Quantum field theory and coalgebraic logic in theoretical computer science.
Basti, Gianfranco; Capolupo, Antonio; Vitiello, Giuseppe
20170504
We suggest that in the framework of the Category Theory it is possible to demonstrate the mathematical and logical dual equivalence between the category of the qdeformed Hopf Coalgebras and the category of the qdeformed Hopf Algebras in quantum field theory (QFT), interpreted as a thermal field theory. Each pair algebracoalgebra characterizes a QFT system and its mirroring thermal bath, respectively, so to model dissipative quantum systems in farfromequilibrium conditions, with an evident significance also for biological sciences. Our study is in fact inspired by applications to neuroscience where the brain memory capacity, for instance, has been modeled by using the QFT unitarily inequivalent representations. The qdeformed Hopf Coalgebras and the qdeformed Hopf Algebras constitute two dual categories because characterized by the same functor T, related with the Bogoliubov transform, and by its contravariant application T(op), respectively. The qdeformation parameter is related to the Bogoliubov angle, and it is effectively a thermal parameter. Therefore, the different values of q identify univocally, and label the vacua appearing in the foliation process of the quantum vacuum. This means that, in the framework of Universal Coalgebra, as general theory of dynamic and computing systems ("labelled statetransition systems"), the so labelled infinitely many quantum vacua can be interpreted as the Final Coalgebra of an "Infinite State BlackBox Machine". All this opens the way to the possibility of designing a new class of universal quantum computing architectures based on this coalgebraic QFT formulation, as its ability of naturally generating a Fibonacci progression demonstrates. Copyright © 2017 Elsevier Ltd. All rights reserved.
Quantum noise in the mirrorfield system: A field theoretic approach
Hsiang, JenTsung; Wu, TaiHung; Lee, DaShin; King, SunKun; Wu, ChunHsien
20130215
We revisit the quantum noise problem in the mirrorfield system by a fieldtheoretic approach. Here a perfectly reflecting mirror is illuminated by a singlemode coherent state of the massless scalar field. The associated radiation pressure is described by a surface integral of the stresstensor of the field. The readout field is measured by a monopole detector, from which the effective distance between the detector and mirror can be obtained. In the slowmotion limit of the mirror, this fieldtheoretic approach allows to identify various sources of quantum noise that all in all leads to uncertainty of the readout measurement. In addition to wellknown sources from shot noise and radiation pressure fluctuations, a new source of noise is found from field fluctuations modified by the mirror's displacement. Correlation between different sources of noise can be established in the readout measurement as the consequence of interference between the incident field and the field reflected off the mirror. In the case of negative correlation, we found that the uncertainty can be lowered than the value predicted by the standard quantum limit. Since the particlenumber approach is often used in quantum optics, we compared results obtained by both approaches and examine its validity. We also derive a Langevin equation that describes the stochastic dynamics of the mirror. The underlying fluctuationdissipation relation is briefly mentioned. Finally we discuss the backreaction induced by the radiation pressure. It will alter the mean displacement of the mirror, but we argue this backreaction can be ignored for a slowly moving mirror.  Highlights: BlackRightPointingPointer The quantum noise problem in the mirrorfield system is revisited by a fieldtheoretic approach. BlackRightPointingPointer Other than the shot noise and radiation pressure noise, we show there are new sources of noise and correlation between them. BlackRightPointingPointer The noise correlations can
NASA Astrophysics Data System (ADS)
Schreck, M.
20141001
In the current paper the properties of a quantum field theory based on certain sets of Lorentzviolating coefficients in the nonminimal fermion sector of the Standard Model extension are analyzed. In particular, three families of coefficients are considered, where two of them are C P T even and the third is C P T odd. As a first step the modified fermion dispersion relations are obtained. Then the positive and negativeenergy solutions of the modified Dirac equation and the fermion propagator are derived. These are used to demonstrate the validity of the optical theorem at tree level, which provides a crosscheck for the results obtained. Furthermore unitarity is examined and seems to be valid for the first set of C P T even coefficients. However for the remaining sets certain issues with unitarity are found. The article demonstrates that the adapted quantum field theoretical methods at tree level work for the nonminimal, Lorentzviolating framework considered. Besides, the quantum field theory based on the first family of C P T even coefficients is most likely well behaved at lowest order perturbation theory. The results are important for future phenomenological investigations carried out in the context of field theory, e.g., the computation of decay rates and cross sections at tree level.
Plimak, L.I.; Fleischhauer, M.; Olsen, M.K.; Collett, M.J.
20030101
We present an introduction to phasespace techniques (PST) based on a quantumfieldtheoretical (QFT) approach. In addition to bridging the gap between PST and QFT, our approach results in a number of generalizations of the PST. First, for problems where the usual PST do not result in a genuine FokkerPlanck equation (even after phasespace doubling) and hence fail to produce a stochastic differential equation (SDE), we show how the system in question may be approximated via stochastic difference equations (S{delta}E). Second, we show that introducing sources into the SDE's (or S{delta}E's) generalizes them to a full quantum nonlinear stochastic response problem (thus generalizing Kubo's linear reaction theory to a quantum nonlinear stochastic response theory). Third, we establish general relations linking quantum response properties of the system in question to averages of operator products ordered in a way different from time normal. This extends PST to a much wider assemblage of operator products than are usually considered in phasespace approaches. In all cases, our approach yields a very simple and straightforward way of deriving stochastic equations in phase space.
NASA Astrophysics Data System (ADS)
Schreck, M.
20140501
In the context of the nonminimal Standard Model extension a special subset of the CPTeven higherdimensional operators in the photon sector is discussed from a quantum field theoretical point of view. The modified dispersion laws, photon polarization vectors and the gauge field propagator are obtained and their properties are analyzed. It is demonstrated that for certain sectors of the modified theory a puzzle arises for the optical theorem at tree level. This is followed by a discussion of how it can be interpreted and resolved at first order Lorentz violation. Furthermore the commutator of two gauge fields that are evaluated at different spacetime points is obtained and discussed. The structure of the theory is shown to resemble the structure of the modification based on the corresponding dimension4 operator. However some properties are altered due to the nonrenormalizable nature of the theory considered. The results provide more insight into the characteristics of Lorentzviolating quantum field theories that rest upon contributions of nonrenormalizable dimension.
Semiclassical and quantum field theoretic bounds for traversable Lorentzian stringy wormholes
Nandi, Kamal Kanti; Zhang Yuanzhong; Kumar, K.B. Vijaya
20040915
A lower bound on the size of a Lorentzian wormhole can be obtained by semiclassically introducing the Planck cutoff on the magnitude of tidal forces (HorowitzRoss constraint). Also, an upper bound is provided by the quantum field theoretic constraint in the form of the FordRoman Quantum Inequality for massless minimally coupled scalar fields. To date, however, exact static solutions belonging to this scalar field theory have not been worked out to verify these bounds. To fill this gap, we examine the wormhole features of two examples from the Einstein frame description of the vacuum low energy string theory in four dimensions which is the same as the minimally coupled scalar field theory. Analyses in this paper support the conclusion of Ford and Roman that wormholes in this theory can have sizes that are indeed only a few order of magnitudes larger than the Planck scale. It is shown that the two types of bounds are also compatible. In the process, we point out a 'wormhole' analog of naked black holes.
NASA Technical Reports Server (NTRS)
Zhang, Kuanshou; Xie, Changde; Peng, Kunchi
19960101
The dependence of the quantum fluctuation of the output fundamental and secondharmonic waves upon cavity configuration has been numerically calculated for the intracavity frequencydoubled laser. The results might provide a direct reference for the design of squeezing system through the secondharmonicgeneration.
ERIC Educational Resources Information Center
Matteucci, G.
20070101
In the socalled electric AharonovBohm effect, a quantum interference pattern shift is produced when electrons move in an electric field free region but, at the same time, in the presence of a timedependent electric potential. Analogous fringe shifts are observed in interference experiments where electrons, travelling through an electrostatic…
ERIC Educational Resources Information Center
Matteucci, G.
20070101
In the socalled electric AharonovBohm effect, a quantum interference pattern shift is produced when electrons move in an electric field free region but, at the same time, in the presence of a timedependent electric potential. Analogous fringe shifts are observed in interference experiments where electrons, travelling through an electrostatic…
Quantum turbulence: Theoretical and numerical problems
NASA Astrophysics Data System (ADS)
Nemirovskii, Sergey K.
20130301
The term “quantum turbulence” (QT) unifies the wide class of phenomena where the chaotic set of one dimensional quantized vortex filaments (vortex tangles) appear in quantum fluids and greatly influence various physical features. Quantum turbulence displays itself differently depending on the physical situation, and ranges from quasiclassical turbulence in flowing fluids to a near equilibrium set of loops in phase transition. The statistical configurations of the vortex tangles are certainly different in, say, the cases of counterflowing helium and a rotating bulk, but in all the physical situations very similar theoretical and numerical problems arise. Furthermore, quite similar situations appear in other fields of physics, where a chaotic set of one dimensional topological defects, such as cosmic strings, or linear defects in solids, or lines of darkness in nonlinear light fields, appear in the system. There is an interpenetration of ideas and methods between these scientific topics which are far apart in other respects. The main purpose of this review is to bring together some of the most commonly discussed results on quantum turbulence, focusing on analytic and numerical studies. We set out a series of results on the general theory of quantum turbulence which aim to describe the properties of the chaotic vortex configuration, starting from vortex dynamics. In addition we insert a series of particular questions which are important both for the whole theory and for the various applications. We complete the article with a discussion of the hot topic, which is undoubtedly mainstream in this field, and which deals with the quasiclassical properties of quantum turbulence. We discuss this problem from the point of view of the theoretical results stated in the previous sections. We also included section, which is devoted to the experimental and numerical suggestions based on the discussed theoretical models.
NASA Astrophysics Data System (ADS)
Kohandani, R.; Kaatuzian, H.
20150101
We report a theoretical study of optical properties of AlGaAs/GaAs multiple quantumwell (MQW), slowlight devices based on excitonic population oscillations under applied external magnetic and electric fields using an analytical model for complex dielectric constant of Wannier excitons in fractional dimension. The results are shown for quantum wells (QWs) of different width. The significant characteristics of the exciton in QWs such as exciton energy and exciton oscillator strength (EOS) can be varied by application of external magnetic and electric fields. It is found that a higher bandwidth and an appropriate slowdown factor (SDF) can be achieved by changing the QW width during the fabrication process and by applying magnetic and electric fields during device functioning, respectively. It is shown that a SDF of 105 is obtained at best.
Local, nonlocal quantumness and information theoretic measures
NASA Astrophysics Data System (ADS)
Agrawal, Pankaj; Sazim, Sk; Chakrabarty, Indranil; Pati, Arun K.
20160801
It has been suggested that there may exist quantum correlations that go beyond entanglement. The existence of such correlations can be revealed by information theoretic quantities such as quantum discord, but not by the conventional measures of entanglement. We argue that a state displays quantumness, that can be of local and nonlocal origin. Information theoretic measures not only characterize the nonlocal quantumness, but also the local quantumness, such as the “local superposition”. This can be a reason, why such measures are nonzero, when there is no entanglement. We consider a generalized version of the Werner state to demonstrate the interplay of local quantumness, nonlocal quantumness and classical mixedness of a state.
Classical and quantum fieldtheoretical approach to the nonlinear qKleinGordon equation
NASA Astrophysics Data System (ADS)
Plastino, A.; Rocca, M. C.
20161101
In the wake of efforts made Nobre and RegoMonteiro in EPL, 97 (2012) 41001 and J. Math. Phys., 54 (2913) 103302, we extend them here by developing the conventional Lagrangian treatment of a classical field theory (FT) to the qKleinGordon equation advanced in Phys. Rev. Lett., 106 (2011) 140601 and J. Math. Phys., 54 (2913) 103302 by the same authors, and the quantum theory corresponding to q=\\frac {3} {2} . This makes it possible to generate a putative conjecture regarding black matter. Our theory reduces to the usual FT for q→ 1 .
(Studies in quantum field theory)
Not Available
19900101
During the period 4/1/893/31/90 the theoretical physics group supported by Department of Energy Contract No. AC0278ER04915.A015 and consisting of Professors Bender and Shrauner, Associate Professor Papanicolaou, Assistant Professor Ogilvie, and Senior Research Associate Visser has made progress in many areas of theoretical and mathematical physics. Professors Bender and Shrauner, Associate Professor Papanicolaou, Assistant Professor Ogilvie, and Research Associate Visser are currently conducting research in many areas of high energy theoretical and mathematical physics. These areas include: strongcoupling approximation; classical solutions of nonAbelian gauge theories; meanfield approximation in quantum field theory; path integral and coherent state representations in quantum field theory; lattice gauge calculations; the nature of perturbation theory in large order; quark condensation in QCD; chiral symmetry breaking; the 1/N expansion in quantum field theory; effective potential and action in quantum field theories, including OCD; studies of the early universe and inflation, and quantum gravity.
NASA Astrophysics Data System (ADS)
Banks, Tom
20080901
1. Introduction; 2. Quantum theory of free scalar fields; 3. Interacting field theory; 4. Particles of spin one, and gauge invariance; 5. Spin 1/2 particles and Fermi statistics; 6. Massive quantum electrodynamics; 7. Symmetries, Ward identities and Nambu Goldstone bosons; 8. Nonabelian gauge theory; 9. Renormalization and effective field theory; 10. Instantons and solitons; 11. Concluding remarks; Appendices; References; Index.
Theoretical framework for quantum networks
NASA Astrophysics Data System (ADS)
Chiribella, Giulio; D'Ariano, Giacomo Mauro; Perinotti, Paolo
20090801
We present a framework to treat quantum networks and all possible transformations thereof, including as special cases all possible manipulations of quantum states, measurements, and channels, such as, e.g., cloning, discrimination, estimation, and tomography. Our framework is based on the concepts of quantum comb—which describes all transformations achievable by a given quantum network—and link product—the operation of connecting two quantum networks. Quantum networks are treated both from a constructive point of view—based on connections of elementary circuits—and from an axiomatic one—based on a hierarchy of admissible quantum maps. In the axiomatic context a fundamental property is shown, which we call universality of quantum memory channels: any admissible transformation of quantum networks can be realized by a suitable sequence of memory channels. The open problem whether this property fails for some nonquantum theory, e.g., for nosignaling boxes, is posed.
Pejov, Ljupčo; Petreska, Irina; Kocarev, Ljupčo
20151228
A theoretical proof of the concept that a particularly designed graphenebased moletronics device, constituted by two semiinfinite graphene subunits, acting as source and drain electrodes, and a central benzenoid ring rotator (a "quantum dot"), could act as a fieldcontrollable molecular switch is outlined and analyzed with the density functional theory approach. Besides the ideal (0 K) case, we also consider the operation of such a device under realistic operating (i.e., finitetemperature) conditions. An indepth insight into the physics behind device controllability by an external field was gained by thorough analyses of the torsional potential of the dot under various conditions (absence or presence of an external gating field with varying strength), computing the torsional correlation time and transition probabilities within the BloembergenPurcellPound formalism. Both classical and quantum mechanical tunneling contributions to the intramolecular rotation were considered in the model. The main idea that we put forward in the present study is that intramolecular rotors can be controlled by the gating field even in cases when these groups do not possess a permanent dipole moment (as in cases considered previously by us [I. Petreska et al., J. Chem. Phys. 134, 014708101470812 (2011)] and also by other groups [P. E. Kornilovitch et al., Phys. Rev. B 66, 24541312454137 (2002)]). Consequently, one can control the molecular switching properties by an external electrostatic field utilizing even nonpolar intramolecular rotors (i.e., in a more general case than those considered so far). Molecular admittance of the currently considered graphenebased molecular switch under various conditions is analyzed employing nonequilibrium Green's function formalism, as well as by analysis of frontier molecular orbitals' behavior.
NASA Astrophysics Data System (ADS)
Pejov, Ljupčo; Petreska, Irina; Kocarev, Ljupčo
20151201
A theoretical proof of the concept that a particularly designed graphenebased moletronics device, constituted by two semiinfinite graphene subunits, acting as source and drain electrodes, and a central benzenoid ring rotator (a "quantum dot"), could act as a fieldcontrollable molecular switch is outlined and analyzed with the density functional theory approach. Besides the ideal (0 K) case, we also consider the operation of such a device under realistic operating (i.e., finitetemperature) conditions. An indepth insight into the physics behind device controllability by an external field was gained by thorough analyses of the torsional potential of the dot under various conditions (absence or presence of an external gating field with varying strength), computing the torsional correlation time and transition probabilities within the BloembergenPurcellPound formalism. Both classical and quantum mechanical tunneling contributions to the intramolecular rotation were considered in the model. The main idea that we put forward in the present study is that intramolecular rotors can be controlled by the gating field even in cases when these groups do not possess a permanent dipole moment (as in cases considered previously by us [I. Petreska et al., J. Chem. Phys. 134, 014708101470812 (2011)] and also by other groups [P. E. Kornilovitch et al., Phys. Rev. B 66, 24541312454137 (2002)]). Consequently, one can control the molecular switching properties by an external electrostatic field utilizing even nonpolar intramolecular rotors (i.e., in a more general case than those considered so far). Molecular admittance of the currently considered graphenebased molecular switch under various conditions is analyzed employing nonequilibrium Green's function formalism, as well as by analysis of frontier molecular orbitals' behavior.
Pejov, Ljupčo; Petreska, Irina; Kocarev, Ljupčo
20151228
A theoretical proof of the concept that a particularly designed graphenebased moletronics device, constituted by two semiinfinite graphene subunits, acting as source and drain electrodes, and a central benzenoid ring rotator (a “quantum dot”), could act as a fieldcontrollable molecular switch is outlined and analyzed with the density functional theory approach. Besides the ideal (0 K) case, we also consider the operation of such a device under realistic operating (i.e., finitetemperature) conditions. An indepth insight into the physics behind device controllability by an external field was gained by thorough analyses of the torsional potential of the dot under various conditions (absence or presence of an external gating field with varying strength), computing the torsional correlation time and transition probabilities within the BloembergenPurcellPound formalism. Both classical and quantum mechanical tunneling contributions to the intramolecular rotation were considered in the model. The main idea that we put forward in the present study is that intramolecular rotors can be controlled by the gating field even in cases when these groups do not possess a permanent dipole moment (as in cases considered previously by us [I. Petreska et al., J. Chem. Phys. 134, 0147081–01470812 (2011)] and also by other groups [P. E. Kornilovitch et al., Phys. Rev. B 66, 2454131–2454137 (2002)]). Consequently, one can control the molecular switching properties by an external electrostatic field utilizing even nonpolar intramolecular rotors (i.e., in a more general case than those considered so far). Molecular admittance of the currently considered graphenebased molecular switch under various conditions is analyzed employing nonequilibrium Green’s function formalism, as well as by analysis of frontier molecular orbitals’ behavior.
NASA Astrophysics Data System (ADS)
Steffens, A.; Riofrío, C. A.; Hübener, R.; Eisert, J.
20141201
We introduce the concept of quantum field tomography, the efficient and reliable reconstruction of unknown quantum fields based on data of correlation functions. At the basis of the analysis is the concept of continuous matrix product states (cMPS), a complete set of variational states grasping states in onedimensional quantum field theory. We innovate a practical method, making use of and developing tools in estimation theory used in the context of compressed sensing such as Prony methods and matrix pencils, allowing us to faithfully reconstruct quantum field states based on loworder correlation functions. In the absence of a phase reference, we highlight how specific higher order correlation functions can still be predicted. We exemplify the functioning of the approach by reconstructing randomized cMPS from their correlation data and study the robustness of the reconstruction for different noise models. Furthermore, we apply the method to data generated by simulations based on cMPS and using the timedependent variational principle. The presented approach is expected to open up a new window into experimentally studying continuous quantum systems, such as those encountered in experiments with ultracold atoms on top of atom chips. By virtue of the analogy with the inputoutput formalism in quantum optics, it also allows for studying open quantum systems.
Diffeomorphisms of Quantum Fields
NASA Astrophysics Data System (ADS)
Kreimer, Dirk; Yeats, Karen
20170601
We study field diffeomorphisms φ (x)\\to F(φ (x))=a0φ (x)+a1φ 2(x)+\\ldots ={\\sum }_{j+0}^{\\infty } aj φ ^{j+1}, for free and interacting quantum fields Φ. We find that the theory is invariant under such diffeomorphisms if and only if kinematic renormalization schemes are used.
Matsumoto, Takafumi; Teki, Yoshio
20120807
The population transfer to the spinsublevels of the unique quartet (S = 3/2) highspin state of the strongly exchangecoupled (SC) radicaltriplet pair (for example, an AcceptorDonorRadical triad (ADR)) via a doubletquartet quantummixed (QM) state is theoretically investigated by a stochastic Liouville equation. In this work, we have treated the loss of the quantum coherence (decoherence) due to the dephasing during the population transfer and neglected the effect of other decoherence mechanisms. The dependences on the magnitude of the exchange coupling or the finestructure parameter of the QM state are investigated. The dependence on the velocity of the population transfer (by the electron transfer or the energytransfer) from the QM state to the SC quartet state is also clarified. It is revealed that the decoherence during the population transfer mainly originates from the finestructure term of the QM state in the doublettriplet exchange coupled systems. This decoherence leads to the unique dynamic electron polarization (DEP) on the highfield spin sublevels of the SC state, which is similar to the unique DEP pattern of the photoexcited triplet states of the reaction centers of photosystems I and II. The magnetic field dependence of the population transfer leading to the populations of the spinsublevels of the SC states is also calculated. The possibility of the control of energy transport, spin transport and information technology by using the QM state is discussed based on these results. The knowledge obtained in this work is useful in the spin dynamics of any doublettriplet exchange coupled systems.
Reverse engineering quantum field theory
NASA Astrophysics Data System (ADS)
Oeckl, Robert
20121201
An approach to the foundations of quantum theory is advertised that proceeds by "reverse engineering" quantum field theory. As a concrete instance of this approach, the general boundary formulation of quantum theory is outlined.
Theoretical issues in silicon quantum dot qubits
NASA Astrophysics Data System (ADS)
Koh, Teck Seng
Electricallygated quantum dots in semiconductors is an excellent architecture on which to make qubits for quantum information processing. Silicon is attractive because of the potential for excellent manipulability, scalability, and for integration with classical electronics. This thesis describes several aspects of the theoretical issues related to quantum dot qubits in silicon. It may be broadly divided into three parts — (1) the hybrid qubit and quantum gates, (2) decoherence and (3) charge transport. In the first part, we present a novel architecture for a double quantum dot spin qubit, which we term the hybrid qubit, and demonstrate that implementing this qubit in silicon is feasible. Next, we consider both AC and DC quantum gating protocols and compare the optimal fidelities for these protocols that can be achieved for both the hybrid qubit and the more traditional singlettriplet qubit. In the second part, we present evidence that silicon offers superior coherence properties by analyzing experimental data from which charge dephasing and spin relaxation times are extracted. We show that the internal degrees of freedom of the hybrid qubit enhance charge coherence, and demonstrate tunable spin loading of a quantum dot. In the last part, we explain three key features of spindependent transport — spin blockade, lifetimeenhanced transport and spinflip cotunneling. We explain how these features arise in the conventional twoelectron as well as the unconventional threeelectron regimes, using a theoretical model that captures the key characteristics observed in the data.
Quantum cellular automata and free quantum field theory
NASA Astrophysics Data System (ADS)
D'Ariano, Giacomo Mauro; Perinotti, Paolo
20170201
In a series of recent papers [14] it has been shown how free quantum field theory can be derived without using mechanical primitives (including spacetime, special relativity, quantization rules, etc.), but only considering the easiest quantum algorithm encompassing a countable set of quantum systems whose network of interactions satisfies the simple principles of unitarity, homogeneity, locality, and isotropy. This has opened the route to extending the axiomatic informationtheoretic derivation of the quantum theory of abstract systems [5, 6] to include quantum field theory. The inherent discrete nature of the informational axiomatization leads to an extension of quantum field theory to a quantum cellular automata theory, where the usual field theory is recovered in a regime where the discrete structure of the automata cannot be probed. A simple heuristic argument sets the scale of discreteness to the Planck scale, and the customary physical regime where discreteness is not visible is the relativistic one of small wavevectors. In this paper we provide a thorough derivation from principles that in the most general case the graph of the quantum cellular automaton is the Cayley graph of a finitely presented group, and showing how for the case corresponding to Euclidean emergent space (where the group resorts to an Abelian one) the automata leads to Weyl, Dirac and Maxwell field dynamics in the relativistic limit. We conclude with some perspectives towards the more general scenario of nonlinear automata for interacting quantum field theory.
Quantum field theory of fluids.
Gripaios, Ben; Sutherland, Dave
20150220
The quantum theory of fields is largely based on studying perturbations around noninteracting, or free, field theories, which correspond to a collection of quantummechanical harmonic oscillators. The quantum theory of an ordinary fluid is "freer", in the sense that the noninteracting theory also contains an infinite collection of quantummechanical free particles, corresponding to vortex modes. By computing a variety of correlation functions at tree and loop level, we give evidence that a quantum perfect fluid can be consistently formulated as a lowenergy, effective field theory. We speculate that the quantum behavior is radically different from both classical fluids and quantum fields.
Quantum algorithms for quantum field theories.
Jordan, Stephen P; Lee, Keith S M; Preskill, John
20120601
Quantum field theory reconciles quantum mechanics and special relativity, and plays a central role in many areas of physics. We developed a quantum algorithm to compute relativistic scattering probabilities in a massive quantum field theory with quartic selfinteractions (φ(4) theory) in spacetime of four and fewer dimensions. Its run time is polynomial in the number of particles, their energy, and the desired precision, and applies at both weak and strong coupling. In the strongcoupling and highprecision regimes, our quantum algorithm achieves exponential speedup over the fastest known classical algorithm.
Hybrid quantum teleportation: A theoretical model
Takeda, Shuntaro; Mizuta, Takahiro; Fuwa, Maria; Yoshikawa, Junichi; Yonezawa, Hidehiro; Furusawa, Akira
20141204
Hybrid quantum teleportation – continuousvariable teleportation of qubits – is a promising approach for deterministically teleporting photonic qubits. We propose how to implement it with current technology. Our theoretical model shows that faithful qubit transfer can be achieved for this teleportation by choosing an optimal gain for the teleporter’s classical channel.
Quantum Field Theory, Revised Edition
NASA Astrophysics Data System (ADS)
Mandl, F.; Shaw, G.
