of quantum algorithms have been performed on small quantum computers; these include Shor's prime factorization algorithm, error correction, Grover's search algorithm and a number of analog and digital quantum simulations. Because of the number of gates and qubits necessary, however, digital quantum particle simulations remain untested. A contributing factor to the system size required is the number of ancillary qubits needed to implement matrix exponentials of the potential operator. Here, we show that a set of tunneling problems may be investigated with no ancillary qubits and a cost of one single-qubit operator per time step for the potential evolution, eliminating at least half of the quantum gates required for the algorithm and more than that in the general case. Such simulations are within reach of current quantum computer architectures. PMID:22916333
Dynamic control of plasmon generation by an individual quantum system.
Große, Christoph; Kabakchiev, Alexander; Lutz, Theresa; Froidevaux, Romain; Schramm, Frank; Ruben, Mario; Etzkorn, Markus; Schlickum, Uta; Kuhnke, Klaus; Kern, Klaus
2014-10-01
Controlling light on the nanoscale in a similar way as electric currents has the potential to revolutionize the exchange and processing of information. Although light can be guided on this scale by coupling it to plasmons, that is, collective electron oscillations in metals, their local electronic control remains a challenge. Here, we demonstrate that an individual quantum system is able to dynamically gate the electrical plasmon generation. Using a single molecule in a double tunnel barrier between two electrodes we show that this gating can be exploited to monitor fast changes of the quantum system itself and to realize a single-molecule plasmon-generating field-effect transistor operable in the gigahertz range. This opens new avenues toward atomic scale quantum interfaces bridging nanoelectronics and nanophotonics. PMID:25181332
Transition Phenomena in Networks of Quantum Systems
NASA Astrophysics Data System (ADS)
Kraus, B.; Törmä, P.
The advances in experimental manipulation and theoretical understanding of single quantum systems has fed the interest in quantum networks: quantum computers, quantum communication networks and multimode interferometers. According to statistical physics, a set of probabilistically behaving individual systems can exhibit critical behaviour when connected. In this paper we show that transition phenomena exist also in networks which behave probabilistically not because of finite temperature but due to their quantum nature1. We define a model which carries in its structure a formal analogy to the two-dimensional Ising-model. Such networks can be experimentally realized by various active (non-unitary) and passive (unitary) components. We give physical meaning to the transitions found. In the case of active components, such as amplifiers, the transition point coincides with the fundamental cloning limit given by quantum mechanics. We indicate how the transition phenomena could be observed, and discuss their significance and connection to quantum information related issues such as quantum computation and quantum cellular automata.
Exponential sensitivity and chaos in quantum systems
NASA Astrophysics Data System (ADS)
Blümel, R.
1994-07-01
Exponential sensitivity and chaos can occur in quantum systems. An example is the propagation of spin-1/2 particles through a spin-precession apparatus consisting of a chain of magnetic field sections arranged spatially in a Fibonacci-like sequence. It is shown that the quantum propagation in this apparatus is as chaotic as Arnol'ds' cat map.
Charge transport through weakly open one-dimensional quantum wires.
Kopnin, N. B.; Galperin, Y. M.; Vinokur, V. M.; Materials Science Division; Helsinki Univ. of Technology; L. D. Landau Inst. for Theoretical Physics; Univ. of Oslo; Russian Academy of Sciences
2009-01-01
We consider resonant transmission through a gated finite-length quantum wire connected to leads via finite-transparency junctions, such that the escape time is much smaller than the energy relaxation time in the wire. The coherent electron transport is strongly modified by the Coulomb interaction. The low-temperature current-voltage (IV) curves show steplike dependence on the bias voltage determined by the distance between the quantum levels inside the conductor, the pattern being dependent on the ratio between the charging energy and level spacing. If the system is tuned close to the resonance condition by the gate voltage, the low-voltage IV curve is ohmic. At large Coulomb energy and low temperatures, the conductance is temperature independent for any relationship between temperature, level spacing, and coupling between the wire and the leads.
Charge transport through weakly open one-dimensional quantum wires
NASA Astrophysics Data System (ADS)
Kopnin, N. B.; Galperin, Y. M.; Vinokur, V. M.
2009-01-01
We consider resonant transmission through a gated finite-length quantum wire connected to leads via finite-transparency junctions, such that the escape time is much smaller than the energy relaxation time in the wire. The coherent electron transport is strongly modified by the Coulomb interaction. The low-temperature current-voltage (IV) curves show steplike dependence on the bias voltage determined by the distance between the quantum levels inside the conductor, the pattern being dependent on the ratio between the charging energy and level spacing. If the system is tuned close to the resonance condition by the gate voltage, the low-voltage IV curve is ohmic. At large Coulomb energy and low temperatures, the conductance is temperature independent for any relationship between temperature, level spacing, and coupling between the wire and the leads.
Galilei invariant technique for quantum system description
KamuntaviÄius, Gintautas P.
2014-04-15
Problems with quantum systems models, violating Galilei invariance are examined. The method for arbitrary non-relativistic quantum system Galilei invariant wave function construction, applying a modified basis where center-of-mass excitations have been removed before Hamiltonian matrix diagonalization, is developed. For identical fermion system, the Galilei invariant wave function can be obtained while applying conventional antisymmetrization methods of wave functions, dependent on single particle spatial variables.
Mapping the Schroedinger picture of open quantum dynamics
Jordan, Thomas F.; Shaji, Anil; Sudarshan, E. C. G.
2006-01-15
For systems described by finite matrices, an affine form is developed for the maps that describe evolution of density matrices for a quantum system that interacts with another. This is established directly from the Heisenberg picture. It separates elements that depend only on the dynamics from those that depend on the state of the two systems. While the equivalent linear map is generally not completely positive, the homogeneous part of the affine maps is, and is shown to be composed of multiplication operations that come simply from the Hamiltonian for the larger system. The inhomogeneous part is shown to be zero if and only if the map does not increase the trace of the square of any density matrix. Properties are worked out in detail for two-qubit examples.
Hamiltonian tomography: the quantum (system) measurement problem
NASA Astrophysics Data System (ADS)
Cole, Jared H.
2015-10-01
To harness the power of controllable quantum systems for information processing or quantum simulation, it is essential to be able to accurately characterise the system's Hamiltonian. Although in principle this requires determining less parameters than full quantum process tomography, a general and extendable method for reconstructing a general Hamiltonian has been elusive. In their recent paper, Wang et al (2015 New J. Phys. 17 093017) apply dynamical decoupling to the problem of Hamiltonian tomography and show how to reconstruct a general many-body Hamiltonian comprised of arbitrary interactions between qubits.
Effective constraints for relativistic quantum systems
NASA Astrophysics Data System (ADS)
Bojowald, Martin; Tsobanjan, Artur
2009-12-01
Determining the physical Hilbert space is often considered the most difficult but crucial part of completing the quantization of a constrained system. In such a situation it can be more economical to use effective constraint methods, which are extended here to relativistic systems as they arise for instance in quantum cosmology. By sidestepping explicit constructions of states, such tools allow one to arrive much more feasibly at results for physical observables at least in semiclassical regimes. Several questions discussed recently regarding effective equations and state properties in quantum cosmology, including the spreading of states and quantum backreaction, are addressed by the examples studied here.
Software-defined Quantum Communication Systems
Humble, Travis S; Sadlier, Ronald J
2013-01-01
We show how to extend the paradigm of software-defined communication to include quantum communication systems. We introduce the decomposition of a quantum communication terminal into layers separating the concerns of the hardware, software, and middleware. We provide detailed descriptions of how each component operates and we include results of an implementation of the super-dense coding protocol. We argue that the versatility of software-defined quantum communication test beds can be useful for exploring new regimes in communication and rapidly prototyping new systems.
Multi-valley effective mass theory for device-level modeling of open quantum dynamics
NASA Astrophysics Data System (ADS)
Jacobson, N. Tobias; Baczewski, Andrew D.; Frees, Adam; Gamble, John King; Montano, Ines; Moussa, Jonathan E.; Muller, Richard P.; Nielsen, Erik
2015-03-01
Simple models for semiconductor-based quantum information processors can provide useful qualitative descriptions of device behavior. However, as experimental implementations have matured, more specific guidance from theory has become necessary, particularly in the form of quantitatively reliable yet computationally efficient modeling. Besides modeling static device properties, improved characterization of noisy gate operations requires a more sophisticated description of device dynamics. Making use of recent developments in multi-valley effective mass theory, we discuss device-level simulations of the open system quantum dynamics of a qubit interacting with phonons and other noise sources. Sandia is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the US Department of Energy National Nuclear Security Administration under Contract No. DE-AC04-94AL85000.
Cavity optomechanics mediated by a quantum two-level system
Pirkkalainen, J.-M.; Cho, S.U.; Massel, F.; Tuorila, J.; Heikkilä, T.T.; Hakonen, P.J.; Sillanpää, M.A.
2015-01-01
Coupling electromagnetic waves in a cavity and mechanical vibrations via the radiation pressure of photons is a promising platform for investigations of quantum–mechanical properties of motion. A drawback is that the effect of one photon tends to be tiny, and hence one of the pressing challenges is to substantially increase the interaction strength. A novel scenario is to introduce into the setup a quantum two-level system (qubit), which, besides strengthening the coupling, allows for rich physics via strongly enhanced nonlinearities. Here we present a design of cavity optomechanics in the microwave frequency regime involving a Josephson junction qubit. We demonstrate boosting of the radiation–pressure interaction by six orders of magnitude, allowing to approach the strong coupling regime. We observe nonlinear phenomena at single-photon energies, such as an enhanced damping attributed to the qubit. This work opens up nonlinear cavity optomechanics as a plausible tool for the study of quantum properties of motion. PMID:25912295
Cavity optomechanics mediated by a quantum two-level system
NASA Astrophysics Data System (ADS)
Pirkkalainen, J.-M.; Cho, S. U.; Massel, F.; Tuorila, J.; Heikkilä, T. T.; Hakonen, P. J.; Sillanpää, M. A.
2015-04-01
Coupling electromagnetic waves in a cavity and mechanical vibrations via the radiation pressure of photons is a promising platform for investigations of quantum-mechanical properties of motion. A drawback is that the effect of one photon tends to be tiny, and hence one of the pressing challenges is to substantially increase the interaction strength. A novel scenario is to introduce into the setup a quantum two-level system (qubit), which, besides strengthening the coupling, allows for rich physics via strongly enhanced nonlinearities. Here we present a design of cavity optomechanics in the microwave frequency regime involving a Josephson junction qubit. We demonstrate boosting of the radiation-pressure interaction by six orders of magnitude, allowing to approach the strong coupling regime. We observe nonlinear phenomena at single-photon energies, such as an enhanced damping attributed to the qubit. This work opens up nonlinear cavity optomechanics as a plausible tool for the study of quantum properties of motion.
Bound states in the continuum in open quantum billiards with a variable shape
Sadreev, Almas F.; Bulgakov, Evgeny N.; Rotter, Ingrid
2006-06-15
We show the existence of bound states in the continuum (BICs) in quantum billiards (QBs) that are opened by attaching single-channel leads to them. They may be observed by varying an external parameter continuously, e.g., the shape of the QB. At some values of the parameter, resonance states with vanishing decay width (the BICs) occur. They are localized almost completely in the interior of the closed system. The phenomenon is shown analytically to exist in the simplest case of a two level QB and is complemented by numerical calculations for a real QB.
Combinatorial Approach to Modeling Quantum Systems
NASA Astrophysics Data System (ADS)
Kornyak, Vladimir V.
2016-02-01
Using the fact that any linear representation of a group can be embedded into permutations, we propose a constructive description of quantum behavior that provides, in particular, a natural explanation of the appearance of complex numbers and unitarity in the formalism of the quantum mechanics. In our approach, the quantum behavior can be explained by the fundamental impossibility to trace the identity of the indistinguishable objects in their evolution. Any observation only provides information about the invariant relations between such objects. The trajectory of a quantum system is a sequence of unitary evolutions interspersed with observationsâ€”non-unitary projections. We suggest a scheme to construct combinatorial models of quantum evolution. The principle of selection of the most likely trajectories in such models via the large numbers approximation leads in the continuum limit to the principle of least action with the appropriate Lagrangians and deterministic evolution equations
Carrier Spin Polarization in Quantum Confined System
NASA Astrophysics Data System (ADS)
Long, Gen
In this dissertation, systematic studies of magneto-photoluminescence of manganese-doped lead salt (Mn doped lead sulfide and lead selenide) quantum dots and core/shell quantum dots will be presented. It was observed that large carrier spin polarization can be obtained in manganese doped IV-VI lead salt quantum dots upon excitation by circularly polarized light; and a clear dependence of spin polarization on the sizes of quantum dots and thickness of core/shell quantum dots was observed as well. The quantum dots in this study were synthesized by solution-phase chemical method. The sizes of the quantum dots could be controlled by the growth temperature (50 to 150) and growth time (1min to 24hr). The doping concentrations in the compounds Pb1-xMn xS (or Pb1-xMnxSe) ranging from x = 0 to 8% can be adjusted by varying synthesis conditions as well. Studies on size dependence (from 3 to 10 nm), temperature dependence (from 7K to 50K), magnetic field dependence (from 0 to 7T), and laser power dependence (from 1mW to 20mW) of photoluminescence intensities and peak positions were systematically carried out. The spin-polarization, which was directly calculated from magneto-luminescence measurements, was studied as a function of quantum dot sizes, temperatures and magnetic fields. It was observed that, depending on the sizes and growth conditions (growth temperature and time), the spin polarization, as large as 40% at 7K in a 7T magnetic field, could be tuned in magnitude. Core/shell structured quantum dots with Mn2+ ions doped in the inner core or outer shell were also studied. The spin polarization was observed in core/shell system to decrease as thickness of the shell increases. We believe the wave function overlap between carriers and dopants can be tuned by quantum confinement and therefore the magnitude of exchange interactions can be tuned via varying the sizes of quantum dots or the shell thickness of core/shell quantum dots. There are a couple of measurements that showed inversion of spin polarization but the reproducibility is low. Further studies are needed to verify the possibility of reversing the sign of spin polarization through quantum confinement, i.e., varying the sizes of quantum dots or the shell thickness of core/shell quantum dots.
Software-defined Quantum Communication Systems
Humble, Travis S; Sadlier, Ronald J
2014-01-01
Quantum communication systems harness modern physics through state-of-the-art optical engineering to provide revolutionary capabilities. An important concern for quantum communication engineering is designing and prototyping these systems to prototype proposed capabilities. We apply the paradigm of software-defined communica- tion for engineering quantum communication systems to facilitate rapid prototyping and prototype comparisons. We detail how to decompose quantum communication terminals into functional layers defining hardware, software, and middleware concerns, and we describe how each layer behaves. Using the super-dense coding protocol as a test case, we describe implementations of both the transmitter and receiver, and we present results from numerical simulations of the behavior. We find that while the theoretical benefits of super dense coding are maintained, there is a classical overhead associated with the full implementation.
Superconducting circuitry for quantum electromechanical systems
NASA Astrophysics Data System (ADS)
LaHaye, Matthew D.; Rouxinol, Francisco; Hao, Yu; Shim, Seung-Bo; Irish, Elinor K.
2015-05-01
Superconducting systems have a long history of use in experiments that push the frontiers of mechanical sensing. This includes both applied and fundamental research, which at present day ranges from quantum computing research and e orts to explore Planck-scale physics to fundamental studies on the nature of motion and the quantum limits on our ability to measure it. In this paper, we first provide a short history of the role of superconducting circuitry and devices in mechanical sensing, focusing primarily on efforts in the last decade to push the study of quantum mechanics to include motion on the scale of human-made structures. This background sets the stage for the remainder of the paper, which focuses on the development of quantum electromechanical systems (QEMS) that incorporate superconducting quantum bits (qubits), superconducting transmission line resonators and flexural nanomechanical elements. In addition to providing the motivation and relevant background on the physical behavior of these systems, we discuss our recent efforts to develop a particular type of QEMS that is based upon the Cooper-pair box (CPB) and superconducting coplanar waveguide (CPW) cavities, a system which has the potential to serve as a testbed for studying the quantum properties of motion in engineered systems.
Robust observer for uncertain linear quantum systems
Yamamoto, Naoki
2006-09-15
In the theory of quantum dynamical filtering, one of the biggest issues is that the underlying system dynamics represented by a quantum stochastic differential equation must be known exactly in order that the corresponding filter provides an optimal performance; however, this assumption is generally unrealistic. Therefore, in this paper, we consider a class of linear quantum systems subjected to time-varying norm-bounded parametric uncertainties and then propose a robust observer such that the variance of the estimation error is guaranteed to be within a certain bound. Although in the linear case much of classical control theory can be applied to quantum systems, the quantum robust observer obtained in this paper does not have a classical analog due to the system's specific structure with respect to the uncertainties. Moreover, by considering a typical quantum control problem, we show that the proposed robust observer is fairly robust against a parametric uncertainty of the system even when the other estimators--the optimal Kalman filter and risk-sensitive observer--fail in the estimation.
Dicke model for quantum Hall systems
NASA Astrophysics Data System (ADS)
Hama, Y.; Fauzi, M. H.; Nemoto, K.; Hirayama, Y.; Ezawa, Z. F.
2016-02-01
In GaAs quantum Hall (QH) systems, electrons are coupled with nuclear spins through the hyperfine interaction, which is normally not strong enough to change the dynamics of electrons and nuclear spins. The dynamics of the QH systems, however, may drastically change when the nuclear spins interact with low-energy collective excitation modes of the electron spins. We theoretically investigate the nuclear-electron spin interaction in the QH systems as hybrid quantum systems driven by the hyperfine interaction. In particular, we study the interaction between the nuclear spins and the Nambuâ€“Goldstone (NG) mode with the linear dispersion relation associated with the U(1) spin rotational symmetry breaking. We show that such an interaction is described as nuclear spins collectively coupled to the NG mode, and can be effectively described by the Dicke model. Based on the model we suggest that various collective spin phenomena realized in quantum optical systems can also emerge in the QH systems.
Quantum optical properties in plasmonic systems
Ooi, C. H. Raymond
2015-04-24
Plasmonic metallic particle (MP) can affect the optical properties of a quantum system (QS) in a remarkable way. We develop a general quantum nonlinear formalism with exact vectorial description for the scattered photons by the QS. The formalism enables us to study the variations of the dielectric function and photon spectrum of the QS with the particle distance between QS and MP, exciting laser direction, polarization and phase in the presence of surface plasmon resonance (SPR) in the MP. The quantum formalism also serves as a powerful tool for studying the effects of these parameters on the nonclassical properties of the scattered photons. The plasmonic effect of nanoparticles has promising possibilities as it provides a new way for manipulating quantum optical properties of light in nanophotonic systems.
Levitated Quantum Nano-Magneto-Mechanical Systems
NASA Astrophysics Data System (ADS)
Cirio, Mauro; Twamley, Jason; Brennen, Gavin K.; Milburn, Gerard J.
2011-03-01
Quantum nanomechanical sysems have attracted much attention as they provide new macroscopic platforms for the study of quantum mechanics but may also have applications in ultra-sensitive sensing, high precision measurements and in quantum computing. In this work we study the control and cooling of a quantum nanomechanical system which is magnetically levitated via the Meissner effect. Supercurrents in nano-sized superconducting loops give rise to a motional restoring force (trap), when placed in an highly inhomogenous magnetic field and can yield complete trapping of all translational and rotational motions of the levitated nano-object with motional oscillation frequencies ? ~ 10 - 100 MHz. As the supercurrents experience little damping this system will possess unprecendented motional quality factors, with Qmotion ~109 -1013 , and motional superposition states may remain coherent for days. We describe how to execute sideband cooling through inductive coupling to a nearby flux qubit, cooling the mechanical motion close to the ground state.
Thermalisation of a quantum system from first principles
NASA Astrophysics Data System (ADS)
Ithier, Gregoire; Benaych-Georges, Florent
2015-03-01
How does a quantum system reach thermodynamical equilibrium? Answering such a question from first principles is, perhaps surprisingly, still an open issue (Popescu Nat. Phys. 2006, Goldstein PRL 2006, Genway PRL 2013). We present here a new model comprising an arbitrary quantum system interacting with a large arbitrary quantum environment, both initially prepared in a quantum pure state. We then demonstrate that thermalisation is an emergent property of the unitary evolution under a Schrödinger equation of this large composite system. The key conceptual tool of our method is the phenomenon of ``measure concentration'' appearing with functions defined on large dimension Hilbert spaces, a phenomenon which cancels out any effect of the microscopic structure of interaction Hamiltonians. Using our model, we first characterize the transient evolution or decoherence of the system and show its universal character. We then focus on the stationary regime and recover the canonical state well known from statistical thermodynamics. This finding leads us to propose an alternative and more general definition of the canonical partition function, that includes, among other things, the possibility of describing partial thermalisation.
Quantum discord in matrix product systems
Sun Zhaoyu; Li Liang; Du Guihuan; Yao Kailun; Liu Jiwei; Luo Bo; Li Neng; Li Haina
2010-09-15
We consider a class of quantum systems with spin-flip symmetry and derive the quantum correlation measured by the quantum discord (QD). As an illustration, we investigate the QD in a three-body interaction model and an XYZ interaction model, whose ground states can be expressed as matrix product states, and the QD is exactly soluble. We show that the QD behaves differently than the quantum entanglement (QE) in many ways; for example, they may show opposite monotonicity and completely different finite-size effects. Furthermore, we compare the capability of the QD and the QE to detect quantum phase transitions (QPTs) and find that the QD is more reliable than the QE for signaling QPTs in these models: In the three-body interaction model, the QE is singular at the quantum critical point, however, it exhibits an additional singularity in the noncritical region, while the analyticity of the QD can be used to identify the quantum critical point perfectly; and in the XYZ interaction model, the QE vanishes in the thermodynamic limit, thus losing its ability to detect QPTs, while the QD still functions very well.
Localization in a quantum spin Hall system.
Onoda, Masaru; Avishai, Yshai; Nagaosa, Naoto
2007-02-16
The localization problem of electronic states in a two-dimensional quantum spin Hall system (that is, a symplectic ensemble with topological term) is studied by the transfer matrix method. The phase diagram in the plane of energy and disorder strength is exposed, and demonstrates "levitation" and "pair annihilation" of the domains of extended states analogous to that of the integer quantum Hall system. The critical exponent nu for the divergence of the localization length is estimated as nu congruent with 1.6, which is distinct from both exponents pertaining to the conventional symplectic and the unitary quantum Hall systems. Our analysis strongly suggests a different universality class related to the topology of the pertinent system. PMID:17359045
How does an isolated quantum system relax?
NASA Astrophysics Data System (ADS)
Schmiedmayer, Joerg
2014-03-01
One of the biggest challenges in probing non-equilibrium dynamics of many-body quantum systems is that there is no general approach to characterize the resulting quantum states. Interference experiments give access to the phase of the order parameter. The full distribution functions of the interference amplitude, and the full phase correlation functions allow us to study the relaxation dynamics in one-dimensional quantum systems. Starting form a coherently split 1d quantum gas, the initial coherence slowly decays. Due to the approximate conserved quantities in our nearly integrable system, this relaxation leads to a pre-thermalized state, which is characterized by thermal like distribution functions but exhibits an effective temperature much lower than the kinetic temperature of the initial system. A detailed study of the correlation functions reveals that these thermal-like properties emerge locally in their final form and propagate through the system in a light-cone-like evolution. Furthermore we demonstrate that the pre- thermalized state is connected to a Generalized Gibbs Ensemble and show the pathways for further relaxation towards thermal equilibrium. Supported by the Austrian Science Foundation and the European Research Council ERC AdG: Quantum Relax
Dynamical response theory for driven-dissipative quantum systems
NASA Astrophysics Data System (ADS)
Campos Venuti, Lorenzo; Zanardi, Paolo
2016-03-01
We discuss dynamical response theory of driven-dissipative quantum systems described by Markovian master equations generating semigroups of maps. In this setting thermal equilibrium states are replaced by nonequilibrium steady states, and dissipative perturbations are considered in addition to the Hamiltonian ones. We derive explicit expressions for the linear dynamical response functions for generalized dephasing channels and for Davies thermalizing generators. We introduce the notion of maximal harmonic response and compute it exactly for a single-qubit channel. Finally, we analyze linear response near dynamical phase transitions in quasifree open quantum systems. It is found that the effect of the dynamical phase transition shows up in a peak at the edge of the spectrum in the imaginary part of the dynamical response function.
Heisenberg picture approach to the stability of quantum Markov systems
Pan, Yu E-mail: zibo.miao@anu.edu.au; Miao, Zibo E-mail: zibo.miao@anu.edu.au; Amini, Hadis; Gough, John; Ugrinovskii, Valery; James, Matthew R.
2014-06-15
Quantum Markovian systems, modeled as unitary dilations in the quantum stochastic calculus of Hudson and Parthasarathy, have become standard in current quantum technological applications. This paper investigates the stability theory of such systems. Lyapunov-type conditions in the Heisenberg picture are derived in order to stabilize the evolution of system operators as well as the underlying dynamics of the quantum states. In particular, using the quantum Markov semigroup associated with this quantum stochastic differential equation, we derive sufficient conditions for the existence and stability of a unique and faithful invariant quantum state. Furthermore, this paper proves the quantum invariance principle, which extends the LaSalle invariance principle to quantum systems in the Heisenberg picture. These results are formulated in terms of algebraic constraints suitable for engineering quantum systems that are used in coherent feedback networks.
Light-cone-like spreading of correlations in a quantum many-body system.
Cheneau, Marc; Barmettler, Peter; Poletti, Dario; Endres, Manuel; Schauss, Peter; Fukuhara, Takeshi; Gross, Christian; Bloch, Immanuel; Kollath, Corinna; Kuhr, Stefan
2012-01-26
In relativistic quantum field theory, information propagation is bounded by the speed of light. No such limit exists in the non-relativistic case, although in real physical systems, short-range interactions may be expected to restrict the propagation of information to finite velocities. The question of how fast correlations can spread in quantum many-body systems has been long studied. The existence of a maximal velocity, known as the Lieb-Robinson bound, has been shown theoretically to exist in several interacting many-body systems (for example, spins on a lattice)--such systems can be regarded as exhibiting an effective light cone that bounds the propagation speed of correlations. The existence of such a 'speed of light' has profound implications for condensed matter physics and quantum information, but has not been observed experimentally. Here we report the time-resolved detection of propagating correlations in an interacting quantum many-body system. By quenching a one-dimensional quantum gas in an optical lattice, we reveal how quasiparticle pairs transport correlations with a finite velocity across the system, resulting in an effective light cone for the quantum dynamics. Our results open perspectives for understanding the relaxation of closed quantum systems far from equilibrium, and for engineering the efficient quantum channels necessary for fast quantum computations. PMID:22281597
Quantum temporal probabilities in tunneling systems
NASA Astrophysics Data System (ADS)
Anastopoulos, Charis; Savvidou, Ntina
2013-09-01
We study the temporal aspects of quantum tunneling as manifested in time-of-arrival experiments in which the detected particle tunnels through a potential barrier. In particular, we present a general method for constructing temporal probabilities in tunneling systems that (i) defines 'classical' time observables for quantum systems and (ii) applies to relativistic particles interacting through quantum fields. We show that the relevant probabilities are defined in terms of specific correlation functions of the quantum field associated with tunneling particles. We construct a probability distribution with respect to the time of particle detection that contains all information about the temporal aspects of the tunneling process. In specific cases, this probability distribution leads to the definition of a delay time that, for parity-symmetric potentials, reduces to the phase time of Bohm and Wigner. We apply our results to piecewise constant potentials, by deriving the appropriate junction conditions on the points of discontinuity. For the double square potential, in particular, we demonstrate the existence of (at least) two physically relevant time parameters, the delay time and a decay rate that describes the escape of particles trapped in the inter-barrier region. Finally, we propose a resolution to the paradox of apparent superluminal velocities for tunneling particles. We demonstrate that the idea of faster-than-light speeds in tunneling follows from an inadmissible use of classical reasoning in the description of quantum systems.
Quantum Langevin equations for optomechanical systems
NASA Astrophysics Data System (ADS)
Barchielli, Alberto; Vacchini, Bassano
2015-08-01
We provide a fully quantum description of a mechanical oscillator in the presence of thermal environmental noise by means of a quantum Langevin formulation based on quantum stochastic calculus. The system dynamics is determined by symmetry requirements and equipartition at equilibrium, while the environment is described by quantum Bose fields in a suitable non-Fock representation which allows for the introduction of temperature. A generic spectral density of the environment can be described by introducing its state through a suitable P-representation. Including interaction of the mechanical oscillator with a cavity mode via radiation pressure we obtain a description of a simple optomechanical system in which, besides the Langevin equations for the system, one has the exact input-output relations for the quantum noises. The whole theory is valid at arbitrarily low temperature. This allows the exact calculation of the stationary value of the mean energy of the mechanical oscillator, as well as both homodyne and heterodyne spectra. The present analysis allows in particular to study possible cooling scenarios and to obtain the exact connection between observed spectra and fluctuation spectra of the position of the mechanical oscillator.
Quons in a quantum dissipative system
NASA Astrophysics Data System (ADS)
Lee, Taejin
2016-03-01
String theory proves to be an imperative tool to explore the critical behavior of the quantum dissipative system. We discuss the quantum particles moving in two dimensions, in the presence of a uniform magnetic field, subject to a periodic potential and a dissipative force, which are described by the dissipative Wannier-Azbel-Hofstadter (DWAH) model. Using string theory formulation of the model, we find that the elementary excitations of the system at the generic points of the off-critical regions, in the zero temperature limit are quons, which satisfy q-deformed statistics.
Thermodynamic formalism for quantum-mechanical systems
NASA Astrophysics Data System (ADS)
Beck, Christian
1991-05-01
Based on the thermodynamic formalism of dynamical systems I present an alternative formulation of Euclidean quantum mechanics on the lattice. A class of deterministic chaotic maps is introduced that simulate nonrelativistic quantum-mechanical systems with arbitrary scalar and vector potential. Applying thermodynamic formalism to these maps the partition function converges to the propagator of the Schrödinger equation (with imaginary time) and the free energy to the ground state energy in an appropriate scaling limit. To illustrate the method I determine ground state energies for the harmonic and anharmonic oscillator, and calculate the integrated propagator of the hydrogen atom.
Open Quantum Dynamics Calculations with the Hierarchy Equations of Motion on Parallel Computers.
