Quantum phase estimation using path-symmetric entangled states
NASA Astrophysics Data System (ADS)
Lee, Su-Yong; Lee, Chang-Woo; Lee, Jaehak; Nha, Hyunchul
2016-07-01
We study the sensitivity of phase estimation using a generic class of path-symmetric entangled states |φ>|0> + |0>|φ>, where an arbitrary state |φ> occupies one of two modes in quantum superposition. With this generalization, we identify the fundamental limit of phase estimation under energy constraint that is characterized by the photon statistics of the component state |φ>. We show that quantum Cramer-Rao bound (QCRB) can be indefinitely lowered with super-Poissonianity of the state |φ>. For possible measurement schemes, we demonstrate that a full photon-counting employing the path-symmetric entangled states achieves the QCRB over the entire range [0, 2π] of unknown phase shift ϕ whereas a parity measurement does so in a certain confined range of ϕ. By introducing a component state of the form , we particularly show that an arbitrarily small QCRB can be achieved even with a finite energy in an ideal situation. This component state also provides the most robust resource against photon loss among considered entangled states over the range of the average input energy Nav > 1. Finally we propose experimental schemes to generate these path-symmetric entangled states for phase estimation.
Quantum phase estimation using path-symmetric entangled states
Lee, Su-Yong; Lee, Chang-Woo; Lee, Jaehak; Nha, Hyunchul
2016-01-01
We study the sensitivity of phase estimation using a generic class of path-symmetric entangled states |φ〉|0〉 + |0〉|φ〉, where an arbitrary state |φ〉 occupies one of two modes in quantum superposition. With this generalization, we identify the fundamental limit of phase estimation under energy constraint that is characterized by the photon statistics of the component state |φ〉. We show that quantum Cramer-Rao bound (QCRB) can be indefinitely lowered with super-Poissonianity of the state |φ〉. For possible measurement schemes, we demonstrate that a full photon-counting employing the path-symmetric entangled states achieves the QCRB over the entire range [0, 2π] of unknown phase shift ϕ whereas a parity measurement does so in a certain confined range of ϕ. By introducing a component state of the form , we particularly show that an arbitrarily small QCRB can be achieved even with a finite energy in an ideal situation. This component state also provides the most robust resource against photon loss among considered entangled states over the range of the average input energy Nav > 1. Finally we propose experimental schemes to generate these path-symmetric entangled states for phase estimation. PMID:27457267
Sequential Path Entanglement for Quantum Metrology
Jin, Xian-Min; Peng, Cheng-Zhi; Deng, Youjin; Barbieri, Marco; Nunn, Joshua; Walmsley, Ian A.
2013-01-01
Path entanglement is a key resource for quantum metrology. Using path-entangled states, the standard quantum limit can be beaten, and the Heisenberg limit can be achieved. However, the preparation and detection of such states scales unfavourably with the number of photons. Here we introduce sequential path entanglement, in which photons are distributed across distinct time bins with arbitrary separation, as a resource for quantum metrology. We demonstrate a scheme for converting polarization Greenberger-Horne-Zeilinger entanglement into sequential path entanglement. We observe the same enhanced phase resolution expected for conventional path entanglement, independent of the delay between consecutive photons. Sequential path entanglement can be prepared comparably easily from polarization entanglement, can be detected without using photon-number-resolving detectors, and enables novel applications.
Entanglement by Path Identity.
Krenn, Mario; Hochrainer, Armin; Lahiri, Mayukh; Zeilinger, Anton
2017-02-24
Quantum entanglement is one of the most prominent features of quantum mechanics and forms the basis of quantum information technologies. Here we present a novel method for the creation of quantum entanglement in multipartite and high-dimensional systems. The two ingredients are (i) superposition of photon pairs with different origins and (ii) aligning photons such that their paths are identical. We explain the experimentally feasible creation of various classes of multiphoton entanglement encoded in polarization as well as in high-dimensional Hilbert spaces-starting only from nonentangled photon pairs. For two photons, arbitrary high-dimensional entanglement can be created. The idea of generating entanglement by path identity could also apply to quantum entities other than photons. We discovered the technique by analyzing the output of a computer algorithm. This shows that computer designed quantum experiments can be inspirations for new techniques.
NASA Astrophysics Data System (ADS)
Krenn, Mario; Hochrainer, Armin; Lahiri, Mayukh; Zeilinger, Anton
2017-02-01
Quantum entanglement is one of the most prominent features of quantum mechanics and forms the basis of quantum information technologies. Here we present a novel method for the creation of quantum entanglement in multipartite and high-dimensional systems. The two ingredients are (i) superposition of photon pairs with different origins and (ii) aligning photons such that their paths are identical. We explain the experimentally feasible creation of various classes of multiphoton entanglement encoded in polarization as well as in high-dimensional Hilbert spaces—starting only from nonentangled photon pairs. For two photons, arbitrary high-dimensional entanglement can be created. The idea of generating entanglement by path identity could also apply to quantum entities other than photons. We discovered the technique by analyzing the output of a computer algorithm. This shows that computer designed quantum experiments can be inspirations for new techniques.
Quantum random number generator using photon-number path entanglement
NASA Astrophysics Data System (ADS)
Kwon, Osung; Cho, Young-Wook; Kim, Yoon-Ho
2010-08-01
We report an experimental implementation of quantum random number generator based on the photon-number-path entangled state. The photon-number-path entangled state is prepared by means of two-photon Hong-Ou-Mandel quantum interference at a beam splitter. The randomness in our scheme is of truly quantum mechanical origin as it comes from the projection measurement of the entangled two-photon state. The generated bit sequences satisfy the standard randomness test.
The generation of entangled states from independent particle sources
NASA Technical Reports Server (NTRS)
Rubin, Morton H.; Shih, Yan-Hua
1994-01-01
The generation of entangled states of two systems from product states is discussed for the case in which the paths of the two systems do not overlap. A particular method of measuring allows one to project out the nonlocal entangled state. An application to the production of four photon entangled states is outlined.
Extremal extensions of entanglement witnesses: Finding new bound entangled states
Sengupta, R.; Arvind
2011-09-15
In this paper, we discuss extremal extensions of entanglement witnesses based on Choi's map. The constructions are based on a generalization of the Choi map, from which we construct entanglement witnesses. These extremal extensions are powerful in terms of their capacity to detect entanglement of positive under partial transpose (PPT) entangled states and lead to unearthing of entanglement of new PPT states. We also use the Cholesky-like decomposition to construct entangled states which are revealed by these extremal entanglement witnesses.
Quantum Entanglement Swapping between Two Multipartite Entangled States
NASA Astrophysics Data System (ADS)
Su, Xiaolong; Tian, Caixing; Deng, Xiaowei; Li, Qiang; Xie, Changde; Peng, Kunchi
2016-12-01
Quantum entanglement swapping is one of the most promising ways to realize the quantum connection among local quantum nodes. In this Letter, we present an experimental demonstration of the entanglement swapping between two independent multipartite entangled states, each of which involves a tripartite Greenberger-Horne-Zeilinger (GHZ) entangled state of an optical field. The entanglement swapping is implemented deterministically by means of a joint measurement on two optical modes coming from the two multipartite entangled states respectively and the classical feedforward of the measurement results. After entanglement swapping the two independent multipartite entangled states are merged into a large entangled state in which all unmeasured quantum modes are entangled. The entanglement swapping between a tripartite GHZ state and an Einstein-Podolsky-Rosen entangled state is also demonstrated and the dependence of the resultant entanglement on transmission loss is investigated. The presented experiment provides a feasible technical reference for constructing more complicated quantum networks.
Path Entanglement of Continuous-Variable Quantum Microwaves
NASA Astrophysics Data System (ADS)
Menzel, E. P.; Deppe, F.; Eder, P.; Zhong, L.; Haeberlein, M.; Baust, A.; Hoffmann, E.; Marx, A.; Gross, R.; di Candia, R.; Solano, E.; Ballester, D.; Ihmig, M.; Inomata, K.; Yamamoto, T.; Nakamura, Y.
2013-03-01
Entanglement is a quantum mechanical phenomenon playing a key role in quantum communication and information processing protocols. Here, we report on frequency-degenerate entanglement between continuous-variable quantum microwaves propagating along two separated paths. In our experiment, we combine a squeezed and a vacuum state via a beam splitter. Overcoming the challenges imposed by the low photon energies in the microwave regime, we reconstruct the squeezed state and, independently from this, detect and quantify the produced entanglement via correlation measurements (E. P. Menzel et al., arXiv:1210.4413). Our work paves the way towards quantum communication and teleportation with continuous variables in the microwave regime. This work is supported by SFB 631, German Excellence Initiative via NIM, EU projects SOLID, CCQED and PROMISCE, MEXT Kakenhi ``Quantum Cybernetics'', JSPS FIRST Program, the NICT Commissioned Research, EPSRC EP/H050434/1, Basque Government IT472-10, and Spanish MICINN FIS2009-12773-C02-01.
Entanglement teleportation via werner states
Lee; Kim
2000-05-01
Transfer of entanglement and information is studied for quantum teleportation of an unknown entangled state through noisy quantum channels. We find that the quantum entanglement of the unknown state can be lost during the teleportation even when the channel is quantum correlated. We introduce a fundamental parameter of correlation information which dissipates linearly during the teleportation through the noisy channel. Analyzing the transfer of correlation information, we show that the purity of the initial state is important in determining the entanglement of the replica state.
Quantum Enhanced Imaging by Entangled States
2009-07-01
2009 13 . SUPPLEMENTARY NOTES 14. ABSTRACT The use of entangled states in a prospective standoff imaging sensor has been explored. Specifically... 13 FIGURE 6 UNFOLDED VERSION OF SETUP FOR PSEUDO-THERMAL GHOST IMAGING. ....................... 13 FIGURE 7 SYSTEM...ALONG ATMOSPHERIC PATH. (D)-(E) FFTS OF STARTING AND FINAL DISTRIBUTIONS OF BEAM. ABSCISSA IS IN CYCLES PER METER. ......... 22 FIGURE 13 VARIANCE
Creating multiphoton-polarization bound entangled states
Wei, Tzu-Chieh; Lavoie, Jonathan; Kaltenbaek, Rainer
2011-03-15
Bound entangled states are the exotic objects in the entangled world. They require entanglement to create them, but once they are formed, it is not possible to locally distill any free entanglement from them. It is only until recently that a few bound entangled states were realized in the laboratory. Motivated by these experiments, we propose schemes for creating various classes of bound entangled states with photon polarization. These include Acin-Bruss-Lewenstein-Sanpara states, Duer's states, Lee-Lee-Kim bound entangled states, and an unextendible-product-basis bound entangled state.
Local cloning of entangled states
Gheorghiu, Vlad; Yu Li; Cohen, Scott M.
2010-08-15
We investigate the conditions under which a set S of pure bipartite quantum states on a DxD system can be locally cloned deterministically by separable operations, when at least one of the states is full Schmidt rank. We allow for the possibility of cloning using a resource state that is less than maximally entangled. Our results include that: (i) all states in S must be full Schmidt rank and equally entangled under the G-concurrence measure, and (ii) the set S can be extended to a larger clonable set generated by a finite group G of order |G|=N, the number of states in the larger set. It is then shown that any local cloning apparatus is capable of cloning a number of states that divides D exactly. We provide a complete solution for two central problems in local cloning, giving necessary and sufficient conditions for (i) when a set of maximally entangled states can be locally cloned, valid for all D; and (ii) local cloning of entangled qubit states with nonvanishing entanglement. In both of these cases, we show that a maximally entangled resource is necessary and sufficient, and the states must be related to each other by local unitary 'shift' operations. These shifts are determined by the group structure, so need not be simple cyclic permutations. Assuming this shifted form and partially entangled states, then in D=3 we show that a maximally entangled resource is again necessary and sufficient, while for higher-dimensional systems, we find that the resource state must be strictly more entangled than the states in S. All of our necessary conditions for separable operations are also necessary conditions for local operations and classical communication (LOCC), since the latter is a proper subset of the former. In fact, all our results hold for LOCC, as our sufficient conditions are demonstrated for LOCC, directly.
Entanglement for All Quantum States
ERIC Educational Resources Information Center
de la Torre, A. C.; Goyeneche, D.; Leitao, L.
2010-01-01
It is shown that a state that is factorizable in the Hilbert space corresponding to some choice of degrees of freedom becomes entangled for a different choice of degrees of freedom. Therefore, entanglement is not a special case but is ubiquitous in quantum systems. Simple examples are calculated and a general proof is provided. The physical…
Entanglement and quantum teleportation via decohered tripartite entangled states
Metwally, N.
2014-12-15
The entanglement behavior of two classes of multi-qubit system, GHZ and GHZ like states passing through a generalized amplitude damping channel is discussed. Despite this channel causes degradation of the entangled properties and consequently their abilities to perform quantum teleportation, one can always improve the lower values of the entanglement and the fidelity of the teleported state by controlling on Bell measurements, analyzer angle and channel’s strength. Using GHZ-like state within a generalized amplitude damping channel is much better than using the normal GHZ-state, where the decay rate of entanglement and the fidelity of the teleported states are smaller than those depicted for GHZ state.
NASA Astrophysics Data System (ADS)
Guerreiro, T.; Monteiro, F.; Martin, A.; Brask, J. B.; Vértesi, T.; Korzh, B.; Caloz, M.; Bussières, F.; Verma, V. B.; Lita, A. E.; Mirin, R. P.; Nam, S. W.; Marsilli, F.; Shaw, M. D.; Gisin, N.; Brunner, N.; Zbinden, H.; Thew, R. T.
2016-08-01
We demonstrate the violation of an Einstein-Podolsky-Rosen steering inequality developed for single-photon path entanglement with displacement-based detection. We use a high-rate source of heralded single-photon path-entangled states, combined with high-efficiency superconducting-based detectors, in a scheme that is free of any postselection and thus immune to the detection loophole. This result conclusively demonstrates single-photon entanglement in a one-sided device-independent scenario, and opens the way towards implementations of device-independent quantum technologies within the paradigm of path entanglement.
Generating Entangled State with Parametric Amplifier
NASA Astrophysics Data System (ADS)
Huang, Jian
2017-04-01
We present a scheme for generating entangled state with parametric amplifier with different initial states. Its shown that the entangled state is always generated except some special cases by adjusting the coupling strength and the total number of photons.
Multipartite entanglement in conditional states
NASA Astrophysics Data System (ADS)
Urbina, Juan Diego; Strunz, Walter T.; Viviescas, Carlos
2013-02-01
A key lesson of the decoherence program is that information flowing out from an open system is stored in the quantum state of the surroundings. Simultaneously, quantum measurement theory shows that the evolution of any open system when its environment is measured is nonlinear and leads to pure states conditioned on the measurement record. Here we report the discovery of a fundamental relation between measurement and entanglement which is characteristic of this scenario. It takes the form of a scaling law between the amount of entanglement in the conditional state of the system and the probabilities of the experimental outcomes obtained from measuring the state of the environment, with the latter modeled as a bosonic field linearly coupled with the system. Using the scaling, we construct the distribution of entanglement over the ensemble of experimental outcomes for standard models with one open channel and provide rigorous results on finite-time disentanglement in systems coupled to non-Markovian baths. In principle, the scaling allows the direct experimental detection and quantification of entanglement in conditional states of a large class of open systems by quantum tomography of the bath even when it consists of a single mode.
Family of nonlocal bound entangled states
NASA Astrophysics Data System (ADS)
Yu, Sixia; Oh, C. H.
2017-03-01
Bound entanglement, being entangled yet not distillable, is essential to our understanding of the relations between nonlocality and entanglement besides its applications in certain quantum information tasks. Recently, bound entangled states that violate a Bell inequality have been constructed for a two-qutrit system, disproving a conjecture by Peres that bound entanglement is local. Here we construct this kind of nonlocal bound entangled state for all finite dimensions larger than two, making possible their experimental demonstration in most general systems. We propose a Bell inequality, based on a Hardy-type argument for nonlocality, and a steering inequality to identify their nonlocality. We also provide a family of entanglement witnesses to detect their entanglement beyond the Bell inequality and the steering inequality.
Squashed entanglement and approximate private states
NASA Astrophysics Data System (ADS)
Wilde, Mark M.