19940101
Quantum Field Theory Revised Edition F. Mandl and G. Shaw, Department of Theoretical Physics, The Schuster Laboratory, The University, Manchester, UK When this book first appeared in 1984, only a handful of W± and Z° bosons had been observed and the experimental investigation of high energy electroweak interactions was in its infancy. Nowadays, W± bosons and especially Z° bosons can be produced by the thousand and the study of their properties is a precise science. We have revised the text of the later chapters to incorporate these developments and discuss their implications. We have also taken this opportunity to update the references throughout and to make some improvements in the treatment of dimensional regularization. Finally, we have corrected some minor errors and are grateful to various people for pointing these out. This book is designed as a short and simple introduction to quantum field theory for students beginning research in theoretical and experimental physics. The three main objectives are to explain the basic physics and formalism of quantum field theory, to make the reader fully proficient in theory calculations using Feynman diagrams, and to introduce the reader to gauge theories, which play such a central role in elementary particle physics. The theory is applied to quantum electrodynamics (QED), where quantum field theory had its early triumphs, and to weak interactions where the standard electroweak theory has had many impressive successes. The treatment is based on the canonical quantization method, because readers will be familiar with this, because it brings out lucidly the connection between invariance and conservation laws, and because it leads directly to the Feynman diagram techniques which are so important in many branches of physics. In order to help inexperienced research students grasp the meaning of the theory and learn to handle it confidently, the mathematical formalism is developed from first principles, its physical
Quantum emitters dynamically coupled to a quantum field
NASA Astrophysics Data System (ADS)
Acevedo, O. L.; Quiroga, L.; Rodríguez, F. J.; Johnson, N. F.
20131201
We study theoretically the dynamical response of a set of solidstate quantum emitters arbitrarily coupled to a singlemode microcavity system. Ramping the matterfield coupling strength in round trips, we quantify the hysteresis or irreversible quantum dynamics. The matterfield system is modeled as a finitesize Dicke model which has previously been used to describe equilibrium (including quantum phase transition) properties of systems such as quantum dots in a microcavity. Here we extend this model to address nonequilibrium situations. Analyzing the system's quantum fidelity, we find that the nearadiabatic regime exhibits the richest phenomena, with a strong asymmetry in the internal collective dynamics depending on which phase is chosen as the starting point. We also explore signatures of the crossing of the critical points on the radiation subsystem by monitoring its Wigner function; then, the subsystem can exhibit the emergence of nonclassicality and complexity.
Quantum emitters dynamically coupled to a quantum field
Acevedo, O. L.; Quiroga, L.; Rodríguez, F. J.; Johnson, N. F.
20131204
We study theoretically the dynamical response of a set of solidstate quantum emitters arbitrarily coupled to a singlemode microcavity system. Ramping the matterfield coupling strength in round trips, we quantify the hysteresis or irreversible quantum dynamics. The matterfield system is modeled as a finitesize Dicke model which has previously been used to describe equilibrium (including quantum phase transition) properties of systems such as quantum dots in a microcavity. Here we extend this model to address nonequilibrium situations. Analyzing the system’s quantum fidelity, we find that the nearadiabatic regime exhibits the richest phenomena, with a strong asymmetry in the internal collective dynamics depending on which phase is chosen as the starting point. We also explore signatures of the crossing of the critical points on the radiation subsystem by monitoring its Wigner function; then, the subsystem can exhibit the emergence of nonclassicality and complexity.
Quantum Mechanics and Quantum Field Theory
NASA Astrophysics Data System (ADS)
Dimock, Jonathan
20110201
Introduction; Part I. Nonrelativistic: 1. Mathematical prelude; 2. Classical mechanics; 3. Quantum mechanics; 4. Single particle; 5. Many particles; 6. Statistical mechanics; Part II. Relativistic: 7. Relativity; 8. Scalar particles and fields; 9. Electrons and photons; 10. Field theory on a manifold; Part III. Probabilistic Methods: 11. Path integrals; 12. Fields as random variables; 13. A nonlinear field theory; Appendices; References; Index.
Domain theoretic structures in quantum information theory
NASA Astrophysics Data System (ADS)
Feng, Johnny
20111201
In this thesis, we continue the study of domain theoretic structures in quantum information theory initiated by Keye Martin and Bob Coecke in 2002. The first part of the thesis is focused on exploring the domain theoretic properties of qubit channels. We discover that the Scott continuous qubit channels are exactly those that are unital or constant. We then prove that the unital qubit channels form a continuous dcpo, and identify various measurements on them. We show that Holevo capacity is a measurement on unital qubit channels, and discover the natural measurement in this setting. We find that qubit channels also form a continuous dcpo, but capacity fails to be a measurement. In the second part we focus on the study of exact dcpos, a domain theoretic structure, closely related to continuous dcpos, possessed by quantum states. Exact dcpos admit a topology, called the exact topology, and we show that the exact topology has an order theoretic characterization similar to the characterization of the Scott topology on continuous dcpos. We then explore the connection between exact and continuous dcpos; first, by identifying an important set of points, called the split points, that distinguishes between exact and continuous structures; second, by exploring a continuous completion of exact dcpos, and showing that we can recover the exact topology from the Scott topology of the completion.
Quantum simulation of quantum field theory using continuous variables
NASA Astrophysics Data System (ADS)
Marshall, Kevin; Pooser, Raphael; Siopsis, George; Weedbrook, Christian
20151201
The year 1982 is often credited as the year that theoretical quantum computing was started with a keynote speech by Richard Feynman, who proposed a universal quantum simulator, the idea being that if you had such a machine you could in principle "imitate any quantum system, including the physical world." With that in mind, we present an algorithm for a continuousvariable quantum computing architecture which gives an exponential speedup over the bestknown classical methods. Specifically, this relates to efficiently calculating the scattering amplitudes in scalar bosonic quantum field theory, a problem that is believed to be hard using a classical computer. Building on this, we give an experimental implementation based on continuousvariable states that is feasible with today's technology.
Informationtheoretic temporal Bell inequality and quantum computation
Morikoshi, Fumiaki
20060515
An informationtheoretic temporal Bell inequality is formulated to contrast classical and quantum computations. Any classical algorithm satisfies the inequality, while quantum ones can violate it. Therefore, the violation of the inequality is an immediate consequence of the quantumness in the computation. Furthermore, this approach suggests a notion of temporal nonlocality in quantum computation.
Computational quantum field theory
NASA Astrophysics Data System (ADS)
Grobe, Rainer
20060501
I will give an overview on recent attempts to solve the timedependent Dirac equation for the electronpositron field operator. These numerical solutions permit a first temporally and spatially resolved insight into the mechanisms of how an electronpositron pair can be created from vacuum in a very strong force field. This approach has helped to illuminate a wide range of controversial questions. Some of these questions arise for complicated physical situations such as how an electron scatters off a supercritical potential barrier (Klein paradox). This requires the application of quantum field theory to study the combined effect of the pairproduction due to the supercriticality of the potential together with the scattering at the barrier involving the Pauliprinciple. Other phenomena include Schr"odinger's Zitterbewegung and the localization problem for a relativistic particle. This work has been supported by the NSF and Research Corporation. P. Krekora, K. Cooley, Q. Su and R. Grobe, Phys. Rev. Lett. 95, 070403 (2005). P. Krekora, Q. Su and R. Grobe, Phys. Rev. Lett. 93, 043004 (2004). P. Krekora, Q. Su and R. Grobe, Phys. Rev. Lett. 92, 040406 (2004).
Some Theoretical Studies of Disordered Quantum Systems.
NASA Astrophysics Data System (ADS)
Dobrosavljevic, Vladimir
19881201
In the first part of the thesis, two examples of disordered electronic systems are considered. I first investigate the role of conformational disorder relevant to the electronic structure of conjugated polymers such as polydiacetylene. Both in a solid and in solution the polymer undergoes a conformational transition accompanied by color changes as the temperature is increased. A simple statistical mechanical model for the transition is presented and solved, with the result defining the effective distribution of disorder for the electronic system. Renormalization group methods are then used to calculate the density of states and localization length for the model. Next, I study the fate of a hydrogenic atom in a hard sphere fluid. In this case, the disorder comes from the distribution of open spaces in the fluid accommodating the electron on its way around the nucleus. Simplified models for the electronic propagation in limits of small and large orbitals are presented. Simple variational methods can then be used to calculate the shift and broadening of spectral lines as a function of solvent density. In the second part, I examine the effects of quantum fluctuations on phase transitions in disordered systems. An example where such effects are manifestly important is the proton glassa random mixture of a ferroelectric and an antiferroelectric component. The system can be described using a quantum mechanical Ising spin glass model, and the meanfield theory is solved using a novel combination of discretized path integral methods and replica techniques. The results show that the glassy phase is more susceptible to destruction by tunneling than are the ordered phases. Finally, I also consider the role of randomness in the size of quantum fluctuations, on the example of an Ising model with randomly mixed classical and quantum spins. For this model, the existence of a critical concentration of quantum spins is demonstrated, below which tunneling cannot destroy the ordered
The facets of relativistic quantum field theory
NASA Astrophysics Data System (ADS)
Dosch, H. G.; Müller, V. F.
20110401
Relativistic quantum field theory is generally recognized to form the adequate theoretical frame for subatomic physics, with the Standard Model of Particle Physics as a major achievement. We point out that quantum field theory in its present form is not a monolithic theory, but rather consists of distinct facets, which aim at a common ideal goal. We give a short overview of the strengths and limitations of these facets. We emphasize the theorydependent relation between the quantum fields, and the basic objects in the empirical domain, the particles. Given the marked conceptual differences between the facets, we argue to view these, and therefore also the Standard Model, as symbolic constructions. We finally note that this view of physical theories originated in the 19th century and is related to the emergence of the classical field as an autonomous concept.
Monari, Antonio; Rivail, JeanLouis; Assfeld, Xavier
20130219
Molecular mechanics methods can efficiently compute the macroscopic properties of a large molecular system but cannot represent the electronic changes that occur during a chemical reaction or an electronic transition. Quantum mechanical methods can accurately simulate these processes, but they require considerably greater computational resources. Because electronic changes typically occur in a limited part of the system, such as the solute in a molecular solution or the substrate within the active site of enzymatic reactions, researchers can limit the quantum computation to this part of the system. Researchers take into account the influence of the surroundings by embedding this quantum computation into a calculation of the whole system described at the molecular mechanical level, a strategy known as the mixed quantum mechanics/molecular mechanics (QM/MM) approach. The accuracy of this embedding varies according to the types of interactions included, whether they are purely mechanical or classically electrostatic. This embedding can also introduce the induced polarization of the surroundings. The difficulty in QM/MM calculations comes from the splitting of the system into two parts, which requires severing the chemical bonds that link the quantum mechanical subsystem to the classical subsystem. Typically, researchers replace the quantoclassical atoms, those at the boundary between the subsystems, with a monovalent link atom. For example, researchers might add a hydrogen atom when a CC bond is cut. This Account describes another approach, the Local Self Consistent Field (LSCF), which was developed in our laboratory. LSCF links the quantum mechanical portion of the molecule to the classical portion using a strictly localized bond orbital extracted from a small model molecule for each bond. In this scenario, the quantoclassical atom has an apparent nuclear charge of +1. To achieve correct bond lengths and force constants, we must take into account the inner shell of
A Generalized Information Theoretical Model for Quantum Secret Sharing
NASA Astrophysics Data System (ADS)
Bai, ChenMing; Li, ZhiHui; Xu, TingTing; Li, YongMing
20161101
An information theoretical model for quantum secret sharing was introduced by H. Imai et al. (Quantum Inf. Comput. 5(1), 6980 2005), which was analyzed by quantum information theory. In this paper, we analyze this information theoretical model using the properties of the quantum access structure. By the analysis we propose a generalized model definition for the quantum secret sharing schemes. In our model, there are more quantum access structures which can be realized by our generalized quantum secret sharing schemes than those of the previous one. In addition, we also analyse two kinds of important quantum access structures to illustrate the existence and rationality for the generalized quantum secret sharing schemes and consider the security of the scheme by simple examples.
Noncommutative Quantum Scalar Field Cosmology
Diaz Barron, L. R.; LopezDominguez, J. C.; Sabido, M.; Yee, C.
20100712
In this work we study noncommutative FriedmannRobertsonWalker (FRW) cosmology coupled to a scalar field endowed with an exponential potential. The quantum scenario is analyzed in the Bohmian formalism of quantum trajectories to investigate the effects of noncommutativity in the evolution of the universe.
Quantum Field Theory in (0 + 1) Dimensions
ERIC Educational Resources Information Center
Boozer, A. D.
20070101
We show that many of the key ideas of quantum field theory can be illustrated simply and straightforwardly by using toy models in (0 + 1) dimensions. Because quantum field theory in (0 + 1) dimensions is equivalent to quantum mechanics, these models allow us to use techniques from quantum mechanics to gain insight into quantum field theory. In…
Quantum Field Theory in (0 + 1) Dimensions
ERIC Educational Resources Information Center
Boozer, A. D.
20070101
We show that many of the key ideas of quantum field theory can be illustrated simply and straightforwardly by using toy models in (0 + 1) dimensions. Because quantum field theory in (0 + 1) dimensions is equivalent to quantum mechanics, these models allow us to use techniques from quantum mechanics to gain insight into quantum field theory. In…
Quantum spectral dimension in quantum field theory
NASA Astrophysics Data System (ADS)
Calcagni, Gianluca; Modesto, Leonardo; Nardelli, Giuseppe
20160301
We reinterpret the spectral dimension of spacetimes as the scaling of an effective selfenergy transition amplitude in quantum field theory (QFT), when the system is probed at a given resolution. This picture has four main advantages: (a) it dispenses with the usual interpretation (unsatisfactory in covariant approaches) where, instead of a transition amplitude, one has a probability density solving a nonrelativistic diffusion equation in an abstract diffusion time; (b) it solves the problem of negative probabilities known for higherorder and nonlocal dispersion relations in classical and quantum gravity; (c) it clarifies the concept of quantum spectral dimension as opposed to the classical one. We then consider a class of logarithmic dispersion relations associated with quantum particles and show that the spectral dimension dS of spacetime as felt by these quantum probes can deviate from its classical value, equal to the topological dimension D. In particular, in the presence of higher momentum powers it changes with the scale, dropping from D in the infrared (IR) to a value dSUV ≤ D in the ultraviolet (UV). We apply this general result to Stelle theory of renormalizable gravity, which attains the universal value dSUV = 2 for any dimension D.
Sheaftheoretic representation of quantum measure algebras
Zafiris, Elias
20060915
We construct a sheaftheoretic representation of quantum probabilistic structures, in terms of covering systems of Boolean measure algebras. These systems coordinatize quantum states by means of Boolean coefficients, interpreted as Boolean localization measures. The representation is based on the existence of a pair of adjoint functors between the category of presheaves of Boolean measure algebras and the category of quantum measure algebras. The sheaftheoretic semantic transition of quantum structures shifts their physical significance from the orthoposet axiomatization at the level of events, to the sheaftheoretic gluing conditions at the level of Boolean localization systems.
Electric fields and quantum wormholes
NASA Astrophysics Data System (ADS)
Engelhardt, Dalit; Freivogel, Ben; Iqbal, Nabil
20150901
Electric fields can thread a classical EinsteinRosen bridge. Maldacena and Susskind have recently suggested that in a theory of dynamical gravity the entanglement of ordinary perturbative quanta should be viewed as creating a quantum version of an EinsteinRosen bridge between the particles, or a "quantum wormhole." We demonstrate within lowenergy effective field theory that there is a precise sense in which electric fields can also thread such quantum wormholes. We define a nonperturbative "wormhole susceptibility" that measures the ease of passing an electric field through any sort of wormhole. The susceptibility of a quantum wormhole is suppressed by powers of the U (1 ) gauge coupling relative to that for a classical wormhole but can be made numerically equal with a sufficiently large amount of entangled matter.
Quantum Simulation of Quantum Field Theories in Trapped Ions
Casanova, J.; Lamata, L.; Egusquiza, I. L.; Gerritsma, R.; Roos, C. F.; GarciaRipoll, J. J.; Solano, E.
20111223
We propose the quantum simulation of fermion and antifermion field modes interacting via a bosonic field mode, and present a possible implementation with two trapped ions. This quantum platform allows for the scalable add up of bosonic and fermionic modes, and represents an avenue towards quantum simulations of quantum field theories in perturbative and nonperturbative regimes.
Quantum simulation of quantum field theories in trapped ions.
Casanova, J; Lamata, L; Egusquiza, I L; Gerritsma, R; Roos, C F; GarcíaRipoll, J J; Solano, E
20111223
We propose the quantum simulation of fermion and antifermion field modes interacting via a bosonic field mode, and present a possible implementation with two trapped ions. This quantum platform allows for the scalable add up of bosonic and fermionic modes, and represents an avenue towards quantum simulations of quantum field theories in perturbative and nonperturbative regimes.
Some theoretical aspects of quantum mechanical equations in Rindler space
NASA Astrophysics Data System (ADS)
Mitra, Soma; Chakrabarty, Somenath
20170301
In this article we have investigated theoretical aspects of the solutions of some of the quantum mechanical problems in Rindler space. We have developed formalisms for the exact analytical solutions for the relativistic equations, along with the approximate form of solutions for the Schrödinger equation. The Hamiltonian operator in Rindler space is found to be nonHermitian in nature, whereas the energy eigen values are observed to be real in nature. We have noticed that the sole reason behind such real behavior is the PT symmetric form of the Hamiltonian operator. We have also observed that the energy eigen values are negative, lineraly quantized and the quantum mechanical system becomes more and more bound with the increase in the strength of gravitational field strength produced by the strongly gravitating objects, e.g., black holes, which is classical in nature.
NASA Astrophysics Data System (ADS)
Weinberg, Steven
19960801
In this second volume of The Quantum Theory of Fields, available for the first time in paperback, Nobel Laureate Steven Weinberg continues his masterly expoistion of quantum theory. Volume 2 provides an uptodate and selfcontained account of the methods of quantum field theory, and how they have led to an understanding of the weak, strong, and electromagnetic interactions of the elementary particles. The presentation of modern mathematical methods is throughout interwoven with accounts of the problems of elementary particle physics and condensed matter physics to which they have been applied. Exercises are included at the end of each chapter.
A quantum theoretical study of polyimides
NASA Technical Reports Server (NTRS)
Burke, Luke A.
19870101
One of the most important contributions of theoretical chemistry is the correct prediction of properties of materials before any costly experimental work begins. This is especially true in the field of electrically conducting polymers. Development of the Valence Effective Hamiltonian (VEH) technique for the calculation of the band structure of polymers was initiated. The necessary VEH potentials were developed for the sulfur and oxygen atoms within the particular molecular environments and the explanation explored for the success of this approximate method in predicting the optical properties of conducting polymers.
Quantum oscillations without magnetic field
NASA Astrophysics Data System (ADS)
Liu, Tianyu; Pikulin, D. I.; Franz, M.
20170101
When the magnetic field B is applied to a metal, nearly all observable quantities exhibit oscillations periodic in 1 /B . Such quantum oscillations reflect the fundamental reorganization of electron states into Landau levels as a canonical response of the metal to the applied magnetic field. We predict here that, remarkably, in the recently discovered Dirac and Weyl semimetals, quantum oscillations can occur in the complete absence of magnetic field. These zerofield quantum oscillations are driven by elastic strain which, in the space of the lowenergy Dirac fermions, acts as a chiral gauge potential. We propose an experimental setup in which the strain in a thin film (or nanowire) can generate a pseudomagnetic field b as large as 15 T and demonstrate the resulting de Haasvan Alphen and Shubnikovde Haas oscillations periodic in 1 /b .
Theoretical investigation of photonic quantum wells and defects
NASA Astrophysics Data System (ADS)
Jiang, Yuankai
In this dissertation, band gaps of photonic crystal slabs are calculated and single and multiple photonic quantum well systems are theoretically investigated. A comprehensive study of defects in the photonic crystal is also presented in the dissertation. The major milestones and current developments in the photonic crystal research are briefly outlined in the introduction. Four theoretical approaches most commonly applied in the photonic crystal studies are reviewed. They are the plane wave expansion method, finite difference time domain method, transfer matrix method and modal expansion with Rmatrix propagation algorithm. A comparison of these theoretical methods is discussed and the Rmatrix formalism is implemented in the present work. The modal expansion with Rmatrix propagation algorithm is applied to calculate the band gap for twodimensional photonic crystal slabs and the results are compared with experimental measurements and with other numerical calculations. Excellent agreement with experiments is found and the Rmatrix formalism proves to be more advantageous than other approaches. These advantages include its stability, efficiency and the fact that it can deal with finite photonic crystal slabs. The effect of the finite photonic slab on the band gap is also discussed. It is demonstrated that the band gap for a photonic slab structure can be controlled by the dielectric contrast, filling factor, filling geometry, lattice structure and polarization of the electric field. A photonic quantum well structure is proposed and investigated by the Rmatrix algorithm. The band gap of photonic materials with periodic spatial modulation of the refractive index greater than unity can actually be regarded as a potential barrier for photons. Similar to the semiconductor quantum well systems, a photonic quantum well can be constructed by sandwiching a uniform medium between two photonic barriers due to the photonic band gap mismatch. The transmission and reflection
Theoretical realization and application of paritytimesymmetric oscillators in a quantum regime
NASA Astrophysics Data System (ADS)
Li, Wenlin; Li, Chong; Song, Heshan
20170201
In the existing paritytime (PT ) symmetry with the balanced gain and loss, the gain is derived from semiclassical but not full quantum theories, which significantly restricts the applications of PT symmetry in quantum fields. In this work, we propose and analyze a theoretical scheme to realize full quantum oscillator PT symmetry. The quantum gain is provided by a dissipation optical cavity with a bluedetuned laser field. After adiabatically eliminating the cavity modes, we give an effective master equation, which is a complete quantum description compared with the nonHermitian Hamiltonian, to reveal the quantum behaviors of such a gain oscillator. This kind of PT symmetry can eliminate the dissipation effect in the quantum regime. As an example, we apply PT symmetric oscillators to enhance optomechanically induced transparency.
Gametheoretic discussion of quantum state estimation and cloning
NASA Astrophysics Data System (ADS)
Lee, Chiu Fan; Johnson, Neil F.
20031201
We present a gametheoretic perspective on the problems of quantum state estimation and quantum cloning. This enables us to show why the focus on universal machines and the different measures of success, as employed in previous works, are in fact legitimite.
Neutrino oscillations: quantum mechanics vs. quantum field theory
NASA Astrophysics Data System (ADS)
Akhmedov, Evgeny Kh.; Kopp, Joachim
20100401
A consistent description of neutrino oscillations requires either the quantummechanical (QM) wave packet approach or a quantum field theoretic (QFT) treatment. We compare these two approaches to neutrino oscillations and discuss the correspondence between them. In particular, we derive expressions for the QM neutrino wave packets from QFT and relate the free parameters of the QM framework, in particular the effective momentum uncertainty of the neutrino state, to the more fundamental parameters of the QFT approach. We include in our discussion the possibilities that some of the neutrino’s interaction partners are not detected, that the neutrino is produced in the decay of an unstable parent particle, and that the overlap of the wave packets of the particles involved in the neutrino production (or detection) process is not maximal. Finally, we demonstrate how the properly normalized oscillation probabilities can be obtained in the QFT framework without an ad hoc normalization procedure employed in the QM approach.
Neutrino oscillations: Quantum mechanics vs. quantum field theory
Akhmedov, Evgeny Kh.; Kopp, Joachim
20100101
A consistent description of neutrino oscillations requires either the quantummechanical (QM) wave packet approach or a quantum field theoretic (QFT) treatment. We compare these two approaches to neutrino oscillations and discuss the correspondence between them. In particular, we derive expressions for the QM neutrino wave packets from QFT and relate the free parameters of the QM framework, in particular the effective momentum uncertainty of the neutrino state, to the more fundamental parameters of the QFT approach. We include in our discussion the possibilities that some of the neutrino's interaction partners are not detected, that the neutrino is produced in the decay of an unstable parent particle, and that the overlap of the wave packets of the particles involved in the neutrino production (or detection) process is not maximal. Finally, we demonstrate how the properly normalized oscillation probabilities can be obtained in the QFT framework without an ad hoc normalization procedure employed in the QM approach.
Infinitetime average of local fields in an integrable quantum field theory after a quantum quench.
Mussardo, G
20130906
The infinitetime average of the expectation values of local fields of any interacting quantum theory after a global quench process are key quantities for matching theoretical and experimental results. For quantum integrable field theories, we show that they can be obtained by an ensemble average that employs a particular limit of the form factors of local fields and quantities extracted by the generalized Bethe ansatz.
A theoretical model of multiagent quantum computing
NASA Astrophysics Data System (ADS)
Mihelic, F. Matthew
20110501
The best design for practical quantum computing is one that emulates the multiagent quantum logic function of natural biological systems. Such systems are theorized to be based upon a quantum gate formed by a nucleic acid Szilard engine (NASE) that converts Shannon entropy of encountered molecules into useful work of nucleic acid geometric reconfiguration. This theoretical mechanism is logically and thermodynamically reversible in this special case because it is literally constructed out of the (nucleic acid) information necessary for its function, thereby allowing the nucleic acid Szilard engine to function reversibly because, since the information by which it functions exists on both sides of the theoretical mechanism simultaneously, there would be no buildup of information within the theoretical mechanism, and therefore no irreversible thermodynamic energy cost would be necessary to erase information inside the mechanism. This symmetry breaking Szilard engine function is associated with emission and/or absorption of entangled photons that can provide quantum synchronization of other nucleic acid segments within and between cells. In this manner nucleic acids can be considered as a natural model of topological quantum computing in which the nonabelian interaction of genes can be represented within quantum knot/braid theory as anyon crosses determined by entropic loss or gain that leads to changes in nucleic acid covalent bond angles. This naturally occurring biological form of topological quantum computing can serve as a model for workable manmade multiagent quantum computing systems.
Bohmian mechanics and quantum field theory.
Dürr, Detlef; Goldstein, Sheldon; Tumulka, Roderich; Zanghì, Nino
20040827
We discuss a recently proposed extension of Bohmian mechanics to quantum field theory. For more or less any regularized quantum field theory there is a corresponding theory of particle motion, which, in particular, ascribes trajectories to the electrons or whatever sort of particles the quantum field theory is about. Corresponding to the nonconservation of the particle number operator in the quantum field theory, the theory describes explicit creation and annihilation events: the world lines for the particles can begin and end.