Strümpfer, Johan; Schulten, Klaus
2012-08-14
Calculating the evolution of an open quantum system, i.e., a system in contact with a thermal environment, has presented a theoretical and computational challenge for many years. With the advent of supercomputers containing large amounts of memory and many processors, the computational challenge posed by the previously intractable theoretical models can now be addressed. The hierarchy equations of motion present one such model and offer a powerful method that remained under-utilized so far due to its considerable computational expense. By exploiting concurrent processing on parallel computers the hierarchy equations of motion can be applied to biological-scale systems. Herein we introduce the quantum dynamics software PHI, that solves the hierarchical equations of motion. We describe the integrator employed by PHI and demonstrate PHI's scaling and efficiency running on large parallel computers by applying the software to the calculation of inter-complex excitation transfer between the light harvesting complexes 1 and 2 of purple photosynthetic bacteria, a 50 pigment system. PMID:23105920
Open Quantum Dynamics Calculations with the Hierarchy Equations of Motion on Parallel Computers
Strümpfer, Johan; Schulten, Klaus
2012-01-01
Calculating the evolution of an open quantum system, i.e., a system in contact with a thermal environment, has presented a theoretical and computational challenge for many years. With the advent of supercomputers containing large amounts of memory and many processors, the computational challenge posed by the previously intractable theoretical models can now be addressed. The hierarchy equations of motion present one such model and offer a powerful method that remained under-utilized so far due to its considerable computational expense. By exploiting concurrent processing on parallel computers the hierarchy equations of motion can be applied to biological-scale systems. Herein we introduce the quantum dynamics software PHI, that solves the hierarchical equations of motion. We describe the integrator employed by PHI and demonstrate PHI’s scaling and efficiency running on large parallel computers by applying the software to the calculation of inter-complex excitation transfer between the light harvesting complexes 1 and 2 of purple photosynthetic bacteria, a 50 pigment system. PMID:23105920
Quantum Discord for d?2 Systems
Ma, Zhihao; Chen, Zhihua; Fanchini, Felipe Fernandes; Fei, Shao-Ming
2015-01-01
We present an analytical solution for classical correlation, defined in terms of linear entropy, in an arbitrary system when the second subsystem is measured. We show that the optimal measurements used in the maximization of the classical correlation in terms of linear entropy, when used to calculate the quantum discord in terms of von Neumann entropy, result in a tight upper bound for arbitrary systems. This bound agrees with all known analytical results about quantum discord in terms of von Neumann entropy and, when comparing it with the numerical results for 106 two-qubit random density matrices, we obtain an average deviation of order 10?4. Furthermore, our results give a way to calculate the quantum discord for arbitrary n-qubit GHZ and W states evolving under the action of the amplitude damping noisy channel. PMID:26036771
Witnessing Quantum Coherence: from solid-state to biological systems
Li, Che-Ming; Lambert, Neill; Chen, Yueh-Nan; Chen, Guang-Yin; Nori, Franco
2012-01-01
Quantum coherence is one of the primary non-classical features of quantum systems. While protocols such as the Leggett-Garg inequality (LGI) and quantum tomography can be used to test for the existence of quantum coherence and dynamics in a given system, unambiguously detecting inherent â€œquantumnessâ€ still faces serious obstacles in terms of experimental feasibility and efficiency, particularly in complex systems. Here we introduce two â€œquantum witnessesâ€ to efficiently verify quantum coherence and dynamics in the time domain, without the expense and burden of non-invasive measurements or full tomographic processes. Using several physical examples, including quantum transport in solid-state nanostructures and in biological organisms, we show that these quantum witnesses are robust and have a much finer resolution in their detection window than the LGI has. These robust quantum indicators may assist in reducing the experimental overhead in unambiguously verifying quantum coherence in complex systems. PMID:23185690
Quantum temporal probabilities in tunneling systems
Anastopoulos, Charis Savvidou, Ntina
2013-09-15
We study the temporal aspects of quantum tunneling as manifested in time-of-arrival experiments in which the detected particle tunnels through a potential barrier. In particular, we present a general method for constructing temporal probabilities in tunneling systems that (i) defines â€˜classicalâ€™ time observables for quantum systems and (ii) applies to relativistic particles interacting through quantum fields. We show that the relevant probabilities are defined in terms of specific correlation functions of the quantum field associated with tunneling particles. We construct a probability distribution with respect to the time of particle detection that contains all information about the temporal aspects of the tunneling process. In specific cases, this probability distribution leads to the definition of a delay time that, for parity-symmetric potentials, reduces to the phase time of Bohm and Wigner. We apply our results to piecewise constant potentials, by deriving the appropriate junction conditions on the points of discontinuity. For the double square potential, in particular, we demonstrate the existence of (at least) two physically relevant time parameters, the delay time and a decay rate that describes the escape of particles trapped in the inter-barrier region. Finally, we propose a resolution to the paradox of apparent superluminal velocities for tunneling particles. We demonstrate that the idea of faster-than-light speeds in tunneling follows from an inadmissible use of classical reasoning in the description of quantum systems. -- Highlights: â€¢Present a general methodology for deriving temporal probabilities in tunneling systems. â€¢Treatment applies to relativistic particles interacting through quantum fields. â€¢Derive a new expression for tunneling time. â€¢Identify new time parameters relevant to tunneling. â€¢Propose a resolution of the superluminality paradox in tunneling.
Alonso, Daniel; Vega, Ines de
2010-06-15
Open quantum systems are often encountered in many different physical situations. From quantum optics to statistical mechanics, they are fundamental in the understanding of a great variety of different phenomena. Some of the most common examples are the relaxation to equilibrium, the existence of nonequilibrium stationary states, and the dynamics of atoms in interaction with electromagnetic fields. A crucial step in the analysis is to consider the quantum open system and its environment as the two mutually interacting components of a larger isolated system. Thereafter, the so-called Markov approximation is often considered, which consists on assuming that the time scales associated to the dynamics of the quantum open system are larger than those of the environment. It is the interplay of the different time scales associated with the system and the environment what determines the validity of the different approximations made. In this paper we will discuss the dynamics of a open quantum system in contact with a reservoir when the Markov approximation is not valid, and we have to include some non-Markovian or memory effects.
Semiclassical analysis of quantum systems with constraints
NASA Astrophysics Data System (ADS)
Tsobanjan, Artur
This dissertation addresses the problem of constructing true degrees of freedom in quantum mechanical systems with constraints. The method developed relies on assuming the behavior of the system of interest is "nearly classical", or semiclassical, in a precise quantitative sense. The approximation is formulated as a perturbative hierarchy of the expectation values of quantum observables and their non-linear combinations, such as spreads and correlations. We formulate the constraint conditions and additional quantum gauge transformations that arise directly on the aforementioned quantities. We specialize this framework to several situations of particular interest. The first situation considered is the case of a constraint that commutes with all quantum observables, which is appropriate for quantization of a Lie algebra with a single Casimir polynomial. Through explicit order-by order counting argue that the true degrees of freedom are captured correctly at each order of the approximation. The rest of the models considered are motivated by the canonical approach to quantizing general relativity. The homogeneous sector of general relativity splits into classes of models, according to topology, which are described by a finite number of degrees of freedom and can therefore be quantized as quantum mechanical systems, making our construction directly applicable. In the Hamiltonian formulation the dynamics of these systems is governed by the Hamiltonian constraint, which, in the quantum theory, gives rise to several conceptual and technical issues collectively known as the Problem of Time. One of the aspects of this problem that does not possess a general solution is the dynamical interpretation of the theory. We use our construction, truncated at the leading order in quantum corrections, together with the intuition gained from dealing with constrained systems in classical mechanics, to define local notion of dynamics relative to a chosen configuration clock variable. We consider a class of models, where the chosen clock in not globally valid, eventually leading to singular dynamics. Within these models we construct an explicit transformation between dynamical evolution relative to two distinct clocks, thus providing a consistent local dynamical interpretation of the true degrees of freedom of the quantum theory.
Photorefractive quantum wells: Materials, devices and systems
NASA Astrophysics Data System (ADS)
Lahiri, Indrajit
Photorefractive quantum wells are dynamic holographic materials that combine the advantages of large excitonic electroabsorption with large carrier mobilities to produce high-sensitivity holographic devices operable at extremely low optical intensities compatible with image processing applications. They are finding a niche as versatile optical devices in systems such as joint image correlators, femtosecond autocorrelators, laser-based ultrasound detection, and time-to-space mapping. These devices contain high defect densities which trap and store photogenerated carriers. The trapped space-charge results in a spatially varying space-charge field that matches the periodicity of the incident intensity pattern, which alters the optical properties of the device. The principal objective of the present study was to develop a new material system (low-temperature-grown AlGaAs/GaAs quantum wells) for photorefractive applications. We have achieved ultrafast electron recombination lifetimes in combination with sharp excitonic features, a goal which was considered mutually exclusive, by engineering low-temperature-grown AlAs/GaAs quantum wells. This material system was used to develop photorefractive p-i-n quantum well diodes operating in the quantum-confined Stark geometry for holographic applications. These photorefractive diodes operate with photocarrier transport perpendicular to the grating vector, unlike traditional photorefractive materials. They operate under transient electrical excitation resulting in a rich variety of spatio-temporal dynamics. We have optimized these devices to achieve record output diffraction efficiencies and shown that the design of these devices is relatively flexible as long as the principal functions of photoconductivity, electro-optics, and charge trapping are supplied by one or several functional layers. Nonreciprocal energy transfer, normally forbidden in Stark-effect devices, has been achieved using moving gratings. This led to the development of these photorefractive diodes to measure Doppler shifts by using electrically strobed gratings. Related to this work on longitudinal geometries, transverse-field photorefractive quantum wells were developed as adaptive beamsplitters to interrogate surface vibrations for laser-based ultrasound detection systems. These devices are tuned to quadrature for true linear detection by tailoring the excitonic spectral phase, a new contribution that is unique to the photorefractive quantum wells. This work has evolved from the physics of semi-insulating materials, to optimizing devices, to building complete systems using photorefractive quantum wells.
Coherent control in simple quantum systems
NASA Technical Reports Server (NTRS)
Prants, Sergey V.
1995-01-01
Coherent dynamics of two, three, and four-level quantum systems, simultaneously driven by concurrent laser pulses of arbitrary and different forms, is treated by using a nonperturbative, group-theoretical approach. The respective evolution matrices are calculated in an explicit form. General aspects of controllability of few-level atoms by using laser fields are treated analytically.
Lithography system using quantum entangled photons
NASA Technical Reports Server (NTRS)
Williams, Colin (Inventor); Dowling, Jonathan (Inventor); della Rossa, Giovanni (Inventor)
2002-01-01
A system of etching using quantum entangled particles to get shorter interference fringes. An interferometer is used to obtain an interference fringe. N entangled photons are input to the interferometer. This reduces the distance between interference fringes by n, where again n is the number of entangled photons.
Classical system boundaries cannot be determined within quantum Darwinism
NASA Astrophysics Data System (ADS)
Fields, Chris
Multiple observers who interact with environmental encodings of the states of a macroscopic quantum system S as required by quantum Darwinism cannot demonstrate that they are jointly observing S without a joint a priori assumption of a classical boundary separating S from its environment E. Quantum Darwinism cannot, therefore, be regarded as providing a purely quantum-mechanical explanation of the "emergence" of classicality.
Open Source, Open Standards, and Health Care Information Systems
2011-01-01
Recognition of the improvements in patient safety, quality of patient care, and efficiency that health care information systems have the potential to bring has led to significant investment. Globally the sale of health care information systems now represents a multibillion dollar industry. As policy makers, health care professionals, and patients, we have a responsibility to maximize the return on this investment. To this end we analyze alternative licensing and software development models, as well as the role of standards. We describe how licensing affects development. We argue for the superiority of open source licensing to promote safer, more effective health care information systems. We claim that open source licensing in health care information systems is essential to rational procurement strategy. PMID:21447469
Quantum cryptographic system with reduced data loss
Lo, Hoi-Kwong (1309, Low Block, Lei Moon House Ap Lei Chau Estate, Hong Kong, HK); Chau, Hoi Fung (Flat C, 42nd Floor, Tower 1, University Heights 23 Pokfield Road, Pokfulam, Hong Kong, HK)
1998-01-01
A secure method for distributing a random cryptographic key with reduced data loss. Traditional quantum key distribution systems employ similar probabilities for the different communication modes and thus reject at least half of the transmitted data. The invention substantially reduces the amount of discarded data (those that are encoded and decoded in different communication modes e.g. using different operators) in quantum key distribution without compromising security by using significantly different probabilities for the different communication modes. Data is separated into various sets according to the actual operators used in the encoding and decoding process and the error rate for each set is determined individually. The invention increases the key distribution rate of the BB84 key distribution scheme proposed by Bennett and Brassard in 1984. Using the invention, the key distribution rate increases with the number of quantum signals transmitted and can be doubled asymptotically.
Quantum cryptographic system with reduced data loss
Lo, H.K.; Chau, H.F.
1998-03-24
A secure method for distributing a random cryptographic key with reduced data loss is disclosed. Traditional quantum key distribution systems employ similar probabilities for the different communication modes and thus reject at least half of the transmitted data. The invention substantially reduces the amount of discarded data (those that are encoded and decoded in different communication modes e.g. using different operators) in quantum key distribution without compromising security by using significantly different probabilities for the different communication modes. Data is separated into various sets according to the actual operators used in the encoding and decoding process and the error rate for each set is determined individually. The invention increases the key distribution rate of the BB84 key distribution scheme proposed by Bennett and Brassard in 1984. Using the invention, the key distribution rate increases with the number of quantum signals transmitted and can be doubled asymptotically. 23 figs.
An impurity-induced gap system as a quantum data bus for quantum state transfer
NASA Astrophysics Data System (ADS)
Chen, Bing; Li, Yong; Song, Z.; Sun, C.-P.
2014-09-01
We introduce a tight-binding chain with a single impurity to act as a quantum data bus for perfect quantum state transfer. Our proposal is based on the weak coupling limit of the two outermost quantum dots to the data bus, which is a gapped system induced by the impurity. By connecting two quantum dots to two sites of the data bus, the system can accomplish a high-fidelity and long-distance quantum state transfer. Numerical simulations for finite system show that the numerical and analytical results of the effective coupling strength agree well with each other. Moreover, we study the robustness of this quantum communication protocol in the presence of disorder in the couplings between the nearest-neighbor quantum dots. We find that the gap of the system plays an important role in robust quantum state transfer.
An impurity-induced gap system as a quantum data bus for quantum state transfer
Chen, Bing; Li, Yong; Song, Z.; Sun, C.-P.
2014-09-15
We introduce a tight-binding chain with a single impurity to act as a quantum data bus for perfect quantum state transfer. Our proposal is based on the weak coupling limit of the two outermost quantum dots to the data bus, which is a gapped system induced by the impurity. By connecting two quantum dots to two sites of the data bus, the system can accomplish a high-fidelity and long-distance quantum state transfer. Numerical simulations for finite system show that the numerical and analytical results of the effective coupling strength agree well with each other. Moreover, we study the robustness of this quantum communication protocol in the presence of disorder in the couplings between the nearest-neighbor quantum dots. We find that the gap of the system plays an important role in robust quantum state transfer.
Repeated Interactions Quantum Systems:. Deterministic and Random
NASA Astrophysics Data System (ADS)
Joye, Alain
2008-08-01
This paper gives an overview of recent results concerning the long time dynamics of repeated interaction quantum systems in a deterministic and random framework. We describe the non equilibrium steady states (NESS) such systems display and we present, as a macroscopic consequence, a second law of thermodynamics these NESS give rise to. We also explain in some details the analysis of products of certain random matrices underlying this dynamical problem.
Open Problems in the Theory of Nuclear Open Quantum Systems
Michel, N.; Nazarewicz, Witold; Okolowicz, J.; Ploszajczak, M.
2010-01-01
Is there a connection between the branch point singularity at the particle emission threshold and the appearance of cluster states which reveal the structure of a corresponding reaction channel? Which nuclear states are most impacted by the coupling to the scattering continuum? What should be the most important steps in developing the theory that will truly unify nuclear structure and nuclear reactions? The common denominator of these questions is the continuum shell-model approach to bound and unbound nuclear states, nuclear decays, and reactions.
Uncertainty relation for non-Hamiltonian quantum systems
NASA Astrophysics Data System (ADS)
Tarasov, Vasily E.
2013-01-01
General forms of uncertainty relations for quantum observables of non-Hamiltonian quantum systems are considered. Special cases of uncertainty relations are discussed. The uncertainty relations for non-Hamiltonian quantum systems are considered in the Schrödinger-Robertson form since it allows us to take into account Lie-Jordan algebra of quantum observables. In uncertainty relations, the time dependence of quantum observables and the properties of this dependence are discussed. We take into account that a time evolution of observables of a non-Hamiltonian quantum system is not an endomorphism with respect to Lie, Jordan, and associative multiplications.
Uncertainty relation for non-Hamiltonian quantum systems
Tarasov, Vasily E.
2013-01-15
General forms of uncertainty relations for quantum observables of non-Hamiltonian quantum systems are considered. Special cases of uncertainty relations are discussed. The uncertainty relations for non-Hamiltonian quantum systems are considered in the Schroedinger-Robertson form since it allows us to take into account Lie-Jordan algebra of quantum observables. In uncertainty relations, the time dependence of quantum observables and the properties of this dependence are discussed. We take into account that a time evolution of observables of a non-Hamiltonian quantum system is not an endomorphism with respect to Lie, Jordan, and associative multiplications.
OpenRIMS: an open architecture radiology informatics Management system.
Langer, Steve G
2002-01-01
The following are benefits of an integrated picture archiving and communication system/radiology information system archive built with open-source tools and methods: open source, inexpensive interfaces can be updated as needed, and reduced risk of redundant and inconsistent data. Also, wide adoption would promote standard data mining tools, reducing user needs to learn multiple methods to perform the same task. A model has been constructed capable of accepting orders, performing exam resource scheduling, providing Digital communications in Medicine (DICOM) work list information to modalities, archiving studies, and supporting DICOM query/retrieve from third-party viewing software. The multitiered architecture uses a single database communicating via an open database connectivity bridge to a Linux server with Health Level 7 (HL7), DICOM, and HTTP connections. Human interaction is supported via a browser, whereas other informatics systems communicate over the HL7 and DICOM links. The system is still under development, but the primary database schema is complete, as are key pieces of the Web user interface. Additional work is needed on the DICOM/HL7 interface broker and completion of the base DICOM service classes. PMID:12105742
Thermalization of field driven quantum systems
Fotso, H.; Mikelsons, K.; Freericks, J. K.
2014-01-01
There is much interest in how quantum systems thermalize after a sudden change, because unitary evolution should preclude thermalization. The eigenstate thermalization hypothesis resolves this because all observables for quantum states in a small energy window have essentially the same value; it is violated for integrable systems due to the infinite number of conserved quantities. Here, we show that when a system is driven by a DC electric field there are five generic behaviors: (i) monotonic or (ii) oscillatory approach to an infinite-temperature steady state; (iii) monotonic or (iv) oscillatory approach to a nonthermal steady state; or (v) evolution to an oscillatory state. Examining the Hubbard model (which thermalizes under a quench) and the Falicov-Kimball model (which does not), we find both exhibit scenarios (i–iv), while only Hubbard shows scenario (v). This shows richer behavior than in interaction quenches and integrability in the absence of a field plays no role. PMID:24736404
An E-payment system based on quantum group signature
NASA Astrophysics Data System (ADS)
Xiaojun, Wen
2010-12-01
Security and anonymity are essential to E-payment systems. However, existing E-payment systems will easily be broken into soon with the emergence of quantum computers. In this paper, we propose an E-payment system based on quantum group signature. In contrast to classical E-payment systems, our quantum E-payment system can protect not only the users' anonymity but also the inner structure of customer groups. Because of adopting the two techniques of quantum key distribution, a one-time pad and quantum group signature, unconditional security of our E-payment system is guaranteed.
Charge and momentum in quantum electromechanical systems
NASA Astrophysics Data System (ADS)
Bennett, Steven D.
We address theoretical questions in quantum nanoelectromechanical systems. These are systems where a mechanical oscillator is coupled to a conductor in which single electrons or the quantum coherence of electrons plays an important role. The interplay of quantum electronics with the motion of a relatively macroscopic object provides a way to probe both the mechanics and the electronics with extraordinary sensitivity. We address three problems based on monitoring either the electronic or mechanical component to measure quantum properties of the coupled system. First, we study the full charge transfer statistics and correlations in a tunnel junction coupled to a mechanical oscillator, viewing the current measured through the junction as a detector of the oscillator position. We find several surprising results that are not obtained in a study of only the average and variance of tunneled charge. Even when the oscillator is weakly coupled to the tunnel junction, it can lead to highly non-Gaussian tunneling statistics; moreover, non-Gaussian correlations between the oscillator motion and transferred charge show that the backaction of tunneling electrons on the oscillator cannot be fully described as coupling the oscillator to an effective thermal bath. Second, we use a general scattering approach to study the backaction of a quantum point contact position detector on a mechanical oscillator. Our results remain valid far from the tunneling limit, an important experimental regime and where previous calculations of backaction break down. We obtain the backaction damping and heating directly in terms of the scattering matrix, and find that not only the transmission but also the scattering phases play an important role. Finally, we study a quantum dot capacitively coupled to an oscillating cantilever. In this case, the damping of the mechanical oscillator is monitored to measure quantum electronic properties of the dot. For weak electromechanical coupling, we find an effective temperature-dependent level repulsion of Coulomb blockade peaks in the damping versus gate voltage, and show that this is a result of degenerate energy levels on the dot. We further consider the regime of strong coupling, where the cantilever motion strongly and nonlinearly affects the charge on the dot. In this regime, the lineshape asymmetry of Coulomb blockade peaks in the damping, also a result of degeneracy, is dramatically enhanced. These results are in excellent agreement with experimental observations.
NASA Astrophysics Data System (ADS)
Aspelmeyer, Markus; Schwab, Keith
2008-09-01
The last five years have witnessed an amazing development in the field of nano- and micromechanics. What was widely considered fantasy ten years ago is about to become an experimental reality: the quantum regime of mechanical systems is within reach of current experiments. Two factors (among many) have contributed significantly to this situation. As part of the widespread effort into nanoscience and nanofabrication, it is now possible to produce high-quality nanomechanical and micromechanical resonators, spanning length scales of millimetres to nanometres, and frequencies from kilohertz to gigahertz. Researchers coupled these mechanical elements to high-sensitivity actuation and readout systems such as single-electron transistors, quantum dots, atomic point contacts, SQUID loops, high-finesse optical or microwave-cavities etc. Some of these ultra-sensitive readout schemes are in principle capable of detection at the quantum limit and a large part of the experimental effort is at present devoted to achieving this. On the other hand, the fact that the groups working in the field come from various different physics backgrounds—the authors of this editorial are a representative sample—has been a constant source of inspiration for helpful theoretical and experimental tools that have been adapted from other fields to the mechanical realm. To name just one example: ideas from quantum optics have led to the recent demonstration (both in theory and experiment) that coupling a mechanical resonator to a high-finesse optical cavity can be fully analogous to the well-known sideband-resolved laser cooling of ions and hence is capable in principle of cooling a mechanical mode into its quantum ground state. There is no doubt that such interdisciplinarity has been a crucial element for the development of the field. It is interesting to note that a very similar sociological phenomenon occurred earlier in the quantum information community, an area which is deeply enriched by the diverse backgrounds and approaches of the researchers. As diverse as the approaches are the manifold of goals and perspectives for operating mechanical systems close to or within the quantum regime. Already now, nanomechanical sensors achieve single-molecule mass detection and magnetic resonance force detection from single-electron spins although they are operated far from quantum. Quantum-limited mechanical devices promise a new technology with hitherto unachieved performance for high-resolution sensing. This is also of high relevance for macroscopic mechanical resonators used in gravitational wave detectors. Furthermore, the increasing capability to couple mechanical modes to individual quantum systems raises the interesting question of whether mechanics can serve as a quantum bus in hybrid implementations of quantum information processing. Finally, the possibility of generating quantum superposition states that involve displacements of a massive macroscopic object (such as the center of mass of a mechanical beam) provides a completely new parameter regime for testing quantum theory over the amazing range from nanomechanical objects of several picograms up to gram-scale mirrors used in gravitational wave interferometers. We are looking forward to these fascinating developments! This Focus Issue is intended to highlight the present status of the field and to provide both introduction and motivation for students and researchers who want to get familiar with this exciting area or even want to join it. It also complements the conference activities of our community during the last year, where a series of dedicated invited sessions at several international conferences (APS March Meeting 2008, CLEO/QELS 2008, OSA Frontiers in Optics 2008, PQE 2008/2009 etc) culminated in the first Gordon Conference on 'Mechanical Systems at the Quantum Limit'. Given the fast development of the field it was not surprising to see that during the collection of the following contributions new progress was reported almost on a monthly basis and new groups entered the field. We intend to keep submission to this Focus Issue open for some time and invite everyone to share their latest results with us. And finally, a note to our fellow colleagues: keep up the good work! We would like to call the next Focus Issue 'Mechanical Systems IN the Quantum Regime'. Focus on Mechanical Systems at the Quantum Limit Contents Classical to quantum transition of a driven nonlinear nanomechanical resonator Itamar Katz, Ron Lifshitz, Alex Retzker and Raphael Straub Experimental optomechanics with silicon micromirrors Olivier Arcizet, Chiara Molinelli, Tristan Briant, Pierre-François Cohadon, Antoine Heidmann, Jean-Marie Mackowski, Christophe Michel, Laurent Pinard, Olivier Français and Lionel Rousseau Nonlinear quantum metrology using coupled nanomechanical resonators M J Woolley, G J Milburn and Carlton M Caves All mechanical mixing by means of orthogonally coupled cantilevers A Knoll, O Züger and U Duerig Parametric coupling between macroscopic quantum resonators L Tian, M S Allman and R W Simmonds Quantum noise in a nanomechanical Duffing resonator E Babourina-Brooks, A Doherty and G J Milburn Creating and verifying a quantum superposition in a micro-optomechanical system Dustin Kleckner, Igor Pikovski, Evan Jeffrey, Luuk Ament, Eric Eliel, Jeroen van den Brink and Dirk Bouwmeester Ground-state cooling of a nanomechanical resonator via a Cooper-pair box qubit Konstanze Jaehne, Klemens Hammerer and Margareta Wallquist Dissipation in circuit quantum electrodynamics: lasing and cooling of a low-frequency oscillator Julian Hauss, Arkady Fedorov, Stephan André, Valentina Brosco, Carsten Hutter, Robin Kothari, Sunil Yeshwanth, Alexander Shnirman and Gerd Schön Route to ponderomotive entanglement of light via optically trapped mirrors Christopher Wipf, Thomas Corbitt, Yanbei Chen and Nergis Mavalvala Nanomechanical-resonator-assisted induced transparency in a Cooper-pair box system Xiao-Zhong Yuan, Hsi-Sheng Goan, Chien-Hung Lin, Ka-Di Zhu and Yi-Wen Jiang High-sensitivity monitoring of micromechanical vibration using optical whispering gallery mode resonators A Schliesser, G Anetsberger, R Rivière, O Arcizet and T J Kippenberg Optomechanical to mechanical entanglement transformation Giovanni Vacanti, Mauro Paternostro, G Massimo Palma and Vlatko Vedral The optomechanical instability in the quantum regime Max Ludwig, Björn Kubala and Florian Marquardt Quantum limits of photothermal and radiation pressure cooling of a movable mirror M Pinard and A Dantan Mechanical feedback in the high-frequency limit R El Boubsi, O Usmani and Ya M Blanter Back-action evasion and squeezing of a mechanical resonator using a cavity detector A A Clerk, F Marquardt and K Jacobs Simultaneous cooling and entanglement of mechanical modes of a micromirror in an optical cavity Claudiu Genes, David Vitali and Paolo Tombesi Dispersive optomechanics: a membrane inside a cavity A M Jayich, J C Sankey, B M Zwickl, C Yang, J D Thompson, S M Girvin, A A Clerk, F Marquardt and J G E Harris Cavity-assisted backaction cooling of mechanical resonators I Wilson-Rae, N Nooshi, J Dobrindt, T J Kippenberg and W Zwerger Cavity cooling of a nanomechanical resonator by light scattering I Favero and K Karrai Probing the quantum coherence of a nanomechanical resonator using a superconducting qubit: II. Implementation M P Blencowe and A D Armour Probing the quantum coherence of a nanomechanical resonator using a superconducting qubit: I. Echo scheme A D Armour and M P Blencowe Nanoelectromechanics of suspended carbon nanotubes A K Hüttel, M Poot, B Witkamp and H S J van der Zant Prospects for cooling nanomechanical motion by coupling to a superconducting microwave resonator J D Teufel, C A Regal and K W Lehnert
Focus on coherent control of complex quantum systems
NASA Astrophysics Data System (ADS)
Whaley, Birgitta; Milburn, Gerard
2015-10-01
The rapid growth of quantum information sciences over the past few decades has fueled a corresponding rise in high profile applications in fields such as metrology, sensors, spintronics, and attosecond dynamics, in addition to quantum information processing. Realizing this potential of todayâ€™s quantum science and the novel technologies based on this requires a high degree of coherent control of quantum systems. While early efforts in systematizing methods for high fidelity quantum control focused on isolated or closed quantum systems, recent advances in experimental design, measurement and monitoring, have stimulated both need and interest in the control of complex or large scale quantum systems that may also be coupled to an interactive environment or reservoir. This focus issue brings together new theoretical and experimental work addressing the formulation and implementation of quantum control for a broad range of applications in quantum science and technology today.
Observable measure of quantum coherence in finite dimensional systems.
Girolami, Davide
2014-10-24
Quantum coherence is the key resource for quantum technology, with applications in quantum optics, information processing, metrology, and cryptography. Yet, there is no universally efficient method for quantifying coherence either in theoretical or in experimental practice. I introduce a framework for measuring quantum coherence in finite dimensional systems. I define a theoretical measure which satisfies the reliability criteria established in the context of quantum resource theories. Then, I present an experimental scheme implementable with current technology which evaluates the quantum coherence of an unknown state of a d-dimensional system by performing two programmable measurements on an ancillary qubit, in place of the O(d2) direct measurements required by full state reconstruction. The result yields a benchmark for monitoring quantum effects in complex systems, e.g., certifying nonclassicality in quantum protocols and probing the quantum behavior of biological complexes. PMID:25379903
Multiple-state quantum Otto engine, 1D box system
Latifah, E.; Purwanto, A.
2014-03-24
Quantum heat engines produce work using quantum matter as their working substance. We studied adiabatic and isochoric processes and defined the general force according to quantum system. The processes and general force are used to evaluate a quantum Otto engine based on multiple-state of one dimensional box system and calculate the efficiency. As a result, the efficiency depends on the ratio of initial and final width of system under adiabatic processes.
Multiple-state quantum Otto engine, 1D box system
NASA Astrophysics Data System (ADS)
Latifah, E.; Purwanto, A.
2014-03-01
Quantum heat engines produce work using quantum matter as their working substance. We studied adiabatic and isochoric processes and defined the general force according to quantum system. The processes and general force are used to evaluate a quantum Otto engine based on multiple-state of one dimensional box system and calculate the efficiency. As a result, the efficiency depends on the ratio of initial and final width of system under adiabatic processes.
Electron Dynamics in Finite Quantum Systems
NASA Astrophysics Data System (ADS)
McDonald, Christopher R.
The multiconfiguration time-dependent Hartree-Fock (MCTDHF) and multiconfiguration time-dependent Hartree (MCTDH) methods are employed to investigate nonperturbative multielectron dynamics in finite quantum systems. MCTDHF is a powerful tool that allows for the investigation of multielectron dynamics in strongly perturbed quantum systems. We have developed an MCTDHF code that is capable of treating problems involving three dimensional (3D) atoms and molecules exposed to strong laser fields. This code will allow for the theoretical treatment of multielectron phenomena in attosecond science that were previously inaccessible. These problems include complex ionization processes in pump-probe experiments on noble gas atoms, the nonlinear effects that have been observed in Ne atoms in the presence of an x-ray free-electron laser (XFEL) and the molecular rearrangement of cations after ionization. An implementation of MCTDH that is optimized for two electrons, each moving in two dimensions (2D), is also presented. This implementation of MCTDH allows for the efficient treatment of 2D spin-free systems involving two electrons; however, it does not scale well to 3D or to systems containing more that two electrons. Both MCTDHF and MCTDH were used to treat 2D problems in nanophysics and attosecond science. MCTDHF is used to investigate plasmon dynamics and the quantum breathing mode for several electrons in finite lateral quantum dots. MCTDHF is also used to study the effects of manipulating the potential of a double lateral quantum dot containing two electrons; applications to quantum computing are discussed. MCTDH is used to examine a diatomic model molecular system exposed to a strong laser field; nonsequential double ionization and high harmonic generation are studied and new processes identified and explained. An implementation of MCTDHF is developed for nonuniform tensor product grids; this will allow for the full 3D implementation of MCTDHF and will provide a means to investigate a wide variety of problems that cannot be currently treated by any other method. Finally, the time it takes for an electron to tunnel from a bound state is investigated; a definition of the tunnel time is established and the Keldysh time is connected to the wavefunction dynamics.
Quantum phase transitions in frustrated magnetic systems
NASA Astrophysics Data System (ADS)
Wölfle, P.; Schmitteckert, P.
2015-07-01
We review our recent work on quantum phase transitions in frustrated magnetic systems. In the first part a Pseudo Fermion Functional Renormalization Group (PFFRG) method is presented. By using an exact representation of spin 1/2 operators in terms of pseudofermions a quantum spin Hamiltonian may be mapped onto an interacting fermion system. For the latter an FRG treatment is employed. The results for the J1-J2 model and similar models of frustrated interaction show phase diagrams in agreement with those obtained by other methods, but give more detailed information on the nature of correlations, in particular in the non-magnetic phases. Applications of PFFRG to geometrically frustrated systems and to highly anisotropic Kitaev type models are also reported. In the second part the derivation of quantum spin models from the microscopic many-body Hamiltonian is discussed. The results for multiband systems with strong spin-orbit interaction encountered in the iridates class of compounds are shown to resolve some of the questions posed by experiment.