2016-11-01
The squashed entanglement is a fundamental entanglement measure in quantum information theory, finding application as an upper bound on the distillable secret key or distillable entanglement of a quantum state or a quantum channel. This paper simplifies proofs that the squashed entanglement is an upper bound on distillable key for finite-dimensional quantum systems and solidifies such proofs for infinite-dimensional quantum systems. More specifically, this paper establishes that the logarithm of the dimension of the key system (call it log 2K) in an ɛ -approximate private state is bounded from above by the squashed entanglement of that state plus a term that depends only ɛ and log 2K. Importantly, the extra term does not depend on the dimension of the shield systems of the private state. The result holds for the bipartite squashed entanglement, and an extension of this result is established for two different flavors of the multipartite squashed entanglement.
NASA Astrophysics Data System (ADS)
Uchida, Nariya; Grest, Gary S.; Everaers, Ralf
2008-01-01
We combine computer simulations and scaling arguments to develop a unified view of polymer entanglement based on the primitive path analysis of the microscopic topological state. Our results agree with experimentally measured plateau moduli for three different polymer classes over a wide range of reduced polymer densities: (i) semidilute theta solutions of synthetic polymers, (ii) the corresponding dense melts above the glass transition or crystallization temperature, and (iii) solutions of semiflexible (bio)polymers such as F-actin or suspensions of rodlike viruses. Together, these systems cover the entire range from loosely to tightly entangled polymers. In particular, we argue that the primitive path analysis renormalizes a loosely to a tightly entangled system and provide a new explanation of the successful Lin-Noolandi packing conjecture for polymer melts.
Entangled States, Holography and Quantum Surfaces
Chapline, G F
2003-08-13
Starting with an elementary discussion of quantum holography, we show that entangled quantum states of qubits provide a ''local'' representation of the global geometry and topology of quantum Riemann surfaces. This representation may play an important role in both mathematics and physics. Indeed, the simplest way to represent the fundamental objects in a ''theory of everything'' may be as muti-qubit entangled states.
Diagnosing Topological Edge States via Entanglement Monogamy
NASA Astrophysics Data System (ADS)
Meichanetzidis, K.; Eisert, J.; Cirio, M.; Lahtinen, V.; Pachos, J. K.
2016-04-01
Topological phases of matter possess intricate correlation patterns typically probed by entanglement entropies or entanglement spectra. In this Letter, we propose an alternative approach to assessing topologically induced edge states in free and interacting fermionic systems. We do so by focussing on the fermionic covariance matrix. This matrix is often tractable either analytically or numerically, and it precisely captures the relevant correlations of the system. By invoking the concept of monogamy of entanglement, we show that highly entangled states supported across a system bipartition are largely disentangled from the rest of the system, thus, usually appearing as gapless edge states. We then define an entanglement qualifier that identifies the presence of topological edge states based purely on correlations present in the ground states. We demonstrate the versatility of this qualifier by applying it to various free and interacting fermionic topological systems.
Chen Lixiang; She Weilong
2011-03-15
We propose a scheme to generate hybrid Greenberger-Horne-Zeilinger (GHZ) entanglement where multiple photons are entangled in different degrees of freedom of spin, orbital angular momentum (OAM), and path (linear momentum). The generation involves mapping the preliminary OAM entanglement of photon pairs onto their spin-orbit and spin-path degrees of freedom, respectively. Based on the hybrid GHZ entanglement, we demonstrate an open-destination teleportation with multiples degrees of freedom, via which a spin state of a single photon is teleported onto a superposition of multiple photons with the postselection technique and the original information could be read out at any photon in individual spin, OAM, or the linear-momentum state. Our scheme holds promise for asymmetric optical quantum network.
Entanglement as minimal discord over state extensions
NASA Astrophysics Data System (ADS)
Luo, Shunlong
2016-09-01
The characterization and quantification of quantum correlations, which play an instrumental role in exploring and exploiting the quantum world, have been extensively and intensively studied in the past few decades. Of special prominence and significance are the concepts of entanglement and discord, which are usually regarded as very distinctive quantum correlations, with the latter going beyond the former. In this work we establish a direct and natural link between entanglement and discord via state extensions and reveal that entanglement is actually the intrinsic discord, by which we mean that entanglement is the irreducible residue of discord viewed from ambient spaces. Our approach, taking into account the contextuality of a quantum state and being of a global nature, stands in sharp contrast to the local operations and classical communication paradigm of entanglement, which focuses on the state itself via a local approach. Furthermore, we introduce a figure of merit which, on the one hand, captures the essence of entanglement, i.e., nonlocality and quantumness of correlations, and, on the other hand, leads to a quantitative decomposition of total correlations into classical correlations, dissonance, and entanglement. This demystifies the meaning of entanglement from the perspective of quantum measurements and provides a unified framework for the interplay of various correlations in terms of quantum measurements and mutual information.
Concentration for unknown atomic entangled states via cavity decay
Cao Zhuoliang; Yang Ming; Zhang Lihua
2006-01-15
We present a physical scheme for entanglement concentration of unknown atomic entangled states via cavity decay. In the scheme, the atomic state is used as a stationary qubit and the photonic state as a flying qubit, and a close maximally entangled state can be obtained from pairs of partially entangled states probabilistically.
Non-Markovianity-assisted steady state entanglement.
Huelga, Susana F; Rivas, Ángel; Plenio, Martin B
2012-04-20
We analyze the steady state entanglement generated in a coherently coupled dimer system subject to dephasing noise as a function of the degree of Markovianity of the evolution. By keeping fixed the effective noise strength while varying the memory time of the environment, we demonstrate that non-Markovianity is an essential, quantifiable resource that may support the formation of steady state entanglement whereas purely Markovian dynamics governed by Lindblad master equations lead to separable steady states. This result illustrates possible mechanisms leading to long-lived entanglement in purely decohering, possibly local, environments. We present a feasible experimental demonstration of this noise assisted phenomenon using a system of trapped ions.
Tensor eigenvalues and entanglement of symmetric states
NASA Astrophysics Data System (ADS)
Bohnet-Waldraff, F.; Braun, D.; Giraud, O.
2016-10-01
Tensor eigenvalues and eigenvectors have been introduced in the recent mathematical literature as a generalization of the usual matrix eigenvalues and eigenvectors. We apply this formalism to a tensor that describes a multipartite symmetric state or a spin state, and we investigate to what extent the corresponding tensor eigenvalues contain information about the multipartite entanglement (or, equivalently, the quantumness) of the state. This extends previous results connecting entanglement to spectral properties related to the state. We show that if the smallest tensor eigenvalue is negative, the state is detected as entangled. While for spin-1 states the positivity of the smallest tensor eigenvalue is equivalent to separability, we show that for higher values of the angular momentum there is a correlation between entanglement and the value of the smallest tensor eigenvalue.
Entanglement sharing in one-particle states
NASA Astrophysics Data System (ADS)
Lakshminarayan, Arul; Subrahmanyam, V.
2003-05-01
Entanglement sharing among sites of one-particle states is considered using the measure of concurrence. These are the simplest in a hierarchy of number-specific states of many qubits and correspond to “one-magnon” states of spins. We study the effects of onsite potentials that are both integrable and nonintegrable. In the integrable case, we point to a metal-insulator transition that reflects on the way entanglement is shared. In the nonintegrable case, the average entanglement content increases and saturates along with a transition to classical chaos. Such quantum chaotic states are shown to have universal concurrence distributions that are modified Bessel functions derivable within random matrix theory. Time-reversal breaking and time-evolving states are shown to possess significantly higher entanglement sharing capacity than eigenstates of time-reversal symmetric systems. We use the ordinary Harper and the kicked Harper Hamiltonians as model systems.
Entanglement and the shareability of quantum states
NASA Astrophysics Data System (ADS)
Doherty, Andrew C.
2014-10-01
This brief review discusses the problem of determining whether a given quantum state is separable or entangled. I describe an established approach to this problem that is based on the monogamy of entanglement, which is the observation that a pair of quantum systems that are strongly entangled must be uncorrelated with the rest of the world. Unentangled states on the other hand involve correlations that can be shared with many other parties. Checking whether a given quantum state is shareable involves constructing certain symmetric quantum state extensions and I discuss how to do this using a class of optimizations known as semidefinite programs. An attractive feature of this approach is that it generates explicit entanglement witnesses that can be measured to demonstrate the entanglement experimentally. In recent years analysis of this approach has greatly increased our understanding of the complexity of determining whether a given quantum state is entangled and this review aims to give a unified discussion of these developments. Specifically, I describe how to use finite quantum de Finetti theorems to prove that highly shareable states are nearly separable and use these results to understand the computational complexity of the problem. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘50 years of Bell’s theorem’.
Entanglement classification with matrix product states
Sanz, M.; Egusquiza, I. L.; Di Candia, R.; Saberi, H.; Lamata, L.; Solano, E.
2016-01-01
We propose an entanglement classification for symmetric quantum states based on their diagonal matrix-product-state (MPS) representation. The proposed classification, which preserves the stochastic local operation assisted with classical communication (SLOCC) criterion, relates entanglement families to the interaction length of Hamiltonians. In this manner, we establish a connection between entanglement classification and condensed matter models from a quantum information perspective. Moreover, we introduce a scalable nesting property for the proposed entanglement classification, in which the families for N parties carry over to the N + 1 case. Finally, using techniques from algebraic geometry, we prove that the minimal nontrivial interaction length n for any symmetric state is bounded by . PMID:27457273
Two-Mode Excited Entangled Coherent State: Nonclassicality and Entanglement
NASA Astrophysics Data System (ADS)
Zhang, Hao-Liang; Wu, Jia-Ni; Liu, Cun-Jin; Hu, Yin-Quan; Hu, Li-Yun
2017-03-01
Two-mode excited entangled coherent states (TME-ECSs) are introduced by operating repeatedly the photon-excited operator on the ECSs. It is shown that the normalization constant is related to the product of two Laguerre polynomials. The influence of the operation on nonclassical behaviour of the ECSs is investigated in terms of cross-correlation function, anti-bunching effect and the negativity of Wigner function, which show that nonclassical properties can be enhanced. In addition, inseparability properties of the TME-ECSs are discussed by using Bell inequality and concurrence. It is found that the degree of quantum entanglement of even ECSs increases with the increase of the total excited photon number, and the violation of Bell inequality can be present for both even and odd case only when the total excited photon numbers are even and odd, respectively.
Telecloning of qudits via partially entangled states
NASA Astrophysics Data System (ADS)
Araneda, Gabriel; Cisternas, Nataly; Delgado, Aldo
2016-08-01
We study the process of quantum telecloning of d-dimensional pure quantum states using partially entangled pure states as quantum channel. This process efficiently mixes optimal universal symmetric cloning with quantum teleportation. It is shown that it is possible to implement universal symmetric telecloning in a probabilistic way using unambiguous state discrimination and quantum state separation schemes. It is also shown that other strategies, such as minimum error discrimination, lead to a decrease in the fidelity of the copies and that certain partially entangled pure states with maximal Schmidt rank lead to an average telecloning fidelity which is always above the optimal fidelity of measuring and preparation of quantum states. We also discuss the case of partially entangled pure states with non-maximal Schmidt rank. The results presented here are valid for arbitrary numbers of copies of a single-input qudit state of any dimension.
Topological minimally entangled states via geometric measure
NASA Astrophysics Data System (ADS)
Buerschaper, Oliver; García-Saez, Artur; Orús, Román; Wei, Tzu-Chieh
2014-11-01
Here we show how the Minimally Entangled States (MES) of a 2d system with topological order can be identified using the geometric measure of entanglement. We show this by minimizing this measure for the doubled semion, doubled Fibonacci and toric code models on a torus with non-trivial topological partitions. Our calculations are done either quasi-exactly for small system sizes, or using the tensor network approach in Orús et al (arXiv:1406.0585) for large sizes. As a byproduct of our methods, we see that the minimisation of the geometric entanglement can also determine the number of Abelian quasiparticle excitations in a given model. The results in this paper provide a very efficient and accurate way of extracting the full topological information of a 2d quantum lattice model from the multipartite entanglement structure of its ground states.
Entanglement transitions in random definite particle states
Vijayaraghavan, Vikram S.; Bhosale, Udaysinh T.; Lakshminarayan, Arul
2011-09-15
Entanglements within qubits are studied for the subspace of definite particle states or definite number of up spins. A transition from an algebraic decay of entanglement within two qubits with the total number N of qubits to an exponential one when the number of particles is increased from two to three is studied in detail. In particular the probability that the concurrence is nonzero is calculated using statistical methods and is shown to agree with numerical simulations. Further entanglement within a block of m qubits is studied using the log-negativity measure, which indicates that a transition from algebraic to exponential decay occurs when the number of particles exceeds m. Several algebraic exponents for the decay of the log negativity are analytically calculated. The transition is shown to be possibly connected to the changes in the density of states of the reduced density matrix, which has a divergence at the zero eigenvalue when the entanglement decays algebraically.
Nonbilocal measurement via an entangled state
Shmaya, Eran
2005-08-15
Two observers, who share a pair of particles in an entangled mixed state, can use it to perform some nonbilocal measurements over another bipartite system. In particular, one can construct a specific game played by the observers against a coordinator, in which they can score better than a pair of observers who only share a classical communication channel. The existence of such a game is an operational implication of an entanglement witness.
Entanglement and Coherence in Quantum State Merging.
Streltsov, A; Chitambar, E; Rana, S; Bera, M N; Winter, A; Lewenstein, M
2016-06-17
Understanding the resource consumption in distributed scenarios is one of the main goals of quantum information theory. A prominent example for such a scenario is the task of quantum state merging, where two parties aim to merge their tripartite quantum state parts. In standard quantum state merging, entanglement is considered to be an expensive resource, while local quantum operations can be performed at no additional cost. However, recent developments show that some local operations could be more expensive than others: it is reasonable to distinguish between local incoherent operations and local operations which can create coherence. This idea leads us to the task of incoherent quantum state merging, where one of the parties has free access to local incoherent operations only. In this case the resources of the process are quantified by pairs of entanglement and coherence. Here, we develop tools for studying this process and apply them to several relevant scenarios. While quantum state merging can lead to a gain of entanglement, our results imply that no merging procedure can gain entanglement and coherence at the same time. We also provide a general lower bound on the entanglement-coherence sum and show that the bound is tight for all pure states. Our results also lead to an incoherent version of Schumacher compression: in this case the compression rate is equal to the von Neumann entropy of the diagonal elements of the corresponding quantum state.
Multipartite entangled states in particle mixing
Blasone, M.; Dell'Anno, F.; De Siena, S.; Di Mauro, M.; Illuminati, F.
2008-05-01
In the physics of flavor mixing, the flavor states are given by superpositions of mass eigenstates. By using the occupation number to define a multiqubit space, the flavor states can be interpreted as multipartite mode-entangled states. By exploiting a suitable global measure of entanglement, based on the entropies related to all possible bipartitions of the system, we analyze the correlation properties of such states in the instances of three- and four-flavor mixing. Depending on the mixing parameters, and, in particular, on the values taken by the free phases, responsible for the CP-violation, entanglement concentrates in certain bipartitions. We quantify in detail the amount and the distribution of entanglement in the physically relevant cases of flavor mixing in quark and neutrino systems. By using the wave packet description for localized particles, we use the global measure of entanglement, suitably adapted for the instance of multipartite mixed states, to analyze the decoherence, induced by the free evolution dynamics, on the quantum correlations of stationary neutrino beams. We define a decoherence length as the distance associated with the vanishing of the coherent interference effects among massive neutrino states. We investigate the role of the CP-violating phase in the decoherence process.
Nonlocal entanglement of coherent states, complementarity, and quantum erasure
Gerry, Christopher C.; Grobe, R.
2007-03-15
We describe a nonlocal method for generating entangled coherent states of a two-mode field wherein the field modes never meet. The proposed method is an extension of an earlier proposal [C. C. Gerry, Phys. Rev. A 59, 4095 (1999)] for the generation of superpositions of coherent states. A single photon injected into a Mach-Zehnder interferometer with cross-Kerr media in both arms coupling with two external fields in coherent states produces entangled coherent states upon detection at one of the output ports. We point out that our proposal can be alternatively viewed as a 'which path' experiment, and in the case of only one external field, we describe the implementation of a quantum eraser.