Theoretical study of excitons in semiconductor quantum wires and related systems
NASA Astrophysics Data System (ADS)
Sidor, Yosyp
The main goal of this thesis is a theoretical study of the excitonic properties in semiconductor quantum wires. Excitons dominate the optical properties of these onedimensional structures, producing broad or sharp absorption and photoluminescence lines. The confinement of the electron and the hole is responsible for the properties of the exciton in a quantum wire. Confinement of the particles can be controlled through the size and shape of the quantum wire as well as through the selection of structure and barrier materials to produce various band offsets. The application of a magnetic field can give important information about the exciton confinement. Therefore, theoretical investigations of excitons in quantum wires is a strong theoretical tool to provide valuable information about quantum wire characteristics, as size uniformity, dimensions and photoluminescence spectrum. In the present thesis selfassembled InAs/InP and GaAs/AlGaAs Vshaped quantum wires are considered. The calculated photoluminescence transition energies in these structures are compared with available experimental data in order to deduce the dimensions of the wires. Both wires are investigated theoretically in the presence of an external magnetic field applied along different directions of the quantum wires. The computed exciton diamagnetic shift for both Vshaped and selfassembled quantum wires are reported and a detailed comparison is obtained with available magnetophotoluminescence experimental data. Since strain is important for the formation of the selfassembled quantum wires, results on the influence of strain on the electron and hole confinement will also be presented. Further, exciton coupling in selfassembled InAs/InP coupled quantum wires is considered. The charge confinement in InAs/InP based quantum wells and selfassembled quantum wires is examined, where for the narrow quantum well a local circular width fluctuation is included in order to describe the localization of the
Dirac's equation and the nature of quantum field theory
NASA Astrophysics Data System (ADS)
Plotnitsky, Arkady
20121101
This paper reexamines the key aspects of Dirac's derivation of his relativistic equation for the electron in order advance our understanding of the nature of quantum field theory. Dirac's derivation, the paper argues, follows the key principles behind Heisenberg's discovery of quantum mechanics, which, the paper also argues, transformed the nature of both theoretical and experimental physics visàvis classical physics and relativity. However, the limit theory (a crucial consideration for both Dirac and Heisenberg) in the case of Dirac's theory was quantum mechanics, specifically, Schrödinger's equation, while in the case of quantum mechanics, in Heisenberg's version, the limit theory was classical mechanics. Dirac had to find a new equation, Dirac's equation, along with a new type of quantum variables, while Heisenberg, to find new theory, was able to use the equations of classical physics, applied to different, quantummechanical variables. In this respect, Dirac's task was more similar to that of Schrödinger in his work on his version of quantum mechanics. Dirac's equation reflects a more complex character of quantum electrodynamics or quantum field theory in general and of the corresponding (highenergy) experimental quantum physics visàvis that of quantum mechanics and the (lowenergy) experimental quantum physics. The final section examines this greater complexity and its implications for fundamental physics.
Quantum field theory on a cosmological, quantum spacetime
Ashtekar, Abhay; Kaminski, Wojciech; Lewandowski, Jerzy
20090315
In loop quantum cosmology, FriedmannLeMaitreRobertsonWalker spacetimes arise as welldefined approximations to specific quantum geometries. We initiate the development of a quantum theory of test scalar fields on these quantum geometries. Emphasis is on the new conceptual ingredients required in the transition from classical spacetime backgrounds to quantum spacetimes. These include a ''relational time''a la Leibniz, the emergence of the Hamiltonian operator of the test field from the quantum constraint equation, and ramifications of the quantum fluctuations of the background geometry on the resulting dynamics. The familiar quantum field theory on classical FriedmannLeMaitreRobertsonWalker models arises as a welldefined reduction of this more fundamental theory.
A Universal Operator Theoretic Framework for Quantum Fault Tolerance.
NASA Astrophysics Data System (ADS)
Gilbert, Gerald; Calderbank, Robert; Aggarwal, Vaneet; Hamrick, Michael; Weinstein, Yaakov
20080301
We introduce a universal operator theoretic framework for quantum fault tolerance. This incorporates a topdown approach that implements a systemlevel criterion based on specification of the full system dynamics, applied at every level of error correction concatenation. This leads to more accurate determinations of error thresholds than could previously be obtained. The basis for the approach is the Quantum Computer Condition (QCC), an inequality governing the evolution of a quantum computer. In addition to more accurate determination of error threshold values, we show that the QCC provides a means to systematically determine optimality (or nonoptimality) of different choices of error correction coding and error avoidance strategies. This is possible because, as we show, all known coding schemes are actually special cases of the QCC. We demonstrate this by introducing a new, operator theoretic form of entanglement assisted quantum error correction.
Theoretically extensible quantum digital signature with starlike cluster states
NASA Astrophysics Data System (ADS)
Yang, YuGuang; Liu, ZhiChao; Li, Jian; Chen, XiuBo; Zuo, HuiJuan; Zhou, YiHua; Shi, WeiMin
20170101
Chen et al. (Phys Rev A 73:012303,
Quantum dynamics in strong fluctuating fields
NASA Astrophysics Data System (ADS)
Goychuk, Igor; Hänggi, Peter
A large number of multifaceted quantum transport processes in molecular systems and physical nanosystems, such as e.g. nonadiabatic electron transfer in proteins, can be treated in terms of quantum relaxation processes which couple to one or several fluctuating environments. A thermal equilibrium environment can conveniently be modelled by a thermal bath of harmonic oscillators. An archetype situation provides a twostate dissipative quantum dynamics, commonly known under the label of a spinboson dynamics. An interesting and nontrivial physical situation emerges, however, when the quantum dynamics evolves far away from thermal equilibrium. This occurs, for example, when a charge transferring medium possesses nonequilibrium degrees of freedom, or when a strong timedependent control field is applied externally. Accordingly, certain parameters of underlying quantum subsystem acquire stochastic character. This may occur, for example, for the tunnelling coupling between the donor and acceptor states of the transferring electron, or for the corresponding energy difference between electronic states which assume via the coupling to the fluctuating environment an explicit stochastic or deterministic timedependence. Here, we review the general theoretical framework which is based on the method of projector operators, yielding the quantum master equations for systems that are exposed to strong external fields. This allows one to investigate on a common basis, the influence of nonequilibrium fluctuations and periodic electrical fields on those already mentioned dynamics and related quantum transport processes. Most importantly, such strong fluctuating fields induce a whole variety of nonlinear and nonequilibrium phenomena. A characteristic feature of such dynamics is the absence of thermal (quantum) detailed balance.ContentsPAGE1. Introduction5262. Quantum dynamics in stochastic fields531 2.1. Stochastic Liouville equation531 2.2. NonMarkovian vs. Markovian discrete
Limitations on informationtheoreticallysecure quantum homomorphic encryption
NASA Astrophysics Data System (ADS)
Yu, Li; PérezDelgado, Carlos A.; Fitzsimons, Joseph F.
20141101
Homomorphic encryption is a form of encryption which allows computation to be carried out on the encrypted data without the need for decryption. The success of quantum approaches to related tasks in a delegated computation setting has raised the question of whether quantum mechanics may be used to achieve informationtheoreticallysecure fully homomorphic encryption. Here we show, via an information localization argument, that deterministic fully homomorphic encryption necessarily incurs exponential overhead if perfect security is required.
Zitterbewegung and quantum revivals in monolayer graphene quantum dots in magnetic fields
NASA Astrophysics Data System (ADS)
García, Trinidad; Cordero, Nicolás A.; Romera, Elvira
20140201
The wavepacket evolution in graphene quantum dots in magnetic fields has been theoretically studied. By analyzing an effective Hamiltonian model we show the wavepacket dynamics exhibits three types of periodicities (Zitterbewegung, classical, and revival times). The influence of the size of the quantum dot and the strength of the external magnetic field in these periodicities has been considered. In addition, we have found that valley degeneracy breaking is shown by both classical and revival times.
Quantum mechanics of Proca fields
NASA Astrophysics Data System (ADS)
Zamani, Farhad; Mostafazadeh, Ali
20090501
We construct the most general physically admissible positivedefinite inner product on the space of Proca fields. Up to a trivial scaling this defines a fiveparameter family of Lorentz invariant inner products that we use to construct a genuine Hilbert space for the quantum mechanics of Proca fields. If we identify the generator of time translations with the Hamiltonian, we obtain a unitary quantum system that describes firstquantized Proca fields and does not involve the conventional restriction to the positivefrequency fields. We provide a rather comprehensive analysis of this system. In particular, we examine the conserved current density responsible for the conservation of the probabilities, explore the global gauge symmetry underlying the conservation of the probabilities, obtain a probability current density, construct position, momentum, helicity, spin, and angular momentum operators, and determine the localized Proca fields. We also compute the generalized parity (P), generalized timereversal (T), and generalized charge or chirality (C) operators for this system and offer a physical interpretation for its PT, C, and CPTsymmetries.
Computational approach for calculating bound states in quantum field theory
NASA Astrophysics Data System (ADS)
Lv, Q. Z.; Norris, S.; Brennan, R.; Stefanovich, E.; Su, Q.; Grobe, R.
20160901
We propose a nonperturbative approach to calculate boundstate energies and wave functions for quantum field theoretical models. It is based on the direct diagonalization of the corresponding quantum field theoretical Hamiltonian in an effectively discretized and truncated Hilbert space. We illustrate this approach for a Yukawalike interaction between fermions and bosons in one spatial dimension and show where it agrees with the traditional method based on the potential picture and where it deviates due to recoil and radiative corrections. This method permits us also to obtain some insight into the spatial characteristics of the distribution of the fermions in the ground state, such as the bremsstrahlunginduced widening.
3D quantum gravity and effective noncommutative quantum field theory.
Freidel, Laurent; Livine, Etera R
20060609
We show that the effective dynamics of matter fields coupled to 3D quantum gravity is described after integration over the gravitational degrees of freedom by a braided noncommutative quantum field theory symmetric under a kappa deformation of the Poincaré group.
Haag's theorem in noncommutative quantum field theory
Antipin, K. V.; Mnatsakanova, M. N.; Vernov, Yu. S.
20130815
Haag's theorem was extended to the general case of noncommutative quantum field theory when time does not commute with spatial variables. It was proven that if S matrix is equal to unity in one of two theories related by unitary transformation, then the corresponding one in the other theory is equal to unity as well. In fact, this result is valid in any SO(1, 1)invariant quantum field theory, an important example of which is noncommutative quantum field theory.
Quantum transport in a twolevel quantum dot driven by coherent and stochastic fields
NASA Astrophysics Data System (ADS)
Ke, ShaSha; Miao, LingE.; Guo, Zhen; Guo, Yong; Zhang, HuaiWu; Lü, HaiFeng
20161201
We study theoretically the current and shot noise properties flowing through a twolevel quantum dot driven by a strong coherent field and a weak stochastic field. The interaction x(t) between the quantum dot and the stochastic field is assumed to be a GaussianMarkovian random process with zero mean value and correlation function < x (t) x (t ‧) > = Dκe  κ  t  t ‧  , where D and κ are the strength and bandwidth of the stochastic field, respectively. It is found that the stochastic field could enhance the resonant effect between the quantum dot and the coherent field, and generate new resonant points. At the resonant points, the state population difference between two levels is suppressed and the current is considerably enhanced. The zerofrequency shot noise of the current varies dramatically between sub and superPoissonian characteristics by tuning the stochastic field appropriately.
"Quantum Field Theory and QCD"
Jaffe, Arthur M.
20060225
This grant partially funded a meeting, "QFT & QCD: Past, Present and Future" held at Harvard University, Cambridge, MA on March 1819, 2005. The participants ranged from senior scientists (including at least 9 Nobel Prize winners, and 1 Fields medalist) to graduate students and undergraduates. There were several hundred persons in attendance at each lecture. The lectures ranged from superlative reviews of past progress, lists of important, unsolved questions, to provocative hypotheses for future discovery. The project generated a great deal of interest on the internet, raising awareness and interest in the open questions of theoretical physics.
Unusual signs in quantum field theory
NASA Astrophysics Data System (ADS)
O'Connell, Donal
Quantum field theory is by now a mature field. Nevertheless, certain physical phenomena remain difficult to understand. This occurs in some cases because wellestablished quantum field theories are strongly coupled and therefore difficult to solve; in other cases, our current understanding of quantum field theory seems to be inadequate. In this thesis, we will discuss various modifications of quantum field theory which can help to alleviate certain of these problems, either in their own right or as a component of a greater computational scheme. The modified theories we will consider all include unusual signs in some aspect of the theory. We will also discuss limitations on what we might expect to see in experiments, imposed by sign constraints in the customary formulation of quantum field theory.
Informationtheoretic implications of quantum causal structures.
Chaves, Rafael; Majenz, Christian; Gross, David
20150106
It is a relatively new insight of classical statistics that empirical data can contain information about causation rather than mere correlation. First algorithms have been proposed that are capable of testing whether a presumed causal relationship is compatible with an observed distribution. However, no systematic method is known for treating such problems in a way that generalizes to quantum systems. Here, we describe a general algorithm for computing informationtheoretic constraints on the correlations that can arise from a given causal structure, where we allow for quantum systems as well as classical random variables. The general technique is applied to two relevant cases: first, we show that the principle of information causality appears naturally in our framework and go on to generalize and strengthen it. Second, we derive bounds on the correlations that can occur in a networked architecture, where a set of fewbody quantum systems is distributed among some parties.
Atomic beam deflection in a quantum field
Graham, L.A.; Bharucha, C.; Moore, F.L.
19930501
Atomic beam deflection in a quantum field is studied theoretically for the case of an atom passing through the mode of a resonant optical cavity. Deflection probability is calculated for a coupling rate g of order g/2{pi}=1 MHz, which is experimentally feasible in a short optical cavity. Atomic velocities are taken in the range of 110 m/s, which can be reached with current cooling and trapping techniques. We calculate deflection for a coherent state with mean photon number
Exact integrability in quantum field theory
Thacker, H.B.
19800801
The treatment of exactly integrable systems in various branches of twodimensional classical and quantum physics has recently been placed in a unified framework by the development of the quantum inverse method. This method consolidates a broad range of developments in classical nonlinear wave (soliton) physics, statistical mechanics, and quantum field theory. The essential technique for analyzing exactly integrable quantum systems was invested by Bethe in 1931. The quantummechanical extension of the inverse scattering method and its relationship to the methods associated with Bethe's ansatz are examined here. (RWR)
Quantum simulation of quantum field theory using continuous variables
Marshall, Kevin; Pooser, Raphael C.; Siopsis, George; Weedbrook, Christian
20151214
Much progress has been made in the field of quantum computing using continuous variables over the last couple of years. This includes the generation of extremely large entangled cluster states (10,000 modes, in fact) as well as a fault tolerant architecture. This has lead to the point that continuousvariable quantum computing can indeed be thought of as a viable alternative for universal quantum computing. With that in mind, we present a new algorithm for continuousvariable quantum computers which gives an exponential speedup over the best known classical methods. Specifically, this relates to efficiently calculating the scattering amplitudes in scalar bosonic quantum field theory, a problem that is known to be hard using a classical computer. Thus, we give an experimental implementation based on cluster states that is feasible with today's technology.
Quantum simulation of quantum field theory using continuous variables
Marshall, Kevin; Pooser, Raphael C.; Siopsis, George; ...
20151214
Much progress has been made in the field of quantum computing using continuous variables over the last couple of years. This includes the generation of extremely large entangled cluster states (10,000 modes, in fact) as well as a fault tolerant architecture. This has lead to the point that continuousvariable quantum computing can indeed be thought of as a viable alternative for universal quantum computing. With that in mind, we present a new algorithm for continuousvariable quantum computers which gives an exponential speedup over the best known classical methods. Specifically, this relates to efficiently calculating the scattering amplitudes in scalar bosonicmore » quantum field theory, a problem that is known to be hard using a classical computer. Thus, we give an experimental implementation based on cluster states that is feasible with today's technology.« less
Theoretical discussion for quantum computation in biological systems
NASA Astrophysics Data System (ADS)
Baer, Wolfgang
20100401
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 selfmeasurement process described by quantum theory. Assuming physical reality is a universe of interacting selfmeasurement loops, we present a model of space as a field of cells executing such selfmeasurement 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 ψ interpreted as masscharge displacements. The illusion of space and its content incorporated into cognitive biological systems is evidence of selfmeasurement activity that can be associated with quantum operations.
Dissipative quantum transport in macromolecules: Effective field theory approach
NASA Astrophysics Data System (ADS)
Schneider, E.; a Beccara, S.; Faccioli, P.
20130801
We introduce an atomistic approach to the dissipative quantum dynamics of charged or neutral excitations propagating through macromolecular systems. Using the FeynmanVernon path integral formalism, we analytically trace out from the density matrix the atomic coordinates and the heat bath degrees of freedom. This way we obtain an effective field theory which describes the realtime evolution of the quantum excitation and is fully consistent with the fluctuationdissipation relation. The main advantage of the fieldtheoretic approach is that it allows us to avoid using the Keldysh contour formulation. This simplification makes it straightforward to derive Feynman diagrams to analytically compute the effects of the interaction of the propagating quantum excitation with the heat bath and with the molecular atomic vibrations. For illustration purposes, we apply this formalism to investigate the loss of quantum coherence of holes propagating through a poly(3alkylthiophene) polymer.
Nearfield levitated quantum optomechanics with nanodiamonds
NASA Astrophysics Data System (ADS)
Juan, M. L.; MolinaTerriza, G.; Volz, T.; RomeroIsart, O.
20160801
We theoretically show that the dipole force of an ensemble of quantum emitters embedded in a dielectric nanosphere can be exploited to achieve nearfield optical levitation. The key ingredient is that the polarizability from the ensemble of embedded quantum emitters can be larger than the bulk polarizability of the sphere, thereby enabling the use of repulsive optical potentials and consequently the levitation using optical near fields. In levitated cavity quantum optomechanics, this could be used to boost the singlephoton coupling by combining larger polarizability to mass ratio, larger field gradients, and smaller cavity volumes while remaining in the resolved sideband regime and at room temperature. A case study is done with a nanodiamond containing a high density of siliconvacancy color centers that is optically levitated in the evanescent field of a tapered nanofiber and coupled to a highfinesse microsphere cavity.
Simulating quantum fields with cavity QED.
Barrett, Sean; Hammerer, Klemens; Harrison, Sarah; Northup, Tracy E; Osborne, Tobias J
20130301
As the realization of a fully operational quantum computer remains distant, quantum simulation, whereby one quantum system is engineered to simulate another, becomes a key goal of great practical importance. Here we report on a variational method exploiting the natural physics of cavity QED architectures to simulate strongly interacting quantum fields. Our scheme is broadly applicable to any architecture involving tunable and strongly nonlinear interactions with light; as an example, we demonstrate that existing cavity devices could simulate models of strongly interacting bosons. The scheme can be extended to simulate systems of entangled multicomponent fields, beyond the reach of existing classical simulation methods.
Quantum critical scaling in betaYbAlB4 and theoretical implications
NASA Astrophysics Data System (ADS)
Nevidomskyy, Andriy
20120201
Emergent phenomena in quantum materials are subject of intense experimental and theoretical research at present. A wonderful example thereof are the sister phases of YbAlB4  a newly discovered heavy fermion material [1]. While one phase (αYbAlB4) is a heavy Fermi liquid, its sibling βYbAlB4 is quantum critical, supporting an unconventional superconductivity with a tiny transition temperature of ˜80 mK. Latest experiments [2] uncover the quantum critical T/Bscaling in βYbAlB4 and prove that superconductivity emerges from a strange metal governed by an extremely fragile quantum criticality, which apparently occurs at zero field, without any external tuning. Here, we will present a theoretical perspective on the quantum critical scaling in βYbAlB4 and will show that the critical exponents can be derived from the nodal structure of the hybridization matrix between Yb fband and the conduction electrons. It follows that the free energy at low temperatures can be written in a scaling form F[(kBT)^2 + (gμBB)^2]^3/4, which predicts the divergent Sommerfeld coefficient γ and quasiparticle effective mass as B>0: γ˜m^*/m B1/2. This is indeed observed in the experiment [1,2], which places a tiny upper bound on the critical magnetic field Bc<0.2 mT. We will discuss theoritical implications of this fragile intrinsic quantum criticality in βYbAlB4 and discuss the possibility of a quantum critical phase, rather than a quantum critical point, in this material. [1] S. Nakatsuji et al., Nature Physics 4, 603 (2008). [2] Y. Matsumoto, S. Nakatsuji, K. Kuga, Y. Karaki, Y. Shimura, T. Sakakibara, A. H. Nevidomskyy, and P. Coleman, Science 331, 316 (2011).
Externally controlled local magnetic field in a conducting mesoscopic ring coupled to a quantum wire
Maiti, Santanu K.
20150114
In the present work, the possibility of regulating local magnetic field in a quantum ring is investigated theoretically. The ring is coupled to a quantum wire and subjected to an inplane electric field. Under a finite bias voltage across the wire a net circulating current is established in the ring which produces a strong magnetic field at its centre. This magnetic field can be tuned externally in a wide range by regulating the inplane electric field, and thus, our present system can be utilized to control magnetic field at a specific region. The feasibility of this quantum system in designing spinbased quantum devices is also analyzed.
Free Quantum Field Theory from Quantum Cellular Automata
NASA Astrophysics Data System (ADS)
Bisio, Alessandro; D'Ariano, Giacomo Mauro; Perinotti, Paolo; Tosini, Alessandro
20151001
After leading to a new axiomatic derivation of quantum theory (see D'Ariano et al. in Found Phys, 2015), the new informational paradigm is entering the domain of quantum field theory, suggesting a quantum automata framework that can be regarded as an extension of quantum field theory to including an hypothetical Planck scale, and with the usual quantum field theory recovered in the relativistic limit of small wavevectors. Being derived from simple principles (linearity, unitarity, locality, homogeneity, isotropy, and minimality of dimension), the automata theory is quantum abinitio, and does not assume Lorentz covariance and mechanical notions. Being discrete it can describe localized states and measurements (unmanageable by quantum field theory), solving all the issues plaguing field theory originated from the continuum. These features make the theory an ideal framework for quantum gravity, with relativistic covariance and spacetime emergent solely from the interactions, and not assumed a priori. The paper presents a synthetic derivation of the automata theory, showing how the principles lead to a description in terms of a quantum automaton over a Cayley graph of a group. Restricting to Abelian groups we show how the automata recover the Weyl, Dirac and Maxwell dynamics in the relativistic limit. We conclude with some new routes about the more general scenario of nonAbelian Cayley graphs. The phenomenology arising from the automata theory in the ultrarelativistic domain and the analysis of corresponding distorted Lorentz covariance is reviewed in Bisio et al. (Found Phys 2015, in this same issue).
NASA Astrophysics Data System (ADS)
Jooya, Hossein Z.; Reihani, Kamran; Chu, ShihI.
20161101
We propose a graphtheoretical formalism to study generic circuit quantum electrodynamics systems consisting of a two level qubit coupled with a singlemode resonator in arbitrary coupling strength regimes beyond rotatingwave approximation. We define coloredweighted graphs, and introduce different products between them to investigate the dynamics of superconducting qubits in transverse, longitudinal, and bidirectional coupling schemes. The intuitive and predictive picture provided by this method, and the simplicity of the mathematical construction, are demonstrated with some numerical studies of the multiphoton resonance processes and quantum interference phenomena for the superconducting qubit systems driven by intense ac fields.
Jooya, Hossein Z.; Reihani, Kamran; Chu, ShihI
20161121
We propose a graphtheoretical formalism to study generic circuit quantum electrodynamics systems consisting of a two level qubit coupled with a singlemode resonator in arbitrary coupling strength regimes beyond rotatingwave approximation. We define coloredweighted graphs, and introduce different products between them to investigate the dynamics of superconducting qubits in transverse, longitudinal, and bidirectional coupling schemes. In conclusion, the intuitive and predictive picture provided by this method, and the simplicity of the mathematical construction, are demonstrated with some numerical studies of the multiphoton resonance processes and quantum interference phenomena for the superconducting qubit systems driven by intense ac fields.
Jooya, Hossein Z.; Reihani, Kamran; Chu, ShihI
20160101
We propose a graphtheoretical formalism to study generic circuit quantum electrodynamics systems consisting of a two level qubit coupled with a singlemode resonator in arbitrary coupling strength regimes beyond rotatingwave approximation. We define coloredweighted graphs, and introduce different products between them to investigate the dynamics of superconducting qubits in transverse, longitudinal, and bidirectional coupling schemes. The intuitive and predictive picture provided by this method, and the simplicity of the mathematical construction, are demonstrated with some numerical studies of the multiphoton resonance processes and quantum interference phenomena for the superconducting qubit systems driven by intense ac fields. PMID:27869230
Jooya, Hossein Z.; Reihani, Kamran; Chu, ShihI
20161121
We propose a graphtheoretical formalism to study generic circuit quantum electrodynamics systems consisting of a two level qubit coupled with a singlemode resonator in arbitrary coupling strength regimes beyond rotatingwave approximation. We define coloredweighted graphs, and introduce different products between them to investigate the dynamics of superconducting qubits in transverse, longitudinal, and bidirectional coupling schemes. The intuitive and predictive picture provided by this method, and the simplicity of the mathematical construction, are demonstrated with some numerical studies of the multiphoton resonance processes and quantum interference phenomena for the superconducting qubit systems driven by intense ac fields.
Classical field approach to quantum weak measurements.
Dressel, Justin; Bliokh, Konstantin Y; Nori, Franco
20140321
By generalizing the quantum weak measurement protocol to the case of quantum fields, we show that weak measurements probe an effective classical background field that describes the average field configuration in the spacetime region between pre and postselection boundary conditions. The classical field is itself a weak value of the corresponding quantum field operator and satisfies equations of motion that extremize an effective action. Weak measurements perturb this effective action, producing measurable changes to the classical field dynamics. As such, weakly measured effects always correspond to an effective classical field. This general result explains why these effects appear to be robust for pre and postselected ensembles, and why they can also be measured using classical field techniques that are not weak for individual excitations of the field.