Quantum phase transitions in magnetic systems
NASA Astrophysics Data System (ADS)
Nohadani, Omid
Phase transitions in quantum antiferromagnets offer exciting and novel insights into the critical behavior of matter at ultra-low temperatures. In this thesis, we apply the stochastic series expansion quantum Monte Carlo method to study the critical properties of ensembles of antiferromagnetically coupled spins subject to quantum phase transitions. The zero-temperature phase diagram, describing various phase transitions induced by an applied magnetic field, is constructed. The corresponding quantum critical points are determined to highest accuracy, allowing a conclusive interpretation of recent experimental measurements. Moreover, the scaling properties of uniform magnetization and staggered transverse magnetizationin magnetic fields are calculated, allowing the determination of the universality class of the system. The associated critical exponents are derived from Ginzburg-Landau theory as well. We find excellent agreement between the quantum Monte Carlo simulations and the analytical results, as well as previous bond-operator calculations. Furthermore, the critical scaling exponent, which governs the power-law dependence of the transition temperature on the applied magnetic field, is extracted from the numerical data. We show that this exponent is independent of material specific inter-constituent interactions. Moreover, it converges to the value predicted for Bose-Einstein condensation of magnons. These results are of direct relevance to compounds such as TlCuCl3 and KCuCl 3, and explain the broad range of exponents reported my exponents for field-induced ordering transitions. Finally, we introduce geometric randomness into a model of coupled dimers. The calculations show that at finite randomness, field-induced quantum phase transitions into and out of ordered Bose-Einstein condensates pass through a Bose-Glass phase. The localization of the bosons and their finite compressibility manifests this unique regime. Once delocalized, the bosons condense, and long-range order sets in. We further detect that an intermediate magnetization plateau can occur for a parameter range, in which the spins of the doped bonds become fully polarized. This rich field-dependence is expected to be experimentally observable in weakly coupled dimer compounds with small doping and negligible spin-orbit coupling or directionality effects. The calculations in this thesis cover fundamental phases and transitions between them, as they can occur in antiferromagnetic quantum spin systems.
On Mathematical Modeling Of Quantum Systems
Achuthan, P.; Narayanankutty, Karuppath
2009-07-02
The world of physical systems at the most fundamental levels is replete with efficient, interesting models possessing sufficient ability to represent the reality to a considerable extent. So far, quantum mechanics (QM) forming the basis of almost all natural phenomena, has found beyond doubt its intrinsic ingenuity, capacity and robustness to stand the rigorous tests of validity from and through appropriate calculations and experiments. No serious failures of quantum mechanical predictions have been reported, yet. However, Albert Einstein, the greatest theoretical physicist of the twentieth century and some other eminent men of science have stated firmly and categorically that QM, though successful by and large, is incomplete. There are classical and quantum reality models including those based on consciousness. Relativistic quantum theoretical approaches to clearly understand the ultimate nature of matter as well as radiation have still much to accomplish in order to qualify for a final theory of everything (TOE). Mathematical models of better, suitable character as also strength are needed to achieve satisfactory explanation of natural processes and phenomena. We, in this paper, discuss some of these matters with certain apt illustrations as well.
Exchange fluctuation theorem for correlated quantum systems.
Jevtic, Sania; Rudolph, Terry; Jennings, David; Hirono, Yuji; Nakayama, Shojun; Murao, Mio
2015-10-01
We extend the exchange fluctuation theorem for energy exchange between thermal quantum systems beyond the assumption of molecular chaos, and describe the nonequilibrium exchange dynamics of correlated quantum states. The relation quantifies how the tendency for systems to equilibrate is modified in high-correlation environments. In addition, a more abstract approach leads us to a "correlation fluctuation theorem". Our results elucidate the role of measurement disturbance for such scenarios. We show a simple application by finding a semiclassical maximum work theorem in the presence of correlations. We also present a toy example of qubit-qudit heat exchange, and find that non-classical behaviour such as deterministic energy transfer and anomalous heat flow are reflected in our exchange fluctuation theorem. PMID:26565174
Exchange fluctuation theorem for correlated quantum systems
NASA Astrophysics Data System (ADS)
Jevtic, Sania; Rudolph, Terry; Jennings, David; Hirono, Yuji; Nakayama, Shojun; Murao, Mio
2015-10-01
We extend the exchange fluctuation theorem for energy exchange between thermal quantum systems beyond the assumption of molecular chaos, and describe the nonequilibrium exchange dynamics of correlated quantum states. The relation quantifies how the tendency for systems to equilibrate is modified in high-correlation environments. In addition, a more abstract approach leads us to a "correlation fluctuation theorem". Our results elucidate the role of measurement disturbance for such scenarios. We show a simple application by finding a semiclassical maximum work theorem in the presence of correlations. We also present a toy example of qubit-qudit heat exchange, and find that non-classical behaviour such as deterministic energy transfer and anomalous heat flow are reflected in our exchange fluctuation theorem.
Quantum Systems Based upon Galois Fields — from Sub-Quantum to Super-Quantum Correlations
NASA Astrophysics Data System (ADS)
Chang, L. N.; Lewis, Z.; Minic, D.; Takeuchi, T.
2014-01-01
In this paper, we describe our recent work on discrete quantum theory based on Galois fields. In particular, we discuss how discrete quantum theory sheds new light on the foundations of quantum theory and we review an explicit model of super-quantum correlations we have constructed in this context. We also discuss the larger questions of the origins and foundations of quantum theory, as well as the relevance of super-quantum theory for the quantum theory of gravity.
Open Systems Sing a Siren Song.
ERIC Educational Resources Information Center
Webb, Terry D.
1987-01-01
Comparison of the use in libraries of open systems--a configuration of software and hardware components from separate vendors linked by interfaces--and integrated systems considers selection of services; reliability; relationships with vendors; time needed to implement systems; and overall effectiveness of both approaches. (CLB)
Time fractional development of quantum systems
NASA Astrophysics Data System (ADS)
Ertik, HÃ¼seyin; Demirhan, DoÇ§an; Åžirin, HÃ¼seyin; BÃ¼yÃ¼kkÄ±lÄ±Ã§, Fevzi
2010-08-01
In this study, the effect of time fractionalization on the development of quantum systems is taken under consideration by making use of fractional calculus. In this context, a Mittag-Leffler function is introduced as an important mathematical tool in the generalization of the evolution operator. In order to investigate the time fractional evolution of the quantum (nano) systems, time fractional forms of motion are obtained for a SchrÃ¶dinger equation and a Heisenberg equation. As an application of the concomitant formalism, the wave functions, energy eigenvalues, and probability densities of the potential well and harmonic oscillator are time fractionally obtained via the fractional derivative order Î±, which is a measure of the fractality of time. In the case Î± =1, where time becomes homogenous and continuous, traditional physical conclusions are recovered. Since energy and time are conjugate to each other, the fractional derivative order Î± is relevant to time. It is understood that the fractionalization of time gives rise to energy fluctuations of the quantum (nano) systems.
NASA Astrophysics Data System (ADS)
Wu, Feng; Chen, Lingen; Sun, Fengrui; Wu, Chih; Li, Qing
2006-01-01
The purpose of this paper is to establish a model of an irreversible quantum Brayton engine using many noninteracting spin systems as the working substance and consisting of two irreversible adiabatic and two isomagnetic field processes. The time evolution of the total magnetic moment M is determined by solving the generalized quantum master equation of an open system in the Heisenberg picture. The time of two irreversible adiabatic processes is considered based on finite-rate evolution. The relationship between the power output P and the efficiency ? for the irreversible quantum Brayton engine with spin systems is derived. The optimally operating region (or criteria) for the engine is determined. The influences of these important parameters on the performances ( P and ? ) of the engine are discussed. The results obtained herein will be useful for the further understanding and the selection of the optimal operating conditions for an irreversible quantum Brayton engine with spin systems.
Coarse-grained kinetic equations for quantum systems
NASA Astrophysics Data System (ADS)
Petrov, E. G.
2013-01-01
The nonequilibrium density matrix method is employed to derive a master equation for the averaged state populations of an open quantum system subjected to an external high frequency stochastic field. It is shown that if the characteristic time Ï„stoch of the stochastic process is much lower than the characteristic time Ï„steady of the establishment of the system steady state populations, then on the time scale Î” t Ëœ Ï„steady, the evolution of the system populations can be described by the coarse-grained kinetic equations with the averaged transition rates. As an example, the exact averaging is carried out for the dichotomous Markov process of the kangaroo type.
Preparing ground states of quantum many-body systems on a quantum computer
NASA Astrophysics Data System (ADS)
Poulin, David
2009-03-01
The simulation of quantum many-body systems is a notoriously hard problem in condensed matter physics, but it could easily be handled by a quantum computer [4,1]. There is however one catch: while a quantum computer can naturally implement the dynamics of a quantum system --- i.e. solve Schr"odinger's equation --- there was until now no general method to initialize the computer in a low-energy state of the simulated system. We present a quantum algorithm [5] that can prepare the ground state and thermal states of a quantum many-body system in a time proportional to the square-root of its Hilbert space dimension. This is the same scaling as required by the best known algorithm to prepare the ground state of a classical many-body system on a quantum computer [3,2]. This provides strong evidence that for a quantum computer, preparing the ground state of a quantum system is in the worst case no more difficult than preparing the ground state of a classical system. 1 D. Aharonov and A. Ta-Shma, Adiabatic quantum state generation and statistical zero knowledge, Proc. 35th Annual ACM Symp. on Theo. Comp., (2003), p. 20. F. Barahona, On the computational complexity of ising spin glass models, J. Phys. A. Math. Gen., 15 (1982), p. 3241. C. H. Bennett, E. Bernstein, G. Brassard, and U. Vazirani, Strengths and weaknessess of quantum computing, SIAM J. Comput., 26 (1997), pp. 1510--1523, quant-ph/9701001. S. Lloyd, Universal quantum simulators, Science, 273 (1996), pp. 1073--1078. D. Poulin and P. Wocjan, Preparing ground states of quantum many-body systems on a quantum computer, 2008, arXiv:0809.2705.
Quantum entanglement in multiparticle systems of two-level atoms
Deb, Ram Narayan
2011-09-15
We propose the necessary and sufficient condition for the presence of quantum entanglement in arbitrary symmetric pure states of two-level atomic systems. We introduce a parameter to quantify quantum entanglement in such systems. We express the inherent quantum fluctuations of a composite system of two-level atoms as a sum of the quantum fluctuations of the individual constituent atoms and their correlation terms. This helps to separate out and study solely the quantum correlations among the atoms and obtain the criterion for the presence of entanglement in such multiatomic systems.
Phase transitions in quantum Hall multiple layer systems
Pusep, Yu A.; Fernandes dos Santos, L.; Smirnov, D.; Bakarov, A. K.; Toropov, A. I.
2013-12-04
Polarized photoluminescence from multiple well electron systems was studied in the regime of the integer quantum Hall effect. Two quantum Hall ferromagnetic ground states assigned to the uncorrelated miniband quantum Hall state and to the spontaneous interwell phase coherent dimer quantum Hall state were observed. The photoluminescence associated with these states exhibits features caused by finite-size skyrmions. The depolarization of the ferromagnetic ground state was observed in bilayer system.
NASA Astrophysics Data System (ADS)
Molotkov, S. N.
2011-11-01
The security of keys in quantum cryptography is based on fundamental quantum mechanical exclusions (the exclusion of cloning and copying of nonorthogonal quantum states. The physical type of a quantum object that carries information (photon, electron, atom, etc.) is insignificant; only its state vector is important. In relativistic quantum cryptography for open space, both the time of the information carrier (photon that propagates with the extremely allowable velocity in a vacuum) and its quantum state are of fundamental importance. Joint fundamental constraints that are dictated by both special relativity and quantum mechanics on the discrimination of nonorthogonal quantum states allow one to formulate fundamentally new key distribution protocols that are stable against any attacks on a key and guarantee the security of keys for a nonstrictly single-photon source and any losses in the communication channel. Although this protocol is a real-time protocol in the Minkowski space-time, where the attack to the communication channel is detected by the delay of eavesdropper measurement results, the protocol does not require clock synchronization on the transmitter and receiver sides.
EDITORIAL: CAMOP: Quantum Non-Stationary Systems CAMOP: Quantum Non-Stationary Systems
NASA Astrophysics Data System (ADS)
Dodonov, Victor V.; Man'ko, Margarita A.
2010-09-01
Although time-dependent quantum systems have been studied since the very beginning of quantum mechanics, they continue to attract the attention of many researchers, and almost every decade new important discoveries or new fields of application are made. Among the impressive results or by-products of these studies, one should note the discovery of the path integral method in the 1940s, coherent and squeezed states in the 1960-70s, quantum tunneling in Josephson contacts and SQUIDs in the 1960s, the theory of time-dependent quantum invariants in the 1960-70s, different forms of quantum master equations in the 1960-70s, the Zeno effect in the 1970s, the concept of geometric phase in the 1980s, decoherence of macroscopic superpositions in the 1980s, quantum non-demolition measurements in the 1980s, dynamics of particles in quantum traps and cavity QED in the 1980-90s, and time-dependent processes in mesoscopic quantum devices in the 1990s. All these topics continue to be the subject of many publications. Now we are witnessing a new wave of interest in quantum non-stationary systems in different areas, from cosmology (the very first moments of the Universe) and quantum field theory (particle pair creation in ultra-strong fields) to elementary particle physics (neutrino oscillations). A rapid increase in the number of theoretical and experimental works on time-dependent phenomena is also observed in quantum optics, quantum information theory and condensed matter physics. Time-dependent tunneling and time-dependent transport in nano-structures are examples of such phenomena. Another emerging direction of study, stimulated by impressive progress in experimental techniques, is related to attempts to observe the quantum behavior of macroscopic objects, such as mirrors interacting with quantum fields in nano-resonators. Quantum effects manifest themselves in the dynamics of nano-electromechanical systems; they are dominant in the quite new and very promising field of circuit QED. Another rapidly growing research field (although its origin can be traced to the beginning of the 1980s) is the quantum control of evolution at the microscopic level. These examples show that quantum non-stationary systems continue to be a living and very interesting part of quantum physics, uniting researchers from many different areas. Thus it is no mere chance that several special scientific meetings devoted to these topics have been organized recently. One was the international seminar 'Time-Dependent Phenomena in Quantum Mechanics' organized by Manfred Kleber and Tobias Kramer in 2007 at Blaubeuren, Germany. The proceedings of that event were published in 2008 as volume 99 of Journal of Physics: Conference Series. Another recent meeting was the International Workshop on Quantum Non-Stationary Systems, held on 19-23 October 2009 at the International Center for Condensed Matter Physics (ICCMP) in Brasilia, Brazil. It was organized and directed by Victor Dodonov (Institute of Physics, University of Brasilia, Brazil), Vladimir Man'ko (P N Lebedev Physical Institute, Moscow, Russia) and Salomon Mizrahi (Physics Department, Federal University of Sao Carlos, Brazil). This event was accompanied by a satellite workshop 'Quantum Dynamics in Optics and Matter', organized by Salomon Mizrahi and Victor Dodonov on 25-26 October 2009 at the Physics Department of the Federal University of Sao Carlos, Brazil. These two workshops, supported by the Brazilian federal agencies CAPES and CNPq and the local agencies FAP-DF and FAPESP, were attended by more than 120 participants from 16 countries. Almost 50 invited talks and 20 poster presentations covered a wide area of research in quantum mechanics, quantum optics and quantum information. This special issue of CAMOP/Physica Scripta contains contributions presented by some invited speakers and participants of the workshop in Brasilia. Although they do not cover all of the wide spectrum of problems related to quantum non-stationary systems, they nonetheless show some general trends. However, readers should remember that thes
Seniority in quantum many-body systems
Van Isacker, P.
2010-12-23
The use of the seniority quantum number in many-body systems is reviewed. A brief summary is given of its introduction by Racah in the context of atomic spectroscopy. Several extensions of Racah's original idea are discussed: seniority for identical nucleons in a single-j shell, its extension to the case of many, non-degenerate j shells and to systems with neutrons and protons. To illustrate its usefulness to this day, a recent application of seniority is presented in Bose-Einstein condensates of atoms with spin.
High Speed Quantum Key Distribution System
NASA Astrophysics Data System (ADS)
Tajima, Akio; Tanaka, Akihiro; Takahashi, Seigo; Yoshino, Ken-Ichiro; Nambu, Yoshihiro
Quantum key distribution (QKD) systems can generate unconditionally secure common keys between remote users. Improvements of QKD performance, particularly in key generation rate, have been required to meet current network traffic. A high-speed QKD system should be equipped with low-loss receivers with high visibility, highly efficient photon detectors with small dark count probability. A solution to these issues is to employ planar lightwave circuit (PLC) interferometers, single photon detection circuits and modules, together with multi-wavelength channels transmission using wavelength division multiplexing (WDM) technique.
Quantum Random Access Codes Using Single d -Level Systems
NASA Astrophysics Data System (ADS)
Tavakoli, Armin; Hameedi, Alley; Marques, Breno; Bourennane, Mohamed
2015-05-01
Random access codes (RACs) are used by a party to, with limited communication, access an arbitrary subset of information held by another party. Quantum resources are known to enable RACs that break classical limitations. Here, we study quantum and classical RACs with high-level communication. We derive average performances of classical RACs and present families of high-level quantum RACs. Our results show that high-level quantum systems can significantly increase the advantage of quantum RACs over their classical counterparts. We demonstrate our findings in an experimental realization of a quantum RAC with four-level communication.
OPEN PROBLEM: Spatially localized structures in dissipative systems: open problems
NASA Astrophysics Data System (ADS)
Knobloch, E.
2008-04-01
Stationary spatially localized structures, sometimes called dissipative solitons, arise in many interesting and important applications, including buckling of slender structures under compression, nonlinear optics, fluid flow, surface catalysis, neurobiology and many more. The recent resurgence in interest in these structures has led to significant advances in our understanding of the origin and properties of these states, and these in turn suggest new questions, both general and system-specific. This paper surveys these results focusing on open problems, both mathematical and computational, as well as on new applications.
OpenRIMS: an open architecture radiology informatics management system.
Langer, Steve
2002-06-01
The benefits of an integrated picture archiving and communication system/radiology information system (PACS/RIS) archive built with open source tools and methods are 2-fold. Open source permits an inexpensive development model where interfaces can be updated as needed, and the code is peer reviewed by many eyes (analogous to the scientific model). Integration of PACS/RIS functionality reduces the risk of inconsistent data by reducing interfaces among databases that contain largely redundant information. Also, wide adoption would promote standard data mining tools--reducing user needs to learn multiple methods to perform the same task. A model has been constructed capable of accepting HL7 orders, performing examination and resource scheduling, providing digital imaging and communications in medicine (DICOM) worklist information to modalities, archiving studies, and supporting DICOM query/retrieve from third party viewing software. The multitiered architecture uses a single database communicating via an ODBC bridge to a Linux server with HL7, DICOM, and HTTP connections. Human interaction is supported via a web browser, whereas automated informatics services communicate over the HL7 and DICOM links. The system is still under development, but the primary database schema is complete as well as key pieces of the web user interface. Additional work is needed on the DICOM/HL7 interface broker and completion of the base DICOM service classes. PMID:12297975
Open-Path High Sensitivity Atmospheric Ammonia Sensing with a Quantum Cascade Laser Instrument
NASA Astrophysics Data System (ADS)
Miller, D. J.; Dirisu, A.; Rafferty, K.; Parkes, B.; Zondlo, M. A.
2009-12-01
Atmospheric trace-gas sensing with quantum cascade laser (QCL) spectroscopy offers the potential for high sensitivity, fast, selective mid-infrared absorption measurements of atmospheric species such as ammonia (NH3). As the third most abundant nitrogen species and most gaseous base in the atmosphere, ammonia plays important roles in neutralizing acidic species and as a gas-phase precursor to ammoniated fine particulate matter. High precision gas phase measurements are necessary to constrain highly uncertain emission sources and sinks with implications for understanding how chemical components of fine particulate matter affect air quality and climate as well as nitrogen deposition to ecosystems. Conventional ammonia sensors employing chemical ionization, denuder or filter techniques are labor-intensive, not gas-selective and exhibit low time resolution. As an advantageous alternative to conventional measurement techniques, we develop an open-path quantum cascade laser-based ammonia sensor operating at 9.06 ?m for ground-based measurements. A continuous wave, thermoelectrically cooled quantum cascade laser is used to perform wavelength modulation absorption spectroscopy (WMS). Room-temperature, unattended operation with minimal surface adsorption effects due to the open-path configuration represent significant improvements over cryogenically cooled, closed path systems. The feasibility of a cylindrical mirror multi-pass optical cell for achieving long path lengths near 50 m in a compact design is also assessed. Meaningful ammonia measurements require fast sub-ppbv detection limits due to ammonia’s large dynamic range and temporal and spatial atmospheric variability. When fully developed, our instrument will achieve high time resolution (up to 10 Hz) measurements with ammonia detection limits in the 100 pptv range. Initial results include ambient laboratory ammonia detection at 58 ppbv relative to a 0.4% ammonia reference cell based on the WMS signal integrated area. We estimate a limit of detection based on our signal to noise ratio of ~400 pptv NH3. Non-cryogenic, unattended operation of this compact sensor offers the potential for applications in particulate matter gas-phase precursor monitoring networks. Future sensor measurements can also be utilized for evaluations of and data assimilation into air quality and aerosol forecast models of particular importance for regions where ammonia plays a critical role in fine particulate matter formation.
Observation of Non-Hermitian Quantum Correlation Criterion in Mesoscopic Optomechanical System
NASA Astrophysics Data System (ADS)
Li, Wenlin; Zhang, Fengyang; Li, Chong; Song, Heshan
2015-11-01
Although many quantum correlation criteria have been proposed successively in recent years, it is still an open question how to observe these criteria with the non-Hermitian terms in themselves. We propose an indirect scheme in this paper to observe non-Hermitian criteria and to judge whether or not quantum correlation exists in the system even though the expectation value measurement of non-Hermitian operator is invalid in quantum mechanics system. Our idea is to establish a critical state of mesoscopic oscillator under mean-field approximation, and the oscillator state will take place transition when the quantum correlation destroys the mean-field approximation. The non-Hermitian measurement will replace the position measurement in this process and it can be seen as a non-destructive detection. We give an example to explain this idea in a designed mesoscopic optomechanical system.
Quantum Rotational Effects in Nanomagnetic Systems
NASA Astrophysics Data System (ADS)
O'Keeffe, Michael F.
Quantum tunneling of the magnetic moment in a nanomagnet must conserve the total angular momentum. For a nanomagnet embedded in a rigid body, reversal of the magnetic moment will cause the body to rotate as a whole. When embedded in an elastic environment, tunneling of the magnetic moment will cause local elastic twists of the crystal structure. In this thesis, I will present a theoretical study of the interplay between magnetization and rotations in a variety of nanomagnetic systems which have some degree of rotational freedom. We investigate the effect of rotational freedom on the tunnel splitting of a nanomagnet which is free to rotate about its easy axis. Calculating the exact instanton of the coupled equations of motion shows that mechanical freedom of the particle renormalizes the easy axis anisotropy, increasing the tunnel splitting. To understand magnetization dynamics in free particles, we study a quantum mechanical model of a tunneling spin embedded in a rigid rotor. The exact energy levels for a symmetric rotor exhibit first and second order quantum phase transitions between states with different values the magnetic moment. A quantum phase diagram is obtained in which the magnetic moment depends strongly on the moments of inertia. An intrinsic contribution to decoherence of current oscillations of a flux qubit must come from the angular momentum it transfers to the surrounding body. Within exactly solvable models of a qubit embedded in a rigid body and an elastic medium, we show that slow decoherence is permitted if the solid is macroscopically large. The spin-boson model is one of the simplest representations of a two-level system interacting with a quantum harmonic oscillator, yet has eluded a closed-form solution. I investigate some possible approaches to understanding its spectrum. The Landau-Zener dynamics of a tunneling spin coupled to a torsional resonator show that for certain parameter ranges the system exhibits multiple Landau-Zener transitions. These transitions coincide in time with changes in the oscillator dynamics. A large number of spins on a single oscillator coupled only through the in-phase oscillations behaves as a single large spin, greatly enhancing the spin-phonon coupling.
Wu, Chia-Ching; Liou, Jian-Chiun; Diao, Chien-Chen
2015-08-14
A self-powered complementary electrochromic device (CECD) driven by a high open-circuit voltage InGaN/GaN multiple quantum well (MQW) solar cell has been designed. The coloration and bleaching time of the system were 5 and 8 s, respectively. PMID:26158586
Rewriting Modulo SMT and Open System Analysis
NASA Technical Reports Server (NTRS)
Rocha, Camilo; Meseguer, Jose; Munoz, Cesar
2014-01-01
This paper proposes rewriting modulo SMT, a new technique that combines the power of SMT solving, rewriting modulo theories, and model checking. Rewriting modulo SMT is ideally suited to model and analyze infinite-state open systems, i.e., systems that interact with a non-deterministic environment. Such systems exhibit both internal non-determinism, which is proper to the system, and external non-determinism, which is due to the environment. In a reflective formalism, such as rewriting logic, rewriting modulo SMT can be reduced to standard rewriting. Hence, rewriting modulo SMT naturally extends rewriting-based reachability analysis techniques, which are available for closed systems, to open systems. The proposed technique is illustrated with the formal analysis of: (i) a real-time system that is beyond the scope of timed-automata methods and (ii) automatic detection of reachability violations in a synchronous language developed to support autonomous spacecraft operations.
A toy model of a macroscopic quantum coherent system
NASA Astrophysics Data System (ADS)
Muñoz-Vega, R.; Flores-Godoy, J. J.; Fernández-Anaya, G.; Salinas-Hernández, E.
2013-03-01
This paper deals with macroscopic quantum coherence while using only basic quantum mechanics. A square double well is used to illustrate Leggett-Caldeira oscillations. The effect of thermal radiation on two-level systems is discussed. The concept of decoherence is introduced at an elementary level. Reference values are deduced for the energy, temperature and time scales involved in macroscopic quantum coherence.
Controlled Population Transfer in a Double Quantum Dot System
NASA Astrophysics Data System (ADS)
Fountoulakis, Antonios; Terzis, Andreas F.; Paspalakis, Emmanuel
2007-12-01
We study the potential for controlled population transfer between the ground states of two anharmonic coupled quantum dots. We propose a method based on the interaction of the quantum dot structure with external electromagnetic fields. The interaction of the quantum dot system with the electromagnetic fields is studied with the use of the time-dependent Schrödinger equation. We present numerical results for an asymmetric quantum dot structure.
Quantum Mechanics and the Role of Time:. are Quantum Systems Markovian?
NASA Astrophysics Data System (ADS)
Durt, Thomas
2013-06-01
The predictions of the Quantum Theory have been verified so far with astonishingly high accuracy. Despite of its impressive successes, the theory still presents mysterious features such as the border line between the classical and quantum world, or the deep nature of quantum nonlocality. These open questions motivated in the past several proposals of alternative and/or generalized approaches. We shall discuss in the present paper alternative theories that can be infered from a reconsideration of the status of time in quantum mechanics. Roughly speaking, quantum mechanics is usually formulated as a memory free (Markovian) theory at a fundamental level, but alternative, nonMarkovian, formulations are possible, and some of them can be tested in the laboratory. In our paper we shall give a survey of these alternative proposals, describe related experiments that were realized in the past and also formulate new experimental proposals.
Open Hardware for CERN's accelerator control systems
NASA Astrophysics Data System (ADS)
van der Bij, E.; Serrano, J.; Wlostowski, T.; Cattin, M.; Gousiou, E.; Alvarez Sanchez, P.; Boccardi, A.; Voumard, N.; Penacoba, G.
2012-01-01
The accelerator control systems at CERN will be upgraded and many electronics modules such as analog and digital I/O, level converters and repeaters, serial links and timing modules are being redesigned. The new developments are based on the FPGA Mezzanine Card, PCI Express and VME64x standards while the Wishbone specification is used as a system on a chip bus. To attract partners, the projects are developed in an `Open' fashion. Within this Open Hardware project new ways of working with industry are being evaluated and it has been proven that industry can be involved at all stages, from design to production and support.
Dynamics of quantum discord for a two-qubit system
NASA Astrophysics Data System (ADS)
Yang, Xiong; Xiao, Jia-hua
2013-01-01
We study the dynamics of quantum discord of a two-qubit system coupled to a common structured reservoir at zero temperature. The conditions to maximize reservoir-induced quantum discord for the two-qubit system wiht an initially factorized state are derived. In particular, when the two qubits are placed in a lossy cavity, high values of quantum discord can be obtained in the dispersive regime, even in the bad-cavity limit. Finally, we show that under certain conditions, the quantum discord dynamics exhibits quantum beats.
Black holes and nonrelativistic quantum systems.
Kovtun, Pavel; Nickel, Dominik
2009-01-01
We describe black holes in d+3 dimensions, whose thermodynamic properties correspond to those of a scale-invariant nonrelativistic (d+1)-dimensional quantum system with a dynamical exponent z=2. The gravitational model involves a massive Abelian vector field and a scalar field, in addition to the metric. The energy per particle in the dual theory is |micro|d/(d+2) at any temperature (micro is the chemical potential). The ratio of shear viscosity to entropy density is variant Planck's over 2pi/4pi in any dimension d > or =2. PMID:19257179
Partitioning technique for discrete quantum systems
Jin, L.; Song, Z.
2011-06-15
We develop the partitioning technique for quantum discrete systems. The graph consists of several subgraphs: a central graph and several branch graphs, with each branch graph being rooted by an individual node on the central one. We show that the effective Hamiltonian on the central graph can be constructed by adding additional potentials on the branch-root nodes, which generates the same result as does the the original Hamiltonian on the entire graph. Exactly solvable models are presented to demonstrate the main points of this paper.
On quantum Lie algebras and quantum root systems
NASA Astrophysics Data System (ADS)
Delius, Gustav W.; HÃ¼ffmann, Andreas
1996-04-01
As a natural generalization of ordinary Lie algebras we introduce the concept of quantum Lie algebras 0305-4470/29/8/018/img1. We define these in terms of certain adjoint submodules of quantized enveloping algebras 0305-4470/29/8/018/img2 endowed with a quantum Lie bracket given by the quantum adjoint action. The structure constants of these algebras depend on the quantum deformation parameter q and they go over into the usual Lie algebras when q = 1. The notions of q-conjugation and q-linearity are introduced. q-linear analogues of the classical antipode and Cartan involution are defined and a generalized Killing form, q-linear in the first entry and linear in the second, is obtained. These structures allow the derivation of symmetries between the structure constants of quantum Lie algebras. The explicitly worked out examples of 0305-4470/29/8/018/img3 and 0305-4470/29/8/018/img4 illustrate the results.
Measuring entanglement entropy in a quantum many-body system
NASA Astrophysics Data System (ADS)
Islam, Rajibul; Ma, Ruichao; Preiss, Philipp M.; Eric Tai, M.; Lukin, Alexander; Rispoli, Matthew; Greiner, Markus
2015-12-01
Entanglement is one of the most intriguing features of quantum mechanics. It describes non-local correlations between quantum objects, and is at the heart of quantum information sciences. Entanglement is now being studied in diverse fields ranging from condensed matter to quantum gravity. However, measuring entanglement remains a challenge. This is especially so in systems of interacting delocalized particles, for which a direct experimental measurement of spatial entanglement has been elusive. Here, we measure entanglement in such a system of itinerant particles using quantum interference of many-body twins. Making use of our single-site-resolved control of ultracold bosonic atoms in optical lattices, we prepare two identical copies of a many-body state and interfere them. This enables us to directly measure quantum purity, RÃ©nyi entanglement entropy, and mutual information. These experiments pave the way for using entanglement to characterize quantum phases and dynamics of strongly correlated many-body systems.
Measuring entanglement entropy in a quantum many-body system.
Islam, Rajibul; Ma, Ruichao; Preiss, Philipp M; Tai, M Eric; Lukin, Alexander; Rispoli, Matthew; Greiner, Markus
2015-12-01
Entanglement is one of the most intriguing features of quantum mechanics. It describes non-local correlations between quantum objects, and is at the heart of quantum information sciences. Entanglement is now being studied in diverse fields ranging from condensed matter to quantum gravity. However, measuring entanglement remains a challenge. This is especially so in systems of interacting delocalized particles, for which a direct experimental measurement of spatial entanglement has been elusive. Here, we measure entanglement in such a system of itinerant particles using quantum interference of many-body twins. Making use of our single-site-resolved control of ultracold bosonic atoms in optical lattices, we prepare two identical copies of a many-body state and interfere them. This enables us to directly measure quantum purity, Rényi entanglement entropy, and mutual information. These experiments pave the way for using entanglement to characterize quantum phases and dynamics of strongly correlated many-body systems. PMID:26632587
Optimal dynamics for quantum-state and entanglement transfer through homogeneous quantum systems
Banchi, L.; Apollaro, T. J. G.; Cuccoli, A.; Vaia, R.; Verrucchi, P.