Delayed birth of distillable entanglement in the evolution of bound entangled states
Derkacz, Lukasz; Jakobczyk, Lech
2010-08-15
The dynamical creation of entanglement between three-level atoms coupled to the common vacuum is investigated. For the class of bound entangled initial states, we show that the dynamics of closely separated atoms generates stationary distillable entanglement of asymptotic states. We also find that the effect of delayed sudden birth of distillable entanglement occurs in the case of atoms separated by a distance comparable with the radiation wavelength.
Entanglement and Decoherence in Two-Dimensional Coherent State Superpositions
NASA Astrophysics Data System (ADS)
Maleki, Y.
2017-03-01
A detailed investigation of entanglement in the generalized two-dimensional nonorthogonal states, which are expressed in the framework of superposed coherent states, is presented. In addition to quantifying entanglement of the generalized two-dimensional coherent states superposition, necessary and sufficient conditions for maximality of entanglement of these states are found. We show that a large class of maximally entangled coherent states can be constructed, and hence, some new maximally entangled coherent states are explicitly manipulated. The investigation is extended to the mixed system states and entanglement properties of such mixed states are investigated. It is shown that in some cases maximally entangled mixed states can be detected. Furthermore, the effect of decoherence, due to both cavity losses and noisy channel process, on such entangled states are studied and its features are discussed.
Quantum entanglement of quark colour states
Buividovich, P. V.; Kuvshinov, V. I.
2010-03-24
An analysis of quantum entanglement between the states of static colour charges in the vacuum of pure Yang-Mills theory is carried out. Hilbert space of physical states of the fields and the charges is endowed with a direct product structure by attaching an infinite Dirac string to each charge.
NASA Astrophysics Data System (ADS)
Assadi, Leila; Jafarpour, Mojtaba
2016-11-01
We use concurrence to study bipartite entanglement, Meyer-Wallach measure and its generalizations to study multi-partite entanglement and MABK and SASA inequalities to study the non-local properties of the 4-qubit entangled graph states, quantitatively. Then, we present 3 classifications, each one in accordance with one of the aforementioned properties. We also observe that the classification according to multipartite entanglement does exactly coincide with that according to nonlocal properties, but does not match with that according to bipartite entanglement. This observation signifies the fact that non-locality and multipartite entanglement enjoy the same basic underlying principles, while bipartite entanglement may not reveal the non-locality issue in its entirety.
Creating maximally entangled states by gluing
NASA Astrophysics Data System (ADS)
Raissi, Zahra; Karimipour, Vahid
2017-03-01
We introduce a general method of gluing multi-partite states and show that entanglement swapping is a special class of a wider range of gluing operations. The gluing operation of two m and n qudit states consists of an entangling operation on two given qudits of the two states followed by operations of measurements of the two qudits in the computational basis. Depending on how many qudits (two, one or zero) we measure, we have three classes of gluing operation, resulting respectively in m+n-2, m+n-1, or m+n qudit states. Entanglement swapping belongs to the first class and has been widely studied, while the other two classes are presented and studied here. In particular, we study how larger GHZ and W states can be constructed when we glue the smaller GHZ and W states by the second method. Finally we prove that when we glue two states by the third method, the k-uniformity of the states is preserved. That is when a k-uniform state of m qudits is glued to a k'-uniform state of n qudits, the resulting state will be a min(k,k')-uniform of m+n qudits.
Testing nonlocal realism with entangled coherent states
Paternostro, Mauro; Jeong, Hyunseok
2010-03-15
We investigate the violation of nonlocal realism using entangled coherent states (ECSs) under nonlinear operations and homodyne measurements. We address recently proposed Leggett-type inequalities, including a class of optimized incompatibility inequalities proposed by Branciard et al. [Nature Phys. 4, 681 (2008)], and thoroughly assess the effects of detection inefficiency.
Generating coherent states of entangled spins
Yu Hongyi; Luo Yu; Yao Wang
2011-09-15
A coherent state of many spins contains quantum entanglement, which increases with a decrease in the collective spin value. We present a scheme to engineer this class of pure state based on incoherent spin pumping with a few collective raising or lowering operators. In a pumping scenario aimed for maximum entanglement, the steady state of N-pumped spin qubits realizes the ideal resource for the 1{yields}(N/2) quantum telecloning. We show how the scheme can be implemented in a realistic system of atomic spin qubits in an optical lattice. Error analysis shows that high-fidelity state engineering is possible for N{approx}O(100) spins in the presence of decoherence. The scheme can also prepare a resource state for the secret sharing protocol and for the construction of the large-scale Affleck-Kennedy-Lieb-Tasaki state.
Teleportation of entangled states without Bell-state measurement
Cardoso, Wesley B.; Baseia, B.; Avelar, A.T.; Almeida, N.G. de
2005-10-15
In a recent paper [Phys. Rev. A 70, 025803 (2004)] we presented a scheme to teleport an entanglement of zero- and one-photon states from a bimodal cavity to another one, with 100% success probability. Here, inspired by recent results in the literature, we have modified our previous proposal to teleport the same entangled state without using Bell-state measurements. For comparison, the time spent, the fidelity, and the success probability for this teleportation are considered.
Unitarily localizable entanglement of Gaussian states
Serafini, Alessio; Adesso, Gerardo; Illuminati, Fabrizio
2005-03-01
We consider generic (mxn)-mode bipartitions of continuous-variable systems, and study the associated bisymmetric multimode Gaussian states. They are defined as (m+n)-mode Gaussian states invariant under local mode permutations on the m-mode and n-mode subsystems. We prove that such states are equivalent, under local unitary transformations, to the tensor product of a two-mode state and of m+n-2 uncorrelated single-mode states. The entanglement between the m-mode and the n-mode blocks can then be completely concentrated on a single pair of modes by means of local unitary operations alone. This result allows us to prove that the PPT (positivity of the partial transpose) condition is necessary and sufficient for the separability of (m+n)-mode bisymmetric Gaussian states. We determine exactly their negativity and identify a subset of bisymmetric states whose multimode entanglement of formation can be computed analytically. We consider explicit examples of pure and mixed bisymmetric states and study their entanglement scaling with the number of modes.
Multiple teleportation via partially entangled GHZ state
NASA Astrophysics Data System (ADS)
Xiong, Pei-Ying; Yu, Xu-Tao; Zhan, Hai-Tao; Zhang, Zai-Chen
2016-08-01
Quantum teleportation is important for quantum communication. We propose a protocol that uses a partially entangled Greenberger-Horne-Zeilinger (GHZ) state for single hop teleportation. Quantum teleportation will succeed if the sender makes a Bell state measurement, and the receiver performs the Hadamard gate operation, applies appropriate Pauli operators, introduces an auxiliary particle, and applies the corresponding unitary matrix to recover the transmitted state.We also present a protocol to realize multiple teleportation of partially entangled GHZ state without an auxiliary particle. We show that the success probability of the teleportation is always 0 when the number of teleportations is odd. In order to improve the success probability of a multihop, we introduce the method used in our single hop teleportation, thus proposing a multiple teleportation protocol using auxiliary particles and a unitary matrix. The final success probability is shown to be improved significantly for the method without auxiliary particles for both an odd or even number of teleportations.
Faithful teleportation with partially entangled states
Gour, Gilad
2004-10-01
We write explicitly a general protocol for faithful teleportation of a d-state particle (qudit) via a partially entangled pair of (pure) n-state particles. The classical communication cost (CCC) of the protocol is log{sub 2}(nd) bits, and it is implemented by a projective measurement performed by Alice, and a unitary operator performed by Bob (after receiving from Alice the measurement result). We prove the optimality of our protocol by a comparison with the concentrate and teleport strategy. We also show that if d>n/2, or if there is no residual entanglement left after the faithful teleportation, the CCC of any protocol is at least log{sub 2}(nd) bits. Furthermore, we find a lower bound on the CCC in the process transforming one bipartite state to another by means of local operation and classical communication.
Quantum Discord and Entanglement of Quasi-Werner States Based on Bipartite Entangled Coherent States
NASA Astrophysics Data System (ADS)
Mishra, Manoj K.; Maurya, Ajay K.; Prakash, Hari
2016-06-01
Present work is an attempt to compare quantum discord and quantum entanglement of quasi-Werner states formed with the four bipartite entangled coherent states (ECS) used recently for quantum teleportation of a qubit encoded in superposed coherent state. Out of these, the quasi-Werner states based on maximally ECS due to its invariant nature under local operation is independent of measurement basis and mean photon numbers, while for quasi-Werner states based on non-maximally ECS, it depends upon measurement basis as well as on mean photon number. However, for large mean photon numbers since non-maximally ECS becomes almost maximally entangled therefore dependence of quantum discord for non-maximally ECS based quasi-Werner states on the measurement basis disappears.
Entanglement of π-locally-maximally-entangleable states and the satisfiability problem
NASA Astrophysics Data System (ADS)
Makmal, Adi; Tiersch, Markus; Dunjko, Vedran; Wu, Shengjun
2014-10-01
In this paper we investigate the entanglement properties of the class of π-locally-maximally-entangleable (π-LME) states, which are also known as the real equally weighted states or the hypergraph states. The π-LME states comprise well-studied classes of quantum states (e.g., graph states) and exhibit a large degree of symmetry. Motivated by the structure of LME states, we show that the capacity to (efficiently) determine if a π-LME state is entangled would imply an efficient solution to the Boolean satisfiability problem. More concretely, we show that this particular problem of entanglement detection, phrased as a decision problem, is NP-complete. The restricted setting we consider yields a technically uninvolved proof, and illustrates that entanglement detection, even when quantum states under consideration are highly restricted, still remains difficult.
Entanglement and Squeezing in Solid State Circuits
Wen Yihuo; Gui Lulong
2008-11-07
We investigate the dynamics of a system consisting of a Cooper-pair box and two superconducting transmission line resonators. There exist both linear and nonlinear interactions in such a system. We show that single-photon entanglement state can be generated in a simple way in the linear interaction regime. In nonlinear interaction regime, we derive the Hamiltonian of degenerate three-wave mixing and propose a scheme for generating squeezed state of microwave using the three-wave mixing in solid state circuits. In the following, we design a system for generating squeezed states of nanamechanical resonator.
Entanglement of remote transmon qubits by concurrent measurement using Fock states
NASA Astrophysics Data System (ADS)
Narla, A.; Hatridge, M.; Shankar, S.; Leghtas, Z.; Sliwa, K. M.; Vlastakis, B.; Zalys-Geller, E.; Mirrahimi, M.; Devoret, M. H.
2015-03-01
A requirement of any modular quantum computer is the ability to maintain individual qubits in isolated environments while also being able to entangle arbitrary distant qubits on demand. For superconducting qubits, such a protocol can be realized by first entangling the qubits with flying microwave coherent states which are then concurrently detected by a parametric amplifier. This protocol has a 50% success probability but is vulnerable to losses between the qubits and the amplifier which reduce the entanglement fidelity. An alternative is to use itinerant Fock states, since losses now tend to reduce the success probability of creating an entangled state but not its fidelity. Such single-photon protocols have been implemented in trapped-ion and NV-center experiments. We present such a protocol tailored for entangling two transmon qubits in the circuit QED architecture. Each qubit is entangled with a Fock state of its cavity using sideband pulses. The Fock states leak out of the cavity, interfere on a beam-splitter which erases their which-path information, and are subsequently detected using a novel photo-detector realized by another qubit-cavity system. Simulations suggest that we can realize a high-fidelity entangled state with a success probability as large as 1%.
Wang Chuan; Zhang Yong; Jin Guangsheng
2011-09-15
We present an entanglement purification protocol and an entanglement concentration protocol for electron-spin entangled states, resorting to quantum-dot spin and optical-microcavity-coupled systems. The parity-check gates (PCGs) constructed by the cavity-spin-coupling system provide a different method for the entanglement purification of electron-spin entangled states. This protocol can efficiently purify an electron ensemble in a mixed entangled state. The PCGs can also concentrate electron-spin pairs in less-entangled pure states efficiently. The proposed methods are more flexible as only single-photon detection and single-electron detection are needed.
Loss-resilient photonic entanglement swapping using optical hybrid states
NASA Astrophysics Data System (ADS)
Lim, Youngrong; Joo, Jaewoo; Spiller, Timothy P.; Jeong, Hyunseok
2016-12-01
We propose a scheme of loss-resilient entanglement swapping between two distant parties via an imperfect optical channel. In this scheme, two copies of hybrid entangled states are prepared and the continuous-variable parts propagate through lossy media. In order to perform successful entanglement swapping, several different measurement schemes are considered for the continuous-variable parts such as single-photon detection for ideal cases and a homodyne detection for practical cases. We find that the entanglement swapping using hybrid states with small amplitudes offers larger entanglement than the discrete-variable entanglement swapping in the presence of large losses. Remarkably, this hybrid scheme still offers excellent robustness of entanglement to the detection inefficiency. Thus, the proposed scheme could be used for the practical quantum key distribution in hybrid optical states under photon losses.
Classical simulation of entangled states
NASA Astrophysics Data System (ADS)
Bharath, H. M.; Ravishankar, V.
2014-06-01
Characterization of nonclassicality or quantumness of a state is fundamental to foundations of quantum mechanics and quantum information. At the heart of the problem is the question whether there exist classical systems—howsoever complicated—that can mimic a given quantum state. Whilst this has been traditionally addressed through the violation of Bell inequality or nonseparability, we show that it is possible to go beyond them, by introducing the concept of classical simulation. Focusing on the two-qubit case, we show that, while for pure states, classical simulability is equivalent to existence of a local hidden variable (LHV) model, the conditions for simulability can be weaker for mixed states, demanding what we call only a generalized LHV description. Consequently, quantum states which defy a classical simulation—which we call exceptional—may require conditions which are more stringent than violation of Bell inequalities. We illustrate these features with a number of representative examples and discuss the underlying reasons, by employing fairly simple arguments.
Computational complexity of projected entangled pair states.
Schuch, Norbert; Wolf, Michael M; Verstraete, Frank; Cirac, J Ignacio
2007-04-06
We determine the computational power of preparing projected entangled pair states (PEPS), as well as the complexity of classically simulating them, and generally the complexity of contracting tensor networks. While creating PEPS allows us to solve PP problems, the latter two tasks are both proven to be #P-complete. We further show how PEPS can be used to approximate ground states of gapped Hamiltonians and that creating them is easier than creating arbitrary PEPS. The main tool for our proofs is a duality between PEPS and postselection which allows us to use existing results from quantum complexity.
Multipartite entanglement accumulation in quantum states: Localizable generalized geometric measure
NASA Astrophysics Data System (ADS)
Sadhukhan, Debasis; Roy, Sudipto Singha; Pal, Amit Kumar; Rakshit, Debraj; SenDe, Aditi; Sen, Ujjwal
2017-02-01
Multiparty quantum states are useful for a variety of quantum information and computation protocols. We define a multiparty entanglement measure based on local measurements on a multiparty quantum state and an entanglement measure averaged on the postmeasurement ensemble. Using the generalized geometric measure as the measure of multipartite entanglement for the ensemble, we demonstrate, in the case of several well-known classes of multipartite pure states, that the localized multipartite entanglement can exceed the entanglement present in the original state. We also show that measurement over multiple parties may be beneficial in enhancing localizable multipartite entanglement. We point out that localizable generalized geometric measure faithfully signals quantum critical phenomena in well-known quantum spin models even when considerable finite-size effect is present in the system.
Preparing entangled states by Lyapunov control
NASA Astrophysics Data System (ADS)
Shi, Z. C.; Wang, L. C.; Yi, X. X.
2016-12-01
By Lyapunov control, we present a protocol to prepare entangled states such as Bell states in the context of cavity QED system. The advantage of our method is of threefold. Firstly, we can only control the phase of classical fields to complete the preparation process. Secondly, the evolution time is sharply shortened when compared to adiabatic control. Thirdly, the final state is steady after removing control fields. The influence of decoherence caused by the atomic spontaneous emission and the cavity decay is discussed. The numerical results show that the control scheme is immune to decoherence, especially for the atomic spontaneous emission from |2rangle to |1rangle . This can be understood as the state staying in an invariant subspace. Finally, we generalize this method in preparation of W state.
Entangled states and superradiant phase transitions
Aparicio Alcalde, M.; Cardenas, A. H.; Svaiter, N. F.; Bezerra, V. B.