Pilotwave theory and quantum fields
NASA Astrophysics Data System (ADS)
Struyve, Ward
20101001
Pilotwave theories provide possible solutions to the measurement problem. In such theories, quantum systems are not only described by the state vector but also by some additional variables. These additional variables, also called beables, can be particle positions, field configurations, strings, etc. In this paper we focus our attention on pilotwave theories in which the additional variables are field configurations. The first such theory was proposed by Bohm for the free electromagnetic field. Since Bohm, similar pilotwave theories have been proposed for other quantum fields. The purpose of this paper is to present an overview and further development of these proposals. We discuss various bosonic quantum field theories such as the Schrödinger field, the free electromagnetic field, scalar quantum electrodynamics and the Abelian Higgs model. In particular, we compare the pilotwave theories proposed by Bohm and by Valentini for the electromagnetic field, finding that they are equivalent. We further discuss the proposals for fermionic fields by Holland and Valentini. In the case of Holland's model we indicate that further work is required in order to show that the model is capable of reproducing the standard quantum predictions. We also consider a similar model, which does not seem to reproduce the standard quantum predictions. In the case of Valentini's model we point out a problem that seems hard to overcome.
Magneticfield and quantum confinement asymmetry effects on excitons
Pereyra, P.; Ulloa, S. E.
20000115
A theoretical analysis and calculation of the excitonic states in asymmetric quantum dots is carried out in the presence of magnetic fields. The lack of rotational symmetry, introduced by strains and structural factors, produces splittings of the excitonic states with corresponding consequences on the optical oscillator strengths and polarization dependence. For example, we find that the asymmetry produces Zeeman splittings that are smaller than those for symmetric dots at small fields, which could be used as an additional diagnostic of the geometry of the structure. We focus our calculations on naturally occurring quantum dots due to layer fluctuations in narrow quantum wells. Moreover, we observe that increasing magnetic fields produce an interesting crossover to pure angular momentum states for all the excitonic eigenstates, regardless of the degree of asymmetry of the dots and their size. Explicit calculations of photoluminescence excitation yields are presented and related to the different degrees of freedom of the system. (c) 2000 The American Physical Society.
Maxwell's demon. (II) A quantumtheoretic exorcism
NASA Astrophysics Data System (ADS)
Gyftopoulos, Elias P.
20020501
In Part II of this twopart paper we prove that Maxwell's demon is unable to accomplish his task of sorting air molecules into swift and slow because in air in a thermodynamic equilibrium state there are no such molecules. The proof is based on the principles of a unified quantum theory of mechanics and thermodynamics. The key idea of the unified theory is that von Neumann's concept of a homogeneous ensemble of identical systems, identically prepared, is valid not only for a density operator ρ equal to a projector (every member of the ensemble is assigned the same projector, ρi= ψi> < ψi= ρi2, or the same wave function ψ i as any other member) but also for a density operator that is not a projector (every member of the ensemble is assigned the same density operator, ρ>ρ 2, as any other member). So, the latter ensemble is not a statistical mixture of projectors. The broadening of the validity of the homogeneous ensemble is consistent with the quantumtheoretic postulates about observables, measurement results, and value of any observable. In the context of the unified theory, among the many novel results is the theorem that each molecule of a system in a thermodynamic equilibrium state has zero value of momentum, that is, each molecule is at a standstill and, therefore, there are no molecules to be sorted as swift and slow. Said differently, if Maxwell were cognizant of quantum theory, he would not have conceived of the idea of the demon. It is noteworthy that the zero value of momentum is not the result of averaging over different momenta of many molecules. Under the specified conditions, it is the quantumtheoretic value of the momentum of any one molecule, and the same result is valid even if the system consists of only one molecule.
Exact quantum field mappings between different experiments on quantum gases
NASA Astrophysics Data System (ADS)
Wamba, Etienne; Pelster, Axel; Anglin, James R.
20161001
Experiments on trapped quantum gases can probe challenging regimes of quantum manybody dynamics, where strong interactions or nonequilibrium states prevent exact solutions. Here we present a different kind of exact result, which applies even in the absence of actual solutions: a class of spacetime mappings of different experiments onto each other. Since our result is an identity relating secondquantized field operators in the Heisenberg picture of quantum mechanics, it is extremely general; it applies to arbitrary measurements on any mixtures of Bose or Fermi gases, in arbitrary initial states. It represents a strong prediction of quantum field theory which can be tested in current laboratories, and whose practical applications include perfect simulation of interesting experiments with other experiments which may be easier to perform.
Theoretical analysis of quantum ghost imaging through turbulence
Chan, Kam Wai Clifford; Simon, D. S.; Sergienko, A. V.; Hardy, Nicholas D.; Shapiro, Jeffrey H.; Dixon, P. Ben; Howland, Gregory A.; Howell, John C.; Eberly, Joseph H.; O'Sullivan, Malcolm N.; Rodenburg, Brandon; Boyd, Robert W.
20111015
Atmospheric turbulence generally affects the resolution and visibility of an image in longdistance imaging. In a recent quantum ghost imaging experiment [P. B. Dixon et al., Phys. Rev. A 83, 051803 (2011)], it was found that the effect of the turbulence can nevertheless be mitigated under certain conditions. This paper gives a detailed theoretical analysis to the setup and results reported in the experiment. Entangled photons with a finite correlation area and a turbulence model beyond the phase screen approximation are considered.
Fields and Laplacians on Quantum Geometries
NASA Astrophysics Data System (ADS)
Thürigen, Johannes
20150101
In fundamentally discrete approaches to quantum gravity such as loop quantum gravity, spinfoam models, group field theories or Regge calculus observables are functions on discrete geometries. We present a braket formalism of function spaces and discrete calculus on abstract simplicial complexes equipped with geometry and apply it to the mentioned theories of quantum gravity. In particular we focus on the quantum geometric Laplacian and discuss as an example the expectation value of the heat kernel trace from which the spectral dimension follows.
Role of information theoretic uncertainty relations in quantum theory
Jizba, Petr; Dunningham, Jacob A.; Joo, Jaewoo
20150415
Uncertainty relations based on information theory for both discrete and continuous distribution functions are briefly reviewed. We extend these results to account for (differential) Rényi entropy and its related entropy power. This allows us to find a new class of informationtheoretic uncertainty relations (ITURs). The potency of such uncertainty relations in quantum mechanics is illustrated with a simple twoenergylevel model where they outperform both the usual Robertson–Schrödinger uncertainty relation and Shannon entropy based uncertainty relation. In the continuous case the ensuing entropy power uncertainty relations are discussed in the context of heavy tailed wave functions and Schrödinger cat states. Again, improvement over both the Robertson–Schrödinger uncertainty principle and Shannon ITUR is demonstrated in these cases. Further salient issues such as the proof of a generalized entropy power inequality and a geometric picture of informationtheoretic uncertainty relations are also discussed.
Quantum equivalence of dual field theories
NASA Astrophysics Data System (ADS)
Fradkin, E. S.; Tseytlin, A. A.
19850601
Motivated by the study of ultraviolet properties of different versions of supergravities duality transformations at the quantum level are discussed. Using the background field method it is proven on shell quantum equivalence for several pairs of dual field theories known to be classically equivalent. The examples considered include duality in chiral model, duality of scalars and second rank antisymmetric gauge tensors, vector duality and duality of the Einstein theory with cosmological term and the EddingtonSchrödinger theory.
Geometric continuum regularization of quantum field theory
Halpern, M.B. . Dept. of Physics)
19891108
An overview of the continuum regularization program is given. The program is traced from its roots in stochastic quantization, with emphasis on the examples of regularized gauge theory, the regularized general nonlinear sigma model and regularized quantum gravity. In its coordinateinvariant form, the regularization is seen as entirely geometric: only the supermetric on field deformations is regularized, and the prescription provides universal nonperturbative invariant continuum regularization across all quantum field theory. 54 refs.
Arrival time in quantum field theory
NASA Astrophysics Data System (ADS)
Wang, ZhiYong; Xiong, CaiDong; He, Bing
20080901
Via the propertime eigenstates (event states) instead of the propermass eigenstates (particle states), freemotion timeofarrival theory for massive spin1/2 particles is developed at the level of quantum field theory. The approach is based on a positionmomentum dual formalism. Within the framework of field quantization, the total timeofarrival is the sum of the single eventofarrival contributions, and contains zeropoint quantum fluctuations because the clocks under consideration follow the laws of quantum mechanics.
Macroscopic QuantumType Potentials in Theoretical Systems Biology
Nottale, Laurent
20140101
We review in this paper the use of the theory of scale relativity and fractal spacetime as a tool particularly well adapted to the possible development of a future genuine systems theoretical biology. We emphasize in particular the concept of quantumtype potentials, since, in many situations, the effect of the fractality of space—or of the underlying medium—can be reduced to the addition of such a potential energy to the classical equations of motion. Various equivalent representations—geodesic, quantumlike, fluid mechanical, stochastic—of these equations are given, as well as several forms of generalized quantum potentials. Examples of their possible intervention in high critical temperature superconductivity and in turbulence are also described, since some biological processes may be similar in some aspects to these physical phenomena. These potential extra energy contributions could have emerged in biology from the very fractal nature of the medium, or from an evolutive advantage, since they involve spontaneous properties of selforganization, morphogenesis, structuration and multiscale integration. Finally, some examples of applications of the theory to actual biologicallike processes and functions are also provided. PMID:24709901
Macroscopic quantumtype potentials in theoretical systems biology.
Nottale, Laurent
20131230
We review in this paper the use of the theory of scale relativity and fractal spacetime as a tool particularly well adapted to the possible development of a future genuine systems theoretical biology. We emphasize in particular the concept of quantumtype potentials, since, in many situations, the effect of the fractality of spaceor of the underlying mediumcan be reduced to the addition of such a potential energy to the classical equations of motion. Various equivalent representationsgeodesic, quantumlike, fluid mechanical, stochasticof these equations are given, as well as several forms of generalized quantum potentials. Examples of their possible intervention in high critical temperature superconductivity and in turbulence are also described, since some biological processes may be similar in some aspects to these physical phenomena. These potential extra energy contributions could have emerged in biology from the very fractal nature of the medium, or from an evolutive advantage, since they involve spontaneous properties of selforganization, morphogenesis, structuration and multiscale integration. Finally, some examples of applications of the theory to actual biologicallike processes and functions are also provided.
Nearfield magnetoabsorption of quantum dots
NASA Astrophysics Data System (ADS)
Simserides, Constantinos; Zora, Anna; Triberis, Georgios
20060401
We investigate the effect of an external magnetic field of variable orientation and magnitude (up to 20T ) on the linear nearfield optical absorption spectra of single and coupled IIIV semiconductor quantum dots. We focus on the spatial as well as on the magnetic confinement, varying the dimensions of the quantum dots and the magnetic field. We show that the groundstate exciton binding energy can be manipulated utilizing the spatial and magnetic confinement. The effect of the magnetic field on the absorption spectra, increasing the nearfield illumination spot, is also investigated. The zeromagneticfield “structural” symmetry can be destroyed varying the magnetic field orientation and this affects the nearfield spectra. The asymmetry induced (except for specific orientations along symmetry axes) by the magnetic field can be revealed in the nearfield but not in the farfield spectra. We predict that nearfield magnetoabsorption experiments, of realistic spatial resolution, will be in the position to bring to light the quantum dot symmetry. This exceptional symmetryresolving power of the nearfield magnetoabsorption is lost in the far field. The influence of the Coulomb interactions on the absorption spectra is also discussed. Finally, we show that certain modifications of the magnetoexcitonic structure can be uncovered using a realistically acute nearfield probe of ≈20nm .
Approach to nonequilibrium behaviour in quantum field theory
Kripfganz, J.; Perlt, H.
19890501
We study the realtime evolution of quantum field theoretic systems in nonequilibrium situations. Results are presented for the example of scalar /lambda//phi//sup 4/ theory. The degrees of freedom are discretized by studying the system on a torus. Shortwavelength modes are integrated out to oneloop order. The longwavelength modes considered to be the relevant degrees of freedom are treated by semiclassical phasespace methods. /copyright/ 1989 Academic Press, Inc.
Quantum processes: A Whiteheadian interpretation of quantum field theory
NASA Astrophysics Data System (ADS)
Bain, Jonathan
Quantum processes: A Whiteheadian interpretation of quantum field theory is an ambitious and thoughtprovoking exercise in physics and metaphysics, combining an erudite study of the very complex metaphysics of A.N. Whitehead with a wellinformed discussion of contemporary issues in the philosophy of algebraic quantum field theory. Hättich's overall goal is to construct an interpretation of quantum field theory. He does this by translating key concepts in Whitehead's metaphysics into the language of algebraic quantum field theory. In brief, this HättichWhitehead (HW, hereafter) interpretation takes "actual occasions" as the fundamental ontological entities of quantum field theory. An actual occasion is the result of two types of processes: a "transition process" in which a set of initial possiblypossessed properties for the occasion (in the form of "eternal objects") is localized to a spacetime region; and a "concrescence process" in which a subset of these initial possiblypossessed properties is selected and actualized to produce the occasion. Essential to these processes is the "underlying activity", which conditions the way in which properties are initially selected and subsequently actualized. In short, under the HW interpretation of quantum field theory, an initial set of possiblypossessed eternal objects is represented by a Boolean sublattice of the lattice of projection operators determined by a von Neumann algebra R (O) associated with a region O of Minkowski spacetime, and the underlying activity is represented by a state on R (O) obtained by conditionalizing off of the vacuum state. The details associated with the HW interpretation involve imposing constraints on these representations motivated by principles found in Whitehead's metaphysics. These details are spelled out in the three sections of the book. The first section is a summary and critique of Whitehead's metaphysics, the second section introduces the formalism of algebraic quantum field
Effects of Electric Fields on Quantum Well Intersubband Transitions
NASA Astrophysics Data System (ADS)
Harwit, Alex
A new technique is described to calculate the exact eigenstates of a quantum well superlattice of Gallium Arsenide/Aluminum Gallium Arsenide (GaAs/AlGaAs) in a perpendicular electric field. In the model the sloping potential of the conduction band is approximated by a series of small steps. Plane wave states are propagated across the quantum well structure and the quasieigenstates and quasieigenenergies are found at the transmission resonances of the system. We have used the technique to quantify the tunability of a new infrared modulator utilizing an intraconduction band transition in the quantum well. Two such quantum well samples were grown by Molecular Beam Epitaxy (MBE). They consisted of 92 and 110 Angstrom GaAs quantum wells separated by AlGaAs barriers. Under the application of a perpendicular electric field, shifts were observed in the quantum well intersubband absorption energies, in good agreement with theoretical calculations. These tunable transitions can be applied to far infrared light modulators.
Regaining quantum incoherence for matter fields
GonzalezDriaaaz, P.F. )
19920115
The possible quantum state of wormholes or little baby universes should be described by a nonfactorizable density matrix given by the path integral over the class of asymptotically flat fourgeometries and asymptotically vanishing matterfield configurations which suitably match the prescribed data on threesurfaces which do not divide the manifold on the inner boundary. An instanton is here obtained which can represent such a nonsimply connected wormhole manifold, and is used to evaluate the asymptotic effective interaction of the resulting correlated baby universes with ordinary quantum fields at low energies in the Fock representation. It is argued that the demand of locality on the interacting quantum field commutators is no longer valid for correlated baby universes, and it is therefore concluded that quantum coherence in the matterfield sector is lost as a consequence of the interaction with nonsimply connected wormholes. A proposal is advanced that wormholes may provide us with a complementary quantum state sector that would induce the collapse of the state vector in the quantum measurement of any observable for ordinary microscopic matter systems.
Singularities in a scalar field quantum cosmology
NASA Astrophysics Data System (ADS)
Lemos, Nivaldo A.
19960401
The quantum theory of a spatially flat FriedmannRobertsonWalker universe with a massless scalar field as the source is further investigated. The classical model is singular and in the framework of a genuine canonical quantization (ArnowittDeserMisner formalism) a discussion is made of the cosmic evolution, particularly of the quantum gravitational collapse problem. It is shown that in a mattertime gauge such that time is identified with the scalar field the classical model is singular either at t=∞ or at t=+∞, but the quantum model is nonsingular. The latter behavior disproves a conjecture according to which quantum cosmological singularities are predetermined on the classical level by the choice of time.
Classical simulation of quantum fields I
NASA Astrophysics Data System (ADS)
Hirayama, T.; Holdom, B.
20061001
We study classical field theories in a background field configuration where all modes of the theory are excited, matching the zeropoint energy spectrum of quantum field theory. Our construction involves elements of a theory of classical electrodynamics by WheelerFeynman and the theory of stochastic electrodynamics of Boyer. The nonperturbative effects of interactions in these theories can be very efficiently studied on the lattice. In lambda phi(4) theory in 1 + 1 dimensions, we find results, in particular, for mass renormalization and the critical coupling for symmetry breaking that are in agreement with their quantum counterparts. We then study the perturbative expansion of the npoint Green's functions and find a loop expansion very similar to that of quantum field theory. When compared to the usual Feynman rules, we find some differences associated with particular combinations of internal lines going onshell simultaneously.
Quantum Enhanced Estimation of a Multidimensional Field.
Baumgratz, Tillmann; Datta, Animesh
20160122
We present a framework for the quantum enhanced estimation of multiple parameters corresponding to noncommuting unitary generators. Our formalism provides a recipe for the simultaneous estimation of all three components of a magnetic field. We propose a probe state that surpasses the precision of estimating the three components individually, and we discuss measurements that come close to attaining the quantum limit. Our study also reveals that too much quantum entanglement may be detrimental to attaining the Heisenberg scaling in the estimation of unitarily generated parameters.
Quantum switches and nonlocal microwave fields
NASA Astrophysics Data System (ADS)
Davidovich, L.; Maali, A.; Brune, M.; Raimond, J. M.; Haroche, S.
19931001
A scheme to realize an optical switch with quantum coherence between its ``open'' and ``closed'' states is presented. It involves a single atom in a superposition of circular Rydberg states crossing a high Q cavity. A combination of switches could be used to prepare a quantum superposition of coherent microwave field states located simultaneously in two cavities. Such nonclassical states and their decoherence due to cavity dissipation could be studied by performing atom correlation experiments.
Quantum Field Theory and Decoherence in the Early Universe
NASA Astrophysics Data System (ADS)
Koksma, J. F.
20110601
by realising that higher order, nonGaussian correlators are usually perturbatively suppressed. A quantum system with a large entropy corresponds to an effectively classical, stochastic system. To allow for a quantitative comparison between our correlator approach and the conventional approach to decoherence, we apply both formalisms to two simple quantum mechanical models. We find that the entropy in the conventional approach to decoherence quite generically reveals secular growth, indicating physically unacceptable behaviour. The conventional approach furthermore suffers from the fact that no wellestablished treatment to take perturbative corrections into account exists, nor has the framework of renormalisation ever been implemented. Our correlator approach to decoherence is taylored to applications in quantum field theory. We perform the first realistic study of decoherence in a renormalised quantum field theoretical setting. Using outofequilibrium field theory techniques, we extract two quantitative measures of decoherence in our model: the total amount of decoherence and the decoherence rate. The main finding in this part of the thesis is that, although a pure state remains pure under unitary evolution, an observer perceives this state over time as a mixed state with positive entropy as nonGaussianities are dynamically generated. Alternatively, one could say that a realistic observer cannot probe all information about the system and thus discerns a loss of coherence of the pure state
Self field electromagnetism and quantum phenomena
NASA Astrophysics Data System (ADS)
Schatten, Kenneth H.
19940701
Quantum Electrodynamics (QED) has been extremely successful inits predictive capability for atomic phenomena. Thus the greatest hope for any alternative view is solely to mimic the predictive capability of quantum mechanics (QM), and perhaps its usefulness will lie in gaining a better understanding of microscopic phenomena. Many ?paradoxes? and problematic situations emerge in QED. To combat the QED problems, the field of Stochastics Electrodynamics (SE) emerged, wherein a random ?zero point radiation? is assumed to fill all of space in an attmept to explain quantum phenomena, without some of the paradoxical concerns. SE, however, has greater failings. One is that the electromagnetic field energy must be infinit eto work. We have examined a deterministic side branch of SE, ?self field? electrodynamics, which may overcome the probelms of SE. Self field electrodynamics (SFE) utilizes the chaotic nature of electromagnetic emissions, as charges lose energy near atomic dimensions, to try to understand and mimic quantum phenomena. These fields and charges can ?interact with themselves? in a nonlinear fashion, and may thereby explain many quantum phenomena from a semiclassical viewpoint. Referred to as self fields, they have gone by other names in the literature: ?evanesccent radiation?, ?virtual photons?, and ?vacuum fluctuations?. Using self fields, we discuss the uncertainty principles, the Casimir effects, and the blackbody radiation spectrum, diffraction and interference effects, Schrodinger's equation, Planck's constant, and the nature of the electron and how they might be understood in the present framework. No new theory could ever replace QED. The self field view (if correct) would, at best, only serve to provide some understanding of the processes by which strange quantum phenomena occur at the atomic level. We discuss possible areas where experiments might be employed to test SFE, and areas where future work may lie.
Quantum Theoretical Study of KCl and LiCl Clusters
NASA Astrophysics Data System (ADS)
Koetter, Ted; Hira, Ajit; Salazar, Justin; Jaramillo, Danelle
20140301
This research focuses on the theoretical study of molecular clusters to examine the chemical properties of small KnClnandLinCln clusters (n = 2  20). The potentially important role of these molecular species in biochemical and medicinal processes is well known. This work applies the hybrid ab initio methods of quantum chemistry to derive the different alkalihalide (MnHn) geometries. Of particular interest is the competition between hexagonal ring geometries and rock salt structures. Electronic energies, rotational constants, dipole moments, and vibrational frequencies for these geometries are calculated. Magic numbers for cluster stability are identified and are related to the property of cluster compactness. Mapping of the singlet, triplet, and quintet, potential energy surfaces is performed. Calculations were performed to examine the interactions of these clusters with some atoms and molecules of biological interest, including O, O2, and Fe. Potential design of new medicinal drugs is explored.
Informationtheoretic limitations on approximate quantum cloning and broadcasting
NASA Astrophysics Data System (ADS)
Lemm, Marius; Wilde, Mark M.
20170701
We prove quantitative limitations on any approximate simultaneous cloning or broadcasting of mixed states. The results are based on informationtheoretic (entropic) considerations and generalize the wellknown nocloning and nobroadcasting theorems. We also observe and exploit the fact that the universal cloning machine on the symmetric subspace of n qudits and symmetrized partial trace channels are dual to each other. This duality manifests itself both in the algebraic sense of adjointness of quantum channels and in the operational sense that a universal cloning machine can be used as an approximate recovery channel for a symmetrized partial trace channel and vice versa. The duality extends to give control of the performance of generalized universal quantum cloning machines (UQCMs) on subspaces more general than the symmetric subspace. This gives a way to quantify the usefulness of a priori information in the context of cloning. For example, we can control the performance of an antisymmetric analog of the UQCM in recovering from the loss of n k fermionic particles.
Relativistic quantum channel of communication through field quanta
Cliche, M.; Kempf, A.
20100115
Setups in which a system Alice emits field quanta that a system Bob receives are prototypical for wireless communication and have been extensively studied. In the most basic setup, Alice and Bob are modeled as UnruhDeWitt detectors for scalar quanta, and the only noise in their communication is due to quantum fluctuations. For this basic setup, we construct the corresponding informationtheoretic quantum channel. We calculate the classical channel capacity as a function of the spacetime separation, and we confirm that the classical as well as the quantum channel capacity are strictly zero for spacelike separations. We show that this channel can be used to entangle Alice and Bob instantaneously. Alice and Bob are shown to extract this entanglement from the vacuum through a CasimirPolder effect.
Holographic geometry of entanglement renormalization in quantum field theories
NASA Astrophysics Data System (ADS)
Nozaki, Masahiro; Ryu, Shinsei; Takayanagi, Tadashi
20121001
We study a conjectured connection between AdS/CFT and a realspace quantum renormalization group scheme, the multiscale entanglement renormalization ansatz (MERA). By making a close contact with the holographic formula of the entanglement entropy, we propose a general definition of the metric in the MERA in the extra holographic direction. The metric is formulated purely in terms of quantum field theoretical data. Using the continuum version of the MERA (cMERA), we calculate this emergent holographic metric explicitly for free scalar boson and free fermions theories, and check that the metric so computed has the properties expected from AdS/CFT. We also discuss the cMERA in a timedependent background induced by quantum quench and estimate its corresponding metric.
Langevin description of nonequilibrium quantum fields
NASA Astrophysics Data System (ADS)
Gautier, F.; Serreau, J.
20121201
We consider the nonequilibrium dynamics of a real quantum scalar field. We show the formal equivalence of the exact evolution equations for the statistical and spectral twopoint functions with a fictitious Langevin process and examine the conditions under which a local Markovian dynamics is a valid approximation. In quantum field theory, the memory kernel and the noise correlator typically exhibit long time power laws and are thus highly nonlocal, thereby questioning the possibility of a local description. We show that despite this fact, there is a finite time range during which a local description is accurate. This requires the theory to be (effectively) weakly coupled. We illustrate the use of such a local description for studies of decoherence and entropy production in quantum field theory.
Dual field theories of quantum computation
NASA Astrophysics Data System (ADS)
Vanchurin, Vitaly
20160601
Given two quantum states of N qbits we are interested to find the shortest quantum circuit consisting of only one and two qbit gates that would transfer one state into another. We call it the quantum maze problem for the reasons described in the paper. We argue that in a large N limit the quantum maze problem is equivalent to the problem of finding a semiclassical trajectory of some lattice field theory (the dual theory) on an N +1 dimensional spacetime with geometrically flat, but topologically compact spatial slices. The spatial fundamental domain is an N dimensional hyperrhombohedron, and the temporal direction describes transitions from an arbitrary initial state to an arbitrary target state and so the initial and final dual field theory conditions are described by these two quantum computational states. We first consider a complex KleinGordon field theory and argue that it can only be used to study the shortest quantum circuits which do not involve generators composed of tensor products of multiple Pauli Z matrices. Since such situation is not generic we call it the Zproblem. On the dual field theory side the Zproblem corresponds to massless excitations of the phase (Goldstone modes) that we attempt to fix using Higgs mechanism. The simplest dual theory which does not suffer from the massless excitation (or from the Zproblem) is the AbelianHiggs model which we argue can be used for finding the shortest quantum circuits. Since every trajectory of the field theory is mapped directly to a quantum circuit, the shortest quantum circuits are identified with semiclassical trajectories. We also discuss the complexity of an actual algorithm that uses a dual theory prospective for solving the quantum maze problem and compare it with a geometric approach. We argue that it might be possible to solve the problem in subexponential time in 2 N , but for that we must consider the KleinGordon theory on curved spatial geometry and/or more complicated (than N torus
Quantum Transport in Solids: Bloch Dynamics and Role of Oscillating Fields
19970728
The objective of this research program is to study theoretically the underlying principles of quantum transport in solids. The specific areas of...research are those of Bloch electron dynamics, quantum transport in oscillating electric fields or in periodic potentials, and the capacitive nature of
Local fieldinduced optical properties of Agcoated CdS quantum dots.