2010-11-15
The capability of faithfully transmit quantum states and entanglement through quantum channels is one of the key requirements for the development of quantum devices. Different solutions have been proposed to accomplish such a challenging task, which, however, require either an ad hoc engineering of the internal interactions of the physical system acting as the channel or specific initialization procedures. Here we show that optimal dynamics for efficient quantum-state and entanglement transfer can be attained in generic quantum systems with homogeneous interactions by tuning the coupling between the system and the two attached qubits. We devise a general procedure to determine the optimal coupling, and we explicitly implement it in the case of a channel consisting of a spin-(1/2)XY chain. The quality of quantum-state and entanglement transfer is found to be very good and, remarkably, almost independent of the channel length.
Quantum simulation. Coherent imaging spectroscopy of a quantum many-body spin system.
Senko, C; Smith, J; Richerme, P; Lee, A; Campbell, W C; Monroe, C
2014-07-25
Quantum simulators, in which well-controlled quantum systems are used to reproduce the dynamics of less understood ones, have the potential to explore physics inaccessible to modeling with classical computers. However, checking the results of such simulations also becomes classically intractable as system sizes increase. Here, we introduce and implement a coherent imaging spectroscopic technique, akin to magnetic resonance imaging, to validate a quantum simulation. We use this method to determine the energy levels and interaction strengths of a fully connected quantum many-body system. Additionally, we directly measure the critical energy gap near a quantum phase transition. We expect this general technique to become a verification tool for quantum simulators once experiments advance beyond proof-of-principle demonstrations and exceed the resources of conventional computers. PMID:25061207
Simulation of Strongly Correlated Quantum Many-Body Systems
NASA Astrophysics Data System (ADS)
Bilgin, Ersen
In this thesis, we address the problem of solving for the properties of interacting quantum many-body systems in thermal equilibrium. The complexity of this problem increases exponentially with system size, limiting exact numerical simulations to very small systems. To tackle more complex systems, one needs to use heuristic algorithms that approximate solutions to these systems. Belief propagation is one such algorithm that we discuss in chapters 2 and 3. Using belief propagation, we demonstrate that it is possible to solve for static properties of highly correlated quantum many-body systems for certain geometries at all temperatures. In chapter 4, we generalize the multiscale renormalization ansatz to the anyonic setting to solve for the ground state properties of anyonic quantum many-body systems. The algorithms we present in chapters 2, 3, and 4 are very successful in certain settings, but they are not applicable to the most general quantum mechanical systems. For this, we propose using quantum computers as we discuss in chapter 5. The dimension reduction algorithm we consider in chapter 5 enables us to prepare thermal states of any quantum many-body system on a quantum computer faster than any previously known algorithm. Using these thermal states as the initialization of a quantum computer, one can study both static and dynamic properties of quantum systems without any memory overhead.
Software-defined quantum communication systems
NASA Astrophysics Data System (ADS)
Humble, Travis S.; Sadlier, Ronald J.
2014-08-01
Quantum communication (QC) systems harness modern physics through state-of-the-art optical engineering to provide revolutionary capabilities. An important concern for QC engineering is designing and prototyping these systems to evaluate the proposed capabilities. We apply the paradigm of software-defined communication for engineering QC systems to facilitate rapid prototyping and prototype comparisons. We detail how to decompose QC terminals into functional layers defining hardware, software, and middleware concerns, and we describe how each layer behaves. Using the superdense coding protocol as an example, we describe implementations of both the transmitter and receiver, and we present results from numerical simulations of the behavior. We conclude that the software-defined QC provides a robust framework in which to explore the large design space offered by this new regime of communication.
Pulse dynamics of quantum systems with pairing
NASA Astrophysics Data System (ADS)
Zvyagin, A. A.
2015-11-01
The evolution of the system of fermions with pairing under the action of a pulse (or a quench) of the external potential has been studied. In the dynamical regime the number of fermions oscillates (with beats) as a function of the duration of the pulse (or as a function of time for the quench) about the value determined by the magnitude of the pulse. Oscillations depend on the values of the potential and the pulse. The parameters of those oscillations permit one to determine characteristics of the dynamical quantum phase transitions, such as Fisher's zeros in one-dimensional systems. The effect is absent for zero pairing. In particular, the response of a topological superconductor to the pulse manifests dynamical oscillations, most pronounced for the range of parameters in which the topological superconductivity can occur. The response of Majorana edge states to the pulse is analyzed. The results are generalized for the bosonic system with pairing under the action of the pulse (quench).
Data Architecture in an Open Systems Environment.
ERIC Educational Resources Information Center
Bernbom, Gerald; Cromwell, Dennis
1993-01-01
The conceptual basis for structured data architecture, and its integration with open systems technology at Indiana University, are described. Key strategic goals guiding these efforts are discussed: commitment to improved data access; migration to relational database technology, and deployment of a high-speed, multiprotocol network; andâ€¦
Characterizing and quantifying frustration in quantum many-body systems.
Giampaolo, S M; Gualdi, G; Monras, A; Illuminati, F
2011-12-23
We present a general scheme for the study of frustration in quantum systems. We introduce a universal measure of frustration for arbitrary quantum systems and we relate it to a class of entanglement monotones via an exact inequality. If all the (pure) ground states of a given Hamiltonian saturate the inequality, then the system is said to be inequality saturating. We introduce sufficient conditions for a quantum spin system to be inequality saturating and confirm them with extensive numerical tests. These conditions provide a generalization to the quantum domain of the Toulouse criteria for classical frustration-free systems. The models satisfying these conditions can be reasonably identified as geometrically unfrustrated and subject to frustration of purely quantum origin. Our results therefore establish a unified framework for studying the intertwining of geometric and quantum contributions to frustration. PMID:22243147
Full distribution of work done on a quantum system for arbitrary initial states
NASA Astrophysics Data System (ADS)
Solinas, P.; Gasparinetti, S.
2015-10-01
We propose an approach to define and measure the statistics of work, internal energy and dissipated heat in a driven quantum system. In our framework the presence of a physical detector arises naturally and work and its statistics can be investigated in the most general case. In particular, we show that the quantum coherence of the initial state can lead to measurable effects on the moments of the work done on the system. At the same time, we recover the known results if the initial state is a statistical mixture of energy eigenstates. Our method can also be applied to measure the dissipated heat in an open quantum system. By sequentially coupling the system to a detector, we can track the energy dissipated in the environment while accessing only the system degrees of freedom.
Topics in biophysics and disordered quantum systems
NASA Astrophysics Data System (ADS)
Schwab, David Jason
We present a collection of problems applying the tools of statistical physics to biology. We also present work on the effects of disorder on quantum systems. First, we derive a mean-field phase diagram for the folding of a generic RNA molecule, focusing on the conditions under which a stable ribozyme may fold. Then, we study the statistical mechanics of nucleosorne positioning and trans-membrane protein alpha-helix prediction, applying related techniques. We compare the physical outcomes of each model, finding nucleosomes suffer from ubiquitous metastability while transmembrane proteins are designed to avoid this problem. Next we study the dynamical properties of a collection of neurons, believed to generate the spontaneous breathing rhythms of mammals, focusing on its ability to produce stable oscillations of activity. Next we address the competition between disorder and strong interaction in 2 D fermionic systems, finding that the Mott gap is completely washed out, leading to a glassy state. Finally, we study the rounding by disorder of first, order quantum phase transitions, both through a general heuristic argument and an in-depth study of a particular model.
Kinetic equations for a nonideal quantum system
NASA Astrophysics Data System (ADS)
Bornath, Th.; Kremp, D.; Kraeft, W. D.; Schlanges, M.
1996-10-01
In the framework of real-time Green's functions, the general kinetic equations are investigated in a first-order gradient expansion. Within this approximation, the problem of the reconstruction of the two-time correlation functions from the one-time Wigner function was solved. For the Wigner function, a cluster expansion is found in terms of a quasiparticle distribution function. In equilibrium, this expansion leads to the well-known generalized Beth-Uhlenbeck expression of the second virial coefficient. As a special case, the T-matrix approximation for the self-energy is investigated. The quantum kinetic equation derived thus has, besides the (Markovian) Boltzmann collision integral, additional terms due to the retardation expansion which reflect memory effects. Special interest is paid to the case that bound states exist in the system. It is shown that the bound state contribution, which can be introduced via a bilinear expansion of the two-particle T matrix, follows from the first-order retardation term in the general kinetic equation. The full Wigner function is now a sum of one function describing the unbound particles and another one for the bound state contribution. The latter two functions have to be determined from a coupled set of kinetic equations. In contrast to the quantum Boltzmann equation, energy and density of a nonideal system are conserved.
Repetitive Interrogation of 2-Level Quantum Systems
NASA Technical Reports Server (NTRS)
Prestage, John D.; Chung, Sang K.
2010-01-01
Trapped ion clocks derive information from a reference atomic transition by repetitive interrogations of the same quantum system, either a single ion or ionized gas of many millions of ions. Atomic beam frequency standards, by contrast, measure reference atomic transitions in a continuously replenished "flow through" configuration where initial ensemble atomic coherence is zero. We will describe some issues and problems that can arise when atomic state selection and preparation of the quantum atomic system is not completed, that is, optical pumping has not fully relaxed the coherence and also not fully transferred atoms to the initial state. We present a simple two-level density matrix analysis showing how frequency shifts during the state-selection process can cause frequency shifts of the measured clock transition. Such considerations are very important when a low intensity lamp light source is used for state selection, where there is relatively weak relaxation and re-pumping of ions to an initial state and much weaker 'environmental' relaxation of the atomic coherence set-up in the atomic sample.
Chapter 5: Quantum Dynamics in Dissipative Molecular Systems
NASA Astrophysics Data System (ADS)
Zhang, Hou-Dao; Xu, J.; Xu, Rui-Xue; Yan, Y. J.
2014-04-01
The following sections are included: * Introduction * HEOM versus Path Integral Formalism: Background * Generic form and terminology of HEOM * Statistical mechanics description of bath influence * Feynman-Vernon influence functional formalism * General comments * Memory-Frequency Decomposition of Bath Correlation Functions * PSD of Bose function * Brownian oscillators decomposition of bath spectral density function * Optimized HEOM Theory With Accuracy Control * Construction of HEOM via path integral formalism * Accuracy control on white-noise residue ansatz * Efficient HEOM propagator: Numerical filtering and indexing algorithm * HEOM in Quantum Mechanics for Open Systems * The HEOM space and the Schrödinger picture * HEOM in the Heisenberg picture * Mixed Heisenberg-Schrödinger block-matrix dynamics in nonlinear optical response functions * Two-Dimensional Spectroscopy: Model Calculations * Concluding Remarks * Acknowledgments * References
Open-system dynamics of entanglement:a key issues review
NASA Astrophysics Data System (ADS)
Aolita, Leandro; de Melo, Fernando; Davidovich, Luiz
2015-04-01
One of the greatest challenges in the fields of quantum information processing and quantum technologies is the detailed coherent control over each and every constituent of quantum systems with an ever increasing number of particles. Within this endeavor, harnessing of many-body entanglement against the detrimental effects of the environment is a major pressing issue. Besides being an important concept from a fundamental standpoint, entanglement has been recognized as a crucial resource for quantum speed-ups or performance enhancements over classical methods. Understanding and controlling many-body entanglement in open systems may have strong implications in quantum computing, quantum simulations of many-body systems, secure quantum communication or cryptography, quantum metrology, our understanding of the quantum-to-classical transition, and other important questions of quantum foundations. In this paper we present an overview of recent theoretical and experimental efforts to underpin the dynamics of entanglement under the influence of noise. Entanglement is thus taken as a dynamic quantity on its own, and we survey how it evolves due to the unavoidable interaction of the entangled system with its surroundings. We analyze several scenarios, corresponding to different families of states and environments, which render a very rich diversity of dynamical behaviors. In contrast to single-particle quantities, like populations and coherences, which typically vanish only asymptotically in time, entanglement may disappear at a finite time. In addition, important classes of entanglement display an exponential decay with the number of particles when subject to local noise, which poses yet another threat to the already-challenging scaling of quantum technologies. Other classes, however, turn out to be extremely robust against local noise. Theoretical results and recent experiments regarding the difference between local and global decoherence are summarized. Control and robustness-enhancement techniques, scaling laws, statistical and geometrical aspects of multipartite-entanglement decay are also reviewed; all in order to give a broad picture of entanglement dynamics in open quantum systems addressed to both theorists and experimentalists inside and outside the field of quantum information.
Coulomb crystallization in classical and quantum systems
NASA Astrophysics Data System (ADS)
Bonitz, Michael
2007-11-01
Coulomb crystallization occurs in one-component plasmas when the average interaction energy exceeds the kinetic energy by about two orders of magnitude. A simple road to reach such strong coupling consists in using external confinement potentials the strength of which controls the density. This has been succsessfully realized with ions in traps and storage rings and also in dusty plasma. Recently a three-dimensional spherical confinement could be created [1] which allows to produce spherical dust crystals containing concentric shells. I will give an overview on our recent results for these ``Yukawa balls'' and compare them to experiments. The shell structure of these systems can be very well explained by using an isotropic statically screened pair interaction. Further, the thermodynamic properties of these systems, such as the radial density distribution are discussed based on an analytical theory [3]. I then will discuss Coulomb crystallization in trapped quantum systems, such as mesoscopic electron and electron hole plasmas in coupled layers [4,5]. These systems show a very rich correlation behavior, including liquid and solid like states and bound states (excitons, biexcitons) and their crystals. On the other hand, also collective quantum and spin effects are observed, including Bose-Einstein condensation and superfluidity of bound electron-hole pairs [4]. Finally, I consider Coulomb crystallization in two-component neutral plasmas in three dimensions. I discuss the necessary conditions for crystals of heavy charges to exist in the presence of a light component which typically is in the Fermi gas or liquid state. It can be shown that their exists a critical ratio of the masses of the species of the order of 80 [5] which is confirmed by Quantum Monte Carlo simulations [6]. Familiar examples are crystals of nuclei in the core of White dwarf stars, but the results also suggest the existence of other crystals, including proton or ?-particle crystals in dense matter and of hole crystals in semiconductors. [1] O. Arp, D. Block, A. Piel, and A. Melzer, Phys. Rev. Lett. 93, 165004 (2004). [2] M. Bonitz, D. Block, O. Arp, V. Golubnychiy, H. Baumgartner, P. Ludwig, A. Piel, and A. Filinov, Phys. Rev. Lett. 96, 075001 (2006). [3] C. Henning, H. Baumgartner, A. Piel, P. Ludwig, V. Golubnychiy, M. Bonitz, and D. Block, Phys. Rev. E 74, 056403 (2006) and Phys. Rev. E (2007). [4] A. Filinov, M. Bonitz, and Yu. Lozovik, Phys. Rev. Lett. 86, 3851 (2001). [5] M. Bonitz, V. Filinov, P. Levashov, V. Fortov, and H. Fehske, Phys. Rev. Lett. 95, 235006 (2005) and J. Phys. A: Math. Gen. 39, 4717 (2006). [6] Introduction to Computational Methods for Many-Body Systems, M. Bonitz and D. Semkat (eds.), Rinton Press, Princeton (2006)
Optimal dynamic discrimination of similar quantum systems
NASA Astrophysics Data System (ADS)
Li, Baiqing
2005-07-01
The techniques for identifying and separating similar molecules have always been very important to chemistry and other branches of science and engineering. Similar quantum systems share comparable Hamiltonians, so their eigenenergy levels, transition dipole moments, and therefore their ordinary observable properties are alike. Traditional analytical methods have mostly been restricted by working with the subtle differences in the physical and chemical properties of the similar species. Optimal Dynamic Discrimination (ODD) aims at magnifying the dissimilarity of the agents by actively controlling their quantum evolution, drawing on the extremely rich information embedded in their dynamics. ODD is developed based on the tremendous flexibility of Optimal Control Theory (OCT) and on the practical implementation of closed-loop learning control, which has become a more and more indispensable tool for controlling quantum processes. The ODD experimental paradigm is designed to combat a number of factors that are detrimental to the discrimination of similar molecules: laser pulse noise, signal detection errors, finite time resolution in the signals, and environmental decoherence effects. It utilizes either static signals or time series signal, the latter capable of providing more information. Simulations are performed in this dissertation progressing from the wave function to the density matrix formulation, in order to study the decoherence effects. Analysis of the results reveals the roles of the adverse factors, unravels the underlying mechanisms of ODD, and provides insights on laboratory implementation. ODD emphasizes the incorporation of algorithmic development and laboratory design, and seeks to bridge the gap between theoretical/computational chemistry and experimental chemistry, with the help from applied mathematics and computer science.
Particle escapes in an open quantum network via multiple leads
Taniguchi, Tooru; Sawada, Shin-ichi
2011-12-15
Quantum escape of a particle from an end of a one-dimensional finite region to N semi-infinite leads is discussed from a scattering theory approach. Depending on the potential barrier amplitude at the junction, the probability P(t) for a particle to remain in the finite region at time t shows two different decay behaviors at long times; one is proportional to N{sup 2}/t{sup 3} and another is proportional to 1/(N{sup 2}t). In addition, the velocity V(t) for a particle to leave the finite region, defined from a probability current of the particle position, decays asymptotically as a power of time {approx}1/t, independent of the number of leads and the initial wave function. For a finite time, the probability P(t) decays exponentially in time with a smaller decay rate for a greater number of leads, and the velocity V(t) shows a time oscillation whose amplitude is larger for a greater number of leads. Particle escapes from the both ends of a finite region to multiple leads are also discussed using a different boundary condition.
The Foundations of Quantum Mechanics: Historical Analysis and Open Questions -- Cesena, 2004
NASA Astrophysics Data System (ADS)
Garola, Claudio; Rossi, Arcangelo; Sozzo, Sandro
Introduction / C. Garola, A. Rossi and S. Sozzo -- If Bertlmann had three feet / A. Afriat -- Macroscopic interpretability of quantum component systems / R. Ascoli -- Premeasurement versus measurement: a basic form of complementarity / G. Auletta and G. Tarozzi -- Remarks on conditioning / E. G. Beltrametti -- Entangled state preparation in experiments on quantum non-locality / V. Berardi and A. Garuccio -- The first steps of quantum electrodynamics: what is it that's being quantized? / S. Bergia -- On the meaning of element in the science of italic tradition, the question of physical objectivity (and/or physical meaning) and quantum mechanics / G. Boscarino -- Mathematics and epistemology in Planck's theoretical work (1898-1915) / P. Campogalliani -- On the free motion with noise / B. Carazza and R. Tedeschi -- Field quantization and wave/particle duality / M. Cini -- Parastatistics in econophysics? / D. Costantini and U. Garibaldi -- Theory-laden instruments and quantum mechanics / S. D'Agostino -- Quantum non-locality and the mathematical representation of experience / V. Fano -- On the notion of proposition in classical and quantum mechanics / C. Garola and S. Sozzo -- The electromagnetic conception of nature and the origins of quantum physics / E. A. Giannetto -- What we talk about when we talk about universe computability / S. Guccione -- Bohm and Bohmian mechanics / G. Introzzi and M. Rossetti -- An objective background for quantum theory relying on thermodynamic concepts / L. Lanz and B. Vacchini -- The entrance of quantum mechanics in Italy: from Garbasso to Fermi / M. Leone and N. Robotti -- The measure of momentum in quantum mechanics / F. Logiurato and C. Tarsitani -- On the two-slit interference experiment: a statistical discussion / M. Minozzo -- Why the reactivity of the elements is a relational property, and why it matters / V. Mosini -- Detecting non compatible properties in double-slit experiment without erasure / G. Nisticò -- If you can manipulate them, must they be real? The epistemological role of instruments in nanotechnological research / A. Rebaglia -- Mathematical models and physical reality from classical to quantum physics / A. Rossi -- Complex entanglement and quaternionic separability / G. Scolarici and L. Solombrino -- Mach-Zehnder interferometer and quantitative complementarity / C. Tarsitani and F. Logiurato -- Antonio Gramsci's reflection on quantum mechanics / I. Tassani -- The role of logic and mathematics in the Heisenberg formulation of quantum mechanics / A. Venezia -- Space-time at the Planck scale: the quantum computer view / P. A. Zizzi -- Three-dimensional wave behaviour of light / F. Logiurato ... [et al.].
Silaev, Mihail; Heikkilä, Tero T; Virtanen, Pauli
2014-08-01
We formulate the general approach based on the Lindblad equation to calculate the full counting statistics of work and heat produced by driven quantum systems weakly coupled with a Markovian thermal bath. The approach can be applied to a wide class of dissipative quantum systems driven by an arbitrary force protocol. We show the validity of general fluctuation relations and consider several generic examples. The possibilities of using calorimetric measurements to test the presence of coherence and entanglement in the open quantum systems are discussed. PMID:25215685
The Quixote project: Collaborative and Open Quantum Chemistry data management in the Internet age
2011-01-01
Computational Quantum Chemistry has developed into a powerful, efficient, reliable and increasingly routine tool for exploring the structure and properties of small to medium sized molecules. Many thousands of calculations are performed every day, some offering results which approach experimental accuracy. However, in contrast to other disciplines, such as crystallography, or bioinformatics, where standard formats and well-known, unified databases exist, this QC data is generally destined to remain locally held in files which are not designed to be machine-readable. Only a very small subset of these results will become accessible to the wider community through publication. In this paper we describe how the Quixote Project is developing the infrastructure required to convert output from a number of different molecular quantum chemistry packages to a common semantically rich, machine-readable format and to build respositories of QC results. Such an infrastructure offers benefits at many levels. The standardised representation of the results will facilitate software interoperability, for example making it easier for analysis tools to take data from different QC packages, and will also help with archival and deposition of results. The repository infrastructure, which is lightweight and built using Open software components, can be implemented at individual researcher, project, organisation or community level, offering the exciting possibility that in future many of these QC results can be made publically available, to be searched and interpreted just as crystallography and bioinformatics results are today. Although we believe that quantum chemists will appreciate the contribution the Quixote infrastructure can make to the organisation and and exchange of their results, we anticipate that greater rewards will come from enabling their results to be consumed by a wider community. As the respositories grow they will become a valuable source of chemical data for use by other disciplines in both research and education. The Quixote project is unconventional in that the infrastructure is being implemented in advance of a full definition of the data model which will eventually underpin it. We believe that a working system which offers real value to researchers based on tools and shared, searchable repositories will encourage early participation from a broader community, including both producers and consumers of data. In the early stages, searching and indexing can be performed on the chemical subject of the calculations, and well defined calculation meta-data. The process of defining more specific quantum chemical definitions, adding them to dictionaries and extracting them consistently from the results of the various software packages can then proceed in an incremental manner, adding additional value at each stage. Not only will these results help to change the data management model in the field of Quantum Chemistry, but the methodology can be applied to other pressing problems related to data in computational and experimental science. PMID:21999363
Measure synchronization in quantum many-body systems
NASA Astrophysics Data System (ADS)
Qiu, Haibo; Juliá-Díaz, Bruno; Garcia-March, Miguel Angel; Polls, Artur
2014-09-01
The concept of measure synchronization between two coupled quantum many-body systems is presented. In general terms we consider two quantum many-body systems whose dynamics gets coupled through the contact particle-particle interaction. This coupling is shown to produce measure synchronization, a generalization of synchrony to a large class of systems which takes place in absence of dissipation. We find that in quantum measure synchronization, the many-body quantum properties for the two subsystems, e.g., condensed fractions and particle fluctuations, behave in a coordinated way. To illustrate the concept we consider a simple case of two species of bosons occupying two distinct quantum states. Measure synchronization can be readily explored with state-of-the-art techniques in ultracold atomic gases and, if properly controlled, be employed to build targeted quantum correlations in a sympathetic way.
Computable measure of total quantum correlations of multipartite systems
NASA Astrophysics Data System (ADS)
Behdani, Javad; Akhtarshenas, Seyed Javad; Sarbishaei, Mohsen
2016-01-01
Quantum discord as a measure of the quantum correlations cannot be easily computed for most of density operators. In this paper, we present a measure of the total quantum correlations that is operationally simple and can be computed effectively for an arbitrary mixed state of a multipartite system. The measure is based on the coherence vector of the party whose quantumness is investigated as well as the correlation matrix of this part with the remainder of the system. Being able to detect the quantumness of multipartite systems, such as detecting the quantum critical points in spin chains, alongside with the computability characteristic of the measure, makes it a useful indicator to be exploited in the cases which are out of the scope of the other known measures.
Quantum uncertainty in critical systems with three spins interaction
NASA Astrophysics Data System (ADS)
Carrijo, Thiago M.; Avelar, Ardiley T.; Céleri, Lucas C.
2015-06-01
In this article we consider two spin-1/2 chains described, respectively, by the thermodynamic limit of the XY model with the usual two site interaction, and an extension of this model (without taking the thermodynamics limit), called XYT, were a three site interaction term is presented. To investigate the critical behaviour of such systems we employ tools from quantum information theory. Specifically, we show that the local quantum uncertainty, a quantity introduced in order to quantify the minimum quantum share of the variance of a local measurement, can be used to indicate quantum phase transitions presented by these models at zero temperature. Due to the connection of this quantity with the quantum Fisher information, the results presented here may be relevant for quantum metrology and quantum thermodynamics.
Performance comparison between classical and quantum control for a simple quantum system
NASA Astrophysics Data System (ADS)
Xi, Zairong; Jin, Guangsheng
2008-02-01
BraÅ„czyk et al. pointed out that the quantum control scheme is superior to the classical control scheme for a simple quantum system using simulation [A.M. BraÅ„czyk, P.E.M.F. Mendonca, A. Gilchrist, A.C. Doherty, S.D. Barlett, Quantum control theory of a single qubit, Physical Review A 75 (2007) 012329 or arXiv e-print quant-ph/0608037]. Here we rigorously prove the result. Furthermore we will show that any quantum operation does not universally â€œcorrectâ€ the dephasing noise.
Realization of quantum state privacy amplification in a nuclear magnetic resonance quantum system
NASA Astrophysics Data System (ADS)
Hao, Liang; Wang, Chuan; Long, Gui Lu
2010-06-01
Quantum state privacy amplification (QSPA) is the quantum analogue of classical privacy amplification. If the state information of a series of single-particle states has some leakage, QSPA reduces this leakage by condensing the state information of two particles into the state of one particle. Recursive applications of the operations will eliminate the quantum state information leakage to a required minimum level. In this paper, we report the experimental implementation of a quantum state privacy amplification protocol in a nuclear magnetic resonance system. The density matrices of the states are constructed in the experiment, and the experimental results agree well with theory.
Automated drawing system of quantum energy levels
NASA Astrophysics Data System (ADS)
Stampoultzis, M.; Sinatkas, J.; Tsakstara, V.; Kosmas, T. S.
2014-03-01
The purpose of this work is to derive an automated system that provides advantageous drawings of energy spectra for quantum systems (nuclei, atoms, molecules, etc.) required in various physical sciences. The automation involves the development of appropriate computational code and graphical imaging system based on raw data insertion, theoretical calculations and experimental or bibliographic data insertion. The system determines the appropriate scale to depict graphically with the best possible way in the available space. The presently developed code operates locally and the results are displayed on the screen and can be exported to a PostScript file. We note its main features to arrange and visualize in the available space the energy levels with their identity, taking care the existence in the final diagram the least auxiliary deviations. Future improvements can be the use of Java and the availability on the Internet. The work involves the automated plotting of energy levels in molecules, atoms, nuclei and other types of quantized energy spectra. The automation involves the development of an appropriate computational code and graphical imaging system.
Quantum interference induced photon blockade in a coupled single quantum dot-cavity system.
Tang, Jing; Geng, Weidong; Xu, Xiulai
2015-01-01
We propose an experimental scheme to implement a strong photon blockade with a single quantum dot coupled to a nanocavity. The photon blockade effect can be tremendously enhanced by driving the cavity and the quantum dot simultaneously with two classical laser fields. This enhancement of photon blockade is ascribed to the quantum interference effect to avoid two-photon excitation of the cavity field. Comparing with Jaynes-Cummings model, the second-order correlation function at zero time delay g((2))(0) in our scheme can be reduced by two orders of magnitude and the system sustains a large intracavity photon number. A red (blue) cavity-light detuning asymmetry for photon quantum statistics with bunching or antibunching characteristics is also observed. The photon blockade effect has a controllable flexibility by tuning the relative phase between the two pumping laser fields and the Rabi coupling strength between the quantum dot and the pumping field. Moreover, the photon blockade scheme based on quantum interference mechanism does not require a strong coupling strength between the cavity and the quantum dot, even with the pure dephasing of the system. This simple proposal provides an effective way for potential applications in solid state quantum computation and quantum information processing. PMID:25783560
Quantum Interference Induced Photon Blockade in a Coupled Single Quantum Dot-Cavity System
Tang, Jing; Geng, Weidong; Xu, Xiulai
2015-01-01
We propose an experimental scheme to implement a strong photon blockade with a single quantum dot coupled to a nanocavity. The photon blockade effect can be tremendously enhanced by driving the cavity and the quantum dot simultaneously with two classical laser fields. This enhancement of photon blockade is ascribed to the quantum interference effect to avoid two-photon excitation of the cavity field. Comparing with Jaynes-Cummings model, the second-order correlation function at zero time delay g(2)(0) in our scheme can be reduced by two orders of magnitude and the system sustains a large intracavity photon number. A red (blue) cavity-light detuning asymmetry for photon quantum statistics with bunching or antibunching characteristics is also observed. The photon blockade effect has a controllable flexibility by tuning the relative phase between the two pumping laser fields and the Rabi coupling strength between the quantum dot and the pumping field. Moreover, the photon blockade scheme based on quantum interference mechanism does not require a strong coupling strength between the cavity and the quantum dot, even with the pure dephasing of the system. This simple proposal provides an effective way for potential applications in solid state quantum computation and quantum information processing. PMID:25783560
Quantum Interference Induced Photon Blockade in a Coupled Single Quantum Dot-Cavity System
NASA Astrophysics Data System (ADS)
Tang, Jing; Geng, Weidong; Xu, Xiulai
2015-03-01
We propose an experimental scheme to implement a strong photon blockade with a single quantum dot coupled to a nanocavity. The photon blockade effect can be tremendously enhanced by driving the cavity and the quantum dot simultaneously with two classical laser fields. This enhancement of photon blockade is ascribed to the quantum interference effect to avoid two-photon excitation of the cavity field. Comparing with Jaynes-Cummings model, the second-order correlation function at zero time delay g(2)(0) in our scheme can be reduced by two orders of magnitude and the system sustains a large intracavity photon number. A red (blue) cavity-light detuning asymmetry for photon quantum statistics with bunching or antibunching characteristics is also observed. The photon blockade effect has a controllable flexibility by tuning the relative phase between the two pumping laser fields and the Rabi coupling strength between the quantum dot and the pumping field. Moreover, the photon blockade scheme based on quantum interference mechanism does not require a strong coupling strength between the cavity and the quantum dot, even with the pure dephasing of the system. This simple proposal provides an effective way for potential applications in solid state quantum computation and quantum information processing.
Tunable polaritonic molecules in an open microcavity system
NASA Astrophysics Data System (ADS)
Dufferwiel, S.; Li, Feng; Trichet, A. A. P.; Giriunas, L.; Walker, P. M.; Farrer, I.; Ritchie, D. A.; Smith, J. M.; Skolnick, M. S.; Krizhanovskii, D. N.
2015-11-01
We experimentally demonstrate tunable coupled cavities based upon open access zero-dimensional hemispherical microcavities. The modes of the photonic molecules are strongly coupled with quantum well excitons forming a system of tunable polaritonic molecules. The cavity-cavity coupling strength, which is determined by the degree of modal overlap, is controlled through the fabricated centre-to-centre distance and tuned in-situ through manipulation of both the exciton-photon and cavity-cavity detunings by using nanopositioners to vary the mirror separation and angle between them. We demonstrate micron sized confinement combined with high photonic Q-factors of 31 000 and lower polariton linewidths of 150 Î¼eV at resonance along with cavity-cavity coupling strengths between 2.5 meV and 60 Î¼eV for the ground cavity state.