2010-03-15
The full Dicke model is composed of a single bosonic mode and an ensemble of N identical two-level atoms. In the model, the coupling between the bosonic mode and the atoms generates resonant and nonresonant processes. We also consider a dipole-dipole interaction between the atoms, which is able to generate entangled states in the atomic system. By assuming thermal equilibrium with a reservoir at temperature {beta}{sup -1}, the transition from fluorescent to superradiant phase and the quantum phase transition are investigated. It is shown that the critical behavior of the full Dicke model is not modified by the introduction of the dipole-dipole interaction.
Quantum gravity, CPT symmetry and entangled states
NASA Astrophysics Data System (ADS)
Mavromatos, Nick E.
2012-03-01
In this talk I discuss the potential rôle of quantumgravity space-time foam on an induced intrinsic violation of CPT symmetry, resulting in (perturbatively weak) modifications of Einstein-Podolsky-Rosen (EPR) correlations in entangled particle states of neutral mesons. For specific models of foam, inspired from String theory, the modifications may be falsifiable at the current upgrade of the DAΦNE detector in Frascati NL. Advantages of neutral Kaons over other neutral mesons (e.g. B-mesons) for the possible detection of the phenomenon, are outlined.
NASA Astrophysics Data System (ADS)
Huang, Li-Yuan; Fang, Mao-Fa
2008-07-01
The thermal entanglement and teleportation of a thermally mixed entangled state of a two-qubit Heisenberg XXX chain under the Dzyaloshinski-Moriya (DM) anisotropic antisymmetric interaction through a noisy quantum channel given by a Werner state is investigated. The dependences of the thermal entanglement of the teleported state on the DM coupling constant, the temperature and the entanglement of the noisy quantum channel are studied in detail for both the ferromagnetic and the antiferromagnetic cases. The result shows that a minimum entanglement of the noisy quantum channel must be provided in order to realize the entanglement teleportation. The values of fidelity of the teleported state are also studied for these two cases. It is found that under certain conditions, we can transfer an initial state with a better fidelity than that for any classical communication protocol.
Multipartite entanglement in four-qubit graph states
NASA Astrophysics Data System (ADS)
Jafarpour, Mojtaba; Assadi, Leila
2016-03-01
We consider a compendium of the non-trivial four-qubit graphs, derive their corresponding quantum states and classify them into equivalent classes. We use Meyer-Wallach measure and its generalizations to study block-partition and global entanglement in these states. We obtain several entanglement quantities for each graph state, which present a comprehensive characterization of the entanglement properties of the latter. As a result, a number of correlations between the graph structure and multipartite entanglement quantities have also been established.
Multipartite maximally entangled states in symmetric scenarios
NASA Astrophysics Data System (ADS)
González-Guillén, Carlos E.
2012-08-01
We consider the class of (N+1)-partite states suitable for protocols where there is a powerful party, the authority, and the other N parties play the same role, namely, the state of their system lies in the symmetric Hilbert space. We show that, within this scenario, there is a “maximally entangled state” that can be transform by a local operations and classical communication protocol into any other state. In addition, we show how to use the protocol efficiently, including the construction of the state, and discuss security issues for possible applications to cryptographic protocols. As an immediate consequence we recover a sequential protocol that implements the 1-to-N symmetric cloning.
NASA Astrophysics Data System (ADS)
Wang, He; Zhang, Yu Qing; Liu, Xue Feng; Hu, Yu Pu
2016-06-01
We propose a novel quantum dialogue protocol by using the generalized Bell states and entanglement swapping. In the protocol, a sequence of ordered two-qutrit entangled states acts as quantum information channel for exchanging secret messages directly and simultaneously. Besides, a secret key string is shared between the communicants to overcome information leakage. Different from those previous information leakage-resistant quantum dialogue protocols, the particles, composed of one of each pair of entangled states, are transmitted only one time in the proposed protocol. Security analysis shows that our protocol can overcome information leakage and resist several well-known attacks. Moreover, the efficiency of our scheme is acceptable.
Entanglement of polar molecules in pendular states
NASA Astrophysics Data System (ADS)
Wei, Qi; Kais, Sabre; Friedrich, Bretislav; Herschbach, Dudley
2011-03-01
In proposals for quantum computers using arrays of trapped ultracold polar molecules as qubits, a strong external field with appreciable gradient is imposed in order to prevent quenching of the dipole moments by rotation and to distinguish among the qubit sites. That field induces the molecular dipoles to undergo pendular oscillations, which markedly affect the qubit states and the dipole-dipole interaction. We evaluate entanglement of the pendular qubit states for two linear dipoles, characterized by pairwise concurrence, as a function of the molecular dipole moment and rotational constant, strengths of the external field and the dipole-dipole coupling, and ambient temperature. We also evaluate a key frequency shift, △ω, produced by the dipole-dipole interaction. Under conditions envisioned for the proposed quantum computers, both the concurrence and △ω become very small for the ground eigenstate. In principle, such weak entanglement can be sufficient for operation of logic gates, provided the resolution is high enough to detect the △ω shift unambiguously. In practice, however, for many candidate polar molecules it appears a challenging task to attain adequate resolution. Simple approximate formulas fitted to our numerical results are provided from which the concurrence and △ω shift can be obtained in terms of unitless reduced variables.
Entanglement criteria for noise resistance of two-qudit states
NASA Astrophysics Data System (ADS)
Dutta, Arijit; Ryu, Junghee; Laskowski, Wiesław; Żukowski, Marek
2016-06-01
Noise affects production and transmission of entanglement. We use a handy approach for a noise resistance of entanglement of two-qudit systems. A geometric concept using correlation tensors of separable and entangled states is implemented to formulate entanglement criterion. We apply the criterion to the various types of noise (white, colored, local depolarizing and amplitude damping) admixtures with the initial (pure) state. We also study the noise resistance with respect to the violation of specific family of Bell inequalities (CGLMP). A broad set of numerical and analytical results is presented.
Classification of multipartite entangled states by multidimensional determinants
Miyake, Akimasa
2003-01-01
We find that multidimensional determinants 'hyperdeterminants', related to entanglement measures (the so-called concurrence, or 3-tangle for two or three qubits, respectively), are derived from a duality between entangled states and separable states. By means of the hyperdeterminant and its singularities, the single copy of multipartite pure entangled states is classified into an onion structure of every closed subset, similar to that by the local rank in the bipartite case. This reveals how inequivalent multipartite entangled classes are partially ordered under local actions. In particular, the generic entangled class of the maximal dimension, distinguished as the nonzero hyperdeterminant, does not include the maximally entangled states in Bell's inequalities in general (e.g., in the n{>=}4 qubits), contrary to the widely known bipartite or three-qubit cases. It suggests that not only are they never locally interconvertible with the majority of multipartite entangled states, but they would have no grounds for the canonical n-partite entangled states. Our classification is also useful for the mixed states.
Tsirelson's bound and supersymmetric entangled states
Borsten, L.; Brádler, K.; Duff, M. J.
2014-01-01
A superqubit, belonging to a (2|1)-dimensional super-Hilbert space, constitutes the minimal supersymmetric extension of the conventional qubit. In order to see whether superqubits are more non-local than ordinary qubits, we construct a class of two-superqubit entangled states as a non-local resource in the CHSH game. Since super Hilbert space amplitudes are Grassmann numbers, the result depends on how we extract real probabilities and we examine three choices of map: (1) DeWitt (2) Trigonometric and (3) Modified Rogers. In cases (1) and (2), the winning probability reaches the Tsirelson bound pwin=cos2π/8≃0.8536 of standard quantum mechanics. Case (3) crosses Tsirelson's bound with pwin≃0.9265. Although all states used in the game involve probabilities lying between 0 and 1, case (3) permits other changes of basis inducing negative transition probabilities. PMID:25294964
Entangled states of spin and clock oscillators
NASA Astrophysics Data System (ADS)
Polzik, Eugene
2016-05-01
Measurements of one quadrature of an oscillator with precision beyond its vacuum state uncertainty have occupied a central place in quantum physics for decades. We have recently reported the first experimental implementation of such measurement with a magnetic oscillator. However, a much more intriguing goal is to trace an oscillator trajectory with the precision beyond the vacuum state uncertainty in both position and momentum, a feat naively assumed not possible due to the Heisenberg uncertainty principle. We have demonstrated that such measurement is possible if the oscillator is entangled with a quantum reference oscillator with an effective negative mass. The key element is the cancellation of the back action of the measurement on the composite system of two oscillators. Applications include measurements of e.-m. fields, accelleration, force and time with practically unlimited accuracy. In a more general sense, this approach leads to trajectories without quantum uncertainties and to achieving new fundamental bounds on the measurement precision.
Entanglement of Formation for Werner States and Isotropic States via Logical Gates
NASA Astrophysics Data System (ADS)
Bertini, Cesarino; Chiara, Maria Luisa Dalla; Leporini, Roberto
To what extent is a logical characterization of entanglement possible? We investigate some correlations that hold between the concept of entanglement of formation for Werner states and for isotropic states and the probabilistic behavior of some quantum logical gates.
Cluster-type entangled coherent states: Generation and application
An, Nguyen Ba; Kim, Jaewan
2009-10-15
We consider a type of (M+N)-mode entangled coherent states and propose a simple deterministic scheme to generate these states that can fly freely in space. We then exploit such free-flying states to teleport certain kinds of superpositions of multimode coherent states. We also address the issue of manipulating size and type of entangled coherent states by means of linear optics elements only.
Semiquantum secret sharing using entangled states
Li Qin; Chan, W. H.; Long Dongyang
2010-08-15
Secret sharing is a procedure for sharing a secret among a number of participants such that only the qualified subsets of participants have the ability to reconstruct the secret. Even in the presence of eavesdropping, secret sharing can be achieved when all the members are quantum. So what happens if not all the members are quantum? In this paper, we propose two semiquantum secret sharing protocols by using maximally entangled Greenberger-Horne-Zeilinger-type states in which quantum Alice shares a secret with two classical parties, Bob and Charlie, in a way that both parties are sufficient to obtain the secret, but one of them cannot. The presented protocols are also shown to be secure against eavesdropping.
Distillation and purification of symmetric entangled Gaussian states
Fiurasek, Jaromir
2010-10-15
We propose an entanglement distillation and purification scheme for symmetric two-mode entangled Gaussian states that allows to asymptotically extract a pure entangled Gaussian state from any input entangled symmetric Gaussian state. The proposed scheme is a modified and extended version of the entanglement distillation protocol originally developed by Browne et al. [Phys. Rev. A 67, 062320 (2003)]. A key feature of the present protocol is that it utilizes a two-copy degaussification procedure that involves a Mach-Zehnder interferometer with single-mode non-Gaussian filters inserted in its two arms. The required non-Gaussian filtering operations can be implemented by coherently combining two sequences of single-photon addition and subtraction operations.
Entanglement monotones and transformations of symmetric bipartite states
NASA Astrophysics Data System (ADS)
Girard, Mark W.; Gour, Gilad
2017-01-01
The primary goal in the study of entanglement as a resource theory is to find conditions that determine when one quantum state can or cannot be transformed into another via local operations and classical communication operations. This is typically done through entanglement monotones or conversion witnesses. Such quantities cannot be computed for arbitrary quantum states in general, but it is useful to consider classes of symmetric states for which closed-form expressions can be found. In this paper, we show how to compute the convex roof of any entanglement monotone for all Werner states. The convex roofs of the well-known Vidal monotones are computed for all isotropic states, and we show how this method can generalize to other entanglement measures and other types of symmetries as well. We also present necessary and sufficient conditions that determine when a pure bipartite state can be deterministically converted into a Werner state or an isotropic state.
NASA Astrophysics Data System (ADS)
Backens, Miriam
2017-02-01
L. Lamata et al. use an inductive approach to classify the entangled pure states of four qubits under stochastic local operations and classical communication (SLOCC) [Phys. Rev. A 75, 022318 (2007), 10.1103/PhysRevA.75.022318]. The inductive method yields a priori ten entanglement superclasses, of which they discard three as empty. One of the remaining superclasses is split into two, resulting in eight superclasses of genuine four-qubit entanglement. Here, we show that two of the three discarded superclasses are in fact nonempty and should have been retained. We give explicit expressions for the canonical states of those superclasses, up to SLOCC and qubit permutations. Furthermore, we confirm that the third discarded superclass is indeed empty, yielding a total of ten superclasses of genuine four-qubit entanglement under the inductive classification scheme.
Engineering of triply entangled states in a single-neutron system
Hasegawa, Yuji; Loidl, Rudolf; Rauch, Helmut; Badurek, Gerald; Durstberger-Rennhofer, Katharina; Sponar, Stephan
2010-03-15
Entanglement between degrees of freedom, namely between the spin, path, and (total) energy degrees of freedom, in a single-neutron system is exploited. We implemented a triply entangled Greenberger-Horne-Zeilinger (GHZ)-like state and coherently manipulated relative phases of two-level quantum subsystems. An equality derived by Mermin was applied to analyze the generated GHZ-like state: We determined the four expectation values and finally obtained M=2.558{+-}0.004{<=}e2. This demonstrates a violation of Mermin-like inequality for triply entangled GHZ-like state in a single-particle system, which, in turn, clearly contradicts the noncontextual assumption and confirms quantum contextuality.
Maximum entanglement in squeezed boson and fermion states
Khanna, F. C.; Malbouisson, J. M. C.; Santana, A. E.; Santos, E. S.
2007-08-15
A class of squeezed boson and fermion states is studied with particular emphasis on the nature of entanglement. We first investigate the case of bosons, considering two-mode squeezed states. Then we construct the fermion version to show that such states are maximum entangled, for both bosons and fermions. To achieve these results, we demonstrate some relations involving squeezed boson states. The generalization to the case of fermions is made by using Grassmann variables.
Photon-number entangled states generated in Kerr media with optical parametric pumping
Kowalewska-Kudlaszyk, A.; Leonski, W.; Perina, Jan Jr.
2011-05-15
Two nonlinear Kerr oscillators mutually coupled by parametric pumping are studied as a source of states entangled in photon numbers. Temporal evolution of entanglement quantified by negativity shows the effects of sudden death and birth of entanglement. Entanglement is preserved even in asymptotic states under certain conditions. The role of reservoirs at finite temperature in entanglement evolution is elucidated. Relation between generation of entangled states and violation of Cauchy-Schwartz inequality for oscillator intensities is found.
Quantum frequency up-conversion of continuous variable entangled states
Liu, Wenyuan; Wang, Ning; Li, Zongyang; Li, Yongmin
2015-12-07
We demonstrate experimentally quantum frequency up-conversion of a continuous variable entangled optical field via sum-frequency-generation process. The two-color entangled state initially entangled at 806 and 1518 nm with an amplitude quadrature difference squeezing of 3.2 dB and phase quadrature sum squeezing of 3.1 dB is converted to a new entangled state at 530 and 1518 nm with the amplitude quadrature difference squeezing of 1.7 dB and phase quadrature sum squeezing of 1.8 dB. Our implementation enables the observation of entanglement between two light fields spanning approximately 1.5 octaves in optical frequency. The presented scheme is robust to the excess amplitude and phase noises of the pump field, making it a practical building block for quantum information processing and communication networks.
Entanglement as a resource to distinguish orthogonal product states
Zhang, Zhi-Chao; Gao, Fei; Cao, Tian-Qing; Qin, Su-Juan; Wen, Qiao-Yan
2016-01-01
It is known that there are many sets of orthogonal product states which cannot be distinguished perfectly by local operations and classical communication (LOCC). However, these discussions have left the following open question: What entanglement resources are necessary and/or sufficient for this task to be possible with LOCC? In m ⊗ n, certain classes of unextendible product bases (UPB) which can be distinguished perfectly using entanglement as a resource, had been presented in 2008. In this paper, we present protocols which use entanglement more efficiently than teleportation to distinguish some classes of orthogonal product states in m ⊗ n, which are not UPB. For the open question, our results offer rather general insight into why entanglement is useful for such tasks, and present a better understanding of the relationship between entanglement and nonlocality. PMID:27458034
Entanglement as a resource to distinguish orthogonal product states
NASA Astrophysics Data System (ADS)
Zhang, Zhi-Chao; Gao, Fei; Cao, Tian-Qing; Qin, Su-Juan; Wen, Qiao-Yan
2016-07-01
It is known that there are many sets of orthogonal product states which cannot be distinguished perfectly by local operations and classical communication (LOCC). However, these discussions have left the following open question: What entanglement resources are necessary and/or sufficient for this task to be possible with LOCC? In m ⊗ n, certain classes of unextendible product bases (UPB) which can be distinguished perfectly using entanglement as a resource, had been presented in 2008. In this paper, we present protocols which use entanglement more efficiently than teleportation to distinguish some classes of orthogonal product states in m ⊗ n, which are not UPB. For the open question, our results offer rather general insight into why entanglement is useful for such tasks, and present a better understanding of the relationship between entanglement and nonlocality.