Je, KooChul; Ju, Honglyoul; Treguer, Mona; Cardinal, Thierry; Park, SeungHan
20060821
Local fieldinduced optical properties of Agcoated CdS quantum dot structures are investigated. We experimentally observe a clear exciton peak due to the quantum confinement effect in uncoated CdS quantum dots, and surface plasmon resonance and redshifted exciton peak in Agcoated CdS composite quantum dot structures. We have calculated the Stark shift of the exciton peak as a function of the local field for different silver thicknesses and various sizes of quantum dots based on the effectivemass Hamiltonian using the numericalmatrixdiagonalization method. Our theoretical calculations strongly indicate that the exciton peak is redshifted in the metalsemiconductor composite quantum dots due to a strong local field, i.e., the quantum confined Stark effect.
Quantum phenomena and the zeropoint radiation field
NASA Astrophysics Data System (ADS)
de La Peña, L.; Cetto, A. M.
19940601
The stationary solutions for a bound electron immersed in the random zeropoint radiation field of stochastic electrodynamics are studied, under the assumption that the characteristic Fourier frequencies of these solutions are not random. Under this assumption, the response of the particle to the field is linear and does not mix frequencies, irrespectively of the form of the binding force; the fluctuations of the random field fix the scale of the response. The effective radiation field that supports the stationary states of motion is no longer the free vacuum field, but a modified form of it with new statistical properties. The theory is expressed naturally in terms of matrices (or operators), and it leads to the Heisenberg equations and the Hilbert space formalism of quantum mechanics in the radiationless approximation. The connection with the poissonian formulation of stochastic electrodynamics is also established. At the end we briefly discuss a few important aspects of quantum mechanics which the present theory helps to clarify.
Mean Field Analysis of Quantum Annealing Correction.
Matsuura, Shunji; Nishimori, Hidetoshi; Albash, Tameem; Lidar, Daniel A
20160603
Quantum annealing correction (QAC) is a method that combines encoding with energy penalties and decoding to suppress and correct errors that degrade the performance of quantum annealers in solving optimization problems. While QAC has been experimentally demonstrated to successfully error correct a range of optimization problems, a clear understanding of its operating mechanism has been lacking. Here we bridge this gap using tools from quantum statistical mechanics. We study analytically tractable models using a meanfield analysis, specifically the pbody ferromagnetic infiniterange transversefield Ising model as well as the quantum Hopfield model. We demonstrate that for p=2, where the phase transition is of second order, QAC pushes the transition to increasingly larger transverse field strengths. For p≥3, where the phase transition is of first order, QAC softens the closing of the gap for small energy penalty values and prevents its closure for sufficiently large energy penalty values. Thus QAC provides protection from excitations that occur near the quantum critical point. We find similar results for the Hopfield model, thus demonstrating that our conclusions hold in the presence of disorder.
Physical properties of quantum field theory measures
NASA Astrophysics Data System (ADS)
Mourão, J. M.; Thiemann, T.; Velhinho, J. M.
19990501
Well known methods of measure theory on infinite dimensional spaces are used to study physical properties of measures relevant to quantum field theory. The difference of typical configurations of free massive scalar field theories with different masses is studied. We apply the same methods to study the AshtekarLewandowski (AL) measure on spaces of connections. In particular we prove that the diffeomorphism group acts ergodically, with respect to the AL measure, on the AshtekarIsham space of quantum connections modulo gauge transformations. We also prove that a typical, with respect to the AL measure, quantum connection restricted to a (piecewise analytic) curve leads to a parallel transport discontinuous at every point of the curve.
Deterministic strongfield quantum control
NASA Astrophysics Data System (ADS)
Cavaletto, Stefano M.; Harman, Zoltán; Pfeifer, Thomas; Keitel, Christoph H.
20170401
Strongfield quantumstate control is investigated, taking advantage of the full—amplitude and phase—characterization of the interaction between matter and intense ultrashort pulses via transientabsorption spectroscopy. As an example, we apply the method to a nondegenerate V type threelevel system modeling atomic Rb, and use a sequence of intense delayed pulses, whose parameters are tailored to steer the system into a desired quantum state. We show how to experimentally enable this optimization by retrieving all quantum features of the lightmatter interaction from observable spectra. This provides a full characterization of the action of strong fields on the atomic system, including the dependence upon possibly unknown pulse properties and atomic structures. Precision and robustness of the scheme are tested, in the presence of surrounding atomic levels influencing the system's dynamics.
(Studies in quantum field theory: Progress report, April 1, 1991March 31, 1992)
Bender, C M
19920101
Professors Bender, Bernard, and Shrauner, Assistant Professors Ogilvie and Goltermann, Research Assistant Professors Visser and Petcher, and Research Associate Rivas are currently conducting research in many areas of high energy theoretical and mathematical physics. These areas include: lattice gauge calculations of masses and weak matrix elements; strongcoupling approximation; lowenergy effective field theories; classical solutions of nonAbelian gauge theories; meanfield approximation in quantum field theory; path integral and coherent state representations in quantum field theory; the nature of perturbation theory in large order; quark condensation in QCD; chiral fermion theories on the lattice; the 1/N expansion in quantum field theory; effective potential and action in quantum field theories, including QCD; studies of the early universe and inflation; quantum gravity. This work is described in detail in the body of this proposal.
TwoElectron Spherical Quantum Dot in a Magnetic Field
NASA Astrophysics Data System (ADS)
Poszwa, A.
20161201
We investigate threedimensional, twoelectron quantum dots in an external magnetic field B. Due to mixed spherical and cylindrical symmetry the Schrödinger equation is not completely separable. Highly accurate numerical solutions, for a wide range of B, have been obtained by the expansion of wavefunctions in doublepower series and by imposing on the radial functions appropriate boundary conditions. The asymptotic limit of a very strong magnetic field and the 2D approach have been considered. Ground state properties of the twoelectron semiconductor quantum dots are investigated using both the 3D and 2D models. Theoretical calculations have been compared with recent experimental results.
Theoretical and observational analysis of spacecraft fields
NASA Technical Reports Server (NTRS)
Neubauer, F. M.; Schatten, K. H.
19720101
In order to investigate the nondipolar contributions of spacecraft magnetic fields a simple magnetic field model is proposed. This model consists of randomly oriented dipoles in a given volume. Two sets of formulas are presented which give the rmsmultipole field components, for isotropic orientations of the dipoles at given positions and for isotropic orientations of the dipoles distributed uniformly throughout a cube or sphere. The statistical results for an 8 cu m cube together with individual examples computed numerically show the following features: Beyond about 2 to 3 m distance from the center of the cube, the field is dominated by an equivalent dipole. The magnitude of the magnetic moment of the dipolar part is approximated by an expression for equal magnetic moments or generally by the Pythagorean sum of the dipole moments. The radial component is generally greater than either of the transverse components for the dipole portion as well as for the nondipolar field contributions.
Mean Field Theory for Collective Motion of Quantum Meson Fields
NASA Astrophysics Data System (ADS)
Tsue, Y.; Vautherin, D.; Matsui, T.
19990801
Mean field theory for the time evolution of quantum meson fields is studied in terms of the functional Schrödinger picture with a timedependent Gaussian variational wave functional. We first show that the equations of motion for the variational wavefunctional can be rewritten in a compact form similar to the HartreeBogoliubov equations in quantum manybody theory and this result is used to recover the covariance of the theory. We then apply this method to the O(N) model and present analytic solutions of the mean field evolution equations for an Ncomponent scalar field. These solutions correspond to quantum rotations in isospin space and represent generalizations of the classical solutions obtained earlier by Anselm and Ryskin. As compared to classical solutions new effects arise because of the coupling between the average value of the field and its quantum fluctuations. We show how to generalize these solutions to the case of mean field dynamics at finite temperature. The relevance of these solutions for the observation of a coherent collective state or a disoriented chiral condensate in ultrarelativistic nuclear collisions is discussed.
Phantom field dynamics in loop quantum cosmology
Samart, Daris; Gumjudpai, Burin
20070815
We consider a dynamical system of phantom scalar field under exponential potential in the background of loop quantum cosmology. In our analysis, there is neither stable node nor repeller unstable node but only two saddle points, hence no big rip singularity. Physical solutions always possess potential energy greater than the magnitude of the negative kinetic energy. We found that the universe bounces after accelerating even in the domination of the phantom field. After bouncing, the universe finally enters the oscillatory regime.
Banerjee, Subhashish; Alok, Ashutosh Kumar; Srikanth, R; Hiesmayr, Beatrix C
Correlations exhibited by neutrino oscillations are studied via quantuminformation theoretic quantities. We show that the strongest type of entanglement, genuine multipartite entanglement, is persistent in the flavor changing states. We prove the existence of Belltype nonlocal features, in both its absolute and genuine avatars. Finally, we show that a measure of nonclassicality, dissension, which is a generalization of quantum discord to the tripartite case, is nonzero for almost the entire range of time in the evolution of an initial electronneutrino. Via these quantuminformation theoretic quantities, capturing different aspects of quantum correlations, we elucidate the differences between the flavor types, shedding light on the quantuminformation theoretic aspects of the weak force.
Changing Views of Quantum Field Theory
NASA Astrophysics Data System (ADS)
Weinberg, Steven
20100301
The first part of this talk reviews changes in our views regarding quantum field theory since its beginnings, leading eventually to the modern view that our most successful field theories may in fact be effective field theories, valid only as low energy approximations to an underlying theory that may not be a field theory at all. In the second part, I reminisce about the early development of effective field theories of the strong interactions, comment briefly on some other applications of effective field theories, then take up the idea that the Standard Model and General Relativity are the leading terms in an effective field theory, and finally cite recent calculations that suggest that the effective field theory of gravitation and matter is asymptotically safe. The second part is substantially the same as a talk given a month earlier at the 6th International Workshop on Chiral Dynamics, at the University of Bern, which is reproduced here.
Integrable structures in quantum field theory
NASA Astrophysics Data System (ADS)
Negro, Stefano
20160801
This review was born as notes for a lecture given at the Young Researchers Integrability School (YRIS) school on integrability in Durham, in the summer of 2015. It deals with a beautiful method, developed in the midnineties by Bazhanov, Lukyanov and Zamolodchikov and, as such, called BLZ. This method can be interpreted as a field theory version of the quantum inverse scattering, also known as the algebraic Bethe ansatz. Starting with the case of conformal field theories (CFTs) we show how to build the field theory analogues of commuting transfer T matrices and Baxter Qoperators of integrable lattice models. These objects contain the complete information of the integrable structure of the theory, viz. the integrals of motion, and can be used, as we will show, to derive the thermodynamic Bethe ansatz and nonlinear integral equations. This same method can be easily extended to the description of integrable structures of certain particular massive deformations of CFTs; these, in turn, can be described as quantum group reductions of the quantum sineGordon model and it is an easy step to include this last theory in the framework of BLZ approach. Finally we show an interesting and surprising connection of the BLZ structures with classical objects emerging from the study of classical integrable models via the inverse scattering transform method. This connection goes under the name of ODE/IM correspondence and we will present it for the specific case of quantum sineGordon model only.
Kinematic projective quantum states for loop quantum gravity coupled to tensor fields
NASA Astrophysics Data System (ADS)
Okołów, Andrzej
20170401
We present a construction of kinematic quantum states for theories of tensor fields of an arbitrary sort. The construction is based on projective techniques by Kijowski. Applying projective quantum states for Loop Quantum Gravity (LQG) obtained by Lanéry and Thiemann we construct quantum states for LQG coupled to tensor fields.
Theoretical Analysis of a Model for a Field Displacement Isolator
19760601
model for a field displacement isolator. Sharon, Ram Monterey, California. Naval Postgraduate School http://hdl.handle.net/10945/17975 Downloaded from...NPS Archive: Calhoun THEORETICAL ANALYSIS OF A MODEL FOR A FIELD DISPLACEMENT ISOLATOR Ram Sharon NAVAL POSTGRADUATE SCHOOL Monterey, California...THESIS Theoretical Analysis of a Model for a Field Displacement Isolator by Ram Sharon June 1976 Thesis Advisor: J. B. Knorr Approved for public release
Quantum fields on closed timelike curves
Pienaar, J. L.; Myers, C. R.; Ralph, T. C.
20111215
Recently, there has been much interest in the evolution of quantum particles on closed timelike curves (CTCs). However, such models typically assume pointlike particles with only two degrees of freedom; a very questionable assumption given the relativistic setting of the problem. We show that it is possible to generalize the Deutsch model of CTCs to fields using the equivalent circuit formalism. We give examples for coherent, squeezed, and singlephoton states interacting with the CTC via a beamsplitter. The model is then generalized further to account for the smooth transition to normal quantum mechanics as the CTC becomes much smaller than the size of the modes interacting on it. In this limit, we find that the system behaves like a standard quantummechanical feedback loop.
Quantum processes in strong magnetic fields
NASA Technical Reports Server (NTRS)
Canuto, V.
19750101
Quantummechanical processes that occur in a piece of matter embedded in a magnetic field with a strength of the order of 10 to the 13th power G are described which either are entirely due to the presence of the field or become modified because of it. The conversion of rotational energy into electromagnetic energy in pulsars is analyzed as a mechanism for producing such a field, and it is shown that a strong magnetic field is not sufficient for quantum effects to play a significant role; in addition, the density must be adjusted to be as low as possible. The pressure and energy density of a free electron gas in a uniform magnetic field are evaluated, neutron betadecay in the presence of a strong field is examined, and the effect of such a field on neutrino reactions is discussed. The thermal history of a neutron star is studied, and it is concluded that a strong magnetic field helps to increase the cooling rate of the star by producing new channels through which neutrinos can carry away energy.
Quantum processes in strong magnetic fields
NASA Technical Reports Server (NTRS)
Canuto, V.
19750101
Quantummechanical processes that occur in a piece of matter embedded in a magnetic field with a strength of the order of 10 to the 13th power G are described which either are entirely due to the presence of the field or become modified because of it. The conversion of rotational energy into electromagnetic energy in pulsars is analyzed as a mechanism for producing such a field, and it is shown that a strong magnetic field is not sufficient for quantum effects to play a significant role; in addition, the density must be adjusted to be as low as possible. The pressure and energy density of a free electron gas in a uniform magnetic field are evaluated, neutron betadecay in the presence of a strong field is examined, and the effect of such a field on neutrino reactions is discussed. The thermal history of a neutron star is studied, and it is concluded that a strong magnetic field helps to increase the cooling rate of the star by producing new channels through which neutrinos can carry away energy.
Quantum revivals in free field CFT
NASA Astrophysics Data System (ADS)
Dowker, J. S.
20170301
The recent work by Cardy (arXiv:1603.08267) on quantum revivals and higher dimensional CFT is revisited and enlarged upon for free fields. The expressions for the free energy used here are those derived some time ago. The calculation is extended to spin–half fields for which the power spectrum involves the odd divisor function. An explanation of the rational revivals for odd spheres is given in terms of wrongly quantised fields and modular transformations. Comments are made on the equivalence of operator counting and eigenvalue methods, which is quickly verified.
Remote State Preparation for Quantum Fields
NASA Astrophysics Data System (ADS)
Ber, Ran; Zohar, Erez
20160701
Remote state preparation is generation of a desired state by a remote observer. In spite of causality, it is well known, according to the ReehSchlieder theorem, that it is possible for relativistic quantum field theories, and a "physical" process achieving this task, involving superoscillatory functions, has recently been introduced. In this work we deal with nonrelativistic fields, and show that remote state preparation is also possible for them, hence obtaining a ReehSchliederlike result for general fields. Interestingly, in the nonrelativistic case, the process may rely on completely different resources than the ones used in the relativistic case.
Anomalous critical fields in quantum critical superconductors
Putzke, C.; Walmsley, P.; Fletcher, J. D.; Malone, L.; Vignolles, D.; Proust, C.; Badoux, S.; See, P.; Beere, H. E.; Ritchie, D. A.; Kasahara, S.; Mizukami, Y.; Shibauchi, T.; Matsuda, Y.; Carrington, A.
20140101
Fluctuations around an antiferromagnetic quantum critical point (QCP) are believed to lead to unconventional superconductivity and in some cases to hightemperature superconductivity. However, the exact mechanism by which this occurs remains poorly understood. The ironpnictide superconductor BaFe2(As1−xPx)2 is perhaps the clearest example to date of a hightemperature quantum critical superconductor, and so it is a particularly suitable system to study how the quantum critical fluctuations affect the superconducting state. Here we show that the proximity of the QCP yields unexpected anomalies in the superconducting critical fields. We find that both the lower and upper critical fields do not follow the behaviour, predicted by conventional theory, resulting from the observed mass enhancement near the QCP. Our results imply that the energy of superconducting vortices is enhanced, possibly due to a microscopic mixing of antiferromagnetism and superconductivity, suggesting that a highly unusual vortex state is realized in quantum critical superconductors. PMID:25477044
Quantum Field Theory and the Standard Model
NASA Astrophysics Data System (ADS)
Schwartz, Matthew D.
20140301
Part I. Field Theory: 1. Microscopic theory of radiation; 2. Lorentz invariance and second quantization; 3. Classical Field Theory; 4. Oldfashioned perturbation theory; 5. Cross sections and decay rates; 6. The Smatrix and timeordered products; 7. Feynman rules; Part II. Quantum Electrodynamics: 8. Spin 1 and gauge invariance; 9. Scalar QED; 10. Spinors; 11. Spinor solutions and CPT; 12. Spin and statistics; 13. Quantum electrodynamics; 14. Path integrals; Part III. Renormalization: 15. The Casimir effect; 16. Vacuum polarization; 17. The anomalous magnetic moment; 18. Mass renormalization; 19. Renormalized perturbation theory; 20. Infrared divergences; 21. Renormalizability; 22. Nonrenormalizable theories; 23. The renormalization group; 24. Implications of Unitarity; Part IV. The Standard Model: 25. YangMills theory; 26. Quantum YangMills theory; 27. Gluon scattering and the spinorhelicity formalism; 28. Spontaneous symmetry breaking; 29. Weak interactions; 30. Anomalies; 31. Precision tests of the standard model; 32. QCD and the parton model; Part V. Advanced Topics: 33. Effective actions and Schwinger proper time; 34. Background fields; 35. Heavyquark physics; 36. Jets and effective field theory; Appendices; References; Index.
Quantumsize resonance tunneling in the field emission phenomenon
NASA Astrophysics Data System (ADS)
Litovchenko, V.; Evtukh, A.; Kryuchenko, Yu.; Goncharuk, N.; Yilmazoglu, O.; Mutamba, K.; Hartnagel, H. L.; Pavlidis, D.
20040701
Theoretical analyses have been performed of the quantumsize (QS) resonance tunneling in the fieldemission (FE) phenomenon for different models of the emitting structures. Such experimentally observed peculiarities have been considered as the enhancement of the FE current, the deviation from the FowlerNordheim law, the appearance of sharp current peaks, and a negative resistance. Different types of FE cathodes with QS structures (quantized layers, wires, or dots) have been studied experimentally. Resonance current peaks have been observed, from which the values of the energylevel splitting can be estimated.
Nonresonant radiative exciton transfer by near field between quantum wells
Aleshkin, V. Ya.; Gavrilenko, L. V. Gaponova, D. M.; Kadykov, A. M.; Lysenko, V. G.; Krasil’nik, Z. F.
20131115
We experimentally observed an increase in the intensity of photoluminescence from a wider quantum well (QW) when an exciton transition was induced in the neighboring narrower QW separated from the former one by a tunnelingnontransparent AlGaAs barrier. The dependence of the efficiency of the nearfield radiative transfer of excitons on the distance between QWs was studied in heterostructures without coincidence of exciton resonances in the adjacent QWs. Theoretical results were qualitatively consistent with the available experimental data.
Magnetic field induced minigap in double quantum wells
Simmons, J.A.; Lyo, S.K.; Klem, J.F.; Harff, N.E. 
19940701
We report discovery of a partial energy gap, or minigap, in strongly coupled double quantum wells (QWs), due to an anticrossing of the two QW dispersion curves. The anticrossing and minigap are induced by an inplane magnetic field B{sub {parallel}}, and give rise to large distortions in the Fermi surface and density of states, including a Van Hove singularity. Sweeping B{sub {parallel}} moves the minigap through the Fermi level, with the upper and lower gap edges producing a sharp maximum and minimum in the lowtemperature inplane conductance, in agreement with theoretical calculations. The gap energy may be directly determined from the data.
Coherent feedback control of multipartite quantum entanglement for optical fields
Yan, Zhihui; Jia, Xiaojun; Xie, Changde; Peng, Kunchi
20111215
Coherent feedback control (CFC) of multipartite optical entangled states produced by a nondegenerate optical parametric amplifier is theoretically studied. The features of the quantum correlations of amplitude and phase quadratures among more than two entangled optical modes can be controlled by tuning the transmissivity of the optical beam splitter in the CFC loop. The physical conditions to enhance continuous variable multipartite entanglement of optical fields utilizing the CFC loop are obtained. The numeric calculations based on feasible physical parameters of realistic systems provide direct references for the design of experimental devices.
Thermalization of field driven quantum systems
Fotso, H.; Mikelsons, K.; Freericks, J. K.
20140101
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 infinitetemperature 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 FalicovKimball 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
Thermalization of field driven quantum systems
NASA Astrophysics Data System (ADS)
Fotso, H.; Mikelsons, K.; Freericks, J. K.
20140401
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 infinitetemperature 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 FalicovKimball model (which does not), we find both exhibit scenarios (iiv), 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.
Review of Experimental Concepts for Studying the Quantum Vacuum Field
NASA Astrophysics Data System (ADS)
Davis, E. W.; Teofilo, V. L.; Haisch, B.; Puthoff, H. E.; Nickisch, L. J.; Rueda, A.; Cole, D. C.
20060101
We review concepts that provide an experimental framework for exploring the possibility and limitations of accessing energy from the space vacuum environment. Quantum electrodynamics (QED) and stochastic electrodynamics (SED) are the theoretical approaches guiding this experimental investigation. This investigation explores the question of whether the quantum vacuum field contains useful energy that can be exploited for applications under the action of a catalyst, or cavity structure, so that energy conservation is not violated. This is similar to the same technical problem at about the same level of technology as that faced by early nuclear energy pioneers who searched for, and successfully discovered, the unique material structure that caused the release of nuclear energy via the neutron chain reaction.
Review of Experimental Concepts for Studying the Quantum Vacuum Field
Davis, E. W.; Puthoff, H. E.; Teofilo, V. L.; Nickisch, L. J.; Rueda, A.; Cole, D. C.
20060120
We review concepts that provide an experimental framework for exploring the possibility and limitations of accessing energy from the space vacuum environment. Quantum electrodynamics (QED) and stochastic electrodynamics (SED) are the theoretical approaches guiding this experimental investigation. This investigation explores the question of whether the quantum vacuum field contains useful energy that can be exploited for applications under the action of a catalyst, or cavity structure, so that energy conservation is not violated. This is similar to the same technical problem at about the same level of technology as that faced by early nuclear energy pioneers who searched for, and successfully discovered, the unique material structure that caused the release of nuclear energy via the neutron chain reaction.
Effective Particles in Quantum Field Theory
NASA Astrophysics Data System (ADS)
Głazek, Stanisław D.; Trawiński, Arkadiusz P.
20170301
The concept of effective particles is introduced in the Minkowski spacetime Hamiltonians in quantum field theory using a new kind of the relativistic renormalization group procedure that does not integrate out highenergy modes but instead integrates out the large changes of invariant mass. The new procedure is explained using examples of known interactions. Some applications in phenomenology, including processes measurable in colliders, are briefly presented.
Quantum field theory of treasury bonds
NASA Astrophysics Data System (ADS)
Baaquie, Belal E.
20010701
The HeathJarrowMorton (HJM) formulation of treasury bonds in terms of forward rates is recast as a problem in path integration. The HJM model is generalized to the case where all the forward rates are allowed to fluctuate independently. The resulting theory is shown to be a twodimensional Gaussian quantum field theory. The no arbitrage condition is obtained and a functional integral derivation is given for the price of a futures and an options contract.
Quantum field theory of treasury bonds.
Baaquie, B E
20010701
The HeathJarrowMorton (HJM) formulation of treasury bonds in terms of forward rates is recast as a problem in path integration. The HJM model is generalized to the case where all the forward rates are allowed to fluctuate independently. The resulting theory is shown to be a twodimensional Gaussian quantum field theory. The no arbitrage condition is obtained and a functional integral derivation is given for the price of a futures and an options contract.
Hydrodynamic transport functions from quantum kinetic field theory
NASA Astrophysics Data System (ADS)
Calzetta, E. A.; Hu, B. L.; Ramsey, S. A.
20000601
Starting from the quantum kinetic field theory [E. Calzetta and B. L. Hu, Phys. Rev. D 37, 2878 (1988)] constructed from the closedtimepath (CTP), twoparticleirreducible (2PI) effective action we show how to compute from first principles the shear and bulk viscosity functions in the hydrodynamicthermodynamic regime. For a real scalar field with λΦ4 selfinteraction we need to include fourloop graphs in the equation of motion. This work provides a microscopic fieldtheoretical basis to the ``effective kinetic theory'' proposed by Jeon and Yaffe [S. Jeon and L. G. Yaffe, Phys. Rev. D 53, 5799 (1996)], while our result for the bulk viscosity reproduces their expression derived from linearresponse theory and the imaginarytime formalism of thermal field theory. Though unavoidably involved in calculations of this sort, we feel that the approach using fundamental quantum kinetic field theory is conceptually clearer and methodically simpler than the effective kinetic theory approach, as the success of the latter requires a clever rendition of diagrammatic resummations which is neither straightforward nor failsafe. Moreover, the method based on the CTP2PI effective action illustrated here for a scalar field can be formulated entirely in terms of functional integral quantization, which makes it an appealing method for a firstprinciples calculation of transport functions of a thermal nonAbelian gauge theory, e.g., QCD quarkgluon plasma produced from heavy ion collisions.