Quantum Liquid Crystal Phases in Strongly Correlated Fermionic Systems
ERIC Educational Resources Information Center
Sun, Kai
2009-01-01
This thesis is devoted to the investigation of the quantum liquid crystal phases in strongly correlated electronic systems. Such phases are characterized by their partially broken spatial symmetries and are observed in various strongly correlated systems as being summarized in Chapter 1. Although quantum liquid crystal phases often involve…
Quantum Liquid Crystal Phases in Strongly Correlated Fermionic Systems
ERIC Educational Resources Information Center
Sun, Kai
2009-01-01
This thesis is devoted to the investigation of the quantum liquid crystal phases in strongly correlated electronic systems. Such phases are characterized by their partially broken spatial symmetries and are observed in various strongly correlated systems as being summarized in Chapter 1. Although quantum liquid crystal phases often involveâ€¦
Identities for Entropy Change Associated with the Time-Evolution of an Open System
NASA Astrophysics Data System (ADS)
Majima, Hiroki; Suzuki, Akira
2015-08-01
A general relation between entropy and an evolutionary superoperator is derived based on the theory of the real-time formulation. The formulation establishing the relation relies only on the framework of quantum statistical mechanics and the standard definition of the von Neumann entropy. Applying the theory of the imaginary-time formulation, a similar relation is obtained for the entropy change due to the change in reservoir temperatures. To show the usefulness of these formulas, we derived the expression for the entropy production induced by some dissipation in an open quantum system as the exemplary model system.
Experimental quantum simulation of entanglement in many-body systems.
Zhang, Jingfu; Wei, Tzu-Chieh; Laflamme, Raymond
2011-07-01
We employ a nuclear magnetic resonance (NMR) quantum information processor to simulate the ground state of an XXZ spin chain and measure its NMR analog of entanglement, or pseudoentanglement. The observed pseudoentanglement for a small-size system already displays a singularity, a signature which is qualitatively similar to that in the thermodynamical limit across quantum phase transitions, including an infinite-order critical point. The experimental results illustrate a successful approach to investigate quantum correlations in many-body systems using quantum simulators. PMID:21797528
Measures of Quantum Synchronization in Continuous Variable Systems
NASA Astrophysics Data System (ADS)
Mari, A.; Farace, A.; Didier, N.; Giovannetti, V.; Fazio, R.
2013-09-01
We introduce and characterize two different measures which quantify the level of synchronization of coupled continuous variable quantum systems. The two measures allow us to extend to the quantum domain the notions of complete and phase synchronization. The Heisenberg principle sets a universal bound to complete synchronization. The measure of phase synchronization is, in principle, unbounded; however, in the absence of quantum resources (e.g., squeezing) the synchronization level is bounded below a certain threshold. We elucidate some interesting connections between entanglement and synchronization and, finally, discuss an application based on quantum optomechanical systems.
Process tomography via sequential measurements on a single quantum system
NASA Astrophysics Data System (ADS)
Bassa, Humairah; Goyal, Sandeep K.; Choudhary, Sujit K.; Uys, Hermann; Diósi, Lajos; Konrad, Thomas
2015-09-01
We utilize a discrete (sequential) measurement protocol to investigate quantum process tomography of a single two-level quantum system, with an unknown initial state, undergoing Rabi oscillations. The ignorance of the dynamical parameters is encoded into a continuous-variable classical system which is coupled to the two-level quantum system via a generalized Hamiltonian. This combined estimate of the quantum state and dynamical parameters is updated by using the information obtained from sequential measurements on the quantum system and, after a sufficient waiting period, faithful state monitoring and parameter determination is obtained. Numerical evidence is used to demonstrate the convergence of the state estimate to the true state of the hybrid system.
Detective quantum efficiency of the LODOX system
NASA Astrophysics Data System (ADS)
de Villiers, Mattieu; de Jager, Gerhard
2003-06-01
The Detective Quantum Efficiency (DQE) of a digital x-ray imaging system describes how much of the signal to noise ratio of the incident radiation is sustained in the resultant digital image. This measure of dose efficiency is suitable for the comparison of detectors produced by different manufacturers. The International Electrotechnical Commission (IEC) stipulates standard methods and conditions for the measurement of the DQE for single exposure imaging systems such as flat panel detectors. This paper shows how the calculation is adapted for DQE measurements of scanning systems. In this paper it is described how to measure the presampled Modulation Transfer Function (MTF) using an edge test method and how to extract the horizontal and vertical components of the Noise Power Spectrum (NPS) in a way that is insensitive to structured noise patterns often found in scanned images. The calculation of the total number of incident photons from the radiation dose measurement is explained and results are provided for the Lodox low dose full body digital x-ray scanning system which is developed in South Africa.
An Open System for Intravascular Ultrasound Imaging
Qiu, Weibao; Chen, Yan; Li, Xiang; Yu, Yanyan; Cheng, Wang Fai; Tsang, Fu Keung; Zhou, Qifa; Shung, K. Kirk; Dai, Jiyan; Sun, Lei
2013-01-01
Visualization of the blood vessels can provide valuable morphological information for diagnosis and therapy strategies for cardiovascular disease. Intravascular ultrasound (IVUS) is able to delineate internal structures of vessel wall with fine spatial resolution. However, the developed IVUS is insufficient to identify the fibrous cap thickness and tissue composition of atherosclerotic lesions. Novel imaging strategies have been proposed, such as increasing the center frequency of ultrasound or using a modulated excitation technique to improve the accuracy of diagnosis. Dual-mode tomography combining IVUS with optical tomography has also been developed to determine tissue morphology and characteristics. The implementation of these new imaging methods requires an open system that allows users to customize the system for various studies. This paper presents the development of an IVUS system that has open structures to support various imaging strategies. The system design is based on electronic components and printed circuit board, and provides reconfigurable hardware implementation, programmable image processing algorithms, flexible imaging control, and raw RF data acquisition. In addition, the proposed IVUS system utilized a miniaturized ultrasound transducer constructed using PMN-PT single crystal for better piezoelectric constant and electromechanical coupling coefficient than traditional lead zirconate titanate (PZT) ceramics. Testing results showed that the IVUS system could offer a minimum detectable signal of 25 Î¼V, allowing a 51 dB dynamic range at 47 dB gain, with a frequency range from 20 to 80 MHz. Finally, phantom imaging, in vitro IVUS vessel imaging, and multimodality imaging with photoacoustics were conducted to demonstrate the performance of the open system. PMID:23143570
Fate of classical solitons in one-dimensional quantum systems
NASA Astrophysics Data System (ADS)
Pustilnik, M.; Matveev, K. A.
2015-11-01
We study one-dimensional quantum systems near the classical limit described by the Korteweg-de Vries (KdV) equation. The excitations near this limit are the well-known solitons and phonons. The classical description breaks down at long wavelengths, where quantum effects become dominant. Focusing on the spectra of the elementary excitations, we describe analytically the entire classical-to-quantum crossover. We show that the ultimate quantum fate of the classical KdV excitations is to become fermionic particles and holes. We discuss in detail two exactly solvable models exhibiting such crossover, namely the Lieb-Liniger model of bosons with weak contact repulsion and the quantum Toda model. We argue that the results obtained for these models are universally applicable to all quantum one-dimensional systems with a well-defined classical limit described by the KdV equation.
Fate of classical solitons in one-dimensional quantum systems.
Pustilnik, M.; Matveev, K. A.
2015-11-23
We study one-dimensional quantum systems near the classical limit described by the Korteweg-de Vries (KdV) equation. The excitations near this limit are the well-known solitons and phonons. The classical description breaks down at long wavelengths, where quantum effects become dominant. Focusing on the spectra of the elementary excitations, we describe analytically the entire classical-to-quantum crossover. We show that the ultimate quantum fate of the classical KdV excitations is to become fermionic quasiparticles and quasiholes. We discuss in detail two exactly solvable models exhibiting such crossover, the Lieb-Liniger model of bosons with weak contact repulsion and the quantum Toda model, and argue that the results obtained for these models are universally applicable to all quantum one-dimensional systems with a well-defined classical limit described by the KdV equation.
Maps and inverse maps in open quantum dynamics
Jordan, Thomas F.
2010-10-15
Two kinds of maps that describe evolution of states of a subsystem coming from dynamics described by a unitary operator for a larger system, maps defined for fixed mean values and maps defined for fixed correlations, are found to be quite different for the same unitary dynamics in the same situation in the larger system. An affine form is used for both kinds of maps to find necessary and sufficient conditions for inverse maps. All the different maps with the same homogeneous part in their affine forms have inverses if and only if the homogeneous part does. Some of these maps are completely positive; others are not, but the homogeneous part is always completely positive. The conditions for an inverse are the same for maps that are not completely positive as for maps that are. For maps defined for fixed mean values, the homogeneous part depends only on the unitary operator for the dynamics of the larger system, not on any state or mean values or correlations. Necessary and sufficient conditions for an inverse are stated several different ways: in terms of the maps of matrices, basis matrices, density matrices, or mean values. The inverse maps are generally not tied to the dynamics the way the maps forward are. A trace-preserving completely positive map that is unital cannot have an inverse that is obtained from any dynamics described by any unitary operator for any states of a larger system.
Control of the quantum interference in a superconducting qubit system
NASA Astrophysics Data System (ADS)
Ying, Hao; Luo, Da-Wei; Xu, Jing-Bo
2013-10-01
We propose a scheme to control quantum interference pattern in a system of a superconducting qubit coupled to its own data bus by applying a controllable time-dependent electromagnetic field. It is shown that the quantum interference induced by the initial phase difference is closely related to the quantum correlations between two superconducting qubits which are coupled to their own data bus and the geometric discord can also be increased by applying the controllable electromagnetic field.
Strong polygamy of quantum correlations in multi-party quantum systems
NASA Astrophysics Data System (ADS)
Kim, Jeong San
2014-10-01
We propose a new type of polygamy inequality for multi-party quantum entanglement. We first consider the possible amount of bipartite entanglement distributed between a fixed party and any subset of the rest parties in a multi-party quantum system. By using the summation of these distributed entanglements, we provide an upper bound of the distributed entanglement between a party and the rest in multi-party quantum systems. We then show that this upper bound also plays as a lower bound of the usual polygamy inequality, therefore the strong polygamy of multi-party quantum entanglement. For the case of multi-party pure states, we further show that the strong polygamy of entanglement implies the strong polygamy of quantum discord.
OCSEGen: Open Components and Systems Environment Generator
NASA Technical Reports Server (NTRS)
Tkachuk, Oksana
2014-01-01
To analyze a large system, one often needs to break it into smaller components.To analyze a component or unit under analysis, one needs to model its context of execution, called environment, which represents the components with which the unit interacts. Environment generation is a challenging problem, because the environment needs to be general enough to uncover unit errors, yet precise enough to make the analysis tractable. In this paper, we present a tool for automated environment generation for open components and systems. The tool, called OCSEGen, is implemented on top of the Soot framework. We present the tool's current support and discuss its possible future extensions.
The study of classical dynamical systems using quantum theory
NASA Astrophysics Data System (ADS)
Bogdanov, Yu. I.; Bogdanova, N. A.
2014-12-01
We have developed a method for complementing an arbitrary classical dynamical system to a quantum system using the Lorenz and Rössler systems as examples. The Schrödinger equation for the corresponding quantum statistical ensemble is described in terms of the Hamilton-Jacobi formalism. We consider both the original dynamical system in the coordinate space and the conjugate dynamical system corresponding to the momentum space. Such simultaneous consideration of mutually complementary coordinate and momentum frameworks provides a deeper understanding of the nature of chaotic behavior in dynamical systems. We have shown that the new formalism provides a significant simplification of the Lyapunov exponents calculations. From the point of view of quantum optics, the Lorenz and Rössler systems correspond to three modes of a quantized electromagnetic field in a medium with cubic nonlinearity. From the computational point of view, the new formalism provides a basis for the analysis of complex dynamical systems using quantum computers.
Tuning entanglement between two interacting quantum systems using radiation field
NASA Astrophysics Data System (ADS)
Sadiek, Gehad; Abdallah, M. Sebaweh; Aldress, Wiam
2015-03-01
The interaction between a quantum system and a bosonic field has been one of the central problems in physics. It manifests itself in many different systems of interest that have been proposed as promising candidates for the future technology of quantum information processing. One of the most successful approaches in describing the coupling between a two-level quantum system and a bosonic field is the Rabi model. As the Rabi model is not analytically solvable, different approaches were introduced to simplify it, such as the widely used Jaynes-cummings model. Most of the investigations have focused on the coupling between one or more quantum systems at one hand and the radiation fields at the other hand, ignoring the possible coupling between the quantum systems themselves. We consider two interacting two-level quantum systems coupled to a single-mode quantized radiation field, where we present a complete exact analytic solution for the system. We investigate the dynamics of entanglement of the system starting from different initial setups. We demonstrate how the interplay between the coupling strength between the two quantum systems and the applied radiation field parameters can be utilized to tune the entanglement properties, dynamics and its asymptotic behavior. Deanship of scientific research, University of Sharjah.
Density matrix of strongly coupled quantum dot - microcavity system
NASA Astrophysics Data System (ADS)
Van Hop, Nguyen
2009-09-01
Any two-level quantum system can be used as a quantum bit (qubit)-the basic element of all devices and systems for quantum information and quantum computation. Recently it was proposed to study the strongly coupled system consisting of a two-level quantum dot and a monoenergetic photon gas in a microcavity-the strongly coupled quantum dot-microcavity (QD-MC) system for short, with the Jaynes-Cumming total Hamiltonian, for the application in the quantum information processing. Different approximations were applied in the theoretical study of this system. In this work, on the basis of the exact solution of the Schrodinger equation for this system without dissipation we derive the exact formulae for its density matrix. The realization of a qubit in this system is discussed. The solution of the system of rate equation for the strongly coupled QD-MC system in the presence of the interaction with the environment was also established in the first order approximation with respect to this interaction.
Li, Xiaohan; Dasika, Vaishno D.; Li, Ping-Chun; Ji, Li; Bank, Seth R.; Yu, Edward T.
2014-09-22
The use of InGaAs quantum wells with composition graded across the intrinsic region to increase open-circuit voltage in p-i-n GaAs/InGaAs quantum well solar cells is demonstrated and analyzed. By engineering the band-edge energy profile to reduce photo-generated carrier concentration in the quantum wells at high forward bias, simultaneous increases in both open-circuit voltage and short-circuit current density are achieved, compared to those for a structure with the same average In concentration, but constant rather than graded quantum well composition across the intrinsic region. This approach is combined with light trapping to further increase short-circuit current density.
Deterministic quantum logic gates and quantum cloning based on quantum dot-cavity coupled system
NASA Astrophysics Data System (ADS)
Ji, Yan-Qiang; Wen, Jing-Ji; Wang, Yun-Long; Zhu, Ai-Dong; Wang, Hong-Fu; Zhang, Shou; Yeon, Kyu-Hwang
2013-08-01
We propose two theoretical schemes for creating the CNOT gate and Toffoli gate deterministically by using the singly charged quantum dots inside the double-sided microcavities. Both of the two schemes only need one photon to act as an ancilla. A high fidelity can be achieved in the strong coupling regime. Finally, a quantum cloning machine is constructed theoretically to copy a quantum state near a given state by using the CNOT gate and the Toffoli gate, which simplifies the implementation of quantum cloning compared with previous proposals.
Adiabatic response and quantum thermoelectrics for ac-driven quantum systems
NASA Astrophysics Data System (ADS)
Ludovico, MarÃa Florencia; Battista, Francesca; von Oppen, Felix; Arrachea, Liliana
2016-02-01
We generalize the theory of thermoelectrics to include coherent electron systems under adiabatic ac driving, accounting for quantum pumping of charge and heat, as well as for the work exchanged between the electron system and driving potentials. We derive the relevant response coefficients in the adiabatic regime and show that they obey generalized Onsager reciprocity relations. We analyze the consequences of our generalized thermoelectric framework for quantum motors, generators, heat engines, and heat pumps, characterizing them in terms of efficiencies and figures of merit. We illustrate these concepts in a model for a quantum pump.
Enzyme efficiency: An open reaction system perspective.
Banerjee, Kinshuk; Bhattacharyya, Kamal
2015-12-21
A measure of enzyme efficiency is proposed for an open reaction network that, in suitable form, applies to closed systems as well. The idea originates from the description of classical enzyme kinetics in terms of cycles. We derive analytical expressions for the efficiency measure by treating the network not only deterministically but also stochastically. The latter accounts for any significant amount of noise that can be present in biological systems and hence reveals its impact on efficiency. Numerical verification of the results is also performed. It is found that the deterministic equation overestimates the efficiency, the more so for very small system sizes. Roles of various kinetics parameters and system sizes on the efficiency are thoroughly explored and compared with the standard definition k2/KM. Study of substrate fluctuation also indicates an interesting efficiency-accuracy balance. PMID:26696076
Enzyme efficiency: An open reaction system perspective
NASA Astrophysics Data System (ADS)
Banerjee, Kinshuk; Bhattacharyya, Kamal
2015-12-01
A measure of enzyme efficiency is proposed for an open reaction network that, in suitable form, applies to closed systems as well. The idea originates from the description of classical enzyme kinetics in terms of cycles. We derive analytical expressions for the efficiency measure by treating the network not only deterministically but also stochastically. The latter accounts for any significant amount of noise that can be present in biological systems and hence reveals its impact on efficiency. Numerical verification of the results is also performed. It is found that the deterministic equation overestimates the efficiency, the more so for very small system sizes. Roles of various kinetics parameters and system sizes on the efficiency are thoroughly explored and compared with the standard definition k2/KM. Study of substrate fluctuation also indicates an interesting efficiency-accuracy balance.
Control of quantum correlations in solid state systems
NASA Astrophysics Data System (ADS)
Berrada, K.
2015-11-01
The quantum correlations between two independent qubits immersed in an anisotropic and isotropic photonic band-gab (PBG) crystal have been studied without Born or Markovian approximation. We show that the amount of the entanglement and quantum discord between the qubits in the photonic crystal is greatly different from that of qubits in vacuum or that subjected to the usual non-Markovian reservoir. The results also show that, for PBG materials as environment, high values of quantum correlation trapping can be achieved and thus prevention of correlation sudden drop occurs, which seriously enhances the coherence and increase the amount of the correlations. Moreover, we show that the quantum correlations in the isotropic PBG are more easily preserved than that in the anisotropic PBG under the same condition. These features make the quantum systems in PBG materials as a good candidate for implementation of different schemes of quantum optics and information with high performance.
Optimal Correlations in Many-Body Quantum Systems
NASA Astrophysics Data System (ADS)
Amico, L.; Rossini, D.; Hamma, A.; Korepin, V. E.
2012-06-01
Information and correlations in a quantum system are closely related through the process of measurement. We explore such relation in a many-body quantum setting, effectively bridging between quantum metrology and condensed matter physics. To this aim we adopt the information-theory view of correlations and study the amount of correlations after certain classes of positive-operator-valued measurements are locally performed. As many-body systems, we consider a one-dimensional array of interacting two-level systems (a spin chain) at zero temperature, where quantum effects are most pronounced. We demonstrate how the optimal strategy to extract the correlations depends on the quantum phase through a subtle interplay between local interactions and coherence.
A quantum many-body spin system in an optical lattice clock.
Martin, M J; Bishof, M; Swallows, M D; Zhang, X; Benko, C; von-Stecher, J; Gorshkov, A V; Rey, A M; Ye, Jun
2013-08-01
Strongly interacting quantum many-body systems arise in many areas of physics, but their complexity generally precludes exact solutions to their dynamics. We explored a strongly interacting two-level system formed by the clock states in (87)Sr as a laboratory for the study of quantum many-body effects. Our collective spin measurements reveal signatures of the development of many-body correlations during the dynamical evolution. We derived a many-body Hamiltonian that describes the experimental observation of atomic spin coherence decay, density-dependent frequency shifts, severely distorted lineshapes, and correlated spin noise. These investigations open the door to further explorations of quantum many-body effects and entanglement through use of highly coherent and precisely controlled optical lattice clocks. PMID:23929976
21 CFR 11.30 - Controls for open systems.
Code of Federal Regulations, 2013 CFR
2013-04-01
... 21 Food and Drugs 1 2013-04-01 2013-04-01 false Controls for open systems. 11.30 Section 11.30 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES GENERAL ELECTRONIC RECORDS; ELECTRONIC SIGNATURES Electronic Records § 11.30 Controls for open systems. Persons who use open systems to create, modify, maintain,...
21 CFR 11.30 - Controls for open systems.
Code of Federal Regulations, 2012 CFR
2012-04-01
... 21 Food and Drugs 1 2012-04-01 2012-04-01 false Controls for open systems. 11.30 Section 11.30 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES GENERAL ELECTRONIC RECORDS; ELECTRONIC SIGNATURES Electronic Records § 11.30 Controls for open systems. Persons who use open systems to create, modify, maintain,...
Josephson inplane and tunneling currents in bilayer quantum Hall system
Ezawa, Z. F.; Tsitsishvili, G.; Sawada, A.
2013-12-04
A Bose-Einstein condensation is formed by composite bosons in the quantum Hall state. A composite boson carries the fundamental charge (–e). We investigate Josephson tunneling of such charges in the bilayer quantum Hall system at the total filling ? = 1. We show the existence of the critical current for the tunneling current to be coherent and dissipationless in tunneling experiments with various geometries.
Quantum-Classical Connection for Hydrogen Atom-Like Systems
ERIC Educational Resources Information Center
Syam, Debapriyo; Roy, Arup
2011-01-01
The Bohr-Sommerfeld quantum theory specifies the rules of quantization for circular and elliptical orbits for a one-electron hydrogen atom-like system. This article illustrates how a formula connecting the principal quantum number "n" and the length of the major axis of an elliptical orbit may be arrived at starting from the quantumâ€¦
Scaling law and stability for a noisy quantum system
NASA Astrophysics Data System (ADS)
Sadgrove, Mark; Wimberger, Sandro; Parkins, Scott; Leonhardt, Rainer
2008-08-01
We show that a scaling law exists for the near-resonant dynamics of cold kicked atoms in the presence of a randomly fluctuating pulse amplitude. Analysis of a quasiclassical phase-space representation of the quantum system with noise allows a new scaling law to be deduced. The scaling law and associated stability are confirmed by comparison with quantum simulations and experimental data.
A quantum-like description of the planetary systems
NASA Astrophysics Data System (ADS)
Scardigli, Fabio
2007-05-01
The Titius-Bode law for planetary distances is reviewed. A model describing the basic features of this law in the "quantum-like" language of a wave equation is proposed. Some considerations about the 't Hooft idea on the quantum behaviour of deterministic systems with dissipation are discussed.
A Quantum-Like Description of the Planetary Systems
NASA Astrophysics Data System (ADS)
Scardigli, Fabio
2007-08-01
The Titius Bode law for planetary distances is reviewed. A model describing the basic features of this rule in the “quantum-like” language of a wave equation is proposed. Some considerations about the ’t Hooft idea on the quantum behavior of deterministic systems with dissipation are discussed.
Security proof for quantum key distribution using qudit systems
Sheridan, Lana; Scarani, Valerio
2010-09-15
We provide security bounds against coherent attacks for two families of quantum key distribution protocols that use d-dimensional quantum systems. In the asymptotic regime, both the secret key rate for fixed noise and the robustness to noise increase with d. The finite key corrections are found to be almost insensitive to d < or approx. 20.
High open circuit voltages of solar cells based on quantum dot and dye hybrid-sensitization
Zhao, Yujie; Zhao, Wanyu; Chen, Jingkuo; Li, Huayang; Fu, Wuyou E-mail: fuwy56@163.com; Sun, Guang; Cao, Jianliang; Zhang, Zhanying; Bala, Hari E-mail: fuwy56@163.com; College of Chemistry and Chemical Engineering, Inner Mongolia University for the Nationalities, Tongliao 028043
2014-01-06
A type of solar cell based on quantum dot (QD) and dye hybrid-sensitized mesoporous TiO{sub 2} film electrode was designed and reported. The electrode was consisted of a TiO{sub 2} nanoparticle (NP) thin film layer sensitized with CdS quantum dot (QD) and an amorphous TiO{sub 2} coated TiO{sub 2} NP thin film layer that sensitized with C106 dye. The amorphous TiO{sub 2} layer was obtained by TiCl{sub 4} post-treatment to improve the properties of solar cells. Research showed that the solar cells fabricated with as-prepared hybrid-sensitized electrode exhibited excellent photovoltaic performances and a fairly high open circuit voltage of 796â€‰mV was achieved.
CuInSe2 Quantum Dot Solar Cells with High Open-Circuit Voltage.
Panthani, Matthew G; Stolle, C Jackson; Reid, Dariya K; Rhee, Dong Joon; Harvey, Taylor B; Akhavan, Vahid A; Yu, Yixuan; Korgel, Brian A
2013-06-20
CuInSe2 (CISe) quantum dots (QDs) were synthesized with tunable size from less than 2 to 7 nm diameter. Nanocrystals were made using a secondary phosphine selenide as the Se source, which, compared to tertiary phosphine selenide precursors, was found to provide higher product yields and smaller nanocrystals that elicit quantum confinement with a size-dependent optical gap. Photovoltaic devices fabricated from spray-cast CISe QD films exhibited large, size-dependent, open-circuit voltages, up to 849 mV for absorber films with a 1.46 eV optical gap, suggesting that midgap trapping does not dominate the performance of these CISe QD solar cells. PMID:26283248
Certifying single-system steering for quantum-information processing
NASA Astrophysics Data System (ADS)
Li, Che-Ming; Chen, Yueh-Nan; Lambert, Neill; Chiu, Ching-Yi; Nori, Franco
2015-12-01
Einstein-Podolsky-Rosen (EPR) steering describes how different ensembles of quantum states can be remotely prepared by measuring one particle of an entangled pair. Here, we investigate quantum steering for single quantum d -dimensional systems (qudits) and devise efficient conditions to certify the steerability therein, which we find are applicable both to single-system steering and EPR steering. In the single-system case our steering conditions enable the unambiguous ruling out of generic classical means of mimicking steering. Ruling out "false-steering" scenarios has implications for securing channels against both cloning-based individual attack and coherent attacks when implementing quantum key distribution using qudits. We also show that these steering conditions also have applications in quantum computation, in that they can serve as an efficient criterion for the evaluation of quantum logic gates of arbitrary size. Finally, we describe how the nonlocal EPR variant of these conditions also function as tools for identifying faithful one-way quantum computation, secure entanglement-based quantum communication, and genuine multipartite EPR steering.
The Dalton quantum chemistry program system.
Aidas, Kestutis; Angeli, Celestino; Bak, Keld L; Bakken, Vebjørn; Bast, Radovan; Boman, Linus; Christiansen, Ove; Cimiraglia, Renzo; Coriani, Sonia; Dahle, Pål; Dalskov, Erik K; Ekström, Ulf; Enevoldsen, Thomas; Eriksen, Janus J; Ettenhuber, Patrick; Fernández, Berta; Ferrighi, Lara; Fliegl, Heike; Frediani, Luca; Hald, Kasper; Halkier, Asger; Hättig, Christof; Heiberg, Hanne; Helgaker, Trygve; Hennum, Alf Christian; Hettema, Hinne; Hjertenæs, Eirik; Høst, Stinne; Høyvik, Ida-Marie; Iozzi, Maria Francesca; Jansík, Branislav; Jensen, Hans Jørgen Aa; Jonsson, Dan; Jørgensen, Poul; Kauczor, Joanna; Kirpekar, Sheela; Kjærgaard, Thomas; Klopper, Wim; Knecht, Stefan; Kobayashi, Rika; Koch, Henrik; Kongsted, Jacob; Krapp, Andreas; Kristensen, Kasper; Ligabue, Andrea; Lutnæs, Ola B; Melo, Juan I; Mikkelsen, Kurt V; Myhre, Rolf H; Neiss, Christian; Nielsen, Christian B; Norman, Patrick; Olsen, Jeppe; Olsen, Jógvan Magnus H; Osted, Anders; Packer, Martin J; Pawlowski, Filip; Pedersen, Thomas B; Provasi, Patricio F; Reine, Simen; Rinkevicius, Zilvinas; Ruden, Torgeir A; Ruud, Kenneth; Rybkin, Vladimir V; Sa?ek, Pawel; Samson, Claire C M; de Merás, Alfredo Sánchez; Saue, Trond; Sauer, Stephan P A; Schimmelpfennig, Bernd; Sneskov, Kristian; Steindal, Arnfinn H; Sylvester-Hvid, Kristian O; Taylor, Peter R; Teale, Andrew M; Tellgren, Erik I; Tew, David P; Thorvaldsen, Andreas J; Thøgersen, Lea; Vahtras, Olav; Watson, Mark A; Wilson, David J D; Ziolkowski, Marcin; Agren, Hans
2014-05-01
Dalton is a powerful general-purpose program system for the study of molecular electronic structure at the Hartree-Fock, Kohn-Sham, multiconfigurational self-consistent-field, Møller-Plesset, configuration-interaction, and coupled-cluster levels of theory. Apart from the total energy, a wide variety of molecular properties may be calculated using these electronic-structure models. Molecular gradients and Hessians are available for geometry optimizations, molecular dynamics, and vibrational studies, whereas magnetic resonance and optical activity can be studied in a gauge-origin-invariant manner. Frequency-dependent molecular properties can be calculated using linear, quadratic, and cubic response theory. A large number of singlet and triplet perturbation operators are available for the study of one-, two-, and three-photon processes. Environmental effects may be included using various dielectric-medium and quantum-mechanics/molecular-mechanics models. Large molecules may be studied using linear-scaling and massively parallel algorithms. Dalton is distributed at no cost from http://www.daltonprogram.org for a number of UNIX platforms. PMID:25309629
The Dalton quantum chemistry program system
Aidas, Kestutis; Angeli, Celestino; Bak, Keld L; Bakken, VebjÃ¸rn; Bast, Radovan; Boman, Linus; Christiansen, Ove; Cimiraglia, Renzo; Coriani, Sonia; Dahle, PÃ¥l; Dalskov, Erik K; EkstrÃ¶m, Ulf; Enevoldsen, Thomas; Eriksen, Janus J; Ettenhuber, Patrick; FernÃ¡ndez, Berta; Ferrighi, Lara; Fliegl, Heike; Frediani, Luca; Hald, Kasper; Halkier, Asger; HÃ¤ttig, Christof; Heiberg, Hanne; Helgaker, Trygve; Hennum, Alf Christian; Hettema, Hinne; HjertenÃ¦s, Eirik; HÃ¸st, Stinne; HÃ¸yvik, Ida-Marie; Iozzi, Maria Francesca; JansÃk, Branislav; Jensen, Hans JÃ¸rgen Aa; Jonsson, Dan; JÃ¸rgensen, Poul; Kauczor, Joanna; Kirpekar, Sheela; KjÃ¦rgaard, Thomas; Klopper, Wim; Knecht, Stefan; Kobayashi, Rika; Koch, Henrik; Kongsted, Jacob; Krapp, Andreas; Kristensen, Kasper; Ligabue, Andrea; LutnÃ¦s, Ola B; Melo, Juan I; Mikkelsen, Kurt V; Myhre, Rolf H; Neiss, Christian; Nielsen, Christian B; Norman, Patrick; Olsen, Jeppe; Olsen, JÃ³gvan Magnus H; Osted, Anders; Packer, Martin J; Pawlowski, Filip; Pedersen, Thomas B; Provasi, Patricio F; Reine, Simen; Rinkevicius, Zilvinas; Ruden, Torgeir A; Ruud, Kenneth; Rybkin, Vladimir V; SaÅ‚ek, Pawel; Samson, Claire C M; de MerÃ¡s, Alfredo SÃ¡nchez; Saue, Trond; Sauer, Stephan P A; Schimmelpfennig, Bernd; Sneskov, Kristian; Steindal, Arnfinn H; Sylvester-Hvid, Kristian O; Taylor, Peter R; Teale, Andrew M; Tellgren, Erik I; Tew, David P; Thorvaldsen, Andreas J; ThÃ¸gersen, Lea; Vahtras, Olav; Watson, Mark A; Wilson, David J D; Ziolkowski, Marcin; Ã…gren, Hans
2014-01-01
Dalton is a powerful general-purpose program system for the study of molecular electronic structure at the Hartreeâ€“Fock, Kohnâ€“Sham, multiconfigurational self-consistent-field, MÃ¸llerâ€“Plesset, configuration-interaction, and coupled-cluster levels of theory. Apart from the total energy, a wide variety of molecular properties may be calculated using these electronic-structure models. Molecular gradients and Hessians are available for geometry optimizations, molecular dynamics, and vibrational studies, whereas magnetic resonance and optical activity can be studied in a gauge-origin-invariant manner. Frequency-dependent molecular properties can be calculated using linear, quadratic, and cubic response theory. A large number of singlet and triplet perturbation operators are available for the study of one-, two-, and three-photon processes. Environmental effects may be included using various dielectric-medium and quantum-mechanics/molecular-mechanics models. Large molecules may be studied using linear-scaling and massively parallel algorithms. Dalton is distributed at no cost from http://www.daltonprogram.org for a number of UNIX platforms. PMID:25309629
Correlation after reflection in a quantum system
NASA Astrophysics Data System (ADS)
Browne, Ryan S.