Quantum frequency up-conversion of continuous variable entangled states
NASA Astrophysics Data System (ADS)
Liu, Wenyuan; Wang, Ning; Li, Zongyang; Li, Yongmin
2015-12-01
We demonstrate experimentally quantum frequency up-conversion of a continuous variable entangled optical field via sum-frequency-generation process. The two-color entangled state initially entangled at 806 and 1518 nm with an amplitude quadrature difference squeezing of 3.2 dB and phase quadrature sum squeezing of 3.1 dB is converted to a new entangled state at 530 and 1518 nm with the amplitude quadrature difference squeezing of 1.7 dB and phase quadrature sum squeezing of 1.8 dB. Our implementation enables the observation of entanglement between two light fields spanning approximately 1.5 octaves in optical frequency. The presented scheme is robust to the excess amplitude and phase noises of the pump field, making it a practical building block for quantum information processing and communication networks.
Compensated Crystal Assemblies for Type-II Entangled Photon Generation in Quantum Cluster States
2010-03-01
multi-crystal sources, such as cluster states, entanglement swapping, and teleportation . 15. SUBJECT TERMS quantum , entangled photons, joint...entanglement swapping, and teleportation . Key Words: quantum , entangled photons, joint spectral function, spontaneous parametric downconversion 2...DATES COVERED (From - To) OCT 2009 – SEP 2011 4. TITLE AND SUBTITLE COMPENSATED CRYSTAL ASSEMBLIES FOR TYPE-II ENTANGLED PHOTO GENERATION IN QUANTUM
Fast entanglement detection for unknown states of two spatial qutrits
Lima, G.; Gomez, E. S.; Saavedra, C.; Vargas, A.; Vianna, R. O.
2010-07-15
We investigate the practicality of the method proposed by Maciel et al. [Phys. Rev. A. 80, 032325 (2009).] for detecting the entanglement of two spatial qutrits (three-dimensional quantum systems), which are encoded in the discrete transverse momentum of single photons transmitted through a multislit aperture. The method is based on the acquisition of partial information of the quantum state through projective measurements, and a data processing analysis done with semidefinite programs. This analysis relies on generating gradually an optimal entanglement witness operator, and numerical investigations have shown that it allows for the entanglement detection of unknown states with a cost much lower than full state tomography.
Dissipative entanglement of solid-state spins in diamond
NASA Astrophysics Data System (ADS)
Rao, D. D. Bhaktavatsala; Yang, Sen; Wrachtrup, Jörg
2017-02-01
Generating robust entanglement among solid-state spins is key for applications in quantum information processing and precision sensing. Here we show a dissipative approach to generate such entanglement among the hyperfine coupled electron nuclear spins using the rapid optical decay of electronic excited states. The combined dark state interference effects of the optical and microwave driving fields in the presence of spontaneous emission from the short-lived excited state leads to a dissipative formation of an entangled steady state. We show that the dissipative entanglement is generated for any initial state conditions of the spins and is resilient to external field fluctuations. We analyze the scheme for both continuous and pulsed driving fields in the presence of realistic noise sources.
Open-system dynamics of graph-state entanglement.
Cavalcanti, Daniel; Chaves, Rafael; Aolita, Leandro; Davidovich, Luiz; Acín, Antonio
2009-07-17
We consider graph states of an arbitrary number of particles undergoing generic decoherence. We present methods to obtain lower and upper bounds for the system's entanglement in terms of that of considerably smaller subsystems. For an important class of noisy channels, namely, the Pauli maps, these bounds coincide and thus provide the exact analytical expression for the entanglement evolution. All of the results apply also to (mixed) graph-diagonal states and hold true for any convex entanglement monotone. Since any state can be locally depolarized to some graph-diagonal state, our method provides a lower bound for the entanglement decay of any arbitrary state. Finally, this formalism also allows for the direct identification of the robustness under size scaling of graph states in the presence of decoherence, merely by inspection of their connectivities.
Preparing an Eight-Qubit Entangled State in Cavity QED
NASA Astrophysics Data System (ADS)
Li, Yuan-hua; Sang, Ming-huang; Nie, Yi-you
2016-11-01
An experimental protocol for preparing an eight-qubit entangled state in cavity QED is proposed, which is insensitive to the cavity decay and the thermal field. And the experimental feasibility of our protocol is discussed.
Generalizations of entanglement based on coherent states and convex sets
NASA Astrophysics Data System (ADS)
Barnum, Howard; Knill, Emanuel; Ortiz, Gerardo; Viola, Lorenza
2003-09-01
Unentangled pure states on a bipartite system are exactly the coherent states with respect to the group of local transformations. What aspects of the study of entanglement are applicable to generalized coherent states? Conversely, what can be learned about entanglement from the well-studied theory of coherent states? With these questions in mind, we characterize unentangled pure states as extremal states when considered as linear functionals on the local Lie algebra. As a result, a relativized notion of purity emerges, showing that there is a close relationship between purity, coherence, and (non)entanglement. To a large extent, these concepts can be defined and studied in the even more general setting of convex cones of states. Based on the idea that entanglement is relative, we suggest considering these notions in the context of partially ordered families of Lie algebras or convex cones, such as those that arise naturally for multipartite systems. The study of entanglement includes notions of local operations and, for information-theoretic purposes, entanglement measures and ways of scaling systems to enable asymptotic developments. We propose ways in which these may be generalized to the Lie-algebraic setting and, to a lesser extent, to the convex-cones setting. One of our motivations for this program is to understand the role of entanglementlike concepts in condensed matter. We discuss how our work provides tools for analyzing the correlations involved in quantum phase transitions and other aspects of condensed-matter systems.
Average subentropy, coherence and entanglement of random mixed quantum states
NASA Astrophysics Data System (ADS)
Zhang, Lin; Singh, Uttam; Pati, Arun K.
2017-02-01
Compact expressions for the average subentropy and coherence are obtained for random mixed states that are generated via various probability measures. Surprisingly, our results show that the average subentropy of random mixed states approaches the maximum value of the subentropy which is attained for the maximally mixed state as we increase the dimension. In the special case of the random mixed states sampled from the induced measure via partial tracing of random bipartite pure states, we establish the typicality of the relative entropy of coherence for random mixed states invoking the concentration of measure phenomenon. Our results also indicate that mixed quantum states are less useful compared to pure quantum states in higher dimension when we extract quantum coherence as a resource. This is because of the fact that average coherence of random mixed states is bounded uniformly, however, the average coherence of random pure states increases with the increasing dimension. As an important application, we establish the typicality of relative entropy of entanglement and distillable entanglement for a specific class of random bipartite mixed states. In particular, most of the random states in this specific class have relative entropy of entanglement and distillable entanglement equal to some fixed number (to within an arbitrary small error), thereby hugely reducing the complexity of computation of these entanglement measures for this specific class of mixed states.
Squeezed states and path integrals
NASA Technical Reports Server (NTRS)
Daubechies, Ingrid; Klauder, John R.
1992-01-01
The continuous-time regularization scheme for defining phase-space path integrals is briefly reviewed as a method to define a quantization procedure that is completely covariant under all smooth canonical coordinate transformations. As an illustration of this method, a limited set of transformations is discussed that have an image in the set of the usual squeezed states. It is noteworthy that even this limited set of transformations offers new possibilities for stationary phase approximations to quantum mechanical propagators.
Duality in entanglement of macroscopic states of light
NASA Astrophysics Data System (ADS)
Lee, Su-Yong; Lee, Chang-Woo; Kurzyński, Paweł; Kaszlikowski, Dagomir; Kim, Jaewan
2016-08-01
We investigate duality in entanglement of a bipartite multiphoton system generated from a coherent state of light. The system can exhibit polarization entanglement if the two parts are distinguished by their parity, or parity entanglement if the parts are distinguished by polarization. It was shown in Phys. Rev. Lett. 110, 140404 (2013), 10.1103/PhysRevLett.110.140404 that this phenomenon can be exploited as a method to test indistinguishability of two particles and it was conjectured that one can also test indistinguishability of macroscopic systems. We propose a setup to test this conjecture. Contrary to the previous studies using two-particle interference effect as in the Hong-Ou- Mandel setup, our setup neither assumes that the tested state is composed of single particles nor requires that the total number of particles be fixed. Consequently, the notion of entanglement duality is shown to be compatible with a broader class of physical systems. Moreover, by observing duality in entanglement in the above system one can confirm that macroscopic systems exhibit quantum behavior. As a practical side, entanglement duality is a useful concept that enables adaptive conversion of entanglement of one degree of freedom (DOF) to that of another DOF according to varying quantum protocols.
Entanglement witnesses for graph states: General theory and examples
Jungnitsch, Bastian; Moroder, Tobias; Guehne, Otfried
2011-09-15
We present a general theory for the construction of witnesses that detect genuine multipartite entanglement in graph states. First, we present explicit witnesses for all graph states of up to six qubits which are better than all criteria so far. Therefore, lower fidelities are required in experiments that aim at the preparation of graph states. Building on these results, we develop analytical methods to construct two different types of entanglement witnesses for general graph states. For many classes of states, these operators exhibit white noise tolerances that converge to 1 when increasing the number of particles. We illustrate our approach for states such as the linear and the 2D cluster state. Finally, we study an entanglement monotone motivated by our approach for graph states.
Entangled coherent states versus entangled photon pairs for practical quantum-information processing
Park, Kimin; Jeong, Hyunseok
2010-12-15
We compare effects of decoherence and detection inefficiency on entangled coherent states (ECSs) and entangled photon pairs (EPPs), both of which are known to be particularly useful for quantum-information processing (QIP). When decoherence effects caused by photon losses are heavy, the ECSs outperform the EPPs as quantum channels for teleportation both in fidelities and in success probabilities. On the other hand, when inefficient detectors are used, the teleportation scheme using the ECSs suffers undetected errors that result in the degradation of fidelity, while this is not the case for the teleportation scheme using the EPPs. Our study reveals the merits and demerits of the two types of entangled states in realizing practical QIP under realistic conditions.
General monogamy relations of quantum entanglement for multiqubit W-class states
NASA Astrophysics Data System (ADS)
Zhu, Xue-Na; Fei, Shao-Ming
2017-02-01
Entanglement monogamy is a fundamental property of multipartite entangled states. We investigate the monogamy relations for multiqubit generalized W-class states. Analytical monogamy inequalities are obtained for the concurrence of assistance, the entanglement of formation, and the entanglement of assistance.
Minimum-error discrimination of entangled quantum states
Lu, Y.; Coish, N.; Kaltenbaek, R.; Hamel, D. R.; Resch, K. J.; Croke, S.
2010-10-15
Strategies to optimally discriminate between quantum states are critical in quantum technologies. We present an experimental demonstration of minimum-error discrimination between entangled states, encoded in the polarization of pairs of photons. Although the optimal measurement involves projection onto entangled states, we use a result of J. Walgate et al. [Phys. Rev. Lett. 85, 4972 (2000)] to design an optical implementation employing only local polarization measurements and feed-forward, which performs at the Helstrom bound. Our scheme can achieve perfect discrimination of orthogonal states and minimum-error discrimination of nonorthogonal states. Our experimental results show a definite advantage over schemes not using feed-forward.
Entanglement swapping of noisy states: A kind of superadditivity in nonclassicality
Sen, Aditi; Sen, Ujjwal; Brukner, Caslav; Buzek, Vladimir; Zukowski, Marek
2005-10-15
We address the question as to whether an entangled state that satisfies local realism will give a violation of the same after entanglement swapping in a suitable scenario. We consider such a possibility as a kind of superadditivity in nonclassicality. Importantly, it will indicate that checking for violation of local realism, in the state obtained after entanglement swapping, can be a method for detecting entanglement in the input state of the swapping procedure. We investigate various entanglement swapping schemes, which involve mixed initial states. The strength of violation of local realism by the state obtained after entanglement swapping is compared with the one for the input states. We obtain a kind of superadditivity of violation of local realism for Werner states, consequent upon entanglement swapping involving Greenberger-Horne-Zeilinger-state measurements. We also discuss whether entanglement swapping of specific states may be used in quantum repeaters with a substantially reduced need to perform the entanglement distillation step.
Manipulating Frequency-Bin Entangled States in Cold Atoms
Zavatta, A.; Artoni, M.; Viscor, D.; La Rocca, G.
2014-01-01
Optical manipulation of entanglement harnessing the frequency degree of freedom is important for encoding of quantum information. We here devise a phase-resonant excitation mechanism of an atomic interface where full control of a narrowband single-photon two-mode frequency entangled state can be efficiently achieved. We illustrate the working physical mechanism for an interface made of cold 87Rb atoms where entanglement is well preserved from degradation over a typical 100 μm length scale of the interface and with fractional delays of the order of unity. The scheme provides a basis for efficient multi-frequency and multi-photon entanglement, which is not easily accessible to polarization and spatial encoding. PMID:24487523
Entanglement equivalence of N-qubit symmetric states
Mathonet, P.; Krins, S.; Bastin, T.; Godefroid, M.; Solano, E.
2010-05-15
We study the interconversion of multipartite symmetric N-qubit states under stochastic local operations and classical communication (SLOCC). We demonstrate that if two symmetric states can be connected with a nonsymmetric invertible local operation (ILO), then they belong necessarily to the separable, W, or Greenberger-Horne-Zeilinger (GHZ) entanglement class, establishing a practical method of discriminating subsets of entanglement classes. Furthermore, we prove that there always exists a symmetric ILO connecting any pair of symmetric N-qubit states equivalent under SLOCC, simplifying the requirements for experimental implementations of local interconversion of those states.
Quantum teleportation of composite systems via mixed entangled states
Bandyopadhyay, Somshubhro; Sanders, Barry C.
2006-09-15
We analyze quantum teleportation for composite systems, specifically for concatenated teleporation (decomposing a large composite state into smaller states of dimension commensurate with the channel) and partial teleportation (teleporting one component of a larger quantum state). We obtain an exact expression for teleportation fidelity that depends solely on the dimension and singlet fraction for the entanglement channel and entanglement (measures by I concurrence) for the state; in fact quantum teleportation for composite systems provides an operational interpretation for I concurrence. In addition we obtain tight bounds on teleportation fidelity and prove that the average fidelity approaches the lower bound of teleportation fidelity in the high-dimension limit.
Entangled Coherent States Generation in two Superconducting LC Circuits
Chen Meiyu; Zhang Weimin
2008-11-07
We proposed a novel pure electronic (solid state) device consisting of two superconducting LC circuits coupled to a superconducting flux qubit. The entangled coherent states of the two LC modes is generated through the measurement of the flux qubit states. The interaction of the flux qubit and two LC circuits is controlled by the external microwave control lines. The geometrical structure of the LC circuits is adjustable and makes a strong coupling between them achievable. This entangled coherent state generator can be realized by using the conventional microelectronic fabrication techniques which increases the feasibility of the experiment.
Entanglement and Majorana edge states in the Kitaev model
NASA Astrophysics Data System (ADS)
Mandal, Saptarshi; Maiti, Moitri; Varma, Vipin Kerala
2016-07-01
We investigate the von Neumann entanglement entropy and Schmidt gap in the vortex-free ground state of the Kitaev model on the honeycomb lattice for square/rectangular and cylindrical subsystems. We find that, for both the subsystems, the free-fermionic contribution to the entanglement entropy SE exhibits signatures of the phase transitions between the gapless and gapped phases. However, within the gapless phase, we find that SE does not show an expected monotonic behavior as a function of the coupling Jz between the suitably defined one-dimensional chains for either geometry; moreover, the system generically reaches a point of minimum entanglement within the gapless phase before the entanglement saturates or increases again until the gapped phase is reached. This may be attributed to the onset of gapless modes in the bulk spectrum and the competition between the correlation functions along various bonds. In the gapped phase, on the other hand, SE always monotonically varies with Jz independent of the subregion size or shape. Finally, further confirming the Li-Haldane conjecture, we find that the Schmidt gap Δ defined from the entanglement spectrum also signals the topological transitions but only if there are corresponding zero-energy Majorana edge states that simultaneously appear or disappear across the transitions. We analytically corroborate some of our results on entanglement entropy, the Schmidt gap, and the bulk-edge correspondence using perturbation theory.