Planar dipolar polymer brush: field theoretical investigations
NASA Astrophysics Data System (ADS)
Mahalik, Jyoti; Kumar, Rajeev; Sumpter, Bobby
20150301
Physical properties of polymer brushes bearing monomers with permanent dipole moments and immersed in a polar solvent are investigated using selfconsistent field theory (SCFT). It is found that mismatch between the permanent dipole moments of the monomer and the solvent plays a significant role in determining the height of the polymer brush. Sign as well as magnitude of the mismatch determines the extent of collapse of the polymer brush. The mismatch in the dipole moments also affects the forcedistance relations and interpenetration of polymers in opposing planar brushes. In particular, an attractive force between the opposing dipolar brushes is predicted for stronger mismatch parameter. Furthermore, effects of added monovalent salt on the structure of dipolar brushes will also be presented. This investigation highlights the significance of dipolar interactions in affecting the physical properties of polymer brushes. Csmd division, Oak Ridge National Laboratory, 1 Bethel Valley Rd, Oak Ridge, TN 37831, USA.
Noncommutative Common Cause Principles in algebraic quantum field theory
HoferSzabo, Gabor; Vecsernyes, Peter
20130415
States in algebraic quantum field theory 'typically' establish correlation between spacelike separated events. Reichenbach's Common Cause Principle, generalized to the quantum field theoretical setting, offers an apt tool to causally account for these superluminal correlations. In the paper we motivate first why commutativity between the common cause and the correlating events should be abandoned in the definition of the common cause. Then we show that the Noncommutative Weak Common Cause Principle holds in algebraic quantum field theory with locally finite degrees of freedom. Namely, for any pair of projections A, B supported in spacelike separated regions V{sub A} and V{sub B}, respectively, there is a local projection C not necessarily commuting with A and B such that C is supported within the union of the backward light cones of V{sub A} and V{sub B} and the set {l_brace}C, C{sup UpTack }{r_brace} screens off the correlation between A and B.
Efficient fieldtheoretic simulation of polymer solutions.
Villet, Michael C; Fredrickson, Glenn H
20141214
We present several developments that facilitate the efficient fieldtheoretic simulation of polymers by complex Langevin sampling. A regularization scheme using finite Gaussian excluded volume interactions is used to derive a polymer solution model that appears free of ultraviolet divergences and hence is wellsuited for latticediscretized field theoretic simulation. We show that such models can exhibit ultraviolet sensitivity, a numerical pathology that dramatically increases sampling error in the continuum lattice limit, and further show that this pathology can be eliminated by appropriate model reformulation by variable transformation. We present an exponential time differencing algorithm for integrating complex Langevin equations for field theoretic simulation, and show that the algorithm exhibits excellent accuracy and stability properties for our regularized polymer model. These developments collectively enable substantially more efficient fieldtheoretic simulation of polymers, and illustrate the importance of simultaneously addressing analytical and numerical pathologies when implementing such computations.
Efficient fieldtheoretic simulation of polymer solutions
Villet, Michael C.; Fredrickson, Glenn H.
20141214
We present several developments that facilitate the efficient fieldtheoretic simulation of polymers by complex Langevin sampling. A regularization scheme using finite Gaussian excluded volume interactions is used to derive a polymer solution model that appears free of ultraviolet divergences and hence is wellsuited for latticediscretized field theoretic simulation. We show that such models can exhibit ultraviolet sensitivity, a numerical pathology that dramatically increases sampling error in the continuum lattice limit, and further show that this pathology can be eliminated by appropriate model reformulation by variable transformation. We present an exponential time differencing algorithm for integrating complex Langevin equations for field theoretic simulation, and show that the algorithm exhibits excellent accuracy and stability properties for our regularized polymer model. These developments collectively enable substantially more efficient fieldtheoretic simulation of polymers, and illustrate the importance of simultaneously addressing analytical and numerical pathologies when implementing such computations.
Conformal field theory approach to Abelian and nonAbelian quantum Hall quasielectrons.
Hansson, T H; Hermanns, M; Regnault, N; Viefers, S
20090424
The quasiparticles in quantum Hall liquids carry fractional charge and obey fractional quantum statistics. Of particular recent interest are those with nonAbelian statistics, since their braiding properties could, in principle, be used for robust coding of quantum information. There is already a good theoretical understanding of quasiholes in both Abelian and nonAbelian quantum Hall states. Here we develop conformal field theory methods that allow for an equally precise description of quasielectrons and explicitly construct two and fourquasielectron excitations of the nonAbelian MooreRead state.
NASA Astrophysics Data System (ADS)
Malpetti, Daniele; Roscilde, Tommaso
20170201
The meanfield approximation is at the heart of our understanding of complex systems, despite its fundamental limitation of completely neglecting correlations between the elementary constituents. In a recent work [Phys. Rev. Lett. 117, 130401 (2016), 10.1103/PhysRevLett.117.130401], we have shown that in quantum manybody systems at finite temperature, twopoint correlations can be formally separated into a thermal part and a quantum part and that quantum correlations are generically found to decay exponentially at finite temperature, with a characteristic, temperaturedependent quantum coherence length. The existence of these two different forms of correlation in quantum manybody systems suggests the possibility of formulating an approximation, which affects quantum correlations only, without preventing the correct description of classical fluctuations at all length scales. Focusing on lattice boson and quantum Ising models, we make use of the pathintegral formulation of quantum statistical mechanics to introduce such an approximation, which we dub quantum meanfield (QMF) approach, and which can be readily generalized to a cluster form (cluster QMF or cQMF). The cQMF approximation reduces to cluster meanfield theory at T =0 , while at any finite temperature it produces a family of systematically improved, semiclassical approximations to the quantum statistical mechanics of the lattice theory at hand. Contrary to standard MF approximations, the correct nature of thermal critical phenomena is captured by any cluster size. In the two exemplary cases of the twodimensional quantum Ising model and of twodimensional quantum rotors, we study systematically the convergence of the cQMF approximation towards the exact result, and show that the convergence is typically linear or sublinear in the boundarytobulk ratio of the clusters as T →0 , while it becomes faster than linear as T grows. These results pave the way towards the development of semiclassical numerical
A FieldTheoretic Approach to the Wiener Sausage
NASA Astrophysics Data System (ADS)
Nekovar, S.; Pruessner, G.
20160501
The Wiener Sausage, the volume traced out by a sphere attached to a Brownian particle, is a classical problem in statistics and mathematical physics. Initially motivated by a range of fieldtheoretic, technical questions, we present a single loop renormalised perturbation theory of a stochastic process closely related to the Wiener Sausage, which, however, proves to be exact for the exponents and some amplitudes. The fieldtheoretic approach is particularly elegant and very enjoyable to see at work on such a classic problem. While we recover a number of known, classical results, the fieldtheoretic techniques deployed provide a particularly versatile framework, which allows easy calculation with different boundary conditions even of higher momenta and more complicated correlation functions. At the same time, we provide a highly instructive, nontrivial example for some of the technical particularities of the fieldtheoretic description of stochastic processes, such as excluded volume, lack of translational invariance and immobile particles. The aim of the present work is not to improve upon the wellestablished results for the Wiener Sausage, but to provide a fieldtheoretic approach to it, in order to gain a better understanding of the fieldtheoretic obstacles to overcome.
Torque anomaly in quantum field theory
NASA Astrophysics Data System (ADS)
Fulling, S. A.; Mera, F. D.; Trendafilova, C. S.
20130201
The expectation values of energy density and pressure of a quantum field inside a wedgeshaped region appear to violate the expected relationship between torque and total energy as a function of angle. In particular, this is true of the wellknown DeutschCandelas stress tensor for the electromagnetic field, whose definition requires no regularization except possibly at the vertex. Unlike a similar anomaly in the pressure exerted by a reflecting boundary against a perpendicular wall, this problem cannot be dismissed as an artifact of an ad hoc regularization.
A Quantum Theoretical Explanation for Probability Judgment Errors
ERIC Educational Resources Information Center
Busemeyer, Jerome R.; Pothos, Emmanuel M.; Franco, Riccardo; Trueblood, Jennifer S.
20110101
A quantum probability model is introduced and used to explain human probability judgment errors including the conjunction and disjunction fallacies, averaging effects, unpacking effects, and order effects on inference. On the one hand, quantum theory is similar to other categorization and memory models of cognition in that it relies on vector…
A Quantum Theoretical Explanation for Probability Judgment Errors
ERIC Educational Resources Information Center
Busemeyer, Jerome R.; Pothos, Emmanuel M.; Franco, Riccardo; Trueblood, Jennifer S.
20110101
A quantum probability model is introduced and used to explain human probability judgment errors including the conjunction and disjunction fallacies, averaging effects, unpacking effects, and order effects on inference. On the one hand, quantum theory is similar to other categorization and memory models of cognition in that it relies on vector…
Quantum Physics, Fields and Closed Timelike Curves: The DCTC Condition in Quantum Field Theory
NASA Astrophysics Data System (ADS)
Tolksdorf, Jürgen; Verch, Rainer
20170701
The DCTC condition has originally been proposed by David Deutsch as a condition on states of a quantum communication network that contains "backward timesteps" in some of its branches. It has been argued that this is an analogue for quantum processes in the presence of closed timelike curves (CTCs). The unusual properties of states of quantum communication networks that fulfill the DCTC condition have been discussed extensively in recent literature. In this work, the DCTC condition is investigated in the framework of quantum field theory in the local, operatoralgebraic approach due to Haag and Kastler. It is shown that the DCTC condition cannot be fulfilled in states that are analytic in the energy, or satisfy the ReehSchlieder property, for a certain class of processes and initial conditions. On the other hand, if a quantum field theory admits sufficiently many uncorrelated states across acausally related spacetime regions (as implied by the split property), then the DCTC condition can always be fulfilled approximately to arbitrary precision. As this result pertains to quantum field theory on globally hyperbolic spacetimes where CTCs are absent, one may conclude that interpreting the DCTC condition as characteristic for quantum processes in the presence of CTCs could be misleading, and should be regarded with caution. Furthermore, a construction of the quantized massless KleinGordon field on the Politzer spacetime, often viewed as spacetime analogue for quantum communication networks with backward timesteps, is proposed in this work.
On space of integrable quantum field theories
NASA Astrophysics Data System (ADS)
Smirnov, F. A.; Zamolodchikov, A. B.
20170201
We study deformations of 2D Integrable Quantum Field Theories (IQFT) which preserve integrability (the existence of infinitely many local integrals of motion). The IQFT are understood as "effective field theories", with finite ultraviolet cutoff. We show that for any such IQFT there are infinitely many integrable deformations generated by scalar local fields Xs, which are in onetoone correspondence with the local integrals of motion; moreover, the scalars Xs are built from the components of the associated conserved currents in a universal way. The first of these scalars, X1, coincides with the composite field (T T bar) built from the components of the energymomentum tensor. The deformations of quantum field theories generated by X1 are "solvable" in a certain sense, even if the original theory is not integrable. In a massive IQFT the deformations Xs are identified with the deformations of the corresponding factorizable Smatrix via the CDD factor. The situation is illustrated by explicit construction of the form factors of the operators Xs in sineGordon theory. We also make some remarks on the problem of UV completeness of such integrable deformations.
On space of integrable quantum field theories
Smirnov, F. A.; Zamolodchikov, A. B.
20161221
Here, we study deformations of 2D Integrable Quantum Field Theories (IQFT) which preserve integrability (the existence of infinitely many local integrals of motion). The IQFT are understood as “effective field theories”, with finite ultraviolet cutoff. We show that for any such IQFT there are infinitely many integrable deformations generated by scalar local fields Xs, which are in onetoone correspondence with the local integrals of motion; moreover, the scalars Xs are built from the components of the associated conserved currents in a universal way. The first of these scalars, X1, coincides with the composite field View the MathML source(TT¯) built frommore » the components of the energy–momentum tensor. The deformations of quantum field theories generated by X1 are “solvable” in a certain sense, even if the original theory is not integrable. In a massive IQFT the deformations Xs are identified with the deformations of the corresponding factorizable Smatrix via the CDD factor. The situation is illustrated by explicit construction of the form factors of the operators Xs in sineGordon theory. Lastly, we also make some remarks on the problem of UV completeness of such integrable deformations.« less
Underwriting informationtheoretic accounts of quantum mechanics with a realist, psiepistemic model
NASA Astrophysics Data System (ADS)
Stuckey, W. M.; Silberstein, Michael; McDevitt, Timothy
20160501
We propose an adynamical interpretation of quantum theory called Relational Blockworld (RBW) where the fundamental ontological element is a 4D graphical amalgam of space, time and sources called a “spacetimesource element.” These are fundamental elements of space, time and sources, not source elements in space and time. The transition amplitude for a spacetimesource element is computed using a path integral with discrete graphical action. The action for a spacetimesource element is constructed from a difference matrix K and source vector J on the graph, as in lattice gauge theory. K is constructed from graphical field gradients so that it contains a nontrivial null space and J is then restricted to the row space of K, so that it is divergencefree and represents a conserved exchange of energymomentum. This construct of K and J represents an adynamical global constraint between sources, the spacetime metric and the energymomentum content of the spacetimesource element, rather than a dynamical law for timeevolved entities. To illustrate this interpretation, we explain the simple EPRBell and twinslit experiments. This interpretation of quantum mechanics constitutes a realist, psiepistemic model that might underwrite certain informationtheoretic accounts of the quantum.
A master functional for quantum field theory
NASA Astrophysics Data System (ADS)
Anselmi, Damiano
20130401
We study a new generating functional of oneparticle irreducible diagrams in quantum field theory, called master functional, which is invariant under the most general perturbative changes of field variables. The usual functional Γ does not behave as a scalar under the transformation law inherited from its very definition as the Legendre transform of W=ln Z, although it does behave as a scalar under an unusual transformation law. The master functional, on the other hand, is the Legendre transform of an improved functional W with respect to the sources coupled to both elementary and composite fields. The inclusion of certain improvement terms in W and Z is necessary to make this new Legendre transform well defined. The master functional behaves as a scalar under the transformation law inherited from its very definition. Moreover, it admits a proper formulation, obtained extending the set of integrated fields to socalled proper fields, which allows us to work without passing through Z, W or Γ. In the proper formulation the classical action coincides with the classical limit of the master functional, and correlation functions and renormalization are calculated applying the usual diagrammatic rules to the proper fields. Finally, the most general change of field variables, including the map relating bare and renormalized fields, is a linear redefinition of the proper fields.
The actual content of quantum theoretical kinematics and mechanics
NASA Technical Reports Server (NTRS)
Heisenberg, W.
19830101
First, exact definitions are supplied for the terms: position, velocity, energy, etc. (of the electron, for instance), such that they are valid also in quantum mechanics. Canonically conjugated variables are determined simultaneously only with a characteristic uncertainty. This uncertainty is the intrinsic reason for the occurrence of statistical relations in quantum mechanics. Mathematical formulation is made possible by the DiracJordan theory. Beginning from the basic principles thus obtained, macroscopic processes are understood from the viewpoint of quantum mechanics. Several imaginary experiments are discussed to elucidate the theory.
Comments on conformal Killing vector fields and quantum field theory
Brown, M.R.; Ottewill, A.C.; Siklos, S.T.C.
19821015
We give a comprehensive analysis of those vacuums for flat and conformally flat spacetimes which can be defined by timelike, hypersurfaceorthogonal, conformal Killing vector fields. We obtain formulas for the difference in stressenergy density between any two such states and display the correspondence with the renormalized stress tensors. A brief discussion is given of the relevance of these results to quantummechanical measurements made by noninertial observers moving through flat space.
Nonlinear quantum equations: Classical field theory
RegoMonteiro, M. A.; Nobre, F. D.
20131015
An exact classical field theory for nonlinear quantum equations is presented herein. It has been applied recently to a nonlinear Schrödinger equation, and it is shown herein to hold also for a nonlinear generalization of the KleinGordon equation. These generalizations were carried by introducing nonlinear terms, characterized by exponents depending on an index q, in such a way that the standard, linear equations, are recovered in the limit q→ 1. The main characteristic of this field theory consists on the fact that besides the usual Ψ(x(vector sign),t), a new field Φ(x(vector sign),t) needs to be introduced in the Lagrangian, as well. The field Φ(x(vector sign),t), which is defined by means of an additional equation, becomes Ψ{sup *}(x(vector sign),t) only when q→ 1. The solutions for the fields Ψ(x(vector sign),t) and Φ(x(vector sign),t) are found herein, being expressed in terms of a qplane wave; moreover, both field equations lead to the relation E{sup 2}=p{sup 2}c{sup 2}+m{sup 2}c{sup 4}, for all values of q. The fact that such a classical field theory works well for two very distinct nonlinear quantum equations, namely, the Schrödinger and KleinGordon ones, suggests that this procedure should be appropriate for a wider class nonlinear equations. It is shown that the standard global gauge invariance is broken as a consequence of the nonlinearity.
MidInfrared QuantumDot Quantum Cascade Laser: A Theoretical Feasibility Study
Michael, Stephan; Chow, Weng; Schneider, Hans
20160501
In the framework of a microscopic model for intersubband gain from electrically pumped quantumdot structures we investigate electrically pumped quantumdots as active material for a midinfrared quantum cascade laser. Our previous calculations have indicated that these structures could operate with reduced threshold current densities while also achieving a modal gain comparable to that of quantum well active materials. We study the influence of two important quantumdot material parameters, here, namely inhomogeneous broadening and quantumdot sheet density, on the performance of a proposed quantum cascade laser design. In terms of achieving a positive modal net gain, a high quantumdot density can compensate for moderately high inhomogeneous broadening, but at a cost of increased threshold current density. By minimizing quantumdot density with presently achievable inhomogeneous broadening and total losses, significantly lower threshold densities than those reported in quantumwell quantumcascade lasers are predicted by our theory.
A quantum theoretical explanation for probability judgment errors.
Busemeyer, Jerome R; Pothos, Emmanuel M; Franco, Riccardo; Trueblood, Jennifer S
20110401
A quantum probability model is introduced and used to explain human probability judgment errors including the conjunction and disjunction fallacies, averaging effects, unpacking effects, and order effects on inference. On the one hand, quantum theory is similar to other categorization and memory models of cognition in that it relies on vector spaces defined by features and similarities between vectors to determine probability judgments. On the other hand, quantum probability theory is a generalization of Bayesian probability theory because it is based on a set of (von Neumann) axioms that relax some of the classic (Kolmogorov) axioms. The quantum model is compared and contrasted with other competing explanations for these judgment errors, including the anchoring and adjustment model for probability judgments. In the quantum model, a new fundamental concept in cognition is advancedthe compatibility versus incompatibility of questions and the effect this can have on the sequential order of judgments. We conclude that quantum informationprocessing principles provide a viable and promising new way to understand human judgment and reasoning. 2011 APA, all rights reserved
Lyapunov control of quantum systems with impulsive control fields.
Yang, Wei; Sun, Jitao
20130101
We investigate the Lyapunov control of finitedimensional quantum systems with impulsive control fields, where the studied quantum systems are governed by the Schrödinger equation. By three different Lyapunov functions and the invariant principle of impulsive systems, we study the convergence of quantum systems with impulsive control fields and propose new results for the mentioned quantum systems in the form of sufficient conditions. Two numerical simulations are presented to illustrate the effectiveness of the proposed control method.
Lyapunov Control of Quantum Systems with Impulsive Control Fields
Yang, Wei; Sun, Jitao
20130101
We investigate the Lyapunov control of finitedimensional quantum systems with impulsive control fields, where the studied quantum systems are governed by the Schrödinger equation. By three different Lyapunov functions and the invariant principle of impulsive systems, we study the convergence of quantum systems with impulsive control fields and propose new results for the mentioned quantum systems in the form of sufficient conditions. Two numerical simulations are presented to illustrate the effectiveness of the proposed control method. PMID:23766712
Dressed photons in a new paradigm of offshell quantum fields
NASA Astrophysics Data System (ADS)
Sakuma, Hirofumi; Ojima, Izumi; Ohtsu, Motoichi
20170901
This article reviews recent progress in theoretical studies of dressed photons. For providing concrete physical images of dressed photons, several experimental studies are demonstrated. They are applications of dressed photons to novel optical functional devices, nanofabrication technologies, energy conversion technologies, and photon breeding devices. After these experimental demonstrations, as the main part of this review, quantumfield theoretical formulation of dressed photons is attempted in use of the newly introduced Clebschdual variable of electromagnetic field. The reason for introducing the new formulation will be explained in the final section from the viewpoint to exhibit the contrast between free and interacting quantum fields in regard to their energymomentum supports which are seldom touched upon (or forgotten) in the common physical discussions about quantum fields.
NASA Astrophysics Data System (ADS)
Vyas, P. B.; Naquin, C.; Edwards, H.; Lee, M.; Vandenberghe, W. G.; Fischetti, M. V.
20170101
We present a theoretical study of the negative differential transconductance (NDT) recently observed in the lateralquantumwell Si nchannel fieldeffect transistors [J. Appl. Phys. 118, 124505 (2015)]. In these devices, p+ doping extensions are introduced at the sourcechannel and drainchannel junctions, thus creating two potential barriers that define the quantum well across whose quasibound states resonant/sequential tunneling may occur. Our study, based on the quantum transmitting boundary method, predicts the presence of a sharp NDT in devices with a nominal gate length of 10to20 nm at low temperatures ( ˜10 K). At higher temperatures, the NDT weakens and disappears altogether as a result of increasing thermionic emission over the p+ potential barriers. In larger devices (with a gate length of 30 nm or longer), the NDT cannot be observed because of the low transmission probability and small energetic spacing (smaller than kBT ) of the quasibound states in the quantum well. We speculate that the inability of the model to predict the NDT observed in 40 nm gatelength devices may be due to an insufficiently accurate knowledge of the actual doping profiles. On the other hand, our study shows that NDT suitable for novel logic applications may be obtained at room temperature in devices of the current or nearfuture generation (sub10 nm node), provided an optimal design can be found that minimizes the thermionic emission (requiring high p+ potentialbarriers) and punchthrough (that meets the opposite requirement of potentialbarriers low enough to favor the tunneling current).
Fieldtheoretical formulation of Regge–Teitelboim gravity
Sheykin, A. A. Paston, S. A.
20161215
Theory of gravity is considered in the Regge–Teitelboim approach in which the pseudoRimannian space is treated as a surface isometrically embedded in an ambient Minkowski space of higher dimension. This approach is formulated in terms of a field theory in which the original pseudoRimannian space is defined by the field constantvalue surfaces. The symmetry properties of the proposed theory are investigated, and possible structure of the fieldtheoretical Lagrangian is discussed.
Inertial mass and the quantum vacuum fields
NASA Astrophysics Data System (ADS)
Haisch, Bernard; Rueda, Alfonso; Dobyns, York
20010501
Even when the Higgs particle is finally detected, it will continue to be a legitimate question to ask whether the inertia of matter as a reaction force opposing acceleration is an intrinsic or extrinsic property of matter. General relativity specifies which geodesic path a free particle will follow, but geometrodynamics has no mechanism for generating a reaction force for deviation from geodesic motion. We discuss a different approach involving the electromagnetic zeropoint field (ZPF) of the quantum vacuum. It has been found that certain asymmetries arise in the ZPF as perceived from an accelerating reference frame. In such a frame the Poynting vector and momentum flux of the ZPF become nonzero. Scattering of this quantum radiation by the quarks and electrons in matter can result in an accelerationdependent reaction force. Both the ordinary and the relativistic forms of Newton's second law, the equation of motion, can be derived from the electrodynamics of such ZPFparticle interactions. Conjectural arguments are given why this interaction should take place in a resonance at the Compton frequency, and how this could simultaneously provide a physical basis for the de Broglie wavelength of a moving particle. This affords a suggestive perspective on a deep connection between electrodynamics, the origin of inertia and the quantum wave nature of matter.
Nearfield optical properties of quantum dots, applications and perspectives.
Zora, A; Triberis, G P; Simserides, C
20111101
Recent years have witnessed tremendous research in quantum dots as excellent models of quantum physics at the nanoscale and as excellent candidates for various applications based on their optoelectronic properties. This review intends to present theoretical and experimental investigations of the nearfield optical properties of these structures, and their multimodal applications such as biosensors, biological labels, optical fibers, switches and sensors, visual displays, photovoltaic devices and related patents.
Bilinear covariants and spinor fields duality in quantum Clifford algebras
Abłamowicz, Rafał; Gonçalves, Icaro; Rocha, Roldão da
20141015
Classification of quantum spinor fields according to quantum bilinear covariants is introduced in a context of quantum Clifford algebras on Minkowski spacetime. Once the bilinear covariants are expressed in terms of algebraic spinor fields, the duality between spinor and quantum spinor fields can be discussed. Thus, by endowing the underlying spacetime with an arbitrary bilinear form with an antisymmetric part in addition to a symmetric spacetime metric, quantum algebraic spinor fields and deformed bilinear covariants can be constructed. They are thus compared to the classical (non quantum) ones. Classes of quantum spinor fields classes are introduced and compared with Lounesto's spinor field classification. A physical interpretation of the deformed parts and the underlying Zgrading is proposed. The existence of an arbitrary bilinear form endowing the spacetime already has been explored in the literature in the context of quantum gravity [S. W. Hawking, “The unpredictability of quantum gravity,” Commun. Math. Phys. 87, 395 (1982)]. Here, it is shown further to play a prominent role in the structure of Dirac, Weyl, and Majorana spinor fields, besides the most general flagpoles and flagdipoles. We introduce a new duality between the standard and the quantum spinor fields, by showing that when Clifford algebras over vector spaces endowed with an arbitrary bilinear form are taken into account, a mixture among the classes does occur. Consequently, novel features regarding the spinor fields can be derived.
Gravity quantized: Loop quantum gravity with a scalar field
Domagala, Marcin; Kaminski, Wojciech; Giesel, Kristina; Lewandowski, Jerzy
20101115
...''but we do not have quantum gravity.'' This phrase is often used when analysis of a physical problem enters the regime in which quantum gravity effects should be taken into account. In fact, there are several models of the gravitational field coupled to (scalar) fields for which the quantization procedure can be completed using loop quantum gravity techniques. The model we present in this paper consists of the gravitational field coupled to a scalar field. The result has similar structure to the loop quantum cosmology models, except that it involves all the local degrees of freedom of the gravitational field because no symmetry reduction has been performed at the classical level.
Quantum Monte Carlo calculations with chiral effective field theory interactions.