Reflection of a microscopic non-zero rest mass particle from a macroscopic mirror generates two-particle interference from the incident and reflected particle substates and the associated mirror substates. This amplifies effects such as fringe spacing since they are essentially determined not by the mass of the macroscopic mirror but rather by the much smaller mass of the microscopic particle. Coherence can be transferred during reflection from the initial particle substate to the mirror substate. Interference of multiple such two-particle states is discussed. These effects could lead to extending measurements of the quantum-classical boundary to larger masses. The possibility of non-simultaneous measurement of the positions of the particle and the mirror is also discussed. The joint probability density, which is a function both of the different positions and different times at which the particle and mirror are measured, is derived assuming that no interaction occurs between the measurement times. An analog of the Doppler shift for this correlated system is discussed along with interference of multiple such two-particle states.
Quantum Chaos and Entanglement in Atomic Spin Systems
NASA Astrophysics Data System (ADS)
Jessen, Poul
2010-03-01
Chaotic behavior is widespread in nature and plays a role in many scientific disciplines. In classical physics, chaos is characterized by hypersensitivity of the evolution to initial conditions (the ``butterfly effect''). Remarkably, this definition is fundamentally at odds with quantum mechanics, in part due to the uncertainty principle and in part due to the Schrödinger equation which preserves the overlap between quantum states. This disconnect has motivated a longstanding search for quantum signatures of chaos, including dynamical signatures such as the generation of entropy and entanglement. I will discuss an experiment [1] in which we realize a common paradigm for quantum chaos - the quantum kicked top - and observe its behavior directly in quantum phase space. Our system is based on the combined electronic and nuclear spin of a single Cs atom and is therefore deep in the quantum regime. We nevertheless find good correspondence between the quantum dynamics and classical phase space structures, and obtain the first experimental evidence for dynamical entanglement as a signature of chaos.[4pt] [1] ``Quantum signatures of chaos in a kicked top'', S. Chaudhury et al., Nature Vol. 461, 768 (2009).
Luminescence of a semiconductor quantum dot system
NASA Astrophysics Data System (ADS)
Baer, N.; Gies, C.; Wiersig, J.; Jahnke, F.
2006-04-01
A microscopic theory is used to study photoluminescence of semiconductor quantum dots under the influence of Coulomb and carrier-photon correlation effects beyond the Hartree-Fock level. We investigate the emission spectrum and the decay properties of the time-resolved luminescence from initially excited quantum dots. The influence of the correlations is included within a cluster expansion scheme up to the singlet-doublet level.
Why irreversibility? The formulation of classical and quantum mechanics for nonintegrable systems
Prigogine, I.
1995-01-05
Nonintegrable Poincare systems with a continuous spectrum lead to the appearance of diffusive terms in the frame of classical or quantum dynamics. These terms break time symmetry. They lead, therefore, to limitations to classical trajectory theory and of wave-function formalism. These diffusive terms correspond to well-defined classes of dynamical processes. The diffusive effects are amplified in situations corresponding to persistent interactions. As a result, we have to include, already, in the fundamental dynamical description the two basic aspects, probability and irreversibility, which are so conspicuous on the macroscopic level. We have to formulate both classical and quantum mechanics on the Liouville level of probability distributions. For integrable systems, we recover the usual formulation of classical or quantum mechanics. Instead of being primitive concepts, which cannot be further analyzed, trajectories and wave functions appear as special solutions of the Liouville-von Neumann equations. This extension of classical and quantum dynamics permits us to unify the two concepts of nature that we inherited from the nineteenth century, based, on the one hand, on dynamical time-reversible laws and, on the other, on an evolutionary view associated to entropy. It leads also to a unified formulation of quantum theory, avoiding the conventional dual structure based on Schroedinger`s equation, on the one hand, and on the {open_quotes}collapse{close_quotes} of the wave function, on the other. A dynamical interpretation is given to processes such as decoherence or approach to equilibrium without any appeal to extra dynamic considerations. There is a striking parallelism between classical and quantum theory. For large Poincare systems (LPS), we have, in general, both a {open_quotes}collapse{close_quotes} of trajectories and of wave functions. In both cases, we need a generalized formulation of dynamics in terms of probability distributions or density matrices.
Mascarenhas, E.; Marques, B.; Santos, M. Franca; Cavalcanti, D.; Cunha, M. Terra
2010-03-15
We study how to protect quantum information in quantum systems subjected to local dissipation. We show that combining the use of three-level systems, environment monitoring, and local feedback can fully and deterministically protect any available quantum information, including entanglement initially shared by different parties. These results can represent a gain in resources and/or distances in quantum communication protocols such as quantum repeaters and teleportation as well as time for quantum memories. Finally, we show that monitoring local environments physically implements the optimum singlet conversion protocol, which is essential for classical entanglement percolation.
Closed-loop and robust control of quantum systems.
Chen, Chunlin; Wang, Lin-Cheng; Wang, Yuanlong
2013-01-01
For most practical quantum control systems, it is important and difficult to attain robustness and reliability due to unavoidable uncertainties in the system dynamics or models. Three kinds of typical approaches (e.g., closed-loop learning control, feedback control, and robust control) have been proved to be effective to solve these problems. This work presents a self-contained survey on the closed-loop and robust control of quantum systems, as well as a brief introduction to a selection of basic theories and methods in this research area, to provide interested readers with a general idea for further studies. In the area of closed-loop learning control of quantum systems, we survey and introduce such learning control methods as gradient-based methods, genetic algorithms (GA), and reinforcement learning (RL) methods from a unified point of view of exploring the quantum control landscapes. For the feedback control approach, the paper surveys three control strategies including Lyapunov control, measurement-based control, and coherent-feedback control. Then such topics in the field of quantum robust control as H(?) control, sliding mode control, quantum risk-sensitive control, and quantum ensemble control are reviewed. The paper concludes with a perspective of future research directions that are likely to attract more attention. PMID:23997680
Information Theory Density Matrix for a Simple Quantum System.
ERIC Educational Resources Information Center
Titus, William J.
1979-01-01
Derives the density matrix that best describes, according to information theory, a one-dimensional single particle quantum system when the only information available is the values for the linear and quadratic position-momentum moments. (Author/GA)
BEC-Cryostat Interface: A Novel Platform for Hybrid Quantum Systems
NASA Astrophysics Data System (ADS)
Date, Aditya; Patil, Yogesh Sharad; Schwab, Keith; Vengalattore, Mukund
2015-05-01
We present our experimental progress towards the implementation of a unique BEC-cryostat interface. This apparatus allows for the control and manipulation of ultracold atoms in close proximity to cryogenic surfaces. Such a system enables us to realize a hybrid quantum system consisting of a BEC strongly coupled magnetically to an ultra-high Q mechanical resonator, thus enabling precise atomic sensing of mechanical motion. Furthermore, the unprecedented sensitivities afforded by our atomic system open avenues to surface studies of correlated electronic systems at cryogenic temperatures. This work is supported by the DARPA QuASAR program through a grant from the ARO.
Quantum teleportation of composite systems via mixed entangled states
Bandyopadhyay, Somshubhro; Sanders, Barry C.
2006-09-15
We analyze quantum teleportation for composite systems, specifically for concatenated teleporation (decomposing a large composite state into smaller states of dimension commensurate with the channel) and partial teleportation (teleporting one component of a larger quantum state). We obtain an exact expression for teleportation fidelity that depends solely on the dimension and singlet fraction for the entanglement channel and entanglement (measures by I concurrence) for the state; in fact quantum teleportation for composite systems provides an operational interpretation for I concurrence. In addition we obtain tight bounds on teleportation fidelity and prove that the average fidelity approaches the lower bound of teleportation fidelity in the high-dimension limit.
Quantum teleportation of composite systems via mixed entangled states
NASA Astrophysics Data System (ADS)
Bandyopadhyay, Somshubhro; Sanders, Barry C.
2006-09-01
We analyze quantum teleportation for composite systems, specifically for concatenated teleporation (decomposing a large composite state into smaller states of dimension commensurate with the channel) and partial teleportation (teleporting one component of a larger quantum state). We obtain an exact expression for teleportation fidelity that depends solely on the dimension and singlet fraction for the entanglement channel and entanglement (measures by I concurrence) for the state; in fact quantum teleportation for composite systems provides an operational interpretation for I concurrence. In addition we obtain tight bounds on teleportation fidelity and prove that the average fidelity approaches the lower bound of teleportation fidelity in the high-dimension limit.
Quantum speed limit in a qubit-spin-bath system
NASA Astrophysics Data System (ADS)
Hou, Lu; Shao, Bin; Wei, Yong-Bo; Zou, Jian
2015-12-01
We investigate the behavior of quantum speed limit (QSL) time for a typical non-Markovian system, a central spin coupled to a spin star configuration. We connect the QSL time with an external control and show that the effectiveness of the external magnetic field, as well as the coupling strength, is related to the fundamental bounds that affect the maximum speed at which a quantum system can evolve in its state space. We also demonstrate that a spin bath with larger size may shorten the QSL time, while the upper state population plays an important role for the acceleration of quantum evolution in the memory surrounding.
Quantum Brayton cycle with coupled systems as working substance
NASA Astrophysics Data System (ADS)
Huang, X. L.; Wang, L. C.; Yi, X. X.
2013-01-01
We explore the quantum version of the Brayton cycle with a composite system as the working substance. The actual Brayton cycle consists of two adiabatic and two isobaric processes. Two pressures can be defined in our isobaric process; one corresponds to the external magnetic field (characterized by Fx) exerted on the system, while the other corresponds to the coupling constant between the subsystems (characterized by Fy). As a consequence, we can define two types of quantum Brayton cycle for the composite system. We find that the subsystem experiences a quantum Brayton cycle in one quantum Brayton cycle (characterized by Fx), whereas the subsystem's cycle is quantum Otto cycle in another Brayton cycle (characterized by Fy). The efficiency for the composite system equals to that for the subsystem in both cases, but the work done by the total system is usually larger than the sum of the work done by the two subsystems. The other interesting finding is that for the cycle characterized by Fy, the subsystem can be a refrigerator, while the total system is a heat engine. The result in this paper can be generalized to a quantum Brayton cycle with a general coupled system as the working substance.
Quantum Brayton cycle with coupled systems as working substance.
Huang, X L; Wang, L C; Yi, X X
2013-01-01
We explore the quantum version of the Brayton cycle with a composite system as the working substance. The actual Brayton cycle consists of two adiabatic and two isobaric processes. Two pressures can be defined in our isobaric process; one corresponds to the external magnetic field (characterized by F(x)) exerted on the system, while the other corresponds to the coupling constant between the subsystems (characterized by F(y)). As a consequence, we can define two types of quantum Brayton cycle for the composite system. We find that the subsystem experiences a quantum Brayton cycle in one quantum Brayton cycle (characterized by F(x)), whereas the subsystem's cycle is quantum Otto cycle in another Brayton cycle (characterized by F(y)). The efficiency for the composite system equals to that for the subsystem in both cases, but the work done by the total system is usually larger than the sum of the work done by the two subsystems. The other interesting finding is that for the cycle characterized by F(y), the subsystem can be a refrigerator, while the total system is a heat engine. The result in this paper can be generalized to a quantum Brayton cycle with a general coupled system as the working substance. PMID:23410319
Using Local Perturbations To Manipulate and Control Pointer States in Quantum Dot Systems
NASA Astrophysics Data System (ADS)
Akis, Richard; Speyer, Gil; Ferry, David; Brunner, Roland
2012-02-01
Recently, scanning gate microscopy (SGM) was used to image scarred wave functions in an open InAs quantum dot[1]. The SGM tip provides a local potential perturbation and imaging is performed by measuring changes in conductance. Scarred wave functions, long associated with quantum chaos, have been shown in open dots to correspond to pointer states[2], eigenstates that survive the decoherence process that occurs via coupling to the environment. Pointer states modulate the conductance, yielding periodic fluctuations and the scars, normally thought unstable, are stabilized by quantum Darwinism [3]. We shall show that, beyond probing, pointer states can be manipulated by local perturbations. Particularly interesting effects occur in coupled quantum dot arrays, where a pointer state localized in one dot can be shifted over into another with a perturbation in a completely different part of the system. These nonlocal effects may perhaps be exploited to give such systems an exotic functionality. [1] A. M. Burke, R. Akis, T. E. Day, Gil Speyer, D. K. Ferry, and B. R. Bennett, Phys. Rev. Lett. 104, 176801 (2010). [2] D. K. Ferry, R. Akis, and J. P. Bird, Phys. Rev. Lett. 104, 176801 (2004). [3] R. Brunner, R. Akis,D. K. Ferry, F. Kuchar,and R. Meisels, Phys. Rev. Lett. 101, 024102 (2008).
Plausibility of quantum coherent states in biological systems
NASA Astrophysics Data System (ADS)
Salari, V.; Tuszynski, J.; Rahnama, M.; Bernroider, G.
2011-07-01
In this paper we briefly discuss the necessity of using quantum mechanics as a fundamental theory applicable to some key functional aspects of biological systems. This is especially relevant to three important parts of a neuron in the human brain, namely the cell membrane, microtubules (MT) and ion channels. We argue that the recently published papers criticizing the use of quantum theory in these systems are not convincing.
Invisibility of quantum systems to tunneling of matter waves
Cordero, Sergio; Garcia-Calderon, Gaston
2009-05-15
We show that an appropriate choice of the potential parameters in one-dimensional quantum systems allows for unity transmission of the tunneling particle at all incident tunneling energies, except at controllable exceedingly small incident energies. The corresponding dwell time and the transmission amplitude are indistinguishable from those of a free particle in the unity-transmission regime. This implies the possibility of designing quantum systems that are invisible to tunneling by a passing wave packet.
EDITORIAL: How to control decoherence and entanglement in quantum complex systems?
NASA Astrophysics Data System (ADS)
Akulin, V. M.; Kurizki, G.; Lidar, D. A.
2007-05-01
Theory and experiment have not fully resolved the apparent dichotomy, which has agonized physics for the past eighty years: on the one hand, the description of microsystems by quantum mechanics and, on the other, the description of macrosystems by classical dynamics or statistical mechanics. Derivations of the time-irreversible Liouville equation for an open quantum system, based on projecting out its environment, have narrowed the gap between the quantum and classical descriptions. Yet our `classical' intuition continues to be confronted by quantum-mechanical results like the Einstein--Podolsky--Rosen paradox that challenges the classical notion of locality, or the quantum Zeno effect which suggests that the isolation of a system is not the only way to preserve its quantum state. There are two key concepts in any discussion of such issues. The first, which is responsible for the most salient nonclassical properties, is entanglement, that is partial or complete correlation or, more generally, inseparability of the elements comprising a quantum ensemble. Even after their interaction has ceased, this inseparability, originating from their past interaction, can affect the state of one element when another element is subject to a nonunitary action, such as its measurement, tracing- out, or thermalization. The second key concept is decoherence of open quantum systems, which is the consequence of their entanglement with their environment, a `meter' or a thermal `reservoir', followed by the tracing-out of the latter. Despite new insights into entanglement and decoherence, there are still no complete, unequivocal answers to the fundamental questions of the transition from quantal to classical behaviour: how do irreversibility and classicality emerge from unitarity as systems and their environments become increasingly complex? At what stage does system--meter entanglement give rise to a classical readout of the meter? Is there an upper limit on the size or complexity of systems displaying entanglement? Major developments have opened new vistas into controlled entanglement, which is the resource of quantum information processing. However, these developments have mainly focused on ensembles of simple two- and three-level systems that are thoroughly isolated from their environments. Treatments of coherence in quantum computing have mostly assumed that only a single or a few the elements of the quantum ensemble may simultaneously undergo an uncontrolled intervention---a quantum error. Decoherence-control protocols for more general types of errors are still incomplete. In order to resolve the outstanding issues of the quantum--classical transition, and study the control of entanglement and decoherence without the foregoing restrictions, we must venture into the domain of Quantum Complex Systems (QUACS), either consisting of a large number of inseparable elements or having many coupled degrees of freedom. Our conviction is that fundamental understanding and manipulation of entanglement within QUACS or their entanglement with the environment or a meter, call for the creation of a new conceptual framework or paradigm, that would encompass phenomena common to cold atoms in laser fields, large molecules, Josephson junctions, quantum gases and solids, with the view of employing these systems for quantum information processing and computing. Progress within this paradigm should allow us to answer the questions: does entanglement play an essential role in the evolution of large collections of complex systems? What are the size and complexity limits of systems and ensembles still controllable by an external intervention? What are the most appropriate decoherence protection schemes and control algorithms? This special issue addresses the challenge of understanding in depth and manipulating the basic quantum properties of optical, atomic, molecular and condensed-matter QUACS, and large ensembles thereof. In view of the interdisciplinary character of this issue, we find it expedient to look at the presented articles not only according to the physical objects they describe, but also from a unifying standpoint. Several unifying themes may be discerned: memory effects in dephasing and relaxation; protection of quantum information by its distribution throughout the ensemble; control of decoherence and entanglement by time-dependent interventions or measurements; manifestations of entanglement in scattering off statistical ensembles; measurment-induced dynamics. The concerted discussion of the topics outlined above should help us advance the new paradigm that addresses our abilities to diagnose and manipulate the entangled states of complex quantum objects and their robustness against decoherence. These abilities are required for quantum information (QI) applications in matter--wave interferometry in molecular, semiconducting or superconducting systems. On the fundamental level, this book may help establish the notion of dynamical information exchange between quantum systems and chart in detail the route from unitarity to classicality. Further developments within the outlined paradigm should yield novel, advantageous QI processing schemes and high-sensitivity interferometers, owing to decoherence suppression and effective control of many degrees of freedom. In the long run, these strategies may prove to be the first step towards the (hitherto unattempted) use of entanglement in nanotechnology, metrology and chemistry, with potentially remarkable novel applications.
Comment on {open_quotes}Local responsivity in quantum well photodetectors{close_quotes}
Ryzhii, M.; Khmyrova, I.
2001-06-01
The response of multiple quantum well (QW) infrared photodetectors (QW) to the photoexcitation of one QW selected from many identical QWs was recently modeled [M. Ershov, J. Appl. Phys. 86, 7059 (1999)]. We point out here that the presented analysis based on the use of drift-diffusion model for a system with a few electrons is incorrect. {copyright} 2001 American Institute of Physics.
Contexts, Systems and Modalities: A New Ontology for Quantum Mechanics
NASA Astrophysics Data System (ADS)
AuffÃ¨ves, Alexia; Grangier, Philippe
2016-02-01
In this article we present a possible way to make usual quantum mechanics fully compatible with physical realism, defined as the statement that the goal of physics is to study entities of the natural world, existing independently from any particular observer's perception, and obeying universal and intelligible rules. Rather than elaborating on the quantum formalism itself, we propose a new quantum ontology, where physical properties are attributed jointly to the system, and to the context in which it is embedded. In combination with a quantization principle, this non-classical definition of physical reality sheds new light on counter-intuitive features of quantum mechanics such as the origin of probabilities, non-locality, and the quantum-classical boundary.
Contexts, Systems and Modalities: A New Ontology for Quantum Mechanics
NASA Astrophysics Data System (ADS)
Auffèves, Alexia; Grangier, Philippe
2015-09-01
In this article we present a possible way to make usual quantum mechanics fully compatible with physical realism, defined as the statement that the goal of physics is to study entities of the natural world, existing independently from any particular observer's perception, and obeying universal and intelligible rules. Rather than elaborating on the quantum formalism itself, we propose a new quantum ontology, where physical properties are attributed jointly to the system, and to the context in which it is embedded. In combination with a quantization principle, this non-classical definition of physical reality sheds new light on counter-intuitive features of quantum mechanics such as the origin of probabilities, non-locality, and the quantum-classical boundary.
NASA Astrophysics Data System (ADS)
Nurdin, H. I.
2014-07-01
In this paper, we treat the quantum filtering problem for multiple input multiple output (MIMO) Markovian open quantum systems coupled to multiple boson fields in an arbitrary zero-mean jointly Gaussian state, using the reference probability approach formulated by Bouten and van Handel as a quantum version of a well-known method of the same name from classical nonlinear filtering theory, and exploiting the generalized Araki-Woods representation of Gough. This includes Gaussian field states such as vacuum, squeezed vacuum, thermal, and squeezed thermal states as special cases. The contribution is a derivation of the general quantum filtering equation (or stochastic master equation as they are known in the quantum optics community) in the full MIMO setup for any zero-mean jointly Gaussian input field states, up to some mild rank assumptions on certain matrices relating to the measurement vector.
Tampering detection system using quantum-mechanical systems
Humble, Travis S.; Bennink, Ryan S.; Grice, Warren P.
2011-12-13
The use of quantum-mechanically entangled photons for monitoring the integrity of a physical border or a communication link is described. The no-cloning principle of quantum information science is used as protection against an intruder's ability to spoof a sensor receiver using a `classical` intercept-resend attack. Correlated measurement outcomes from polarization-entangled photons are used to protect against quantum intercept-resend attacks, i.e., attacks using quantum teleportation.
Planar quantum squeezing in spin-1/2 systems
NASA Astrophysics Data System (ADS)
Puentes, Graciana
2015-12-01
Planar quantum squeezed (PQS) states, i.e. quantum states which are squeezed in two orthogonal spin components on a plane, have recently attracted attention due to their applications in atomic interferometry and quantum information [1, 2]. In this paper we present an application of the framework described by Puentes et al [3] for planar quantum squeezing via quantum nondemolition (QND) measurement, for the particular case of spin-1/2 systems and nonzero covariance between orthogonal spin components. Our regime, consisting of spin-1/2 entangled planar-squeezed (EPQS) states, is of interest as it can present higher precision for quantum parameter estimation and quantum magnetometry at finite intervals. We show that entangled planar-squeezed states (EPQS) can be used to reconstruct a specific quantum parameter, such as a phase or a magnetic field, within a finite interval with higher precision than PQS states, and without iterative procedures. EPQS is of interest in cases where limited prior knowledge about the specific subinterval location for a phase is available, but it does not require knowledge of the exact phase a priori, as in the case of squeezing on a single spin component.
Mixed quantum-classical versus full quantum dynamics: Coupled quasiparticle-oscillator system
NASA Astrophysics Data System (ADS)
Schanz, Holger; Esser, Bernd
1997-05-01
The relation between the dynamical properties of a coupled quasiparticle-oscillator system in the mixed quantum-classical and fully quantized descriptions is investigated. The system is considered as a model for applying a stepwise quantization. Features of the nonlinear dynamics in the mixed description such as the presence of a separatrix structure or regular and chaotic motion are shown to be reflected in the evolu- tion of the quantum state vector of the fully quantized system. In particular, it is demonstrated how wave packets propagate along the separatrix structure of the mixed description, and that chaotic dynamics leads to a strongly entangled quantum state vector. Special emphasis is given to viewing the system from a dyn- amical Born-Oppenheimer approximation defining integrable reference oscillators, and elucidating the role of the nonadiabatic couplings which complement this approximation into a rigorous quantization scheme.
Quantum fluctuations and CMB anisotropies in one-bubble open inflation models
NASA Astrophysics Data System (ADS)
Yamamoto, Kazuhiro; Sasaki, Misao; Tanaka, Takahiro
1996-10-01
We first develop a method to calculate a complete set of mode functions that describe the quantum fluctuations generated in one-bubble open inflation models. We consider two classes of models. One is a single scalar field model proposed by Bucher, Goldhaber, and Turok and by us as an example of the open inflation scenario, and the other is a two-field model such as the ``supernatural'' inflation proposed by Linde and Mezhlumian. In both cases we assume the difference in the vacuum energy density between inside and outside the bubble is negligible. There are two kinds of mode functions. One kind has the usual continuous spectrum and the other has a discrete spectrum with characteristic wavelengths exceeding the spatial curvature scale. The latter can be further divided into two classes in terms of its origin. One is called the de Sitter supercurvature mode, which arises due to the global spacetime structure of de Sitter space, and the other is due to fluctuations of the bubble wall. We calculate the spectrum of quantum fluctuations in these models and evaluate the resulting large angular scale CMB anisotropies. We find there are ranges of model parameters that are consistent with observed CMB anisotropies.
Enhanced Open-Circuit Voltage of PbS Nanocrystal Quantum Dot Solar Cells
NASA Astrophysics Data System (ADS)
Yoon, Woojun; Boercker, Janice E.; Lumb, Matthew P.; Placencia, Diogenes; Foos, Edward E.; Tischler, Joseph G.
2013-07-01
Nanocrystal quantum dots (QD) show great promise toward improving solar cell efficiencies through the use of quantum confinement to tune absorbance across the solar spectrum and enable multi-exciton generation. Despite this remarkable potential for high photocurrent generation, the achievable open-circuit voltage (Voc) is fundamentally limited due to non-radiative recombination processes in QD solar cells. Here we report the highest open-circuit voltages to date for colloidal QD based solar cells under one sun illumination. This Voc of 692 +/- 7 mV for 1.4 eV PbS QDs is a result of improved passivation of the defective QD surface, demonstrating as a function of the QD bandgap (Eg). Comparing experimental Voc variation with the theoretical upper-limit obtained from one diode modeling of the cells with different Eg, these results clearly demonstrate that there is a tremendous opportunity for improvement of Voc to values greater than 1 V by using smaller QDs in QD solar cells.
Enhanced open-circuit voltage of PbS nanocrystal quantum dot solar cells.
Yoon, Woojun; Boercker, Janice E; Lumb, Matthew P; Placencia, Diogenes; Foos, Edward E; Tischler, Joseph G
2013-01-01
Nanocrystal quantum dots (QD) show great promise toward improving solar cell efficiencies through the use of quantum confinement to tune absorbance across the solar spectrum and enable multi-exciton generation. Despite this remarkable potential for high photocurrent generation, the achievable open-circuit voltage (Voc) is fundamentally limited due to non-radiative recombination processes in QD solar cells. Here we report the highest open-circuit voltages to date for colloidal QD based solar cells under one sun illumination. This Voc of 692 ± 7?mV for 1.4?eV PbS QDs is a result of improved passivation of the defective QD surface, demonstrating Voc(mV)=553Eg/q-59 as a function of the QD bandgap (Eg). Comparing experimental Voc variation with the theoretical upper-limit obtained from one diode modeling of the cells with different Eg, these results clearly demonstrate that there is a tremendous opportunity for improvement of Voc to values greater than 1?V by using smaller QDs in QD solar cells. PMID:23868514
Enhanced Open-Circuit Voltage of PbS Nanocrystal Quantum Dot Solar Cells
Yoon, Woojun; Boercker, Janice E.; Lumb, Matthew P.; Placencia, Diogenes; Foos, Edward E.; Tischler, Joseph G.
2013-01-01
Nanocrystal quantum dots (QD) show great promise toward improving solar cell efficiencies through the use of quantum confinement to tune absorbance across the solar spectrum and enable multi-exciton generation. Despite this remarkable potential for high photocurrent generation, the achievable open-circuit voltage (Voc) is fundamentally limited due to non-radiative recombination processes in QD solar cells. Here we report the highest open-circuit voltages to date for colloidal QD based solar cells under one sun illumination. This Voc of 692 Â± 7â€…mV for 1.4â€…eV PbS QDs is a result of improved passivation of the defective QD surface, demonstrating as a function of the QD bandgap (Eg). Comparing experimental Voc variation with the theoretical upper-limit obtained from one diode modeling of the cells with different Eg, these results clearly demonstrate that there is a tremendous opportunity for improvement of Voc to values greater than 1â€…V by using smaller QDs in QD solar cells. PMID:23868514
The ALPS project release 2.0: open source software for strongly correlated systems
NASA Astrophysics Data System (ADS)
Bauer, B.; Carr, L. D.; Evertz, H. G.; Feiguin, A.; Freire, J.; Fuchs, S.; Gamper, L.; Gukelberger, J.; Gull, E.; Guertler, S.; Hehn, A.; Igarashi, R.; Isakov, S. V.; Koop, D.; Ma, P. N.; Mates, P.; Matsuo, H.; Parcollet, O.; Paw?owski, G.; Picon, J. D.; Pollet, L.; Santos, E.; Scarola, V. W.; Schollwöck, U.; Silva, C.; Surer, B.; Todo, S.; Trebst, S.; Troyer, M.; Wall, M. L.; Werner, P.; Wessel, S.
2011-05-01
We present release 2.0 of the ALPS (Algorithms and Libraries for Physics Simulations) project, an open source software project to develop libraries and application programs for the simulation of strongly correlated quantum lattice models such as quantum magnets, lattice bosons, and strongly correlated fermion systems. The code development is centered on common XML and HDF5 data formats, libraries to simplify and speed up code development, common evaluation and plotting tools, and simulation programs. The programs enable non-experts to start carrying out serial or parallel numerical simulations by providing basic implementations of the important algorithms for quantum lattice models: classical and quantum Monte Carlo (QMC) using non-local updates, extended ensemble simulations, exact and full diagonalization (ED), the density matrix renormalization group (DMRG) both in a static version and a dynamic time-evolving block decimation (TEBD) code, and quantum Monte Carlo solvers for dynamical mean field theory (DMFT). The ALPS libraries provide a powerful framework for programmers to develop their own applications, which, for instance, greatly simplify the steps of porting a serial code onto a parallel, distributed memory machine. Major changes in release 2.0 include the use of HDF5 for binary data, evaluation tools in Python, support for the Windows operating system, the use of CMake as build system and binary installation packages for Mac OS X and Windows, and integration with the VisTrails workflow provenance tool. The software is available from our web server at http://alps.comp-phys.org/.
Nonequilibrium potential and fluctuation theorems for quantum maps.
Manzano, Gonzalo; Horowitz, Jordan M; Parrondo, Juan M R
2015-09-01
We derive a general fluctuation theorem for quantum maps. The theorem applies to a broad class of quantum dynamics, such as unitary evolution, decoherence, thermalization, and other types of evolution for quantum open systems. The theorem reproduces well-known fluctuation theorems in a single and simplified framework and extends the Hatano-Sasa theorem to quantum nonequilibrium processes. Moreover, it helps to elucidate the physical nature of the environment that induces a given dynamics in an open quantum system. PMID:26465448
Nonequilibrium potential and fluctuation theorems for quantum maps
NASA Astrophysics Data System (ADS)
Manzano, Gonzalo; Horowitz, Jordan M.; Parrondo, Juan M. R.
2015-09-01
We derive a general fluctuation theorem for quantum maps. The theorem applies to a broad class of quantum dynamics, such as unitary evolution, decoherence, thermalization, and other types of evolution for quantum open systems. The theorem reproduces well-known fluctuation theorems in a single and simplified framework and extends the Hatano-Sasa theorem to quantum nonequilibrium processes. Moreover, it helps to elucidate the physical nature of the environment that induces a given dynamics in an open quantum system.
NASA Astrophysics Data System (ADS)
Lidar, Daniel A.; Brun, Todd A.