Entanglement universality of two-qubit X-states
Mendonça, Paulo E.M.F.; Marchiolli, Marcelo A.; Galetti, Diógenes
2014-12-15
We demonstrate that for every two-qubit state there is a X-counterpart, i.e., a corresponding two-qubit X-state of same spectrum and entanglement, as measured by concurrence, negativity or relative entropy of entanglement. By parametrizing the set of two-qubit X-states and a family of unitary transformations that preserve the sparse structure of a two-qubit X-state density matrix, we obtain the parametric form of a unitary transformation that converts arbitrary two-qubit states into their X-counterparts. Moreover, we provide a semi-analytic prescription on how to set the parameters of this unitary transformation in order to preserve concurrence or negativity. We also explicitly construct a set of X-state density matrices, parametrized by their purity and concurrence, whose elements are in one-to-one correspondence with the points of the concurrence versus purity (CP) diagram for generic two-qubit states. - Highlights: • Parametrization of separable, entangled and rank-specific two-qubit X-states. • Construction of a set of two-qubit X-states exhausting a two-qubit CP-diagram. • Parametrization of a disentangling unitary transformation for any two-qubit X-state. • Unitary transformation of any two-qubit state into a X-state of same entanglement.
NASA Astrophysics Data System (ADS)
A, Karimi; M, K. Tavassoly
2016-04-01
In this paper, after a brief review on the entangled squeezed states, we produce a new class of the continuous-variable-type entangled states, namely, deformed photon-added entangled squeezed states. These states are obtained via the iterated action of the f-deformed creation operator A = f (n)a † on the entangled squeezed states. In the continuation, by studying the criteria such as the degree of entanglement, quantum polarization as well as sub-Poissonian photon statistics, the two-mode correlation function, one-mode and two-mode squeezing, we investigate the nonclassical behaviors of the introduced states in detail by choosing a particular f-deformation function. It is revealed that the above-mentioned physical properties can be affected and so may be tuned by justifying the excitation number, after choosing a nonlinearity function. Finally, to generate the introduced states, we propose a theoretical scheme using the nonlinear Jaynes-Cummings model.
Geometric descriptions of entangled states by auxiliary varieties
Holweck, Frederic; Luque, Jean-Gabriel; Thibon, Jean-Yves
2012-10-15
The aim of the paper is to propose geometric descriptions of multipartite entangled states using algebraic geometry. In the context of this paper, geometric means each stratum of the Hilbert space, corresponding to an entangled state, is an open subset of an algebraic variety built by classical geometric constructions (tangent lines, secant lines) from the set of separable states. In this setting, we describe well-known classifications of multipartite entanglement such as 2 Multiplication-Sign 2 Multiplication-Sign (n+ 1), for n Greater-Than-Or-Slanted-Equal-To 1, quantum systems and a new description with the 2 Multiplication-Sign 3 Multiplication-Sign 3 quantum system. Our results complete the approach of Miyake and make stronger connections with recent work of algebraic geometers. Moreover, for the quantum systems detailed in this paper, we propose an algorithm, based on the classical theory of invariants, to decide to which subvariety of the Hilbert space a given state belongs.
Minkowski structure for purity and entanglement of Gaussian bipartite states
NASA Astrophysics Data System (ADS)
de Oliveira, Marcos C.; Nicacio, Fernando; Mizrahi, Salomon S.
2013-11-01
The relation between the symplectic and Lorentz groups is explored to investigate entanglement features in a two-mode bipartite Gaussian state. We verify that the correlation matrix of arbitrary Gaussian states can be associated with a hyperbolic space with a Minkowski metric, which is divided in two regions: separabilitylike and entanglementlike, in equivalence to timelike and spacelike in special relativity. This correspondence naturally allows the definition of two insightful invariant squared distance measures: one related to the purity and another related to amount of entanglement. The second distance allows us to define a measure for entanglement in terms of the invariant interval between the given state and its closest separable state, given in a natural manner without the requirement of a minimization procedure.
NASA Astrophysics Data System (ADS)
Wang, Zhen; Li, Heng-Mei; Yuan, Hong-Chun
2016-10-01
We theoretically introduce a kind of non-Gaussian entangled states, i.e., photon-subtracted two-mode squeezed coherent states (PSTMSCS), by successively subtracting photons from each mode of the two-mode squeezed coherent states. The normalization factor which is related to bivariate Hermite polynomials is obtained by virtue of the two-mode squeezing operator in entangled-states representation. The sub-Poissonian photon statistics, antibunching effects, and partial negative Wigner function, respectively, are observed numerically, which fully reflect the nonclassicality of the resultant states. Finally, employing the SV criteria and the EPR correlation, respectively, the entangled property of PSTMSCS is analyzed. It is shown that the photon subtraction operation can effectively enhance the inseparability between the two modes.
NASA Astrophysics Data System (ADS)
Ye, Tian-Yu
2016-09-01
Recently, Liu et al. proposed a two-party quantum private comparison (QPC) protocol using entanglement swapping of Bell entangled state (Commun. Theor. Phys. 57 (2012) 583). Subsequently Liu et al. pointed out that in Liu et al.'s protocol, the TP can extract the two users' secret inputs without being detected by launching the Bell-basis measurement attack, and suggested the corresponding improvement to mend this loophole (Commun. Theor. Phys. 62 (2014) 210). In this paper, we first point out the information leakage problem toward TP existing in both of the above two protocols, and then suggest the corresponding improvement by using the one-way hash function to encrypt the two users' secret inputs. We further put forward the three-party QPC protocol also based on entanglement swapping of Bell entangled state, and then validate its output correctness and its security in detail. Finally, we generalize the three-party QPC protocol into the multi-party case, which can accomplish arbitrary pair's comparison of equality among K users within one execution. Supported by the National Natural Science Foundation of China under Grant No. 61402407
Bipartite quantum channels using multipartite cluster-type entangled coherent states
Munhoz, P. P.; Semiao, F. L.; Roversi, J. A.; Vidiella-Barranco, A.
2010-04-15
We propose a particular encoding for bipartite entangled states derived from multipartite cluster-type entangled coherent states (CTECSs). We investigate the effects of amplitude damping on the entanglement content of this bipartite state, as well as its usefulness as a quantum channel for teleportation. We find interesting relationships among the amplitude of the coherent states constituting the CTECSs, the number of subsystems forming the logical qubits (redundancy), and the extent to which amplitude damping affects the entanglement of the channel. For instance, in the sense of sudden death of entanglement, given a fixed value of the initial coherent state amplitude, the entanglement life span is shortened if redundancy is increased.
Attaining subclassical metrology in lossy systems with entangled coherent states
NASA Astrophysics Data System (ADS)
Knott, P. A.; Munro, W. J.; Dunningham, J. A.
2014-05-01
Quantum mechanics allows entanglement enhanced measurements to be performed, but loss remains an obstacle in constructing realistic quantum metrology schemes. However, recent work has revealed that entangled coherent states (ECSs) have the potential to perform robust subclassical measurements [J. Joo et al., Phys. Rev. Lett. 107, 083601 (2011), 10.1103/PhysRevLett.107.083601]. Up to now no read-out scheme has been devised that exploits this robust nature of ECSs, but we present here an experimentally accessible method of achieving precision close to the theoretical bound, even with loss. We show substantial improvements over unentangled classical states and highly entangled NOON states for a wide range of loss values, elevating quantum metrology to a realizable technology in the near future.
Deterministic generation of a cluster state of entangled photons
NASA Astrophysics Data System (ADS)
Schwartz, I.; Cogan, D.; Schmidgall, E. R.; Don, Y.; Gantz, L.; Kenneth, O.; Lindner, N. H.; Gershoni, D.
2016-10-01
Photonic cluster states are a resource for quantum computation based solely on single-photon measurements. We use semiconductor quantum dots to deterministically generate long strings of polarization-entangled photons in a cluster state by periodic timed excitation of a precessing matter qubit. In each period, an entangled photon is added to the cluster state formed by the matter qubit and the previously emitted photons. In our prototype device, the qubit is the confined dark exciton, and it produces strings of hundreds of photons in which the entanglement persists over five sequential photons. The measured process map characterizing the device has a fidelity of 0.81 with that of an ideal device. Further feasible improvements of this device may reduce the resources needed for optical quantum information processing.
Preparing projected entangled pair states on a quantum computer.
Schwarz, Martin; Temme, Kristan; Verstraete, Frank
2012-03-16
We present a quantum algorithm to prepare injective projected entangled pair states (PEPS) on a quantum computer, a class of open tensor networks representing quantum states. The run time of our algorithm scales polynomially with the inverse of the minimum condition number of the PEPS projectors and, essentially, with the inverse of the spectral gap of the PEPS's parent Hamiltonian.
Quantum discord of bipartite entangled non-linear coherent states
NASA Astrophysics Data System (ADS)
Castro, E.; Zambrano, A.; Ladera, C. L.; Gómez, R.
2013-11-01
Quantum discord measures the fraction of the pair-wise mutual information that is locally inaccessible in a multipartite system. Nonzero quantum discord has interesting and significant applications because although non-zero entanglement guarantees the existence of quantum correlation in a bipartite quantum system, zero entanglement does not guarantee the absence of a quantum correlation. On the other hand, many quantum optics systems can be described as deformed quantum oscillators. In this work, we investigate the quantum discord of bipartite entangled nonlinear coherent states, in the context of the so-called f-deformed coherent states algebra. To calculate the quantum discord, we consider quasi- Werner mixed states bases on bipartite entangled f-deformed coherent states. Two explicit analytic expressions are derived for the quantum discord of two different nonlinear deformed coherent states. The first one considers deformed coherent states obtained as eigenstates of the annihilation deformed operator, and the second one is obtained by using a deformed displacement operator. We compare the quantum discord of those states, when the nonlinear deformation function is either associated with the SU(1,1) coherent states in the Gilmore-Perelomov or Barut-Girardello representations, respectively.
Maximally entangled mixed-state generation via local operations
Aiello, A.; Puentes, G.; Voigt, D.; Woerdman, J. P.
2007-06-15
We present a general theoretical method to generate maximally entangled mixed states of a pair of photons initially prepared in the singlet polarization state. This method requires only local operations upon a single photon of the pair and exploits spatial degrees of freedom to induce decoherence. We report also experimental confirmation of these theoretical results.
Entangled mixed-state generation by twin-photon scattering
Puentes, G.; Aiello, A.; Woerdman, J. P.; Voigt, D.
2007-03-15
We report experimental results on mixed-state generation by multiple scattering of polarization-entangled photon pairs created from parametric down-conversion. By using a large variety of scattering optical systems we have experimentally obtained entangled mixed states that lie upon and below the Werner curve in the linear entropy-tangle plane. We have also introduced a simple phenomenological model built on the analogy between classical polarization optics and quantum maps. Theoretical predictions from such a model are in full agreement with our experimental findings.
Maximally entangled mixed states for qubit-qutrit systems
NASA Astrophysics Data System (ADS)
Mendonça, Paulo E. M. F.; Marchiolli, Marcelo A.; Hedemann, Samuel R.
2017-02-01
We consider the problems of maximizing the entanglement negativity of X-form qubit-qutrit density matrices with (i) a fixed spectrum and (ii) a fixed purity. In the first case, the problem is solved in full generality whereas, in the latter, partial solutions are obtained by imposing extra spectral constraints such as rank deficiency and degeneracy, which enable a semidefinite programming treatment for the optimization problem at hand. Despite the technically motivated assumptions, we provide strong numerical evidence that threefold degenerate X states of purity P reach the highest entanglement negativity accessible to arbitrary qubit-qutrit density matrices of the same purity, hence characterizing a sparse family of likely qubit-qutrit maximally entangled mixed states.
Bulk entanglement spectrum reveals quantum criticality within a topological state.
Hsieh, Timothy H; Fu, Liang
2014-09-05
A quantum phase transition is usually achieved by tuning physical parameters in a Hamiltonian at zero temperature. Here, we show that the ground state of a topological phase itself encodes critical properties of its transition to a trivial phase. To extract this information, we introduce an extensive partition of the system into two subsystems both of which extend throughout the bulk in all directions. The resulting bulk entanglement spectrum has a low-lying part that resembles the excitation spectrum of a bulk Hamiltonian, which allows us to probe a topological phase transition from a single wave function by tuning either the geometry of the partition or the entanglement temperature. As an example, this remarkable correspondence between the topological phase transition and the entanglement criticality is rigorously established for integer quantum Hall states.
Bell-inequality tests with macroscopic entangled states of light
Stobinska, M.; Sekatski, P.; Gisin, N.; Buraczewski, A.; Leuchs, G.
2011-09-15
Quantum correlations may violate the Bell inequalities. Most experimental schemes confirming this prediction have been realized in all-optical Bell tests suffering from the detection loophole. Experiments which simultaneously close this loophole and the locality loophole are highly desirable and remain challenging. An approach to loophole-free Bell tests is based on amplification of the entangled photons (i.e., on macroscopic entanglement), for which an optical signal should be easy to detect. However, the macroscopic states are partially indistinguishable by classical detectors. An interesting idea to overcome these limitations is to replace the postselection by an appropriate preselection immediately after the amplification. This is in the spirit of state preprocessing revealing hidden nonlocality. Here, we examine one of the possible preselections, but the presented tools can be used for analysis of other schemes. Filtering methods making the macroscopic entanglement useful for Bell tests and quantum protocols are the subject of an intensive study in the field nowadays.
Teleportation via thermally entangled states of a two-qubit Heisenberg XX chain
Yeo Ye
2002-12-01
Recently, entanglement teleportation has been investigated by Lee and Kim [Phys. Rev. Lett. 84, 4236 (2000)]. In this paper we study entanglement teleportation via two separate thermally entangled states of a two-qubit Heisenberg XX chain. We established the condition under which the parameters of the model have to satisfy in order to teleport entanglement. The necessary minimum amount of thermal entanglement for some fixed strength of exchange coupling is a function of the magnetic field and the temperature.
Entanglement and nonclassicality for multimode radiation-field states
Ivan, J. Solomon; Chaturvedi, S.; Ercolessi, E.; Marmo, G.; Morandi, G.; Mukunda, N.; Simon, R.
2011-03-15
Nonclassicality in the sense of quantum optics is a prerequisite for entanglement in multimode radiation states. In this work we bring out the possibilities of passing from the former to the latter, via action of classicality preserving systems like beam splitters, in a transparent manner. For single-mode states, a complete description of nonclassicality is available via the classical theory of moments, as a set of necessary and sufficient conditions on the photon number distribution. We show that when the mode is coupled to an ancilla in any coherent state, and the system is then acted upon by a beam splitter, these conditions turn exactly into signatures of negativity under partial transpose (NPT) entanglement of the output state. Since the classical moment problem does not generalize to two or more modes, we turn in these cases to other familiar sufficient but not necessary conditions for nonclassicality, namely the Mandel parameter criterion and its extensions. We generalize the Mandel matrix from one-mode states to the two-mode situation, leading to a natural classification of states with varying levels of nonclassicality. For two-mode states we present a single test that can, if successful, simultaneously show nonclassicality as well as NPT entanglement. We also develop a test for NPT entanglement after beam-splitter action on a nonclassical state, tracing carefully the way in which it goes beyond the Mandel nonclassicality test. The result of three-mode beam-splitter action after coupling to an ancilla in the ground state is treated in the same spirit. The concept of genuine tripartite entanglement, and scalar measures of nonclassicality at the Mandel level for two-mode systems, are discussed. Numerous examples illustrating all these concepts are presented.
Entanglement in a solid-state spin ensemble.