Gezerlis, A; Tews, I; Epelbaum, E; Gandolfi, S; Hebeler, K; Nogga, A; Schwenk, A
20130719
We present the first quantum Monte Carlo (QMC) calculations with chiral effective field theory (EFT) interactions. To achieve this, we remove all sources of nonlocality, which hamper the inclusion in QMC calculations, in nuclear forces to nexttonexttoleading order. We perform auxiliaryfield diffusion Monte Carlo (AFDMC) calculations for the neutron matter energy up to saturation density based on local leadingorder, nexttoleading order, and nexttonexttoleading order nucleonnucleon interactions. Our results exhibit a systematic orderbyorder convergence in chiral EFT and provide nonperturbative benchmarks with theoretical uncertainties. For the softer interactions, perturbative calculations are in excellent agreement with the AFDMC results. This work paves the way for QMC calculations with systematic chiral EFT interactions for nuclei and nuclear matter, for testing the perturbativeness of different orders, and allows for matching to lattice QCD results by varying the pion mass.
Quantum theory for spatial motion of polaritons in inhomogeneous fields
NASA Astrophysics Data System (ADS)
Zhou, Lan; Lu, Jing; Zhou, D. L.; Sun, C. P.
20080201
Polaritons are the collective excitations of many atoms dressed by resonant photons, which can be used to explain the slow light propagation with the mechanism of electromagnetically induced transparency. As quasiparticles, these collective excitations possess the typical feature of the matter particles, which can be reflected and deflected by the inhomogeneous medium in its spatial motion with some velocity. In this paper we develop a quantum theory to systematically describe the spatial motion of polaritons in inhomogeneous magnetic and optical fields. This theoretical approach treats these quasiparticles through an effective Schrödinger equation with anisotropic dispersion that the longitudinal motion is similar to an ultrarelativistic motion of a “slow light velocity” while the transverse motion is of nonrelativity with certain effective mass. We find that, after passing through the EIT medium, the light ray bends due to the spatialdependent profile of external field. This phenomenon explicitly demonstrates the exotic corpuscular and anisotropic property of polaritons.
Haag's Theorem and Parameterized Quantum Field Theory
NASA Astrophysics Data System (ADS)
Seidewitz, Edwin
20170101
``Haag's theorem is very inconvenient; it means that the interaction picture exists only if there is no interaction''. In traditional quantum field theory (QFT), Haag's theorem states that any field unitarily equivalent to a free field must itself be a free field. But the derivation of the Dyson series perturbation expansion relies on the use of the interaction picture, in which the interacting field is unitarily equivalent to the free field, but which must still account for interactions. So, the usual derivation of the scattering matrix in QFT is mathematically ill defined. Nevertheless, perturbative QFT is currently the only practical approach for addressing realistic scattering, and it has been very successful in making empirical predictions. This success can be understood through an alternative derivation of the Dyson series in a covariant formulation of QFT using an invariant, fifth path parameter in addition to the usual four position parameters. The parameterization provides an additional degree of freedom that allows Haag's Theorem to be avoided, permitting the consistent use of a form of interaction picture in deriving the Dyson expansion. The extra symmetry so introduced is then broken by the choice of an interacting vacuum.
Group Theoretical Approach for Controlled Quantum Mechanical Systems
20071106
journals (N/A for none) (1) J. Zhang, C.W. Li, Re Bing Wu, T.J.Tarn, and X.S. Liu,”Maximal suppression of decoherence in Markovian quantum systems...of TimeDependent Quantum Control Systems,” Journal of Mathematical Physics, Vol.46, No.5, May, 2005.pp.0521021 to 21. (3) Re Bing Wu, T.J.Tarn, and...34Optimal Bang  Bang Control for SU(1,1) Coherent States," Physical Review A, Accepted for publication. List of papers submitted or published that
Quantum Field Theory of KosterlitzThouless Phase Transitions.
NASA Astrophysics Data System (ADS)
Ogilvie, Michael Charles
19801201
A general quantum fieldtheoretic formalism for the study of KosterlitzThouless phase transition is developed and applied to several models. The structure of the free, massless scalar field is discussed, making explicit its connection with the Gaussian model. The close connection of the spinwave and vortex operators with twodimensional fermionboson equivalences is stressed. The critical behavior of the planar model is reviewed, using fieldtheoretic methods applied to the sineGordon model. The Kosterlitz Thouless phase transition in twodimensional dislocation mediated melting is studied using a vector generalization of the sineGordon model. Recent secondorder renormalization group calculations are confirmed, and the issue of universal thirdorder corrections is discussed. It is shown that the GrossNeveu model can be interpreted as a massive theory associated with a KosterlitzThouless critical point. Finally, the Ising and Baxter models are studied using the methods developed here. It is shown that the vortex and spinwave excitations in the Ising model conspire to produce a free, massive Majorana fermion field theory in the continuum limit. The formalism is then extended to the Baxter model. Recent results on the Baxter and AshkinTeller models are rederived and extended.
Exotic Bbb R4 and quantum field theory
NASA Astrophysics Data System (ADS)
AsselmeyerMaluga, Torsten; Mader, Roland
20120201
Recent work on exotic smooth Bbb R4,s, i.e. topological Bbb R4 with exotic differential structure, shows the connection of 4exotics with the codimension1 foliations of S3, SU(2) WZW models and twisted Ktheory KH(S3), H in H3(S3,Bbb Z). These results made it possible to explicate some physical effects of exotic 4smoothness. Here we present a relation between exotic smooth Bbb R4 and operator algebras. The correspondence uses the leaf space of the codimension1 foliation of S3 inducing a von Neumann algebra W(S3) as description. This algebra is a type III1 factor lying at the heart of any observable algebra of QFT. By using the relation to factor II, we showed that the algebra W(S3) can be interpreted as DrinfeldTuraev deformation quantization of the space of flat SL(2, Bbb C) connections (or holonomies). Thus, we obtain a natural relation to quantum field theory. Finally we discuss the appearance of concrete action functionals for fermions or gauge fields and its connection to quantumfieldtheoretical models like the Tree QFT of Rivasseau.
Causality Is Inconsistent With Quantum Field Theory
Wolf, Fred Alan
20111129
Causality in quantum field theory means the vanishing of commutators for spacelike separated fields (VCSSF). I will show that VCSSF is not tenable. For VCSSF to be tenable, and therefore, to have both retarded and advanced propagators vanish in the elsewhere, a superposition of negative energy antiparticle and positive energy particle propagators, traveling forward in time, and a superposition of negative energy particle and positive energy antiparticle propagators, traveling backward in time, are required. Hence VCSSF predicts nonvanishing probabilities for both negative energy particles in the forwardthroughtime direction and positive energy antiparticles in the backwardsthroughtime direction. Therefore, since VCSSF is unrealizable in a stable universe, tachyonic propagation must occur in denial of causality.
Quantum fields versus strings at finite temperature
Osorio, M.A.R. . Lyman Lab. of Physics)
19920720
In this paper, the authors study some aspects of the relationship between the oneloop free energy of closed superstrings computed as a sum over the free energies of the quantum field present in the string (the analog model) and the modular invariant expression of the same quantity. In particular, by getting a generalized duality relation for the integrand of the modular invariant expression for the free energy of closed superstrings and using a regularization procedure, the authors connect the contribution to the vacuum energy from the bosonic degrees of freedom in the analog model (one half of the total number) with the coefficient governing the high temperature behavior of the free energy. The authors also study the physical meaning of this regularization and the role played by the leftright constraint defining the physical fields in the lightcone gauge.
Magneticfield control of the exciton quantum beats phase in InGaAs/GaAs quantum dots
NASA Astrophysics Data System (ADS)
Siarry, B.; Eble, B.; Bernardot, F.; Grinberg, P.; Testelin, C.; Chamarro, M.; LemaÃ®tre, A.
20151001
We demonstrate here the phase control of the neutral exciton quantum beats in InGaAs/GaAs quantum dots. A longitudinal magnetic field is used as a tuning parameter to change the phase of the oscillations in a deterministic way. This effect arises from the competition between the Zeeman splitting and the electron/hole exchange interaction on the exciton dipole symmetry. To explore this mechanism, we have developed a pumpprobe setup based on the optical heterodyne detection of the quantum dots reflectivity allowing one to measure the exciton dynamics from a small quantum dots ensemble (˜300 ). Particular attention is paid to give a detailed theoretical analysis of the measurements. The experimental results are in excellent agreement with the model.
NASA Astrophysics Data System (ADS)
Yesilgul, U.; Sari, H.; Ungan, F.; MartínezOrozco, J. C.; Restrepo, R. L.; MoraRamos, M. E.; Duque, C. A.; Sökmen, I.
20170301
In this study, the effects of electric and magnetic fields on the optical rectification and second and third harmonic generation in asymmetric double quantum well under the intense nonresonant laser field is theoretically investigated. We calculate the optical rectification and second and third harmonic generation within the compact densitymatrix approach. The theoretical findings show that the influence of electric, magnetic, and intense laser fields leads to significant changes in the coefficients of nonlinear optical rectification, second and third harmonic generation.
Quantum Field Theory in Condensed Matter Physics
NASA Astrophysics Data System (ADS)
Tsvelik, Alexei M.
20070101
Preface; Acknowledgements; Part I. Introduction to Methods: 1. QFT: language and goals; 2. Connection between quantum and classical: path integrals; 3. Definitions of correlation functions: Wick's theorem; 4. Free bosonic field in an external field; 5. Perturbation theory: Feynman diagrams; 6. Calculation methods for diagram series: divergences and their elimination; 7. Renormalization group procedures; 8. O(N)symmetric vector model below the transition point; 9. Nonlinear sigma models in two dimensions: renormalization group and 1/Nexpansion; 10. O(3) nonlinear sigma model in the strong coupling limit; Part II. Fermions: 11. Path integral and Wick's theorem for fermions; 12. Interaction electrons: the Fermi liquid; 13. Electrodynamics in metals; 14. Relativistic fermions: aspects of quantum electrodynamics; 15. AharonovBohm effect and transmutation of statistics; Part III. Strongly Fluctuating Spin Systems: Introduction; 16. SchwingerWigner quantization procedure: nonlinear sigma models; 17. O(3) nonlinear sigma model in (2+1) dimensions: the phase diagram; 18. Order from disorder; 19. JordanWigner transformations for spin S=1/2 models in D=1, 2, 3; 20. Majorana representation for spin S=1/2 magnets: relationship to Z2 lattice gauge theories; 21. Path integral representations for a doped antiferromagnet; Part IV. Physics in the World of One Spatial Dimension: Introduction; 22. Model of the free bosonic massless scalar field; 23. Relevant and irrelevant fields; 24. KosterlitzThouless transition; 25. Conformal symmetry; 26. Virasoro algebra; 27. Differential equations for the correlation functions; 28. Ising model; 29. Onedimensional spinless fermions: TomonagaLuttinger liquid; 30. Onedimensional fermions with spin: spincharge separation; 31. KacMoody algebras: WessZuminoNovikovWitten model; 32. WessZuminoNovikovWitten model in the Lagrangian form: nonAbelian bosonization; 33. Semiclassical approach to WessZuminoNovikovWitten models; 34
Kaon photoproduction in field theoretic and multipoles approaches
NASA Astrophysics Data System (ADS)
Mart, T.
20170701
In this paper we review our strategy to update the phenomenological model KaonMaid, which has been used since the year of 2000 and starts to indicate some inconsistencies with the presently available experimental data. There are two approaches used to this end, i.e., the fieldtheoretic and multipoles models. The advantages and disadvantages of both models are briefly discussed.
Usman, Muhammad; Tasco, Vittorianna; Todaro, Maria Teresa; De Giorgi, Milena; O'Reilly, Eoin P; Klimeck, Gerhard; Passaseo, Adriana
20120427
IIIV growth and surface conditions strongly influence the physical structure and resulting optical properties of selfassembled quantum dots (QDs). Beyond the design of a desired active optical wavelength, the polarization response of QDs is of particular interest for optical communications and quantum information science. Previous theoretical studies based on a pure InAs QD model failed to reproduce experimentally observed polarization properties. In this work, multimillion atom simulations are performed in an effort to understand the correlation between chemical composition and polarization properties of QDs. A systematic analysis of QD structural parameters leads us to propose a twolayer composition model, mimicking In segregation and InGa intermixing effects. This model, consistent with mostly accepted compositional findings, allows us to accurately fit the experimental PL spectra. The detailed study of QD morphology parameters presented here serves as a tool for using growth dynamics to engineer the strain field inside and around the QD structures, allowing tuning of the polarization response.
A quantum theoretical approach to information processing in neural networks
NASA Astrophysics Data System (ADS)
Barahona da Fonseca, José; Barahona da Fonseca, Isabel; Suarez Araujo, Carmen Paz; Simões da Fonseca, José
20000501
A reinterpretation of experimental data on learning was used to formulate a law on data acquisition similar to the Hamiltonian of a mechanical system. A matrix of costs in decision making specifies values attributable to a barrier that opposed to hypothesis formation about decision making. The interpretation of the encoding costs as frequencies of oscillatory phenomena leads to a quantum paradigm based in the models of photoelectric effect as well as of a particle against a potential barrier. Cognitive processes are envisaged as complex phenomena represented by structures linked by valence bounds. This metaphor is used to find some prerequisites to certain types of conscious experience as well as to find an explanation for some pathological distortions of cognitive operations as they are represented in the context of the isolobal model. Those quantum phenomena are understood as representing an analogue programming for specific special purpose computations. The formation of complex chemical structures within the context of isolobal theory is understood as an analog quantum paradigm for complex cognitive computations.
Protected gates for topological quantum field theories
NASA Astrophysics Data System (ADS)
Beverland, Michael E.; Buerschaper, Oliver; Koenig, Robert; Pastawski, Fernando; Preskill, John; Sijher, Sumit
20160201
We study restrictions on localitypreserving unitary logical gates for topological quantum codes in two spatial dimensions. A localitypreserving operation is one which maps local operators to local operators — for example, a constantdepth quantum circuit of geometrically local gates, or evolution for a constant time governed by a geometrically local boundedstrength Hamiltonian. Localitypreserving logical gates of topological codes are intrinsically fault tolerant because spatially localized errors remain localized, and hence sufficiently dilute errors remain correctable. By invoking general properties of twodimensional topological field theories, we find that the localitypreserving logical gates are severely limited for codes which admit nonabelian anyons, in particular, there are no localitypreserving logical gates on the torus or the sphere with M punctures if the braiding of anyons is computationally universal. Furthermore, for Ising anyons on the Mpunctured sphere, localitypreserving gates must be elements of the logical Pauli group. We derive these results by relating logical gates of a topological code to automorphisms of the Verlinde algebra of the corresponding anyon model, and by requiring the logical gates to be compatible with basis changes in the logical Hilbert space arising from local Fmoves and the mapping class group.
Protected gates for topological quantum field theories
Beverland, Michael E.; Pastawski, Fernando; Preskill, John; Buerschaper, Oliver; Koenig, Robert; Sijher, Sumit
20160215
We study restrictions on localitypreserving unitary logical gates for topological quantum codes in two spatial dimensions. A localitypreserving operation is one which maps local operators to local operators — for example, a constantdepth quantum circuit of geometrically local gates, or evolution for a constant time governed by a geometrically local boundedstrength Hamiltonian. Localitypreserving logical gates of topological codes are intrinsically fault tolerant because spatially localized errors remain localized, and hence sufficiently dilute errors remain correctable. By invoking general properties of twodimensional topological field theories, we find that the localitypreserving logical gates are severely limited for codes which admit nonabelian anyons, in particular, there are no localitypreserving logical gates on the torus or the sphere with M punctures if the braiding of anyons is computationally universal. Furthermore, for Ising anyons on the Mpunctured sphere, localitypreserving gates must be elements of the logical Pauli group. We derive these results by relating logical gates of a topological code to automorphisms of the Verlinde algebra of the corresponding anyon model, and by requiring the logical gates to be compatible with basis changes in the logical Hilbert space arising from local Fmoves and the mapping class group.
The $\\hbar$ Expansion in Quantum Field Theory
Brodsky, Stanley J.; Hoyer, Paul; /Southern Denmark U., CP3Origins /Helsinki U. /Helsinki Inst. of Phys.
20101027
We show how expansions in powers of Planck's constant {h_bar} = h = 2{pi} can give new insights into perturbative and nonperturbative properties of quantum field theories. Since {h_bar} is a fundamental parameter, exact Lorentz invariance and gauge invariance are maintained at each order of the expansion. The physics of the {h_bar} expansion depends on the scheme; i.e., different expansions are obtained depending on which quantities (momenta, couplings and masses) are assumed to be independent of {h_bar}. We show that if the coupling and mass parameters appearing in the Lagrangian density are taken to be independent of {h_bar}, then each loop in perturbation theory brings a factor of {h_bar}. In the case of quantum electrodynamics, this scheme implies that the classical charge e, as well as the fine structure constant are linear in {h_bar}. The connection between the number of loops and factors of {h_bar} is more subtle for bound states since the binding energies and boundstate momenta themselves scale with {h_bar}. The {h_bar} expansion allows one to identify equaltime relativistic bound states in QED and QCD which are of lowest order in {h_bar} and transform dynamically under Lorentz boosts. The possibility to use retarded propagators at the Born level gives valencelike wavefunctions which implicitly describe the sea constituents of the bound states normally present in its Fock state representation.
MidInfrared QuantumDot Quantum Cascade Laser: A Theoretical Feasibility Study
Michael, Stephan; Chow, Weng; Schneider, Hans
20160501
In the framework of a microscopic model for intersubband gain from electrically pumped quantumdot structures we investigate electrically pumped quantumdots as active material for a midinfrared quantum cascade laser. Our previous calculations have indicated that these structures could operate with reduced threshold current densities while also achieving a modal gain comparable to that of quantum well active materials. We study the influence of two important quantumdot material parameters, here, namely inhomogeneous broadening and quantumdot sheet density, on the performance of a proposed quantum cascade laser design. In terms of achieving a positive modal net gain, a high quantumdot density canmore » compensate for moderately high inhomogeneous broadening, but at a cost of increased threshold current density. By minimizing quantumdot density with presently achievable inhomogeneous broadening and total losses, significantly lower threshold densities than those reported in quantumwell quantumcascade lasers are predicted by our theory.« less
Excitons and trions in single and vertically coupled quantum dots under an electric field
NASA Astrophysics Data System (ADS)
Zhai, LiXue; Wang, Yan; An, Zhong
20170801
We present a theoretical study of the exciton (X0), the positive and negative trions (X+ and X) in single and vertically coupled configurations of selfassembled InGaAs quantum dots under an electric field. The quantum states of X0, X+ and X have been investigated using a quasionedimensional (Q1D) model within the effectivemass approximation. For the single quantum dots, the electricfield dependent energy levels and the average interparticle distances for the exciton and trions have been calculated. For the coupled quantum dots, the ground and the excited states for X0, X+ and X have also been calculated and discussed. It is found that either the hole or the electron can be tuned into resonance states by the electric field and that the transition energy spectra for both trions consequently show crossing and anticrossing patterns. The recombination probabilities of the exciton and trion optical transitions are also calculated. The theoretical results have been compared with previously reported photoluminescence data and qualitative agreement is obtained. The trion conditional wave functions are also plotted under different electric field intensities, and it is found that a molecular orbital can be formed at a critical electric field intensity. The evolution of the energy levels of the trions in coupled quantum dots can be explained by the interplay of particle transfer and the electric field.
Charge transfer in algebraic quantum field theory
NASA Astrophysics Data System (ADS)
Wright, Jill Dianne
We discuss aspects of the algebraic structure of quantum field theory. We take the view that the superselection structure of a theory should be determinable from the vacuum representation of the observable algebra, and physical properties of the charge. Hence one determines the nature of the charge transfer operations: the automorphisms of the observable algebra corresponding to the movement of charge along spacetime paths. New superselection sectors are obtained from the vacuum sector by an automorphism which is a limit of charge transfer operations along paths with an endpoint tending to spacelike infinity. Roberts has shown that for a gauge theory of the first kind, the charge transfer operations for a given charge form a certain kind of 1cocycle over Minkowski space. The local 1cohomology group of their equivalence classes corresponds to the superselection structure. The exact definition of the cohomology group depends on the properties of the charge. Using displaced Fock representations of free fields, we develop model field theories which illustrate this structure. The cohomological classification of displaced Fock representations has been elucidated by Araki. For more general representations, explicit determination of the cohomology group is a hard problem. Using our models, we can illustrate ways in which fields with reasonable physical properties depart fromthe abovementioned structure. In 1+1 dimensions, we use the StreaterWilde model to illustrate explicitly the representationdependence of the cohomology structure, and the directiondependence of the limiting charge transfer operation. The cohomology structure may also be representationdependent in higherdimensional theories without strict localization of charge, for example the electromagnetic field. The algebraic structure of the electromagnetic field has many other special features, which we discuss in relation to the concept of charge transfer. We also give some indication of the modifications
Quantum gravity model with fundamental spinor fields
NASA Astrophysics Data System (ADS)
Obukhov, Yu. N.; Hehl, F. W.
20140101
We discuss the possibility that gravitational potentials (metric, coframe and connection) may emerge as composite fields from more fundamental spinor constituents. We use the formalism of Poincaré gauge gravity as an appropriate theoretical scheme for the rigorous development of such an approach. We postulate the constitutive relations of an elastic Cosserat type continuum that models spacetime. These generalized Hooke and MacCullagh type laws consistently take into account the translational and Lorentz rotational deformations, respectively. The resulting theory extends the recently proposed Diakonov model. An intriguing feature of our theory is that in the lowest approximation it reproduces Heisenberg's nonlinear spinor model.
OpenSystem Quantum Annealing in MeanField Models with Exponential Degeneracy*
NASA Astrophysics Data System (ADS)
Kechedzhi, Kostyantyn; Smelyanskiy, Vadim N.
20160401
Reallife quantum computers are inevitably affected by intrinsic noise resulting in dissipative nonunitary dynamics realized by these devices. We consider an opensystem quantum annealing algorithm optimized for such a realistic analog quantum device which takes advantage of noiseinduced thermalization and relies on incoherent quantum tunneling at finite temperature. We theoretically analyze the performance of this algorithm considering a p spin model that allows for a meanfield quasiclassical solution and, at the same time, demonstrates the firstorder phase transition and exponential degeneracy of states, typical characteristics of spin glasses. We demonstrate that finitetemperature effects introduced by the noise are particularly important for the dynamics in the presence of the exponential degeneracy of metastable states. We determine the optimal regime of the opensystem quantum annealing algorithm for this model and find that it can outperform simulated annealing in a range of parameters. Largescale multiqubit quantum tunneling is instrumental for the quantum speedup in this model, which is possible because of the unusual nonmonotonous temperature dependence of the quantumtunneling action in this model, where the most efficient transition rate corresponds to zero temperature. This model calculation is the first analytically tractable example where opensystem quantum annealing algorithm outperforms simulated annealing, which can, in principle, be realized using an analog quantum computer.
Double Exponential Relativity Theory Coupled Theoretically with Quantum Theory?
Montero Garcia, Jose de la Luz; Novoa Blanco, Jesus Francisco
20070428
Here the problem of special relativity is analyzed into the context of a new theoretical formulation: the Double Exponential Theory of Special Relativity with respect to which the current Special or Restricted Theory of Relativity (STR) turns to be a particular case only.
Theoretical Study of Solid State Quantum Information Processing
20130828
odd effects of Heisenberg chains on longrange interaction and entanglement, Physical Review B, (10 2010): 140403. doi: 10.1103/PhysRevB.82.140403 08...interfacebound electrons in silicon: An effective mass study, Physical Review B, (10 2011): 0. doi: 10.1103/PhysRevB.84.155320 08/31/2012 18.00 Xuedong...Xuedong Hu. Effect of randomness on quantum data buses of Heisenberg spin chains, Physical Review B, (06 2012): 0. doi: 10.1103/PhysRevB.85.224418
The informationtheoretical entropy of some quantum oscillators
Popov, D. Pop, N.; Popov, M.
20141124
The Wehrl entropy or the 'classical' entropy associated with a quantum system is the entropy of the probability distribution in phase space, corresponding to the Husimi Qfunction in terms of coherent states. In the present paper, we shall focus our attention on the examination of the Wehrl entropy for both the pure and the mixed (thermal) states of the pseudoharmonic oscillator (PHO). The choice of the PHO is interesting because this oscillator is an intermediate between the ideal onedimensional harmonic oscillator (HO1D) and the more practical anharmonicone.
Quantum phase transition of the transversefield quantum Ising model on scalefree networks.
Yi, Hangmo
20150101
I investigate the quantum phase transition of the transversefield quantum Ising model in which nearest neighbors are defined according to the connectivity of scalefree networks. Using a continuoustime quantum Monte Carlo simulation method and the finitesize scaling analysis, I identify the quantum critical point and study its scaling characteristics. For the degree exponent λ=6, I obtain results that are consistent with the meanfield theory. For λ=4.5 and 4, however, the results suggest that the quantum critical point belongs to a nonmeanfield universality class. Further simulations indicate that the quantum critical point remains meanfieldlike if λ>5, but it continuously deviates from the meanfield theory as λ becomes smaller.
Group Field Theory and Loop Quantum Gravity
NASA Astrophysics Data System (ADS)
Oriti, Daniele
The following sections are included: * GFT from LQG Perspective: The Underlying Ideas * GFT Kinematics: Hilbert Space and Observables * The Quantum Dynamics * The Continuum Limit of Quantum Geometry in GFT * Extracting Effective Continuum Physics from GFTs * Conclusions * References
Quantum reduced loop gravity: Extension to gauge vector field
NASA Astrophysics Data System (ADS)
Bilski, Jakub; Alesci, Emanuele; Cianfrani, Francesco; Donà, Pietro; Marcianò, Antonino
20170501
Within the framework of quantum reduced loop gravity, we quantize the Hamiltonian for a gauge vector field. The regularization can be performed using tools analogous to the ones adopted in full loop quantum gravity, while the matrix elements of the resulting operator between basis states are analytic coefficients. This analysis is the first step toward deriving the full quantum gravity corrections to the vector field semiclassical dynamics.