2013-09-01
Prologue; Preface; Part I. Background: 1. Introduction to decoherence and noise in open quantum systems Daniel Lidar and Todd Brun; 2. Introduction to quantum error correction Dave Bacon; 3. Introduction to decoherence-free subspaces and noiseless subsystems Daniel Lidar; 4. Introduction to quantum dynamical decoupling Lorenza Viola; 5. Introduction to quantum fault tolerance Panos Aliferis; Part II. Generalized Approaches to Quantum Error Correction: 6. Operator quantum error correction David Kribs and David Poulin; 7. Entanglement-assisted quantum error-correcting codes Todd Brun and Min-Hsiu Hsieh; 8. Continuous-time quantum error correction Ognyan Oreshkov; Part III. Advanced Quantum Codes: 9. Quantum convolutional codes Mark Wilde; 10. Non-additive quantum codes Markus Grassl and Martin Rötteler; 11. Iterative quantum coding systems David Poulin; 12. Algebraic quantum coding theory Andreas Klappenecker; 13. Optimization-based quantum error correction Andrew Fletcher; Part IV. Advanced Dynamical Decoupling: 14. High order dynamical decoupling Zhen-Yu Wang and Ren-Bao Liu; 15. Combinatorial approaches to dynamical decoupling Martin Rötteler and Pawel Wocjan; Part V. Alternative Quantum Computation Approaches: 16. Holonomic quantum computation Paolo Zanardi; 17. Fault tolerance for holonomic quantum computation Ognyan Oreshkov, Todd Brun and Daniel Lidar; 18. Fault tolerant measurement-based quantum computing Debbie Leung; Part VI. Topological Methods: 19. Topological codes Héctor Bombín; 20. Fault tolerant topological cluster state quantum computing Austin Fowler and Kovid Goyal; Part VII. Applications and Implementations: 21. Experimental quantum error correction Dave Bacon; 22. Experimental dynamical decoupling Lorenza Viola; 23. Architectures Jacob Taylor; 24. Error correction in quantum communication Mark Wilde; Part VIII. Critical Evaluation of Fault Tolerance: 25. Hamiltonian methods in QEC and fault tolerance Eduardo Novais, Eduardo Mucciolo and Harold Baranger; 26. Critique of fault-tolerant quantum information processing Robert Alicki; References; Index.
De Roeck, W. E-mail: christian.maes@fys.kuleuven.be E-mail: marius.schutz@fys.kuleuven.be; Maes, C. E-mail: christian.maes@fys.kuleuven.be E-mail: marius.schutz@fys.kuleuven.be; SchÃ¼tz, M. E-mail: christian.maes@fys.kuleuven.be E-mail: marius.schutz@fys.kuleuven.be; NetoÄnÃ½, K. E-mail: christian.maes@fys.kuleuven.be E-mail: marius.schutz@fys.kuleuven.be
2015-02-15
We study the projection on classical spins starting from quantum equilibria. We show Gibbsianness or quasi-locality of the resulting classical spin system for a class of gapped quantum systems at low temperatures including quantum ground states. A consequence of Gibbsianness is the validity of a large deviation principle in the quantum system which is known and here recovered in regimes of high temperature or for thermal states in one dimension. On the other hand, we give an example of a quantum ground state with strong nonlocality in the classical restriction, giving rise to what we call measurement induced entanglement and still satisfying a large deviation principle.
A LONE code for the sparse control of quantum systems
NASA Astrophysics Data System (ADS)
Ciaramella, G.; BorzÃ¬, A.
2016-03-01
In many applications with quantum spin systems, control functions with a sparse and pulse-shaped structure are often required. These controls can be obtained by solving quantum optimal control problems with L1-penalized cost functionals. In this paper, the MATLAB package LONE is presented aimed to solving L1-penalized optimal control problems governed by unitary-operator quantum spin models. This package implements a new strategy that includes a globalized semi-smooth Krylov-Newton scheme and a continuation procedure. Results of numerical experiments demonstrate the ability of the LONE code in computing accurate sparse optimal control solutions.
NASA Astrophysics Data System (ADS)
Shushin, A. I.
2011-02-01
The manifestation of measurements, randomly distributed in time, on the evolution of quantum systems are analyzed in detail. The set of randomly distributed measurements (RDM) is modeled within the renewal theory, in which the distribution is characterized by the probability density function (PDF) W(t) of times t between successive events (measurements). The evolution of the quantum system affected by the RDM is shown to be described by the density matrix satisfying the stochastic Liouville equation. This equation is applied to the analysis of the RDM effect on the evolution of a two-level system for different types of RDM statistics, corresponding to different PDFs W(t). Obtained general results are illustrated as applied to the cases of the Poissonian (W(t) \\sim \\,e^{-w_r t}) and anomalous (W(t) ~ 1/t1 + Î±, Î± <= 1) RDM statistics. In particular, specific features of the quantum and inverse Zeno effects, resulting from the RDM, are thoroughly discussed.
Scalar material reference systems and loop quantum gravity
NASA Astrophysics Data System (ADS)
Giesel, K.; Thiemann, T.
2015-07-01
In the past, the possibility to employ (scalar) material reference systems in order to describe classical and quantum gravity directly in terms of gauge invariant (Dirac) observables has been emphasized frequently. This idea has been picked up more recently in loop quantum gravity with the aim to perform a reduced phase space quantization of the theory, thus possibly avoiding problems with the (Dirac) operator constraint quantization method for a constrained system. In this work, we review the models that have been studied on the classical and/or the quantum level and parametrize the space of theories considered so far. We then describe the quantum theory of a model that, to the best of our knowledge, has only been considered classically so far. This model could arguably be called the optimal one in this class of models considered as it displays the simplest possible true Hamiltonian, while at the same time reducing all constraints of general relativity.
Quantum phase transitions in Bose-Fermi systems
Petrellis, D.; Leviatan, A.; Iachello, F.
2011-04-15
Research Highlights: > We study quantum phase transitions in a system of N bosons and a single-j fermion. > Classical order parameters and correlation diagrams of quantum levels are determined. > The odd fermion strongly influences the location and nature of the phase transition. > Experimental evidence for the U(5)-SU(3) transition in odd-even nuclei is presented. - Abstract: Quantum phase transitions in a system of N bosons with angular momentum L = 0, 2 (s, d) and a single fermion with angular momentum j are investigated both classically and quantum mechanically. It is shown that the presence of the odd fermion strongly influences the location and nature of the phase transition, especially the critical value of the control parameter at which the phase transition occurs. Experimental evidence for the U(5)-SU(3) (spherical to axially-deformed) transition in odd-even nuclei is presented.
Superconducting quantum spin Hall systems with giant orbital g factors
NASA Astrophysics Data System (ADS)
Reinthaler, R. W.; Tkachov, G.; Hankiewicz, E. M.
2015-10-01
Topological aspects of superconductivity in quantum spin Hall systems (QSHSs) such as thin layers of three-dimensional topological insulators (TIs) or two-dimensional TIs are the focus of current research. Here, we describe a superconducting quantum spin Hall effect (quantum spin Hall system in proximity to an s -wave superconductor and in orbital in-plane magnetic fields), which is protected against elastic backscattering by combined time-reversal and particle-hole symmetry. This effect is characterized by spin-polarized edge states, which can be manipulated in weak magnetic fields due to a giant effective orbital g factor, allowing the generation of spin currents. The phenomenon provides a solution to the outstanding challenge of detecting the spin polarization of the edge states. Here we propose the detection of the edge polarization in a three-terminal junction using unusual transport properties of the superconducting quantum Hall effect: a nonmonotonic excess current and a zero-bias conductance peak splitting.
Schroedinger-equation formalism for a dissipative quantum system
Anisimovas, E.; Matulis, A.
2007-02-15
We consider a model dissipative quantum-mechanical system realized by coupling a quantum oscillator to a semi-infinite classical string which serves as a means of energy transfer from the oscillator to the infinity and thus plays the role of a dissipative element. The coupling between the two--quantum and classical--parts of the compound system is treated in the spirit of the mean-field approximation and justification of the validity of such an approach is given. The equations of motion of the classical subsystem are solved explicitly and an effective dissipative Schroedinger equation for the quantum subsystem is obtained. The proposed formalism is illustrated by its application to two basic problems: the decay of the quasistationary state and the calculation of the nonlinear resonance line shape.
Real-time monitoring of LÃ©vy flights in a single quantum system
NASA Astrophysics Data System (ADS)
Issler, M.; HÃ¶ller, J.; ImamoÇ§lu, A.
2016-02-01
LÃ©vy flights are random walks where the dynamics is dominated by rare events. Even though they have been studied in vastly different physical systems, their observation in a single quantum system has remained elusive. Here we analyze a periodically driven open central spin system and demonstrate theoretically that the dynamics of the spin environment exhibits LÃ©vy flights. For the particular realization in a single-electron charged quantum dot driven by periodic resonant laser pulses, we use Monte Carlo simulations to confirm that the long waiting times between successive nuclear spin-flip events are governed by a power-law distribution; the corresponding exponent Î· =-3 /2 can be directly measured in real time by observing the waiting time distribution of successive photon emission events. Remarkably, the dominant intrinsic limitation of the scheme arising from nuclear quadrupole coupling can be minimized by adjusting the magnetic field or by implementing spin echo.
Scaling law and stability for a noisy quantum system.
Sadgrove, Mark; Wimberger, Sandro; Parkins, Scott; Leonhardt, Rainer
2008-08-01
We show that a scaling law exists for the near-resonant dynamics of cold kicked atoms in the presence of a randomly fluctuating pulse amplitude. Analysis of a quasiclassical phase-space representation of the quantum system with noise allows a new scaling law to be deduced. The scaling law and associated stability are confirmed by comparison with quantum simulations and experimental data. PMID:18850885
Improving quantum phase estimation via power-law potential systems
NASA Astrophysics Data System (ADS)
Berrada, K.
2014-06-01
Using the quantum Fisher information (QFI), we present an improved phase estimation scheme employing power-law potential (PLP) systems in comparison to NOON states under perfect and lossy conditions for a fixed mean photon number. The study is devoted to the phase estimation of the quantum states resulting from tightly binding, harmonic and loosely binding potentials for modest particle numbers. Finally, we discuss the saturation of the optimal phase uncertainty of this interferometric setting with parity detection.
Scalable quantum mechanical simulation of large polymer systems
Goedecker, S.; Hoisie, A.; Kress, J.; Lubeck, O.; Wasserman, H.
1997-08-01
We describe a program for quantum mechanical calculations of very large hydrocarbon polymer systems. It is based on a new algorithmic approach to the quantum mechanical tight binding equations that naturally leads to a very efficient parallel implementation and that scales linearly with respect to the number of atoms. We get both very high single node performance as well as a significant parallel speedup on the SGI Origin 2000 parallel computer.
Nuclear magnetometry studies of spin dynamics in quantum Hall systems
NASA Astrophysics Data System (ADS)
Fauzi, M. H.; Watanabe, S.; Hirayama, Y.
2014-12-01
We performed a nuclear magnetometry study on quantum Hall ferromagnet with a bilayer total filling factor of ?tot=2 . We found not only a rapid nuclear relaxation but also a sudden change in the nuclear-spin polarization distribution after a one-second interaction with a canted antiferromagnetic phase. We discuss the possibility of observing cooperative phenomena coming from nuclear-spin ensemble triggered by hyperfine interaction in quantum Hall system.
NASA Astrophysics Data System (ADS)
McMahon, Peter
2015-03-01
In this talk I will present some of our recent work on constructing and optically investigating nanostructures consisting of quantum dots coupled to a nearby quantum well, all embedded in a planar microcavity. The overall goal of this line of work is to develop a platform in which long-range (~ 1 micron) two-qubit interactions between quantum dots are possible, following the pioneering proposal of Piermarocchi, Chen, Sham, and Steel. We have succeeded in demonstrating several fundamental aspects of this platform. We have realized a coupled quantum-dot-quantum-well system in a microcavity, and show that quantum dots in this system can be charged (allowing the storage of a spin qubit), and show that both the quantum dots and the quantum well retain favourable optical properties. Most importantly, we have fairly strong evidence suggesting that the operative mechanism of the theoretical proposals, the spin-dependent exchange interaction between a trapped electron in a quantum dot, and an exciton in the quantum well, is observable, and can be engineered to be of the magnitude required for the implementation of universal quantum gates and measurement operations. I will discuss these results, and highlight other recent (unrelated) work on site-controlled quantum dots, including with quantum dots in positioned nanowires. This work was primarily supported by the JSPS through its FIRST program.
Method for adding nodes to a quantum key distribution system
Grice, Warren P
2015-02-24
An improved quantum key distribution (QKD) system and method are provided. The system and method introduce new clients at intermediate points along a quantum channel, where any two clients can establish a secret key without the need for a secret meeting between the clients. The new clients perform operations on photons as they pass through nodes in the quantum channel, and participate in a non-secret protocol that is amended to include the new clients. The system and method significantly increase the number of clients that can be supported by a conventional QKD system, with only a modest increase in cost. The system and method are compatible with a variety of QKD schemes, including polarization, time-bin, continuous variable and entanglement QKD.
Simulation of n-qubit quantum systems. II. Separability and entanglement
NASA Astrophysics Data System (ADS)
Radtke, T.; Fritzsche, S.
2006-07-01
Studies on the entanglement of n-qubit quantum systems have attracted a lot of interest during recent years. Despite the central role of entanglement in quantum information theory, however, there are still a number of open problems in the theoretical characterization of entangled systems that make symbolic and numerical simulation on n-qubit quantum registers indispensable for present-day research. To facilitate the investigation of the separability and entanglement properties of n-qubit quantum registers, here we present a revised version of the FEYNMAN program in the framework of the computer algebra system MAPLE. In addition to all previous capabilities of this MAPLE code for defining and manipulating quantum registers, the program now provides various tools which are necessary for the qualitative and quantitative analysis of entanglement in n-qubit quantum registers. A simple access, in particular, is given to several algebraic separability criteria as well as a number of entanglement measures and related quantities. As in the previous version, symbolic and numeric computations are equally supported. Program summaryTitle of program:FEYNMAN Catalogue identifier:ADWE_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADWE_v2_0 Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions:None Computers for which the program is designed: All computers with a license of the computer algebra system MAPLE [Maple is a registered trademark of Waterloo Maple Inc.] Operating systems under which the program has been tested: Linux, MS Windows XP Programming language used:MAPLE 10 Typical time and memory requirements:Most commands acting on quantum registers with five or less qubits take â©½10 seconds of processor time (on a Pentium 4 with â©¾2 GHz or equivalent) and 5-20 MB of memory. However, storage and time requirements critically depend on the number of qubits, n, in the quantum registers due to the exponential increase of the associated Hilbert space. No. of lines in distributed program, including test data, etc.:3107 No. of bytes in distributed program, including test data, etc.:13 859 Distribution format:tar.gz Reasons for new version:The first program version established the data structures and commands which are needed to build and manipulate quantum registers. Since the (evolution of) entanglement is a central aspect in quantum information processing the current version adds the capability to analyze separability and entanglement of quantum registers by implementing algebraic separability criteria and entanglement measures and related quantities. Does this version supersede the previous version: Yes Nature of the physical problem: Entanglement has been identified as an essential resource in virtually all aspects of quantum information theory. Therefore, the detection and quantification of entanglement is a necessary prerequisite for many applications, such as quantum computation, communications or quantum cryptography. Up to the present, however, the multipartite entanglement of n-qubit systems has remained largely unexplored owing to the exponential growth of complexity with the number of qubits involved. Method of solution: Using the computer algebra system MAPLE, a set of procedures has been developed which supports the definition and manipulation of n-qubit quantum registers and quantum logic gates [T. Radtke, S. Fritzsche, Comput. Phys. Comm. 173 (2005) 91]. The provided hierarchy of commands can be used interactively in order to simulate the behavior of n-qubit quantum systems (by applying a number of unitary or non-unitary operations) and to analyze their separability and entanglement properties. Restrictions onto the complexity of the problem: The present version of the program facilitates the setup and the manipulation of quantum registers by means of (predefined) quantum logic gates; it now also provides the tools for performing a symbolic and/or numeric analysis of the entanglement for the quantum states of such registers. Owing to the rapid increase in the computational complexity of multi-qubit systems, however, the time and memory requirements often grow rapidly, especially for symbolic computations. This increase of complexity limits the application of the program to about 6 or 7 qubits on a standard single processor (Pentium 4 with â©¾2 GHz or equivalent) machine with â©½1 GB of memory. Unusual features of the program: The FEYNMAN program has been designed within the framework of MAPLE for interactive (symbolic or numerical) simulations on n-qubit quantum registers with no other restriction than given by the memory and processor resources of the computer. Whenever possible, both representations of quantum registers in terms of their state vectors and/or density matrices are equally supported by the program. Apart from simulating quantum gates and quantum operations, the program now facilitates also investigations on the separability and the entanglement properties of quantum registers.
Plasma confinement studies in open systems
NASA Astrophysics Data System (ADS)
Yatsu, Kiyoshi
1999-03-01
Studies in open systems in the world are reviewed from viewpoints of the potential confinement and magnetohydrodynamic (MHD) stability. The tandem mirror GAMMA 10 has shown the potential confinement of a high-ion-temperature plasma from an analysis of the time evolution of end-loss ion current and end-loss ion energy distributions. The central cell density was increased by 50% by the potential confinement. In the HIEI tandem mirror H-mode-like phenomena were observed with an increase in density and diamagnetic signal in a limiter biasing experiment. Potential formation phenomena in plasmas are studied by 0741-3335/41/3A/024/img1-like Upgrade under different magnetic field configurations and plasma conditions. The fully axisymmetric tandem mirror AMBAL-M is under construction and its end mirror system has been assembled. Heating experiments of a plasma gun produced plasma by neutral beam injection and ICRF heating are in progress. The gas dynamic trap (GDT) experiment has successfully produced an MHD-stable high-temperature, high-density plasma. In GOL-3-II, a high-density plasma with several 100 eV temperature is created by powerful relativistic electron beam injection. Construction of HANBIT has been completed and experiments on plasma production and ICRF heating have begun.
Advances in quantum teleportation
NASA Astrophysics Data System (ADS)
Pirandola, S.; Eisert, J.; Weedbrook, C.; Furusawa, A.; Braunstein, S. L.
2015-10-01
Quantum teleportation is one of the most important protocols in quantum information. By exploiting the physical resource of entanglement, quantum teleportation serves as a key primitive across a variety of quantum information tasks and represents an important building block for quantum technologies, with a pivotal role in the continuing progress of quantum communication, quantum computing and quantum networks. Here we summarize the basic theoretical ideas behind quantum teleportation and its variant protocols. We focus on the main experiments, together with the technical advantages and disadvantages associated with the use of the various technologies, from photonic qubits and optical modes to atomic ensembles, trapped atoms and solid-state systems. After analysing the current state-of-the-art, we finish by discussing open issues, challenges and potential future implementations.
Quantum metrology in Lipkin-Meshkov-Glick critical systems
NASA Astrophysics Data System (ADS)
Salvatori, Giulio; Mandarino, Antonio; Paris, Matteo G. A.
2014-08-01
The Lipkin-Meshkov-Glick (LMG) model describes critical systems with interaction beyond the first-neighbor approximation. Here we address quantum metrology in LMG systems and show how criticality may be exploited to improve precision. At first we focus on the characterization of LMG systems themselves, i.e., the estimation of anisotropy, and address the problem by considering the quantum Cramér-Rao bound. We evaluate the quantum Fisher information of small-size LMG chains made of N =2, 3, and 4 lattice sites and also analyze the same quantity in the thermodynamical limit. Our results show that criticality is indeed a resource and that the ultimate bounds to precision may be achieved by tuning the external field and measuring the total magnetization of the system. We then address the use of LMG systems as quantum thermometers and show that (i) precision is governed by the gap between the lowest energy levels of the systems and (ii) field-dependent level crossing is a metrological resource to extend the operating range of the quantum thermometer.
Open Source Course Management Systems: A Case Study
ERIC Educational Resources Information Center
Remy, Eric
2005-01-01
In Fall 2003, Randolph-Macon Woman's College rolled out Claroline, an Open Source course management system for all the classes on campus. This document will cover some background on both Open Source in general and course management systems in specific, discuss technical challenges in the introduction and integration of the system and give some…
Non-local propagation of correlations in quantum systems with long-range interactions.
Richerme, Philip; Gong, Zhe-Xuan; Lee, Aaron; Senko, Crystal; Smith, Jacob; Foss-Feig, Michael; Michalakis, Spyridon; Gorshkov, Alexey V; Monroe, Christopher
2014-07-10
The maximum speed with which information can propagate in a quantum many-body system directly affects how quickly disparate parts of the system can become correlated and how difficult the system will be to describe numerically. For systems with only short-range interactions, Lieb and Robinson derived a constant-velocity bound that limits correlations to within a linear effective 'light cone'. However, little is known about the propagation speed in systems with long-range interactions, because analytic solutions rarely exist and because the best long-range bound is too loose to accurately describe the relevant dynamical timescales for any known spin model. Here we apply a variable-range Ising spin chain Hamiltonian and a variable-range XY spin chain Hamiltonian to a far-from-equilibrium quantum many-body system and observe its time evolution. For several different interaction ranges, we determine the spatial and time-dependent correlations, extract the shape of the light cone and measure the velocity with which correlations propagate through the system. This work opens the possibility for studying a wide range of many-body dynamics in quantum systems that are otherwise intractable. PMID:25008525
Double Ramification Cycles and Quantum Integrable Systems
NASA Astrophysics Data System (ADS)
Buryak, Alexandr; Rossi, Paolo
2016-03-01
In this paper, we define a quantization of the Double Ramification Hierarchies of Buryak (Commun Math Phys 336:1085-1107, 2015) and Buryak and Rossi (Commun Math Phys, 2014), using intersection numbers of the double ramification cycle, the full Chern class of the Hodge bundle and psi-classes with a given cohomological field theory. We provide effective recursion formulae which determine the full quantum hierarchy starting from just one Hamiltonian, the one associated with the first descendant of the unit of the cohomological field theory only. We study various examples which provide, in very explicit form, new (1+1)-dimensional integrable quantum field theories whose classical limits are well-known integrable hierarchies such as KdV, Intermediate Long Wave, extended Toda, etc. Finally, we prove polynomiality in the ramification multiplicities of the integral of any tautological class over the double ramification cycle.
Double Ramification Cycles and Quantum Integrable Systems
NASA Astrophysics Data System (ADS)
Buryak, Alexandr; Rossi, Paolo
2015-12-01
In this paper, we define a quantization of the Double Ramification Hierarchies of Buryak (Commun Math Phys 336:1085-1107, 2015) and Buryak and Rossi (Commun Math Phys, 2014), using intersection numbers of the double ramification cycle, the full Chern class of the Hodge bundle and psi-classes with a given cohomological field theory. We provide effective recursion formulae which determine the full quantum hierarchy starting from just one Hamiltonian, the one associated with the first descendant of the unit of the cohomological field theory only. We study various examples which provide, in very explicit form, new (1+1)-dimensional integrable quantum field theories whose classical limits are well-known integrable hierarchies such as KdV, Intermediate Long Wave, extended Toda, etc. Finally, we prove polynomiality in the ramification multiplicities of the integral of any tautological class over the double ramification cycle.
Optimizing entangling quantum gates for physical systems
Mueller, M. M.; Murphy, M.; Calarco, T.; Reich, D. M.; Koch, C. P.; Yuan, H.; Vala, J.; Whaley, K. B.
2011-10-15
Optimal control theory is a versatile tool that presents a route to significantly improving figures of merit for quantum information tasks. We combine it here with the geometric theory for local equivalence classes of two-qubit operations to derive an optimization algorithm that determines the best entangling two-qubit gate for a given physical setting. We demonstrate the power of this approach for trapped polar molecules and neutral atoms.
A generalization of Fermat's principle for classical and quantum systems
NASA Astrophysics Data System (ADS)
Elsayed, Tarek A.
2014-09-01
The analogy between dynamics and optics had a great influence on the development of the foundations of classical and quantum mechanics. We take this analogy one step further and investigate the validity of Fermat's principle in many-dimensional spaces describing dynamical systems (i.e., the quantum Hilbert space and the classical phase and configuration space). We propose that if the notion of a metric distance is well defined in that space and the velocity of the representative point of the system is an invariant of motion, then a generalized version of Fermat's principle will hold. We substantiate this conjecture for time-independent quantum systems and for a classical system consisting of coupled harmonic oscillators. An exception to this principle is the configuration space of a charged particle in a constant magnetic field; in this case the principle is valid in a frame rotating by half the Larmor frequency, not the stationary lab frame.
Nexus: A modular workflow management system for quantum simulation codes
NASA Astrophysics Data System (ADS)
Krogel, Jaron T.
2016-01-01
The management of simulation workflows represents a significant task for the individual computational researcher. Automation of the required tasks involved in simulation work can decrease the overall time to solution and reduce sources of human error. A new simulation workflow management system, Nexus, is presented to address these issues. Nexus is capable of automated job management on workstations and resources at several major supercomputing centers. Its modular design allows many quantum simulation codes to be supported within the same framework. Current support includes quantum Monte Carlo calculations with QMCPACK, density functional theory calculations with Quantum Espresso or VASP, and quantum chemical calculations with GAMESS. Users can compose workflows through a transparent, text-based interface, resembling the input file of a typical simulation code. A usage example is provided to illustrate the process.
Quantum maximum entropy principle for a system of identical particles
Trovato, M.; Reggiani, L.
2010-02-15
By introducing a functional of the reduced density matrix, we generalize the definition of a quantum entropy which incorporates the indistinguishability principle of a system of identical particles. With the present definition, the principle of quantum maximum entropy permits us to solve the closure problem for a quantum hydrodynamic set of balance equations corresponding to an arbitrary number of moments in the framework of extended thermodynamics. The determination of the reduced Wigner function for equilibrium and nonequilibrium conditions is found to become possible only by assuming that the Lagrange multipliers can be expanded in powers of (Planck constant/2pi){sup 2}. Quantum contributions are expressed in powers of (Planck constant/2pi){sup 2} while classical results are recovered in the limit (Planck constant/2pi)->0.
Nexus: a modular workflow management system for quantum simulation codes
Krogel, Jaron T.
2015-08-24
The management of simulation workflows is a significant task for the individual computational researcher. Automation of the required tasks involved in simulation work can decrease the overall time to solution and reduce sources of human error. A new simulation workflow management system, Nexus, is presented to address these issues. Nexus is capable of automated job management on workstations and resources at several major supercomputing centers. Its modular design allows many quantum simulation codes to be supported within the same framework. Current support includes quantum Monte Carlo calculations with QMCPACK, density functional theory calculations with Quantum Espresso or VASP, and quantum chemical calculations with GAMESS. Users can compose workflows through a transparent, text-based interface, resembling the input file of a typical simulation code. A usage example is provided to illustrate the process.
Communication theory of quantum systems. Ph.D. Thesis, 1970
NASA Technical Reports Server (NTRS)
Yuen, H. P. H.
1971-01-01
Communication theory problems incorporating quantum effects for optical-frequency applications are discussed. Under suitable conditions, a unique quantum channel model corresponding to a given classical space-time varying linear random channel is established. A procedure is described by which a proper density-operator representation applicable to any receiver configuration can be constructed directly from the channel output field. Some examples illustrating the application of our methods to the development of optical quantum channel representations are given. Optimizations of communication system performance under different criteria are considered. In particular, certain necessary and sufficient conditions on the optimal detector in M-ary quantum signal detection are derived. Some examples are presented. Parameter estimation and channel capacity are discussed briefly.
Quantum parameter identification for a chaotic atom ensemble system
NASA Astrophysics Data System (ADS)
Li, Wenlin; Li, Chong; Song, Heshan
2016-02-01
We propose an indirect method based on an adaptive technique for analyzing the chaos behavior of a general quantum system with complex nonlinear evolution. Using this method, we design an identification function that effectively recognizes the uncertain parameters in a chaotic quantum system only by measuring the system outputs. As an example, we study an atom ensemble in an optical cavity and we obtain a specific parameter identification scheme after analyzing the chaos behaviors. We also verify the accuracy of the identification scheme using numerical simulations and we discuss the influence of different types of errors on the accuracy.
An Online Banking System Based on Quantum Cryptography Communication
NASA Astrophysics Data System (ADS)
Zhou, Ri-gui; Li, Wei; Huan, Tian-tian; Shen, Chen-yi; Li, Hai-sheng
2014-07-01
In this paper, an online banking system has been built. Based on quantum cryptography communication, this system is proved unconditional secure. Two sets of GHZ states are applied, which can ensure the safety of purchase and payment, respectively. In another word, three trading participants in each triplet state group form an interdependent and interactive relationship. In the meantime, trading authorization and blind signature is introduced by means of controllable quantum teleportation. Thus, an effective monitor is practiced on the premise that the privacy of trading partners is guaranteed. If there is a dispute or deceptive behavior, the system will find out the deceiver immediately according to the relationship mentioned above.
Fluorescence from a quantum dot and metallic nanosphere hybrid system
Schindel, Daniel G.; Singh, Mahi R.
2014-03-31
We present energy absorption and interference in a quantum dot-metallic nanosphere system embedded on a dielectric substrate. A control field is applied to induce dipole moments in the nanosphere and the quantum dot, and a probe field is applied to monitor absorption. Dipole moments in the quantum dot or the metal nanosphere are induced, both by the external fields and by each other's dipole fields. Thus, in addition to direct polarization, the metal nanosphere and the quantum dot will sense one another via the dipole-dipole interaction. The density matrix method was used to show that the absorption spectrum can be split from one peak to two peaks by the control field, and this can also be done by placing the metal sphere close to the quantum dot. When the two are extremely close together, a self-interaction in the quantum dot produces an asymmetry in the absorption peaks. In addition, the fluorescence efficiency can be quenched by the addition of a metal nanosphere. This hybrid system could be used to create ultra-fast switching and sensing nanodevices.
Quantum Processes and Dynamic Networks in Physical and Biological Systems.
NASA Astrophysics Data System (ADS)
Dudziak, Martin Joseph
Quantum theory since its earliest formulations in the Copenhagen Interpretation has been difficult to integrate with general relativity and with classical Newtonian physics. There has been traditionally a regard for quantum phenomena as being a limiting case for a natural order that is fundamentally classical except for microscopic extrema where quantum mechanics must be applied, more as a mathematical reconciliation rather than as a description and explanation. Macroscopic sciences including the study of biological neural networks, cellular energy transports and the broad field of non-linear and chaotic systems point to a quantum dimension extending across all scales of measurement and encompassing all of Nature as a fundamentally quantum universe. Theory and observation lead to a number of hypotheses all of which point to dynamic, evolving networks of fundamental or elementary processes as the underlying logico-physical structure (manifestation) in Nature and a strongly quantized dimension to macroscalar processes such as are found in biological, ecological and social systems. The fundamental thesis advanced and presented herein is that quantum phenomena may be the direct consequence of a universe built not from objects and substance but from interacting, interdependent processes collectively operating as sets and networks, giving rise to systems that on microcosmic or macroscopic scales function wholistically and organically, exhibiting non-locality and other non -classical phenomena. The argument is made that such effects as non-locality are not aberrations or departures from the norm but ordinary consequences of the process-network dynamics of Nature. Quantum processes are taken to be the fundamental action-events within Nature; rather than being the exception quantum theory is the rule. The argument is also presented that the study of quantum physics could benefit from the study of selective higher-scale complex systems, such as neural processes in the brain, by virtue of mathematical and computational models that may be transferred from the macroscopic domain to the microscopic. A consequence of this multi-faceted thesis is that there may be mature analytical tools and techniques that have heretofore not been adequately recognized for their value to quantum physics. These may include adaptations of neural networks, cellular automata, chaotic attractors, and parallel processing systems. Conceptual and practical architectures are presented for the development of software and hardware environments to employ massively parallel computing for the modeling of large populations of dynamic processes.
NASA Astrophysics Data System (ADS)
Wiseman, Howard
2015-03-01
Under noisy observations, one can estimate the state of the measured system, if its a priori statistics are given. In the continuous time situation, three different types of estimation can be distinguished: filtering, which is estimating of the state at time t from earlier records; retro-filtering, which is estimating it from later records; and smoothing, which is estimating it from both earlier and later records. Of the three, smoothing allows the greatest precision. Smoothing has been well developed in classical systems, but its application to quantum systems is very recent. Previous works have used the term ``quantum smoothing'' to mean estimating classical parameters, [Tsang, Phys. Rev. Lett 102, 250403 (2009); Yonezawa et al., Science 337, 1514-1517 (2012)]. This is essentially classical smoothing in which the noisy observation of the classical parameters is mediated by a quantum system. Here we introduce quantum state smoothing, where the state of a partially observed open quantum system itself is smoothed. We achieve this by applying classical smoothing to a hypothetical unobserved noisy measurement record that induces (in part) the stochastic dynamics (``quantum trajectories'') of the system. Using the formalism of linear quantum trajectories, we simulate quantum state smoothing for a qubit, and quantify how well it works. Our investigations shed new light on the nature of open quantum systems and the applicability of classical concepts. Applications to continuous measurement of solid-state qubits will be presented. Supported by the Australian Research Council Centre for Quantum Computation and Communication Technology.