Simmons, Stephanie; Brown, Richard M; Riemann, Helge; Abrosimov, Nikolai V; Becker, Peter; Pohl, Hans-Joachim; Thewalt, Mike L W; Itoh, Kohei M; Morton, John J L
2011-02-03
Entanglement is the quintessential quantum phenomenon. It is a necessary ingredient in most emerging quantum technologies, including quantum repeaters, quantum information processing and the strongest forms of quantum cryptography. Spin ensembles, such as those used in liquid-state nuclear magnetic resonance, have been important for the development of quantum control methods. However, these demonstrations contain no entanglement and ultimately constitute classical simulations of quantum algorithms. Here we report the on-demand generation of entanglement between an ensemble of electron and nuclear spins in isotopically engineered, phosphorus-doped silicon. We combined high-field (3.4 T), low-temperature (2.9 K) electron spin resonance with hyperpolarization of the (31)P nuclear spin to obtain an initial state of sufficient purity to create a non-classical, inseparable state. The state was verified using density matrix tomography based on geometric phase gates, and had a fidelity of 98% relative to the ideal state at this field and temperature. The entanglement operation was performed simultaneously, with high fidelity, on 10(10) spin pairs; this fulfils one of the essential requirements for a silicon-based quantum information processor.
Experimental perfect state transfer of an entangled photonic qubit
Chapman, Robert J.; Santandrea, Matteo; Huang, Zixin; Corrielli, Giacomo; Crespi, Andrea; Yung, Man-Hong; Osellame, Roberto; Peruzzo, Alberto
2016-01-01
The transfer of data is a fundamental task in information systems. Microprocessors contain dedicated data buses that transmit bits across different locations and implement sophisticated routing protocols. Transferring quantum information with high fidelity is a challenging task, due to the intrinsic fragility of quantum states. Here we report on the implementation of the perfect state transfer protocol applied to a photonic qubit entangled with another qubit at a different location. On a single device we perform three routing procedures on entangled states, preserving the encoded quantum state with an average fidelity of 97.1%, measuring in the coincidence basis. Our protocol extends the regular perfect state transfer by maintaining quantum information encoded in the polarization state of the photonic qubit. Our results demonstrate the key principle of perfect state transfer, opening a route towards data transfer for quantum computing systems. PMID:27088483
NASA Astrophysics Data System (ADS)
Cardoso B., W.; Almeida G. de, N.
2008-07-01
We propose a scheme to partially teleport an unknown entangled atomic state. A high-Q cavity, supporting one mode of a weak coherent state, is needed to accomplish this process. By partial teleportation we mean that teleportation will occur by changing one of the partners of the entangled state to be teleported. The entangled state to be teleported is composed by one pair of particles, we called this surprising characteristic of maintaining the entanglement, even when one of the particle of the entangled pair being teleported is changed, of divorce of entangled states.
Maximally Entangled States of a Two-Qubit System
NASA Astrophysics Data System (ADS)
Singh, Manu P.; Rajput, B. S.
2013-12-01
Entanglement has been explored as one of the key resources required for quantum computation, the functional dependence of the entanglement measures on spin correlation functions has been established, correspondence between evolution of maximally entangled states (MES) of two-qubit system and representation of SU(2) group has been worked out and the evolution of MES under a rotating magnetic field has been investigated. Necessary and sufficient conditions for the general two-qubit state to be maximally entangled state (MES) have been obtained and a new set of MES constituting a very powerful and reliable eigen basis (different from magic bases) of two-qubit systems has been constructed. In terms of the MES constituting this basis, Bell’s States have been generated and all the qubits of two-qubit system have been obtained. It has shown that a MES corresponds to a point in the SO(3) sphere and an evolution of MES corresponds to a trajectory connecting two points on this sphere. Analysing the evolution of MES under a rotating magnetic field, it has been demonstrated that a rotating magnetic field is equivalent to a three dimensional rotation in real space leading to the evolution of a MES.
Physical realization of quantum teleportation for a nonmaximal entangled state
Tanaka, Yoshiharu; Asano, Masanari; Ohya, Masanori
2010-08-15
Recently, Kossakowski and Ohya (K-O) proposed a new teleportation scheme which enables perfect teleportation even for a nonmaximal entangled state [A. Kossakowski and M. Ohya, Infinite Dimensional Analysis Quantum Probability and Related Topics 10, 411 (2007)]. To discuss a physical realization of the K-O scheme, we propose a model based on quantum optics. In our model, we take a superposition of Schroedinger's cat states as an input state being sent from Alice to Bob, and their entangled state is generated by a photon number state through a beam splitter. When the average photon number for our input states is equal to half the number of photons into the beam splitter, our model has high fidelity.
Physical realization of quantum teleportation for a nonmaximal entangled state
NASA Astrophysics Data System (ADS)
Tanaka, Yoshiharu; Asano, Masanari; Ohya, Masanori
2010-08-01
Recently, Kossakowski and Ohya (K-O) proposed a new teleportation scheme which enables perfect teleportation even for a nonmaximal entangled state [A. Kossakowski and M. Ohya, Infinite Dimensional Analysis Quantum Probability and Related Topics0219-025710.1142/S021902570700283X 10, 411 (2007)]. To discuss a physical realization of the K-O scheme, we propose a model based on quantum optics. In our model, we take a superposition of Schrödinger’s cat states as an input state being sent from Alice to Bob, and their entangled state is generated by a photon number state through a beam splitter. When the average photon number for our input states is equal to half the number of photons into the beam splitter, our model has high fidelity.
Preparation of Entangled and Antiferromagnetic States by Dissipative Rydberg Pumping
NASA Astrophysics Data System (ADS)
Carr, A. W.; Saffman, M.
2013-07-01
We propose and analyze an approach for preparation of high fidelity entanglement and antiferromagnetic states using Rydberg mediated interactions with dissipation. Using asymmetric Rydberg interactions the two-atom Bell singlet is a dark state of the Rydberg pumping process. Master equation simulations demonstrate Bell singlet preparation fidelity F=0.998. Antiferromagnetic states are generated on a four-spin plaquette in agreement with results found from diagonalization of the transverse field Ising Hamiltonian.
Bandyopadhyay, Somshubhro
2010-02-15
It is shown that while entanglement ensures difficulty in discriminating a set of mutually orthogonal states perfectly by local operations and classical communication (LOCC), entanglement content does not. In particular, for a class of entangled multiqubit states, the maximum number of perfectly LOCC distinguishable orthogonal states is shown to be independent of the average entanglement of the states, and the spatial configuration with respect to which LOCC operations may be carried out. It is also pointed out that for this class, the makeup of an ensemble, that is whether it consists only of entangled states or not, determines the maximum number of perfectly distinguishable states.
A note on entanglement entropy, coherent states and gravity
NASA Astrophysics Data System (ADS)
Varadarajan, Madhavan
2016-03-01
The entanglement entropy of a free quantum field in a coherent state is independent of its stress energy content. We use this result to highlight the fact that while the Einstein equations for first order variations about a locally maximally symmetric vacuum state of geometry and quantum fields seem to follow from Jacobson's principle of maximal vacuum entanglement entropy, their possible derivation from this principle for the physically relevant case of finite but small variations remains an open issue. We also apply this result to the context of Bianchi's identification, independent of unknown Planck scale physics, of the first order variation of Bekenstein-Hawking area with that of vacuum entanglement entropy. We argue that under certain technical assumptions this identification seems not to be extendible to the context of finite but small variations to coherent states. Our particular method of estimation of entanglement entropy variation reveals the existence of certain contributions over and above those of References Jacobson (arXiv:1505.04753, 2015), Bianchi (arXiv:1211.0522 [gr-qc], 2012). We discuss the sense in which these contributions may be subleading to those in References Jacobson (arXiv:1505.04753, 2015), Bianchi (arXiv:1211.0522 [gr-qc], 2012).
Spin-Orbital Entangled States in Transition Metal Oxides
NASA Astrophysics Data System (ADS)
Oleś, Andrzej M.
The phenomenon of spin-orbital entanglement which occurs in superexchange models for transition metal oxides is introduced and explained. We present its consequences in the RVO_3 Mott insulators, with R=La,Pr,\\cdots ,Yb,Lu, and show that entanglement occurs here in excited states of the spin-orbital d^2 model and determines: (i) the temperature dependence of low-energy optical spectral weight, (ii) the phase diagram of the RVO_3 perovskites, and (iii) the dimerization observed in the magnon excitations in YVO_3. Entangled ground states occur in two other model systems: (i) the bilayer d^9 (Kugel-Khomskii) model, and (ii) the d^1 model on the triangular frustrated lattice. In such cases even the predictions concerning the magnetic exchange constants based on the mean field decoupling of spin and orbital operators are incorrect. On the example of a single hole doped to a Mott insulator with coexisting antiferromagnetic and alternating t_{2g} orbital order we show that transport is hindered by spin-orbital excitations. It is suggested that spin-orbital entanglement in Mott insulators might be controlled by doping, leading to orbital disordered states with possible new opportunities for thermoelectric applications.
Speedup of quantum evolution of multiqubit entanglement states
Zhang, Ying-Jie; Han, Wei; Xia, Yun-Jie; Tian, Jian-Xiang; Fan, Heng
2016-01-01
As is well known, quantum speed limit time (QSLT) can be used to characterize the maximal speed of evolution of quantum systems. We mainly investigate the QSLT of generalized N-qubit GHZ-type states and W-type states in the amplitude-damping channels. It is shown that, in the case N qubits coupled with independent noise channels, the QSLT of the entangled GHZ-type state is closely related to the number of qubits in the small-scale system. And the larger entanglement of GHZ-type states can lead to the shorter QSLT of the evolution process. However, the QSLT of the W-type states are independent of the number of qubits and the initial entanglement. Furthermore, by considering only M qubits among the N-qubit system respectively interacting with their own noise channels, QSLTs for these two types states are shorter than in the case N qubits coupled with independent noise channels. We therefore reach the interesting result that the potential speedup of quantum evolution of a given N-qubit GHZ-type state or W-type state can be realized in the case the number of the applied noise channels satisfying M < N. PMID:27283757
Quantum correlations in Gaussian states via Gaussian channels: steering, entanglement, and discord
NASA Astrophysics Data System (ADS)
Wang, Zhong-Xiao; Wang, Shuhao; Li, Qiting; Wang, Tie-Jun; Wang, Chuan
2016-06-01
Here we study the quantum steering, quantum entanglement, and quantum discord for Gaussian Einstein-Podolsky-Rosen states via Gaussian channels. And the sudden death phenomena for Gaussian steering and Gaussian entanglement are theoretically observed. We find that some Gaussian states have only one-way steering, which confirms the asymmetry of quantum steering. Also we investigate that the entangled Gaussian states without Gaussian steering and correlated Gaussian states own no Gaussian entanglement. Meanwhile, our results support the assumption that quantum entanglement is intermediate between quantum discord and quantum steering. Furthermore, we give experimental recipes for preparing quantum states with desired types of quantum correlations.
Quantum entanglement of locally excited states in Maxwell theory
NASA Astrophysics Data System (ADS)
Nozaki, Masahiro; Watamura, Naoki
2016-12-01
In 4 dimensional Maxwell gauge theory, we study the changes of (Rényi) entanglement entropy which are defined by subtracting the entropy for the ground state from the one for the locally excited states, generated by acting with gauge invariant local operators on the state. The changes for the operators which we consider in this paper reflect the electric-magnetic duality. The late-time value of changes can be interpreted in terms of electromagnetic quasi-particles. When the operator constructed of both electric and magnetic fields acts on the ground state, it shows that the operator acts on the late-time structure of quantum entanglement differently from free scalar fields.
NASA Astrophysics Data System (ADS)
Thapliyal, Ashish Vachaspati
Entanglement is an essential element of quantum mechanics. The aim of this work is to explore various properties of entanglement from the viewpoints of both physics and information science, thus providing a unique picture of entanglement from an interdisciplinary point of view. The focus of this work is on quantifying entanglement as a resource. We start with bipartite states, proposing a new measure of bipartite entanglement called entanglement of assistance, showing that bound entangled states of rank two cannot exist, exploring the number of members required in the ensemble achieving the entanglement of formation and the possibility of bound entangled states that are negative under partial transposition (NPT bound entangled states). For multipartite states we introduce the notions of reducibilities and equivalences under entanglement non-increasing operations and we study the relations between various reducibilities and equivalences such as exact and asymptotic LOCC, asymptotic LOCCq, cLOCC, LOc, etc. We use this new language to attempt to quantify entanglement for multiple parties. We introduce the idea of entanglement span and minimal entanglement generating set and entanglement coefficients associated with it which are the entanglement measures, thus proposing a multicomponent measure of entanglement for three or more parties. We show that the class of Schmidt decomposable states have only GHZM or Cat-like entanglement. Further we introduce the class of multiseparable states for quantification of their entanglement and prove that they are equivalent to the Schmidt decomposable states, and thus have only Cat-like entanglement. We further explore the conditions under which LOCO equivalences are possible for multipartite isentropic states. We define Cat-distillability, EPRB-distillability and distillability for multipartite mixed states and show that distillability implies EPRB-distillability. Further we show that all non-factorizable pure states are Cat
Vortex Images, q-Calculus and Entangled Coherent States
NASA Astrophysics Data System (ADS)
Pashaev, Oktay K.
2012-02-01
The two circles theorem for hydrodynamic flow in annular domain bounded by two concentric circles is derived. Complex potential and velocity of the flow are represented as q-periodic functions and rewritten in terms of the Jackson q-integral. This theorem generalizes the Milne-Thomson one circle theorem and reduces to the last on in the limit q → ∞. By this theorem problem of vortex images in annular domain between coaxial cylinders is solved in terms of q-elementary functions. An infinite set of images, as symmetric points under two circles, is determined completely by poles of the q-logarithmic function, where dimensionless parameter q = r22/r21 is given by square ratio of the cylinder radii. Motivated by Möbius transformation for symmetrical points under generalized circle in complex plain, the system of symmetric spin coherent states corresponding to antipodal qubit states is introduced. By these states we construct the maximally entangled orthonormal two qubit spin coherent state basis, in the limiting case reducible to the Bell basis. Average energy of XYZ model in these states, describing finite localized structure with characteristic extremum points, appears as an energy surface in maximally entangled two qubit space. Generalizations to three and higher multiple qubits are found. We show that our entangled N qubit states are determined by set of complex Fibonacci and Lucas polynomials and corresponding Binet-Fibonacci q-calculus.
Nonclassicality tests and entanglement witnesses for macroscopic mechanical superposition states
NASA Astrophysics Data System (ADS)
Gittsovich, Oleg; Moroder, Tobias; Asadian, Ali; Gühne, Otfried; Rabl, Peter
2015-02-01
We describe a set of measurement protocols for performing nonclassicality tests and the verification of entangled superposition states of macroscopic continuous variable systems, such as nanomechanical resonators. Following earlier works, we first consider a setup where a two-level system is used to indirectly probe the motion of the mechanical system via Ramsey measurements and discuss the application of this method for detecting nonclassical mechanical states. We then show that the generalization of this technique to multiple resonator modes allows the conditioned preparation and the detection of entangled mechanical superposition states. The proposed measurement protocols can be implemented in various qubit-resonator systems that are currently under experimental investigation and find applications in future tests of quantum mechanics at a macroscopic scale.
Asymptotic entanglement transformation between W and GHZ states
Vrana, Péter; Christandl, Matthias
2015-02-15
We investigate entanglement transformations with stochastic local operations and classical communication in an asymptotic setting using the concepts of degeneration and border rank of tensors from algebraic complexity theory. Results well-known in that field imply that GHZ states can be transformed into W states at rate 1 for any number of parties. As a generalization, we find that the asymptotic conversion rate from GHZ states to Dicke states is bounded as the number of subsystems increases and the number of excitations is fixed. By generalizing constructions of Coppersmith and Winograd and by using monotones introduced by Strassen, we also compute the conversion rate from W to GHZ states.