Triple quantum imaging of sodium in inhomogeneous fields
NASA Astrophysics Data System (ADS)
Tanase, Costin
Triple quantum filtered sodium MRI techniques have been recently demonstrated in vivo. These techniques have been previously advocated as a means to separate the sodium NMR signal from different physiological compartments based on the differences between their relaxation rates. Among the different triple quantum coherence transfer filters, the threepulse coherence transfer filter has been demonstrated to be better suited for human imaging than the traditional fourpulse implementation. While the threepulse structure has distinct advantages in terms of the radiofrequency power efficiency, it is characterized, also, by an increased dependence on the main magnetic field inhomogeneities. In this thesis, we characterize these dependences and introduce a method for their compensation through the acquisition of a field map and the use of a modified phase cycling scheme. We analyze the dynamics of spin 3/2 systems using the density matrix theory of relaxation. We show that by using the superoperator formalism, we can obtain an algebraic formulation of the density matrix's evolution, in which the contributions from relaxation and radio frequency application are factored out. To achieve this goal, we derive an exact form for the propagator of the density matrix, in the presence of both static quadrupolar couplings and magnetic field inhomogeneities. Using the algebraic formulation, we derive exact expressions for the behavior of the density matrix in the classical one, two and threepulse NMR experiments. These theoretical formulas are then used to illustrate the bias introduced on the measured relaxation parameters by the presence of large spatial variations in the B0 and B1 fields. This approach is proved useful for the characterization of the spatial variations of the signal intensity in multiple quantumfiltered sodium MRI experiments. On the imaging applications side, we demonstrate that the conventional onthefly triple quantum filtered schemes are affected by the
From scalar field theories to supersymmetric quantum mechanics
NASA Astrophysics Data System (ADS)
Bazeia, D.; Bemfica, F. S.
20170401
In this work, we report a new result that appears when one investigates the route that starts from a scalar field theory and ends on a supersymmetric quantum mechanics. The subject has been studied before in several distinct ways and here, we unveil an interesting novelty, showing that the same scalar field model may describe distinct quantum mechanical problems.
Quantum radiation produced by the entanglement of quantum fields
NASA Astrophysics Data System (ADS)
Iso, Satoshi; Oshita, Naritaka; Tatsukawa, Rumi; Yamamoto, Kazuhiro; Zhang, Sen
20170101
We investigate the quantum radiation produced by an UnruhDe Witt detector in a uniformly accelerating motion coupled to the vacuum fluctuations. Quantum radiation is nonvanishing, which is consistent with the previous calculation by Lin and Hu [Phys. Rev. D 73, 124018 (2006), 10.1103/PhysRevD.73.124018]. We infer that this quantum radiation from the UnruhDe Witt detector is generated by the nonlocal correlation of the Minkowski vacuum state, which has its origin in the entanglement of the state between the left and the right Rindler wedges.
On the Notion of Truth in Quantum Mechanics: a CategoryTheoretic Standpoint
NASA Astrophysics Data System (ADS)
Karakostas, Vassilios; Zafiris, Elias
The categorytheoretic representation of quantum event structures provides a canonical setting for confronting the fundamental problem of truth valuation in quantum mechanics as exemplified, in particular, by KochenSpecker's theorem. In the present study, this is realized on the basis of the existence of a categorical adjunction between the category of sheaves of variable local Boolean frames, constituting a topos, and the category of quantum event algebras. We show explicitly that the latter category is equipped with an object of truth values, or classifying object, which constitutes the appropriate tool for assigning truth values to propositions describing the behavior of quantum systems. Effectively, this categorytheoretic representation scheme circumvents consistently the semantic ambiguity with respect to truth valuation that is inherent in conventional quantum mechanics by inducing an objective contextual account of truth in the quantum domain of discourse. The philosophical implications of the resulting account are analyzed. We argue that it subscribes neither to a pragmatic instrumental nor to a relative notion of truth. Such an account essentially denies that there can be a universal context of reference or an Archimedean standpoint from which to evaluate logically the totality of facts of nature. In this light, the transcendence condition of the usual conception of correspondence truth is superseded by a reflectivelike transcendental reasoning of the proposed account of truth that is suitable to the quantum domain of discourse.
Mass renormalization and binding energies in quantum field theory
NASA Astrophysics Data System (ADS)
Lv, Q. Z.; Stefanovich, E.; Su, Q.; Grobe, R.
20171001
We compare the predictions of two methods of determining the amount of binding energy between two distinguishable fermions that interact with each other through forceintermediating bosons. Both measures try to quantify this binding energy by the downward shift of the fully interacting twofermion ground state energy relative to the sum of the corresponding two singleparticle ground state energies. The first method computes this energy difference directly from the standard quantum field theoretical Hamiltonian. The second method uses the mass renormalized form of this Hamiltonian. In order to have a concrete example for this comparison, we employ a simple Yukawalike model system in one spatial dimension. We find that both approaches lead to identical predictions in the second and fourth order perturbation of the coupling constant, and they remain remarkably close even in the strong coupling domain where perturbation theory diverges. This illustrates that there are field theoretical systems for which rather accurate binding energies can be obtained even without the mass renormalization procedure.
The effective field theory treatment of quantum gravity
Donoghue, John F.
20120924
This is a pedagogical introduction to the treatment of quantum general relativity as an effective field theory. It starts with an overview of the methods of effective field theory and includes an explicit example. Quantum general relativity matches this framework and I discuss gravitational examples as well as the limits of the effective field theory. I also discuss the insights from effective field theory on the gravitational effects on running couplings in the perturbative regime.
Entanglement negativity in quantum field theory.
Calabrese, Pasquale; Cardy, John; Tonni, Erik
20120928
We develop a systematic method to extract the negativity in the ground state of a 1+1 dimensional relativistic quantum field theory, using a path integral formalism to construct the partial transpose ρ(A)(T(2) of the reduced density matrix of a subsystem [formula: see text], and introducing a replica approach to obtain its trace norm which gives the logarithmic negativity E=ln//ρ(A)(T(2))//. This is shown to reproduce standard results for a pure state. We then apply this method to conformal field theories, deriving the result E~(c/4)ln[ℓ(1)ℓ(2)/(ℓ(1)+ℓ(2))] for the case of two adjacent intervals of lengths ℓ(1), ℓ(2) in an infinite system, where c is the central charge. For two disjoint intervals it depends only on the harmonic ratio of the four end points and so is manifestly scale invariant. We check our findings against exact numerical results in the harmonic chain.
A note on the fieldtheoretical description of superfluids
NASA Astrophysics Data System (ADS)
Andrianopoli, L.; D'Auria, R.; Grassi, P. A.; Trigiante, M.
20140201
Recently, a Lagrangian description of superfluids attracted some interest from the fluid/gravitycorrespondence viewpoint. In this respect, the work of Dubovksy et al. has proposed a new field theoretical description of fluids, which has several interesting aspects. On another side, we have recently provided a supersymmetric extension of the original works. In the analysis of the Lagrangian structures a new invariant appeared which, although related to known invariants, provides, in our opinion, a better parametrization of the fluid dynamics in order to describe the fluid/superfluid phases. Above the critical temperature TC the fluid has a normal behavior and is invariant under the chemicalshift symmetry [8]. It is described in terms of the comoving coordinates ϕI(x) and by the U(1)phase field ψ(x).On the other hand, below the critical temperature the chemicalshift symmetry is spontaneously broken, giving rise to the superfluid. In particular, at T=0, the superfluid is completely described in terms of ψ. One can consider, following [9], an isotropic and homogeneous background where ψ=y0t, ϕI=b01/3xI. It corresponds to taking a configuration where the fields ϕI are comoving with the normal fluid part (which is at rest in this background), the superfluid field ψ being in relative motion with respect to it. Note that the loss of interactions between the two fluids is expressed by the property that ZI=∂μψ∂μϕI=0 in the background. Small perturbations about the background (28): ψ=y0(t+π0(x)), ϕI=b01/3(xI+πI(x)) introduce a small interaction term ZI≠0. Note that the quantity BIJ1ZIZJ=ɛ stays small in this regime, even if ϕI→0 as T→0. Given these considerations, we can make use of the relation (18) to observe that at very low temperatures the quantity y2=X+BIJ1ZIZJ=X+ɛ approaches the value X, which is not invariant under the chemicalshift symmetry. In this regime the Lagrangian F(b,y) can be expanded in powers of ɛ around the
Quantum electronvibrational dynamics at finite temperature: Thermo field dynamics approach.
Borrelli, Raffaele; Gelin, Maxim F
20161214
Quantum electronvibrational dynamics in molecular systems at finite temperature is described using an approach based on the thermo field dynamics theory. This formulation treats temperature effects in the Hilbert space without introducing the Liouville space. A comparison with the theoretically equivalent density matrix formulation shows the key numerical advantages of the present approach. The solution of thermo field dynamics equations with a novel technique for the propagation of tensor trains (matrix product states) is discussed. Numerical applications to model spinboson systems show that the present approach is a promising tool for the description of quantum dynamics of complex molecular systems at finite temperature.
Relativistic Quantum Mechanics and Introduction to Field Theory
NASA Astrophysics Data System (ADS)
Yndurain, Francisco J.
This is an advanced textbook meant as a primer in quantum theory for graduate students. A full relativistic treatment of particle dynamics needs to be based on quantum field theory. However, there exists a variety of processes that can be discussed with concepts like potentials, classical current distributions, prescribed external fields dealt with in the framework of relativistic quantum mechanics. Then, in an introduction to field theory the author emphasizes the deduction of the said potentials or currents. The unique feature of this book is the modern presentation of the subject together with many exercises and furthermore the underlying concept to combine a reference book on relativistic quantum mechanics with an introduction into quantum field theory.
Wave packet revivals in a graphene quantum dot in a perpendicular magnetic field
Torres, J. J.
20101015
We study the time evolution of localized wave packets in graphene quantum dots in a perpendicular magnetic field, focusing on the quasiclassical and revival periodicities, for different values of the magnetic field intensities in a theoretical framework. We have considered contributions of the two inequivalent points in the Brillouin zone. The revival time has been found as an observable that shows the break valley degeneracy.
Physics in one dimension: theoretical concepts for quantum manybody systems.
Schönhammer, K
20130109
Various sophisticated approximation methods exist for the description of quantum manybody systems. It was realized early on that the theoretical description can simplify considerably in onedimensional systems and various exact solutions exist. The focus in this introductory paper is on fermionic systems and the emergence of the Luttinger liquid concept.
Quantum magnetism in low dimensions and large magnetic fields
NASA Astrophysics Data System (ADS)
Giamarchi, Thierry
20140301
The ability to control the properties of magnetic insulators by magnetic fields large enough to fully polarize the system has opened a host of possibilities. In addition to the intrinsic interest of such questions for magnetic systems, is has been shown that such systems could be efficiently used as quantum simulators to emulate problems pertaining to itinerant fermionic or bosonic systems. The magnetic field can then be viewed as similar to a gate voltage controlling the number of ``particles'' allowing an unprecedented level of control. In parallel with the experimental developments, progress on the theoretical front both on the numerical and the analytical side, have allowed a remarkable level of accuracy in obtaining the physical properties and in particular the correlation functions of these systems. A comparison between theoretical predictions without adjustable parameters or fudging with results from NMR, Neutrons or other probes such as ESR is thus now possible. This has allowed for example to test quantitatively the physics of TomonagaLuttinger liquids and also to tackle the effects of the interactions between spinons by comparing the physics of weak rung ladders with the one of strong rung ones. Comparison between the neutron results and theoretical calculations of the correlation functions has also been demonstrated as a way to reconstruct efficiently the Hamiltonian from the experimental data. I will review the recent results obtained in this domain with the different experimental compounds and will discuss the open questions and challenges. This concerns in particular the issues of finite temperatures, higher dimensional systems and effects of disorder. This work was supported in part by the Swiss NSF under MaNEP and Division II
Quantum Gravity Effects in Scalar, Vector and Tensor Field Propagation
NASA Astrophysics Data System (ADS)
Dutta, Anindita
Quantum theory of gravity deals with the physics of the gravitational field at Planck length scale (1035 m). Even though it is experimentally hard to reach the Planck length scale, on can look for evidence of quantum gravity that is detectable in astrophysics. In this thesis, we try to find effects of loop quantum gravity corrections on observable phenomena. We show that the quantum fluctuation strain for LIGO data would be 10 125 on the Earth. Th correction is, however, substantial near the black hole horizon. We discuss the effect of this for scalar field propagation followed by vector and tensor fields. For the scalar field, the correction introduces a new asymmetry; for the vector field, we found a new perturbation solution and for the tensor field, we found the corrected Einstein equations which are yet to solve. These will affect phenomena like Hawking radiation, black hole entropy and gravitational waves.
Studies on Quantum Field Theory and Statistical Mechanics
NASA Astrophysics Data System (ADS)
Zhang, Shoucheng
This dissertation is a summary of research in various areas of theoretical physics and is divided into three parts. In the first part, quantum fluctuations of the recently proposed superconducting cosmic strings are studied. It is found that vortices on the string world sheet represent an important class of fluctuation modes which tend to disorder the system. Both heuristic arguments and detailed renormalization group analysis reveal that these vortices do not appear in bound pairs but rather form a gas of free vortices. Based on this observation we argue that this fluctuation mode violates the topological conservation law on which superconductivity is based. Anomalies and topological aspects of supersymmetric quantum field theories are studied in the second part of this dissertation. Using the superspace formulation of the N = 1 spinning string, we obtain a path integral measure which is free from the worldsheet general coordinate as well as the supersymmetry anomalies and therefore determine the conformal anomaly and critical dimension of the spinning string. We also apply Fujikawa's formalism to computer the chiral anomaly in conformal as well as ordinary supergravity. Finally, we given a Noethermethod construction of the supersymmetrized ChernSimons term in five dimensional supergravity. In the last part of this dissertation, the soliton excitations in the quarterfilled PeierlsHubbard model are investigated in both the large and the small U limit. For a strictly one dimensional system at zero temperature, we find that solitons in both limits are in onetoone correspondence, while in the presence of weak three dimensional couplings or at finite temperature, the large U systems differ qualitatively from the small U systems in that the spin associated with the solitons ceases to be a sharp quantum observable.
Surface Chemistry of Semiconducting Quantum Dots: Theoretical Perspectives.
Kilina, Svetlana V; Tamukong, Patrick K; Kilin, Dmitri S
20161018
Colloidal quantum dots (QDs) are nearideal nanomaterials for energy conversion and lighting technologies. However, their photophysics exhibits supreme sensitivity to surface passivation and defects, of which control is problematic. The role of passivating ligands in photodynamics remains questionable and is a focus of ongoing research. The optically forbidden nature of surfaceassociated states makes direct measurements on them challenging. Therefore, computational modeling is imperative for insights into surface passivation and its impact on lightdriven processes in QDs. This Account discusses challenges and recent progress in understanding surface effects on the photophysics of QDs addressed via quantumchemical calculations. We overview different methods, including the effective mass approximation (EMA), timedependent density functional theory (TDDFT), and multiconfiguration approaches, considering their strengths and weaknesses relevant to modeling of QDs with a complicated surface. We focus on CdSe, PbSe, and Si QDs, where calculations successfully explain experimental trends sensitive to surface defects, doping, and ligands. We show that the EMA accurately describes both linear and nonlinear optical properties of largesized CdSe QDs (>2.5 nm), while TDDFT is required for smaller QDs where surface effects dominate. Both approaches confirm efficient twophoton absorption enabling applications of QDs as nonlinear optical materials. TDDFT also describes the effects of morphology on the optical response of QDs: the photophysics of stoichiometric, magicsized XnYn (X = Cd, Pb; Y = S, Se) QDs is less sensitive to their passivation compared with nonstoichiometric Xn≠mYm QDs. In the latter, surfacedriven optically inactive midgap states can be eliminated by anionic ligands, explaining the better emission of metalenriched QDs compared with nonmetalenriched QDs. Ideal passivation of magicsized QDs by amines and phosphine oxides leaves lowerenergy transitions
Magnetic Fields: A Comprehensive Theoretical Treatise for Practical Use
NASA Astrophysics Data System (ADS)
Knoepfel, Heinz E.
20000601
A unique resource for physicists and engineers working with magnetic fields An understanding of magnetic phenomena is essential for anyone working on the practical application of electromagnetic theory. Magnetic Fields: A Comprehensive Theoretical Treatise for Practical Use provides physicists and engineers with a thorough treatment of the magnetic aspects of classical electromagnetic theory, focusing on key issues and problems arising in the generation and application of magnetic fields. From magnetic potentials and diffusion phenomena to magnetohydrodynamics and properties of mattertopics are carefully selected for their relevance to the theoretical framework as well as current technologies. Outstanding in its organization, clarity, and scope, Magnetic Fields: Examines a wide range of practical problems, from magnetomechanical devices to magnetic acceleration mechanisms Opens each chapter with reference to pertinent engineering examples Provides sufficient detail enabling readers to follow the derivation of the results Discusses solution methods and their application to different problems Includes more than 300 graphs, 40 tables, 2,000 numbered formulas, and extensive references to the professional literature Reviews the essential mathematics in the appendices
Quantum analysis applied to thermo field dynamics on dissipative systems
Hashizume, Yoichiro; Okamura, Soichiro; Suzuki, Masuo
20150310
Thermo field dynamics is one of formulations useful to treat statistical mechanics in the scheme of field theory. In the present study, we discuss dissipative thermo field dynamics of quantum damped harmonic oscillators. To treat the effective renormalization of quantum dissipation, we use the SuzukiTakano approximation. Finally, we derive a dissipative von Neumann equation in the Lindbrad form. In the present treatment, we can easily obtain the initial damping shown previously by Kubo.
Quantum states of neutrons in the Earth's gravitational field.
Nesvizhevsky, Valery V; Börner, Hans G; Petukhov, Alexander K; Abele, Hartmut; Baessler, Stefan; Ruess, Frank J; Stöferle, Thilo; Westphal, Alexander; Gagarski, Alexei M; Petrov, Guennady A; Strelkov, Alexander V
20020117
The discrete quantum properties of matter are manifest in a variety of phenomena. Any particle that is trapped in a sufficiently deep and wide potential well is settled in quantum bound states. For example, the existence of quantum states of electrons in an electromagnetic field is responsible for the structure of atoms, and quantum states of nucleons in a strong nuclear field give rise to the structure of atomic nuclei. In an analogous way, the gravitational field should lead to the formation of quantum states. But the gravitational force is extremely weak compared to the electromagnetic and nuclear force, so the observation of quantum states of matter in a gravitational field is extremely challenging. Because of their charge neutrality and long lifetime, neutrons are promising candidates with which to observe such an effect. Here we report experimental evidence for gravitational quantum bound states of neutrons. The particles are allowed to fall towards a horizontal mirror which, together with the Earth's gravitational field, provides the necessary confining potential well. Under such conditions, the falling neutrons do not move continuously along the vertical direction, but rather jump from one height to another, as predicted by quantum theory.
PREFACE: Particles and Fields: Classical and Quantum
NASA Astrophysics Data System (ADS)
Asorey, M.; ClementeGallardo, J.; Marmo, G.
20070701
This volume contains some of the contributions to the Conference Particles and Fields: Classical and Quantum, which was held at Jaca (Spain) in September 2006 to honour George Sudarshan on his 75th birthday. Former and current students, associates and friends came to Jaca to share a few wonderful days with George and his family and to present some contributions of their present work as influenced by George's impressive achievements. This book summarizes those scientific contributions which are presented as a modest homage to the master, collaborator and friend. At the social ceremonies various speakers were able to recall instances of his lifelong activity in India, the United States and Europe, adding colourful remarks on the friendly and intense atmosphere which surrounded those collaborations, some of which continued for several decades. This meeting would not have been possible without the financial support of several institutions. We are deeply indebted to Universidad de Zaragoza, Ministerio de Educación y Ciencia de España (CICYT), Departamento de Ciencia, Tecnología y Universidad del Gobierno de Aragón, Universitá di Napoli 'Federico II' and Istituto Nazionale di Fisica Nucleare. Finally, we would like to thank the participants, and particularly George's family, for their contribution to the wonderful atmosphere achieved during the Conference. We would like also to acknowledge the authors of the papers collected in the present volume, the members of the Scientific Committee for their guidance and support and the referees for their generous work. M Asorey, J ClementeGallardo and G Marmo The Local Organizing Committee George Sudarshan
A. Ashtekhar (Pennsylvania State University, USA) 
L. J. Boya (Universidad de Zaragoza, Spain) 
I. Cirac (Max Planck Institute, Garching
Continuum regularization of quantum field theory Bern, Z. 19860401 Possible nonperturbative continuum regularization schemes for quantum field theory are discussed which are based upon the Langevin equation of Parisi and Wu. Breit, Gupta and Zaks made the first proposal for new gauge invariant nonperturbative regularization. The scheme is based on smearing in the ''fifthtime'' of the Langevin equation. An analysis of their stochastic regularization scheme for the case of scalar electrodynamics with the standard covariant gauge fixing is given. Their scheme is shown to preserve the masslessness of the photon and the tensor structure of the photon vacuum polarization at the oneloop level. Although stochastic regularization is viable in oneloop electrodynamics, two difficulties arise which, in general, ruins the scheme. One problem is that the superficial quadratic divergences force a bottomless action for the noise. Another difficulty is that stochastic regularization by fifthtime smearing is incompatible with Zwanziger's gauge fixing, which is the only known nonperturbaive covariant gauge fixing for nonabelian gauge theories. Finally, a successful covariant derivative scheme is discussed which avoids the difficulties encountered with the earlier stochastic regularization by fifthtime smearing. For QCD the regularized formulation is manifestly Lorentz invariant, gauge invariant, ghost free and finite to all orders. A vanishing gluon mass is explicitly verified at one loop. The method is designed to respect relevant symmetries, and is expected to provide suitable regularization for any theory of interest. Hopefully, the scheme will lend itself to nonperturbative analysis. 44 refs., 16 figs. Spacetime resolved quantum field theory NASA Astrophysics Data System (ADS) Grobe, R. 20091101 We have solved simplified model versions of the timedependent Dirac and Yukawa equation numerically to study the time evolution of electrons, positrons and photons with full spatial resolution. The goal is to better understand how various particle creation and annihilation processes that require quantum field theory can be visualized. There are many open ended questions that we will address. Are particles and their antimatter companions created instantly, or do they require a certain minimum amount of time? Are they created at precisely the same location? What is the difference between a bare and a physical particle? Forces between two particles are usually understood on a microscopic level as the result of an exchange of bosonic particles. How can the same microscopic exchange mechanism lead to a repulsion as well as an attraction? Do these force intermediating particles ``know'' about the charges of the two interacting particles? How can one visualize this exchange? Does it really make sense to distinguish between virtual and real particles? We also examine how a bare electron can trigger the creation of a cloud of virtual photons around it.[4pt] In collaboration with R. Wagner, Intense Laser Physics Theory Unit, Illinois State University; C. Gerry, Lehman College and ILPISU; T. Cheng and Q. Su, Intense Laser Physics Theory Unit, Illinois State University. Quantum field theory constrains traversable wormhole geometries Ford, L.H. ; Roman, T.A.  19960501 Recently a bound on negative energy densities in fourdimensional Minkowski spacetime was derived for a minimally coupled, quantized, massless, scalar field in an arbitrary quantum state. The bound has the form of an uncertaintyprincipletype constraint on the magnitude and duration of the negative energy density seen by a timelike geodesic observer. When spacetime is curved and/or has boundaries, we argue that the bound should hold in regions small compared to the minimum local characteristic radius of curvature or the distance to any boundaries, since spacetime can be considered approximately Minkowski on these scales. We apply the bound to the stressenergy of static traversable wormhole spacetimes. Our analysis implies that either the wormhole must be only a little larger than Planck size or that there is a large discrepancy in the length scales which characterize the wormhole. In the latter case, the negative energy must typically be concentrated in a thin band many orders of magnitude smaller than the throat size. These results would seem to make the existence of macroscopic traversable wormholes very improbable. {copyright} {ital 1996 The American Physical Society.} An implementation problem for boson fields and quantum Girsanov transform Ji, Un Cig; Obata, Nobuaki 20160815 We study an implementation problem for quadratic functions of annihilation and creation operators on a boson field in terms of quantum white noise calculus. The implementation problem is shown to be equivalent to a linear differential equation for white noise operators containing quantum white noise derivatives. The solution is explicitly obtained and turns out to form a class of white noise operators including generalized Fourier–Gauss and Fourier–Mehler transforms, Bogoliubov transform, and a quantum extension of the Girsanov transform. Euclidean quantum field theory: Curved spacetimes and gauge fields NASA Astrophysics Data System (ADS) Ritter, William Gordon This thesis presents a new formulation of quantum field theory (QFT) on curved spacetimes, with definite advantages over previous formulations, and an introduction to the millennium prize problem on fourdimensional gauge theory. Our constructions are completely rigorous, making QFT on curved spacetimes into a subfield of mathematics, and we achieve the first analytic control over nonperturbative aspects of interacting theories on curved spacetimes. The success of Euclidean path integrals to capture nonperturbative aspects of QFT has been striking. The Euclidean path integral is the most accurate method of calculating strongcoupling effects in gauge theory (such as glueball masses). Euclidean methods are also useful in the study of black holes, as evidenced by the HartleHawking calculation of blackhole radiance. From a mathematical point of view, on flat spacetimes the Euclidean functional integral provides the most elegant method of constructing examples of interacting relativistic field theories. Yet until now, the incrediblyuseful Euclidean path integral had never been given a definitive mathematical treatment on curved backgrounds. It is our aim to rectify this situation. Along the way, we discover that the Dirac operator on an arbitrary Clifford bundle has a resolvent kernel which is the Laplace transform of a positive measure. In studying spacetime symmetries, we discover a new way of constructing unitary representations of noncompact Lie groups. We also define and explore an interesting notion of convergence for Laplacians. The same mathematical framework applies to scalar fields, fermions, and gauge fields. The later chapters are devoted to gauge theory. We present a rigorous, selfcontained introduction to the subject, aimed at mathematicians and using the language of modern mathematics, with a view towards nonperturbative renormalization in four dimensions. The latter ideas are unfinished. A completion of the final chapter would imply the construction Realization of vector fields for quantum groups as pseudodifferential operators on quantum spaces Chu, ChongSun; Zumino, B. 19950124 The vector fields of the quantum Lie algebra are described for the quantum groups GL{sub q}(n), SL{sub q}(N) and SO{sub q}(N) as pseudodifferential operators on the linear quantum spaces covariant under the corresponding quantum group. Their expressions are simple and compact. It is pointed out that these vector fields satisfy certain characteristic polynomial identities. The real forms SU{sub q}(N) and SO{sub q}(N,R) are discussed in detail. Coupled field induced conversion between destructive and constructive quantum interference NASA Astrophysics Data System (ADS) Jiang, Xiangqian; Sun, Xiudong 20161201 We study the control of quantum interference in a fourlevel atom driven by three coherent fields forming a closed loop. The spontaneous emission spectrum shows two sets of peaks which are dramatically influenced by the fields. Due to destructive quantum interference, a dark line can be observed in the emission spectrum, and the condition of the dark line is given. We found that the conversion between destructive and constructive quantum interference can be achieved through controlling the Rabi frequency of the external fields.