Investigation of the open-circuit voltage in solar cells doped with quantum dots
Tayagaki, Takeshi; Hoshi, Yusuke; Usami, Noritaka
2013-01-01
Quantum dots (QDs) have attracted much attention for use in photovoltaic applications because of their potential for overcoming the limits of conventional single-junction devices. One problem associated with solar cells using QDs is that the open-circuit voltage (Voc) always decreases with the addition of QDs with respect to the reference cell without QDs. Here, we report the investigation of current–voltage characteristics in Ge/Si QD solar cells in the temperature range from 100 to 300?K. We show that even though Voc decreases with increasing temperature, it depends on the nominal Ge thickness, indicating that Voc reduction is primarily caused by a decrease in the bandgap energy of the cell. From photoluminescence decay measurements, we found that rapid carrier extraction from QDs occurred in the solar cells; this process eliminates the quasi-Fermi energy splitting between the QDs and the host semiconductor and causes Voc reduction in QD solar cells. PMID:24067805
Quantum transport through the system of parallel quantum dots with Majorana bound states
Wang, Ning; Li, Yuxian; Lv, Shuhui
2014-02-28
We study the tunneling transport properties through a system of parallel quantum dots which are coupled to Majorana bound states (MBSs). The conductance and spectral function are computed using the retarded Green's function method based on the equation of motion. The conductance of the system is 2e{sup 2}/h at zero Fermi energy and is robust against the coupling between the MBSs and the quantum dots. The dependence of the Fermi energy on the spectral function is different for the first dot (dot1) than for the second dot (dot2) with fixed dot2-MBSs coupling. The influence of the Majorana bound states on the spectral function was studied for the series and parallel configurations of the system. It was found that when the configuration is in series, the Majorana bound states play an important role, resulting in a spectral function with three peaks. However, the spectral function shows two peaks when the system is in a parallel configuration. The zero Fermi energy spectral function is always 1/2 not only in series but also in the parallel configuration and robust against the coupling between the MBSs and the quantum dots. The phase diagram of the Fermi energy versus the quantum dot energy levels was also investigated.
Barnes, George L.; Kellman, Michael E.
2013-12-07
Simulations are performed of a small quantum system interacting with a quantum environment. The system consists of various initial states of two harmonic oscillators coupled to give normal modes. The environment is “designed” by its level pattern to have a thermodynamic temperature. A random coupling causes the system and environment to become entangled in the course of time evolution. The approach to a Boltzmann distribution is observed, and effective fitted temperatures close to the designed temperature are obtained. All initial pure states of the system are driven to equilibrium at very similar rates, with quick loss of memory of the initial state. The time evolution of the von Neumann entropy is calculated as a measure of equilibration and of quantum coherence. It is pointed out using spatial density distribution plots that quantum interference is eliminated only with maximal entropy, which corresponds thermally to infinite temperature. Implications of our results for the notion of “classicalizing” behavior in the approach to thermal equilibrium are briefly considered.
Escape of quantum particles from an open nano-circular microcavity
NASA Astrophysics Data System (ADS)
Liu, Sheng; Wang, De-hua
2014-06-01
When a laser is irradiated on a negative ion, it will provide a coherent, mono-energetic source of detached electrons propagating out from the location of the negative ion. The total escape probability density of the electrons when the negative ion is placed inside an open nano-circular microcavity has been studied on the basis of the semiclassical theory. It is shown that significant oscillations appear in the total escape probability density due to the quantum interference effects. Besides, our study suggests that the escape probability density depends on the laser polarization sensitively. In order to show the correspondence between the escaped probability density and the detached electron's escaped orbits clearly, we calculate the path length spectrum and find that each peak corresponds to the length of one detached electron's escaped orbit. This study provides an example where the quantum nature of the electron's wave function can be observed in the macroscopic world. Our study may guide the future experimental research on the escape and transport process of particles through semiconductor microjunctions.
Comment on [open quotes]Nonlocality, counterfactuals, and quantum mechanics[close quotes
Stapp, H.P. )
1999-09-01
A recent proof [H. P. Stapp, Am. J. Phys. [bold 65], 300 (1997)], formulated in the symbolic language of modal logic, claims to show that contemporary quantum theory, viewed as a set of rules that allow us to calculate statistical predictions among certain kinds of observations, cannot be imbedded in any rational framework that conforms to the principles that (1) the experimenters[close quote] choices of which experiments they will perform can be considered to be free choices, (2) outcomes of measurements are unique, and (3) the free choices just mentioned have no backward-in-time effects of any kind. This claim is similar to Bell[close quote]s theorem, but much stronger, because no reality assumption alien to quantum philosophy is used. The paper being commented on [W. Unruh, Phys. Rev. A [bold 59], 126 (1999)] argues that some such reality assumption has been [open quotes]smuggled[close quotes] in. That argument is examined here and shown, I believe, to be defective. [copyright] [ital 1999] [ital The American Physical Society
Continuity of the entropy of macroscopic quantum systems
NASA Astrophysics Data System (ADS)
Swendsen, Robert H.
2015-11-01
The proper definition of entropy is fundamental to the relationship between statistical mechanics and thermodynamics. It also plays a major role in the recent debate about the validity of the concept of negative temperature. In this paper, I analyze and calculate the thermodynamic entropy for large but finite quantum mechanical systems. A special feature of this analysis is that the thermodynamic energy of a quantum system is shown to be a continuous variable, rather than being associated with discrete energy eigenvalues. Calculations of the entropy as a function of energy can be carried out with a Legendre transform of thermodynamic potentials obtained from a canonical ensemble. The resultant expressions for the entropy are able to describe equilibrium between quantum systems having incommensurate energy-level spacings. This definition of entropy preserves all required thermodynamic properties, including satisfaction of all postulates and laws of thermodynamics. It demonstrates the consistency of the concept of negative temperature with the principles of thermodynamics.
Controllable quantum information network with a superconducting system
Zhang, Feng-yang; Liu, Bao; Chen, Zi-hong; Wu, Song-lin; Song, He-shan
2014-07-15
We propose a controllable and scalable architecture for quantum information processing using a superconducting system network, which is composed of current-biased Josephson junctions (CBJJs) as tunable couplers between the two superconducting transmission line resonators (TLRs), each coupling to multiple superconducting qubits (SQs). We explicitly demonstrate that the entangled state, the phase gate, and the information transfer between any two selected SQs can be implemented, respectively. Lastly, numerical simulation shows that our scheme is robust against the decoherence of the system. -- Highlights: •An architecture for quantum information processing is proposed. •The quantum information transfer between any two selected SQs is implemented. •This proposal is robust against the decoherence of the system. •This architecture can be fabricated on a chip down to the micrometer scale.
Coulomb drag in graphene quantum Hall bilayer systems
NASA Astrophysics Data System (ADS)
Liu, Xiaomeng; Wang, Lei; Fong, Kin Chung; Gao, Yuanda; Maher, Patrick; Watanabe, Kenji; Taniguchi, Takashi; Hone, James; Dean, Cory; Kim, Philip
2015-03-01
Coulomb drag between electrons in closely spaced two-dimensional electron systems has provided an exciting avenue for research on quantum Hall bilayer systems. Employing dual-gated, encapsulated graphene double layers separated by a thin hBN dielectric, we investigate density tunable magneto and Hall drag in quantum Hall bilayer systems. Large variations of magneto-drag and Hall-drag are observed, which can be related to the Landau level (LL) filling status of both driving and drag layers. The measured drag resistivity tensor can be associated with the tensor product of the differential magneto-resistivity tensors of the drive and drag layers. The temperature and field dependence of magneto-drag can be described in terms of the phase space for Coulomb scattering between LLs in the drag and drive layers. In the strong interaction regime and ultra-low temperature, we observe the effect of symmetry broken integer quantum Hall States in magneto and Hall drag signals.
Quantum ergodicity for a class of non-generic systems
NASA Astrophysics Data System (ADS)
Asadi, P.; Bakhshinezhad, F.; Rezakhani, A. T.
2016-02-01
We examine quantum normal typicality and ergodicity properties for quantum systems whose dynamics are generated by Hamiltonians which have residual degeneracy in their spectrum and resonance in their energy gaps. Such systems can be considered atypical in the sense that degeneracy, which is usually a sign of symmetry, is naturally broken in typical systems due to stochastic perturbations. In particular, we prove a version of von Neumann’s quantum ergodic theorem, where a modified condition needs to hold in order to have normal typicality and ergodicity. As a result, we show that degeneracy of spectrum does not considerably modify the condition of the theorem, whereas the existence of resonance is more dominant for obstructing ergodicity.
Continuity of the entropy of macroscopic quantum systems.
Swendsen, Robert H
2015-11-01
The proper definition of entropy is fundamental to the relationship between statistical mechanics and thermodynamics. It also plays a major role in the recent debate about the validity of the concept of negative temperature. In this paper, I analyze and calculate the thermodynamic entropy for large but finite quantum mechanical systems. A special feature of this analysis is that the thermodynamic energy of a quantum system is shown to be a continuous variable, rather than being associated with discrete energy eigenvalues. Calculations of the entropy as a function of energy can be carried out with a Legendre transform of thermodynamic potentials obtained from a canonical ensemble. The resultant expressions for the entropy are able to describe equilibrium between quantum systems having incommensurate energy-level spacings. This definition of entropy preserves all required thermodynamic properties, including satisfaction of all postulates and laws of thermodynamics. It demonstrates the consistency of the concept of negative temperature with the principles of thermodynamics. PMID:26651650
Quantum walks on a circle with optomechanical systems
NASA Astrophysics Data System (ADS)
Moqadam, Jalil Khatibi; Portugal, Renato; de Oliveira, Marcos Cesar
2015-10-01
We propose an implementation of a quantum walk on a circle in an optomechanical system by encoding the walker on the phase space of a radiation field and the coin on a two-level state of a mechanical resonator. The dynamics of the system is obtained by applying Suzuki-Trotter decomposition. We numerically show that the system displays typical behaviors of quantum walks, namely the probability distribution evolves ballistically and the standard deviation of the phase distribution is linearly proportional to the number of steps. We also analyze the effects of decoherence by using the phase-damping channel on the coin space, showing the possibility to implement the quantum walk with present-day technology.
An order parameter for impurity systems at quantum criticality
Bayat, Abolfazl; Johannesson, Henrik; Bose, Sougato; Sodano, Pasquale
2014-01-01
A quantum phase transition may occur in the ground state of a system at zero temperature when a controlling field or interaction is varied. The resulting quantum fluctuations which trigger the transition produce scaling behaviour of various observables, governed by universal critical exponents. A particularly interesting class of such transitions appear in systems with quantum impurities where a non-extensive term in the free energy becomes singular at the critical point. Curiously, the notion of a conventional order parameter that exhibits scaling at the critical point is generically missing in these systems. Here we explore the possibility to use the Schmidt gap, which is an observable obtained from the entanglement spectrum, as an order parameter. A case study of the two-impurity Kondo model confirms that the Schmidt gap faithfully captures the scaling behaviour by correctly predicting the critical exponent of the dynamically generated length scale at the critical point. PMID:24807201
NASA Astrophysics Data System (ADS)
Wang, Dong-Mei; Qian, Yi; Xu, Jing-Bo; Yu, You-Hong
2015-11-01
We investigate the influence of the dynamical decoupling pulses on the quantum correlations in a superconducting system consisting of two noninteracting qubits interacting with their own data buses. It is found that the geometric discord and entanglement between the two superconducting qubits can be increased by applying a train of ?-phase pulses. We then proceed to explore how the decoupling pulses affect the quantum transfer of information between the two superconducting qubits by making use of the change of trace distance. Project supported by the National Natural Science Foundation of China (Grant No. 11274274).
Quantum sweeps, synchronization, and Kibble-Zurek physics in dissipative quantum spin systems
NASA Astrophysics Data System (ADS)
Henriet, LoÃ¯c; Le Hur, Karyn
2016-02-01
We address dissipation effects on the nonequilibrium quantum dynamics of an ensemble of spins-1/2 coupled via an Ising interaction. Dissipation is modeled by a (Ohmic) bath of harmonic oscillators at zero temperature and correspond either to the sound modes of a one-dimensional Bose-Einstein (quasi-)condensate or to the zero-point fluctuations of a long transmission line. We consider the dimer comprising two spins and the quantum Ising chain with long-range interactions and develop an (mathematically and numerically) exact stochastic approach to address nonequilibrium protocols in the presence of an environment. For the two-spin case, we first investigate the dissipative quantum phase transition induced by the environment through quantum quenches and study the effect of the environment on the synchronization properties. Then we address Landau-Zener-Stueckelberg-Majorana protocols for two spins and for the spin array. In this latter case, we adopt a stochastic mean-field point of view and present a Kibble-Zurek-type argument to account for interaction effects in the lattice. Such dissipative quantum spin arrays can be realized in ultracold atoms, trapped ions, and mesoscopic systems and are related to Kondo lattice models.
21 CFR 11.30 - Controls for open systems.
Code of Federal Regulations, 2014 CFR
2014-04-01
... RECORDS; ELECTRONIC SIGNATURES Electronic Records § 11.30 Controls for open systems. Persons who use open systems to create, modify, maintain, or transmit electronic records shall employ procedures and controls... records from the point of their creation to the point of their receipt. Such procedures and controls...
21 CFR 11.30 - Controls for open systems.
Code of Federal Regulations, 2010 CFR
2010-04-01
... RECORDS; ELECTRONIC SIGNATURES Electronic Records § 11.30 Controls for open systems. Persons who use open systems to create, modify, maintain, or transmit electronic records shall employ procedures and controls... records from the point of their creation to the point of their receipt. Such procedures and controls...
21 CFR 11.30 - Controls for open systems.
Code of Federal Regulations, 2011 CFR
2011-04-01
... RECORDS; ELECTRONIC SIGNATURES Electronic Records § 11.30 Controls for open systems. Persons who use open systems to create, modify, maintain, or transmit electronic records shall employ procedures and controls... records from the point of their creation to the point of their receipt. Such procedures and controls...
Room-temperature resonant quantum tunneling transport of macroscopic systems
NASA Astrophysics Data System (ADS)
Xiong, Zhengwei; Wang, Xuemin; Yan, Dawei; Wu, Weidong; Peng, Liping; Li, Weihua; Zhao, Yan; Wang, Xinmin; An, Xinyou; Xiao, Tingting; Zhan, Zhiqiang; Wang, Zhuo; Chen, Xiangrong
2014-10-01
A self-assembled quantum dots array (QDA) is a low dimensional electron system applied to various quantum devices. This QDA, if embedded in a single crystal matrix, could be advantageous for quantum information science and technology. However, the quantum tunneling effect has been difficult to observe around room temperature thus far, because it occurs in a microcosmic and low temperature condition. Herein, we show a designed a quasi-periodic Ni QDA embedded in a single crystal BaTiO3 matrix and demonstrate novel quantum resonant tunneling transport properties around room-temperature according to theoretical calculation and experiments. The quantum tunneling process could be effectively modulated by changing the Ni QDA concentration. The major reason was that an applied weak electric field (~102 V cm-1) could be enhanced by three orders of magnitude (~105 V cm-1) between the Ni QDA because of the higher permittivity of BaTiO3 and the `hot spots' of the Ni QDA. Compared with the pure BaTiO3 films, the samples with embedded Ni QDA displayed a stepped conductivity and temperature (?-T curves) construction.
Universal quench dynamics of interacting quantum impurity systems
NASA Astrophysics Data System (ADS)
Kennes, D. M.; Meden, V.; Vasseur, R.
2014-09-01
The equilibrium physics of quantum impurities frequently involves a universal crossover from weak to strong reservoir-impurity coupling, characterized by single-parameter scaling and an energy scale TK (Kondo temperature) that breaks scale invariance. For the noninteracting resonant level model, the nonequilibrium time evolution of the Loschmidt echo after a local quantum quench was recently computed explicitly [R. Vasseur, K. Trinh, S. Haas, and H. Saleur, Phys. Rev. Lett. 110, 240601 (2013), 10.1103/PhysRevLett.110.240601]. It shows single-parameter scaling with variable TKt. Here, we scrutinize whether similar universal dynamics can be observed in various interacting quantum impurity systems. Using density matrix and functional renormalization group approaches, we analyze the time evolution resulting from abruptly coupling two noninteracting Fermi or interacting Luttinger liquid leads via a quantum dot or a direct link. We also consider the case of a single Luttinger liquid lead suddenly coupled to a quantum dot. We investigate whether the field-theory predictions for the universal scaling as well as for the large-time behavior successfully describe the time evolution of the Loschmidt echo and the entanglement entropy of microscopic models. Our study shows that for the considered local quench protocols the above quantum impurity models fall into a class of problems for which the nonequilibrium dynamics can largely be understood based on the knowledge of the corresponding equilibrium physics.
Empowering open systems through cross-platform interoperability
NASA Astrophysics Data System (ADS)
Lyke, James C.
2014-06-01
Most of the motivations for open systems lie in the expectation of interoperability, sometimes referred to as "plug-and-play". Nothing in the notion of "open-ness", however, guarantees this outcome, which makes the increased interest in open architecture more perplexing. In this paper, we explore certain themes of open architecture. We introduce the concept of "windows of interoperability", which can be used to align disparate portions of architecture. Such "windows of interoperability", which concentrate on a reduced set of protocol and interface features, might achieve many of the broader purposes assigned as benefits in open architecture. Since it is possible to engineer proprietary systems that interoperate effectively, this nuanced definition of interoperability may in fact be a more important concept to understand and nurture for effective systems engineering and maintenance.
New melting transition in Quantum Hall systems
NASA Astrophysics Data System (ADS)
Simion, George; Lin, Tsuging; Watson, John D.; Manfra, Michael J.; Csathy, Gabor; Rokhinson, Leonid; Lyanda-Geller, Yuli
2014-03-01
We discover a new melting transition caused by topological excitations of two dimensional electrons in the quantum Hall regime. Experimentally, strain dependence of resistivity changes sign upon crossing filling-factor-specified boundaries of reentrant integer quantum Hall effect (RIQHE) states. This observation violates the symmetry of electron bubble crystal, whose melting was thought to be responsible for insulator to metal transition in the range of RIQHE filling factors. We demonstrate theoretically that electron bubbles become elongated in the vicinity of charge defects and form textures of finite size. Textures lower the energy of excitations. In the two-electron bubble crystal these textures form hedgehogs (vortices) around defects having (lacking) one extra electron. At low density these textures form an insulating Abrikosov lattice. At densities sufficient to cause the textures to overlap, their interactions are described by the XY-model and the defect lattice melts. This explains the sharp metal-insulator transition observed in finite temperature conductivity measurements. In this regime, melting is a function of several variables and forms a continuous phase boundary in the field-temperature (B - T) plane. Research was partially supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Awards DE-SC0010544 (Y.L-G), DE-SC0008630 (L.P.R.), DE-SC0006671 (G.S. and M.M.).
New topological excitations in quantum Hall systems
NASA Astrophysics Data System (ADS)
Lyanda-Geller, Yuli; Lin, Tsuging; Simion, George; Watson, John D.; Manfra, Michael J.; Csathy, Gabor; Rokhinson, Leonid
2014-03-01
We discover new topological excitations of two dimensional electrons in the quantum Hall regime. The strain dependence of resistivity observed experimentally is shown to change sign upon crossing filling-factor-specified boundaries of reentrant integer quantum Hall effect (RIQHE) states. This observation violates the known symmetry of electron bubbles thought to be responsible for the RIQHE. We demonstrate theoretically that electron bubbles become elongated in the vicinity of charge defects and form textures of finite size. Calculations confirm that textures lower the energy of excitations. In the two-electron bubble crystal these textures form two-dimensional hedgehogs around defects having one extra electron, and vortices around defects lacking one electron. Strain affects vortices and hedgehogs differently, explaining striking strain-dependent resistivity. The sharp transition from insulating RIQHE state to conducting state is caused by melting of Abrikosov crystal comprised of the defects. The proposed physical mechanism of conductivity due to topological defects is shown to lead to an unusually large magnitude of the strain effect on resistivity in the range of RIQHE filling factors, in agreement with experiment. Research was partially supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Awards DE-SC0010544 (Y.L-G), DE-SC0008630 (L.P.R.), DE-SC0006671 (G.S. and M.M.).
Supersymmetric Quantum Mechanics For Atomic Electronic Systems
NASA Astrophysics Data System (ADS)
Markovich, Thomas; Biamonte, Mason; Kouri, Don
2012-02-01
We employ our new approach to non-relativistic supersymmetric quantum mechanics (SUSY-QM), (J. Phys. Chem. A 114, 8202(2010)) for any number of dimensions and distinguishable particles, to treat the hydrogen atom in full three-dimensional detail. In contrast to the standard one-dimensional radial equation SUSY-QM treatment of the hydrogen atom, where the superpotential is a scalar, in a full three-dimensional treatment, it is a vector which is independent of the angular momentum quantum number. The original scalar Schr"odinger Hamiltonian operator is factored into vector ``charge'' operators: Q and Q^. Using these operators, the first sector Hamiltonian is written as H1= Q^.Q + E0^1. The second sector Hamiltonian is a tensor given by H2= Q Q^ + E0^11 and is isospectral with H1. The second sector ground state, ?0^(2), can be used to obtain the excited state wave functions of the first sector by application of the adjoint charge operator. We then adapt the aufbau principle to show this approach can be applied to treat the helium atom.
Optimized pulse sequences for suppressing unwanted transitions in quantum systems
Schroeder, C. A.; Agarwal, G. S.
2011-01-15
We investigate the nature of the pulse sequence so that unwanted transitions in quantum systems can be inhibited optimally. For this purpose we show that the sequence of pulses proposed by Uhrig [Phys. Rev. Lett. 98, 100504 (2007)] in the context of inhibition of environmental dephasing effects is optimal. We derive exact results for inhibiting the transitions and confirm the results numerically. We posit a very significant improvement by usage of the Uhrig sequence over an equidistant sequence in decoupling a quantum system from unwanted transitions. The physics of inhibition is the destructive interference between transition amplitudes before and after each pulse.
Dynamical singularities of glassy systems in a quantum quench.
Obuchi, Tomoyuki; Takahashi, Kazutaka
2012-11-01
We present a prototype of behavior of glassy systems driven by quantum dynamics in a quenching protocol by analyzing the random energy model in a transverse field. We calculate several types of dynamical quantum amplitude and find a freezing transition at some critical time. The behavior is understood by the partition-function zeros in the complex temperature plane. We discuss the properties of the freezing phase as a dynamical chaotic phase, which are contrasted to those of the spin-glass phase in the static system. PMID:23214756
Develop Direct Geo-referencing System Based on Open Source Software and Hardware Platform
NASA Astrophysics Data System (ADS)
Liu, H. S.; Liao, H. M.
2015-08-01
Direct geo-referencing system uses the technology of remote sensing to quickly grasp images, GPS tracks, and camera position. These data allows the construction of large volumes of images with geographic coordinates. So that users can be measured directly on the images. In order to properly calculate positioning, all the sensor signals must be synchronized. Traditional aerial photography use Position and Orientation System (POS) to integrate image, coordinates and camera position. However, it is very expensive. And users could not use the result immediately because the position information does not embed into image. To considerations of economy and efficiency, this study aims to develop a direct geo-referencing system based on open source software and hardware platform. After using Arduino microcontroller board to integrate the signals, we then can calculate positioning with open source software OpenCV. In the end, we use open source panorama browser, panini, and integrate all these to open source GIS software, Quantum GIS. A wholesome collection of data - a data processing system could be constructed.
Classical simulation of quantum many-body systems
NASA Astrophysics Data System (ADS)
Huang, Yichen
Classical simulation of quantum many-body systems is in general a challenging problem for the simple reason that the dimension of the Hilbert space grows exponentially with the system size. In particular, merely encoding a generic quantum many-body state requires an exponential number of bits. However, condensed matter physicists are mostly interested in local Hamiltonians and especially their ground states, which are highly non-generic. Thus, we might hope that at least some physical systems allow efficient classical simulation. Starting with one-dimensional (1D) quantum systems (i.e., the simplest nontrivial case), the first basic question is: Which classes of states have efficient classical representations? It turns out that this question is quantitatively related to the amount of entanglement in the state, for states with "little entanglement'' are well approximated by matrix product states (a data structure that can be manipulated efficiently on a classical computer). At a technical level, the mathematical notion for "little entanglement'' is area law, which has been proved for unique ground states in 1D gapped systems. We establish an area law for constant-fold degenerate ground states in 1D gapped systems and thus explain the effectiveness of matrix-product-state methods in (e.g.) symmetry breaking phases. This result might not be intuitively trivial as degenerate ground states in gapped systems can be long-range correlated. Suppose an efficient classical representation exists. How can one find it efficiently? The density matrix renormalization group is the leading numerical method for computing ground states in 1D quantum systems. However, it is a heuristic algorithm and the possibility that it may fail in some cases cannot be completely ruled out. Recently, a provably efficient variant of the density matrix renormalization group has been developed for frustration-free 1D gapped systems. We generalize this algorithm to all (i.e., possibly frustrated) 1D gapped systems. Note that the ground-state energy of 1D gapless Hamiltonians is computationally intractable even in the presence of translational invariance. It is tempting to extend methods and tools in 1D to two and higher dimensions (2+D), e.g., matrix product states are generalized to tensor network states. Since an area law for entanglement (if formulated properly) implies efficient matrix product state representations in 1D, an interesting question is whether a similar implication holds in 2+D. Roughly speaking, we show that an area law for entanglement (in any reasonable formulation) does not always imply efficient tensor network representations of the ground states of 2+D local Hamiltonians even in the presence of translational invariance. It should be emphasized that this result does not contradict with the common sense that in practice quantum states with more entanglement usually require more space to be stored classically; rather, it demonstrates that the relationship between entanglement and efficient classical representations is still far from being well understood. Excited eigenstates participate in the dynamics of quantum systems and are particularly relevant to the phenomenon of many-body localization (absence of transport at finite temperature in strongly correlated systems). We study the entanglement of excited eigenstates in random spin chains and expect that its singularities coincide with dynamical quantum phase transitions. This expectation is confirmed in the disordered quantum Ising chain using both analytical and numerical methods. Finally, we study the problem of generating ground states (possibly with topological order) in 1D gapped systems using quantum circuits. This is an interesting problem both in theory and in practice. It not only characterizes the essential difference between the entanglement patterns that give rise to trivial and nontrivial topological order, but also quantifies the difficulty of preparing quantum states with a quantum computer (in experiments).
Open cycle ocean thermal energy conversion system
Wittig, J. Michael
1980-01-01
An improved open cycle ocean thermal energy conversion system including a flash evaporator for vaporizing relatively warm ocean surface water and an axial flow, elastic fluid turbine having a vertical shaft and axis of rotation. The warm ocean water is transmitted to the evaporator through a first prestressed concrete skirt-conduit structure circumferentially situated about the axis of rotation. The unflashed warm ocean water exits the evaporator through a second prestressed concrete skirt-conduit structure located circumferentially about and radially within the first skirt-conduit structure. The radially inner surface of the second skirt conduit structure constitutes a cylinder which functions as the turbine's outer casing and obviates the need for a conventional outer housing. The turbine includes a radially enlarged disc element attached to the shaft for supporting at least one axial row of radially directed blades through which the steam is expanded. A prestressed concrete inner casing structure of the turbine has upstream and downstream portions respectively situated upstream and downstream from the disc element. The radially outer surfaces of the inner casing portions and radially outer periphery of the axially interposed disc cooperatively form a downwardly radially inwardly tapered surface. An annular steam flowpath of increasing flow area in the downward axial direction is radially bounded by the inner and outer prestressed concrete casing structures. The inner casing portions each include a transversely situated prestressed concrete circular wall for rotatably supporting the turbine shaft and associated structure. The turbine blades are substantially radially coextensive with the steam flowpath and receive steam from the evaporator through an annular array of prestressed concrete stationary vanes which extend between the inner and outer casings to provide structural support therefor and impart a desired flow direction to the steam.
NASA Astrophysics Data System (ADS)
Petrosyan, Lyudvig S.
2016-01-01
We study coherent transport in a system of periodic linear chain of quantum dots situated between two parallel quantum wires. We show that the resonant-tunneling conductance between the wires exhibits a Rabi splitting of the resonance peak as a function of Fermi energy in the wires. This effect is an electron transport analogue of the Rabi splitting in optical spectra of two interacting systems. The conductance peak splitting originates from the anticrossing of Bloch bands in a periodic system that is caused by a strong coupling between the electron states in the quantum dot chain and quantum wires.
Generalized Kronig-Penney model for ultracold atomic quantum systems
NASA Astrophysics Data System (ADS)
Negretti, A.; Gerritsma, R.; Idziaszek, Z.; Schmidt-Kaler, F.; Calarco, T.
2014-10-01
We study the properties of a quantum particle interacting with a one-dimensional structure of equidistant scattering centers. We derive an analytical expression for the dispersion relation and for the Bloch functions in the presence of both even and odd scattering waves within the pseudopotential approximation. This generalizes the well-known solid-state physics textbook result known as the Kronig-Penney model. Our generalized model can be used to describe systems such as degenerate Fermi gases interacting with ions or with another neutral atomic species confined in an optical lattice, thus enabling the investigation of polaron or Kondo physics within a simple formalism. We focus our attention on the specific atom-ion system and compare our findings with quantum defect theory. Excellent agreement is obtained within the regime of validity of the pseudopotential approximation. This enables us to derive a Bose-Hubbard Hamiltonian for a degenerate quantum Bose gas in a linear chain of ions.
Generation of cluster states in optomechanical quantum systems
NASA Astrophysics Data System (ADS)
Houhou, Oussama; Aissaoui, Habib; Ferraro, Alessandro
2015-12-01
We consider an optomechanical quantum system composed of a single cavity mode interacting with N mechanical resonators. We propose a scheme for generating continuous-variable graph states of arbitrary size and shape, including the so-called cluster states for universal quantum computation. The main feature of this scheme is that, differently from previous approaches, the graph states are hosted in the mechanical degrees of freedom rather than in the radiative ones. Specifically, via a 2 N -tone drive, we engineer a linear Hamiltonian which is instrumental to dissipatively drive the system to the desired target state. The robustness of this scheme is assessed against finite interaction times and mechanical noise, confirming it as a valuable approach towards quantum state engineering for continuous-variable computation in a solid-state platform.
Quantum Bound States in a C-C60 System
NASA Astrophysics Data System (ADS)
Adam, R. M.; Sofianos, S. A.
2015-03-01
We investigate the quantum mechanical system of a carbon "test atom" in the proximity of a C60 molecule, both inside and outside the fullerene "cage". Two sets of bound states are found to exist, a deeply bound set inside the cage and another weakly bound set outside it. Tunnelling between these regions is highly unlikely to happen because of the extreme height and width of the potential barrier. However, we predict that a layer of atoms could be adsorbed onto C60 by forming a quantum mechanical bound state, with the adsorbed atoms being concentrated above the "panels" of the buckyball, consistent with "bucky onions" observed experimentally. Until now analysis of such fullerene systems has been via classical mechanics, but a quantum approach reveals new insights.
Locality, entanglement, and thermalization of isolated quantum systems.
Khlebnikov, S; Kruczenski, M
2014-11-01
A way to understand thermalization in an isolated system is to interpret it as an increase in entanglement between subsystems. Here we test this idea through a combination of analytical and Krylov-subspace-based numerical methods applied to a quantum gas of bosons. We find that the entanglement entropy of a subsystem is rapidly generated at the initial state of the evolution, to quickly approach the thermal value. Our results also provide an accurate numerical test of the eigenstate thermalization hypothesis (ETH), according to which a single energy eigenstate of an isolated system behaves in certain respects as a thermal state. In the context of quantum black holes, we propose that the ETH is a quantum version of the classical no-hair theorem. PMID:25493719
Theoretical discussion for quantum computation in biological systems
NASA Astrophysics Data System (ADS)
Baer, Wolfgang
2010-04-01
Analysis of the brain as a physical system, that has the capacity of generating a display of every day observed experiences and contains some knowledge of the physical reality which stimulates those experiences, suggests the brain executes a self-measurement process described by quantum theory. Assuming physical reality is a universe of interacting self-measurement loops, we present a model of space as a field of cells executing such self-measurement activities. Empty space is the observable associated with the measurement of this field when the mass and charge density defining the material aspect of the cells satisfy the least action principle. Content is the observable associated with the measurement of the quantum wave function ? interpreted as mass-charge displacements. The illusion of space and its content incorporated into cognitive biological systems is evidence of self-measurement activity that can be associated with quantum operations.