NASA Astrophysics Data System (ADS)
Zhang, Zhedong; Wang, Jin
2015-04-01
We develop a population and flux landscape theory for general non-equilibrium quantum systems. We illustrate our theory by modelling the quantum transport of donor-acceptor energy transfer. We find two driving forces for the non-equilibrium quantum dynamics. The symmetric part of the driving force corresponds to the population landscape contribution which mainly governs the equilibrium part of dynamics while the anti-symmetric part of the driving force generates the non-equilibrium curl quantum flux which leads to the detailed-balance-breaking and time-irreversibility. The multi-loop structure of the flux emerges forms the flux-landscape. We study the trend of changes in population and flux-landscape with respect to the voltage (temperature difference induced by environments) and electronic coupling. Improving the voltage and electronic coupling in general facilitates the quantum transport by reducing the population landscape barriers between major states and increasing the mean value of the flux. A limit-cycle mode emerges when the underlying flux-landscape becomes funnelled with a significant gap between the largest flux loop and the rest of them. On the kinetic level, we find that multiple kinetic paths between quantum states emerge and illustrate the interference effects. The degree of interference is determined by the landscape and flux. Furthermore, we quantify kinetic rate which strongly correlates with the population landscape and flux. For quantum transport, we demonstrate that as the coherence or the quantum entanglement is enhanced, the flux and energy transfer efficiency are increased. Finally it is surprising that the non-equilibriumness quantified by voltage has a non-trivial contribution on strengthening the entanglement, which is attributed to the non-local feature of the quantum curl flux.
Cornering Gapless Quantum States via Their Torus Entanglement
NASA Astrophysics Data System (ADS)
Witczak-Krempa, William; Hayward Sierens, Lauren E.; Melko, Roger G.
2017-02-01
The entanglement entropy (EE) has emerged as an important window into the structure of complex quantum states of matter. We analyze the universal part of the EE for gapless systems on tori in 2D and 3D, denoted by χ . Focusing on scale-invariant systems, we derive general nonperturbative properties for the shape dependence of χ and reveal surprising relations to the EE associated with corners in the entangling surface. We obtain closed-form expressions for χ in 2D and 3D within a model that arises in the study of conformal field theories (CFTs), and we use them to obtain Ansätze without fitting parameters for the 2D and 3D free boson CFTs. Our numerical lattice calculations show that the Ansätze are highly accurate. Finally, we discuss how the torus EE can act as a fingerprint of exotic states such as gapless quantum spin liquids, e.g., Kitaev's honeycomb model.
NASA Astrophysics Data System (ADS)
Bartkiewicz, Karol; Lemr, Karel; Černoch, Antonín; Miranowicz, Adam
2017-03-01
We propose and experimentally implement an efficient procedure based on entanglement swapping to determine the Bell nonlocality measure of Horodecki et al. [Phys. Lett. A 200, 340 (1995), 10.1016/0375-9601(95)00214-N] and the fully entangled fraction of Bennett et al. [Phys. Rev. A 54, 3824 (1996), 10.1103/PhysRevA.54.3824] of an arbitrary two-qubit polarization-encoded state. The nonlocality measure corresponds to the amount of the violation of the Clauser-Horne-Shimony-Holt (CHSH) optimized over all measurement settings. By using simultaneously two copies of a given state, we measure directly only six parameters. This is an experimental determination of these quantities without quantum state tomography or continuous monitoring of all measurement bases in the usual CHSH inequality tests. We analyze how well the measured degrees of Bell nonlocality and other entanglement witnesses (including the fully entangled fraction and a nonlinear entropic witness) of an arbitrary two-qubit state can estimate its entanglement. In particular, we measure these witnesses and estimate the negativity of various two-qubit Werner states. Our approach could especially be useful for quantum communication protocols based on entanglement swapping.
Multipartite Continuous-Variable Entanglement Distribution with Separable Gaussian States
NASA Astrophysics Data System (ADS)
Zeng, Chuan; Zhang, Jian-Zhong; Xie, Shu-Cui
2017-03-01
In this paper, a quantum proxy blind signature scheme based on controlled quantum teleportation is proposed. This scheme uses a genuine five-qubit entangled state as quantum channel and adopts the classical Vernam algorithm to blind message. We use the physical characteristics of quantum mechanics to implement delegation, signature and verification. Security analysis shows that our scheme is valid and satisfy the properties of a proxy blind signature, such as blindness, verifiability, unforgeability, undeniability.
Local cloning of arbitrarily entangled multipartite states
Kay, Alastair; Ericsson, Marie
2006-01-15
We examine the perfect cloning of nonlocal, orthogonal states using only local operations and classical communication. We provide a complete characterisation of the states that can be cloned under these restrictions, and their relation to distinguishability. We also consider the case of catalytic cloning, which we show provides no enhancement to the set of clonable states.
Gaussian measures of entanglement versus negativities: Ordering of two-mode Gaussian states
Adesso, Gerardo; Illuminati, Fabrizio
2005-09-15
We study the entanglement of general (pure or mixed) two-mode Gaussian states of continuous-variable systems by comparing the two available classes of computable measures of entanglement: entropy-inspired Gaussian convex-roof measures and positive partial transposition-inspired measures (negativity and logarithmic negativity). We first review the formalism of Gaussian measures of entanglement, adopting the framework introduced in M. M. Wolf et al., Phys. Rev. A 69, 052320 (2004), where the Gaussian entanglement of formation was defined. We compute explicitly Gaussian measures of entanglement for two important families of nonsymmetric two-mode Gaussian state: namely, the states of extremal (maximal and minimal) negativities at fixed global and local purities, introduced in G. Adesso et al., Phys. Rev. Lett. 92, 087901 (2004). This analysis allows us to compare the different orderings induced on the set of entangled two-mode Gaussian states by the negativities and by the Gaussian measures of entanglement. We find that in a certain range of values of the global and local purities (characterizing the covariance matrix of the corresponding extremal states), states of minimum negativity can have more Gaussian entanglement of formation than states of maximum negativity. Consequently, Gaussian measures and negativities are definitely inequivalent measures of entanglement on nonsymmetric two-mode Gaussian states, even when restricted to a class of extremal states. On the other hand, the two families of entanglement measures are completely equivalent on symmetric states, for which the Gaussian entanglement of formation coincides with the true entanglement of formation. Finally, we show that the inequivalence between the two families of continuous-variable entanglement measures is somehow limited. Namely, we rigorously prove that, at fixed negativities, the Gaussian measures of entanglement are bounded from below. Moreover, we provide some strong evidence suggesting that they
Entanglement entropy from one-point functions in holographic states
NASA Astrophysics Data System (ADS)
Beach, Matthew J. S.; Lee, Jaehoon; Rabideau, Charles; Van Raamsdonk, Mark
2016-06-01
For holographic CFT states near the vacuum, entanglement entropies for spatial subsystems can be expressed perturbatively as an expansion in the one-point functions of local operators dual to light bulk fields. Using the connection between quantum Fisher information for CFT states and canonical energy for the dual spacetimes, we describe a general formula for this expansion up to second-order in the one-point functions, for an arbitrary ball-shaped region, extending the first-order result given by the entanglement first law. For two-dimensional CFTs, we use this to derive a completely explicit formula for the second-order contribution to the entanglement entropy from the stress tensor. We show that this stress tensor formula can be reproduced by a direct CFT calculation for states related to the vacuum by a local conformal transformation. This result can also be reproduced via the perturbative solution to a non-linear scalar wave equation on an auxiliary de Sitter spacetime, extending the first-order result in arXiv:1509.00113.
Quantum nonlocality of four-qubit entangled states
Wu, Chunfeng; Yeo, Ye; Oh, C. H.; Kwek, L. C.
2007-03-15
We derive a Bell inequality for testing violation of local realism. Quantum nonlocality of several four-qubit states is investigated. These include the Greenberger-Zeilinger-Horne (GHZ) state, W state, linear cluster state, and the state |{chi}> that has recently been proposed in [Phys. Rev. Lett. 96, 060502 (2006)]. The Bell inequality is optimally violated by |{chi}> but not violated by the GHZ state. The linear cluster state also violates the Bell inequality though not optimally. The state |{chi}> can thus be discriminated from the linear cluster state by using the inequality. Different aspects of four-partite entanglement are also studied by considering the usefulness of a family of four-qubit mixed states as resources for two-qubit teleportation. Our results generalize those in [Phys. Rev. Lett. 72, 797 (1994)].
Effects of Number Scaling on Entangled States in Quantum Mechanics
Benioff, Paul
2016-05-19
A summary of number structure scaling is followed by a description of the effects of number scaling in nonrelativistic quantum mechanics. The description extends earlier work to include the effects on the states of two or more interacting particles. Emphasis is placed on the effects on entangled states. The resulting scaling field is generalized to describe the effects on these states. It is also seen that one can use fiber bundles with fibers associated with single locations of the underlying space to describe the effects of scaling on arbitrary numbers of particles.
Conservation relation of nonclassicality and entanglement for Gaussian states in a beam splitter
NASA Astrophysics Data System (ADS)
Ge, Wenchao; Tasgin, Mehmet Emre; Zubairy, M. Suhail
2015-11-01
We study the relation between single-mode nonclassicality and two-mode entanglement in a beam splitter. We show that single-mode nonclassicality (the entanglement potential) of incident light cannot be transformed into two-mode entanglement completely after a single beam splitter. Some of the entanglement potential remains as single-mode nonclassicality in the two entangled output modes. Two-mode entanglement generated in the process can be equivalently quantified as an increase in the minimum uncertainty widths (or decrease in the squeezing) of the output states compared to the input states. We use the nonclassical depth and logarithmic negativity as single-mode nonclassicality and entanglement measures, respectively. We realize that a conservation relation between the two quantities can be adopted for Gaussian states, if one works in terms of uncertainty width. This conservation relation is extended to many sets of beam splitters.
Experimental demonstration of a fully inseparable quantum state with nonlocalizable entanglement
Mičuda, M.; Koutný, D.; Miková, M.; Straka, I.; Ježek, M.; Mišta, L.
2017-01-01
Localizability of entanglement in fully inseparable states is a key ingredient of assisted quantum information protocols as well as measurement-based models of quantum computing. We investigate the existence of fully inseparable states with nonlocalizable entanglement, that is, with entanglement which cannot be localized between any pair of subsystems by any measurement on the remaining part of the system. It is shown, that the nonlocalizable entanglement occurs already in suitable mixtures of a three-qubit GHZ state and white noise. Further, we generalize this set of states to a two-parametric family of fully inseparable three-qubit states with nonlocalizable entanglement. Finally, we demonstrate experimentally the existence of nonlocalizable entanglement by preparing and characterizing one state from the family using correlated single photons and linear optical circuit. PMID:28344336
Experimental demonstration of a fully inseparable quantum state with nonlocalizable entanglement.
Mičuda, M; Koutný, D; Miková, M; Straka, I; Ježek, M; Mišta, L
2017-03-27
Localizability of entanglement in fully inseparable states is a key ingredient of assisted quantum information protocols as well as measurement-based models of quantum computing. We investigate the existence of fully inseparable states with nonlocalizable entanglement, that is, with entanglement which cannot be localized between any pair of subsystems by any measurement on the remaining part of the system. It is shown, that the nonlocalizable entanglement occurs already in suitable mixtures of a three-qubit GHZ state and white noise. Further, we generalize this set of states to a two-parametric family of fully inseparable three-qubit states with nonlocalizable entanglement. Finally, we demonstrate experimentally the existence of nonlocalizable entanglement by preparing and characterizing one state from the family using correlated single photons and linear optical circuit.
Entanglement as a resource for local state discrimination in multipartite systems
NASA Astrophysics Data System (ADS)
Bandyopadhyay, Somshubhro; Halder, Saronath; Nathanson, Michael
2016-08-01
We explore the question of using an entangled state as a universal resource for implementing quantum measurements by local operations and classical communication (LOCC). We show that for most systems consisting of three or more subsystems, there is no entangled state from the same space that can enable all measurements by LOCC. This is in direct contrast to the bipartite case, where a maximally entangled state is a universal resource. Our results are obtained showing an equivalence between the problem of local state transformation and that of entanglement-assisted local unambiguous state discrimination.
Guehne, Otfried; Jungnitsch, Bastian; Moroder, Tobias; Weinstein, Yaakov S.
2011-11-15
The characterization of genuine multiparticle entanglement is important for entanglement theory as well as experimental studies related to quantum-information theory. Here, we completely characterize genuine multiparticle entanglement for four-qubit states diagonal in the cluster-state basis. In addition, we give a complete characterization of multiparticle entanglement for all five-qubit graph states mixed with white noise, for states diagonal in the basis corresponding to the five-qubit Y-shaped graph, and for a family of graph states with an arbitrary number of qubits.
Faithful test of nonlocal realism with entangled coherent states
Lee, Chang-Woo; Jeong, Hyunseok; Paternostro, Mauro
2011-02-15
We investigate the violation of Leggett's inequality for nonlocal realism using entangled coherent states and various types of local measurements. We prove mathematically the relation between the violation of the Clauser-Horne-Shimony-Holt form of Bell's inequality and Leggett's one when tested by the same resources. For Leggett inequalities, we generalize the nonlocal realistic bound to systems in Hilbert spaces larger than bidimensional ones and introduce an optimization technique that allows one to achieve larger degrees of violation by adjusting the local measurement settings. Our work describes the steps that should be performed to produce a self-consistent generalization of Leggett's original arguments to continuous-variable states.
Deterministic creation of stationary entangled states by dissipation
Alharbi, A. F.; Ficek, Z.
2010-11-15
We propose a practical physical system for creation of stationary entanglement by dissipation without employing environmental engineering techniques. The system proposed is composed of two perfectly distinguishable atoms, through their significantly different transition frequencies, with only one atom addressed by an external laser field. We show that the arrangement would easily be realized in practice by trapping the atoms at a distance equal to the quarter-wavelength of a standing-wave laser field and locating one of the atoms at a node and the other at the successive antinode of the wave. The undesirable dipole-dipole interaction between the atoms, which could be large at this small distance, is adjusted to zero by a specific initial preparation of the atoms or by a specific polarization of the atomic dipole moments. Following this arrangement, we show that the dissipative relaxation can create a stationary entanglement on demand by tuning the Rabi frequency of the laser field to the difference between the atomic transition frequencies. The laser field dresses the atom and we identify that the entangled state occurs when the frequency of one of the Rabi sidebands of the driven atom tunes to the frequency of the undriven atom. It is also found that this system behaves as a cascade open system where the fluorescence from the dressed atom drives the other atom with no feedback.
NASA Astrophysics Data System (ADS)
Barasiński, Artur; Nowotarski, Mateusz
2016-12-01
We analyze the entanglement properties for the not-completely-permutation-symmetric states of quantum systems composed of two subsystems with an equal but arbitrary finite local Hilbert space dimension. We investigate both pure and mixed states with such a symmetry obtained by relaxing the symmetry requirement of the axisymmetric states. For such states we discuss the entanglement classification with respect to stochastic local operations and classical communication and establish the entanglement quantitatively by means of concurrence and negativity. In particular, we determine the separability criterion in the frame of various methods, including the k -positive map witness, optimal Schmidt-number witnesses, and entanglement measures.
Nonmaximally entangled states can be better for multiple linear optical teleportation.
Modławska, Joanna; Grudka, Andrzej
2008-03-21
We investigate multiple linear optical teleportation in the Knill-Laflamme-Milburn scheme with both maximally and nonmaximally entangled states. We show that if the qubit is teleported several times via a nonmaximally entangled state, then the errors introduced in the previous teleportations can be corrected by the errors introduced in the following teleportations. This effect is so strong that it leads to another interesting phenomenon: i.e., the total probability of successful multiple linear optical teleportation is higher for nonmaximally entangled states than maximally entangled states.
Experimental generation of complex noisy photonic entanglement
NASA Astrophysics Data System (ADS)
Dobek, K.; Karpiński, M.; Demkowicz-Dobrzański, R.; Banaszek, K.; Horodecki, P.
2013-02-01
We present an experimental scheme based on spontaneous parametric down-conversion to produce multiple-photon pairs in maximally entangled polarization states using an arrangement of two type-I nonlinear crystals. By introducing correlated polarization noise in the paths of the generated photons we prepare mixed-entangled states whose properties illustrate fundamental results obtained recently in quantum information theory, in particular those concerning bound entanglement and privacy.
Experimental generation of tripartite polarization entangled states of bright optical beams
NASA Astrophysics Data System (ADS)
Wu, Liang; Yan, Zhihui; Liu, Yanhong; Deng, Ruijie; Jia, Xiaojun; Xie, Changde; Peng, Kunchi
2016-04-01
The multipartite polarization entangled states of bright optical beams directly associating with the spin states of atomic ensembles are one of the essential resources in the future quantum information networks, which can be conveniently utilized to transfer and convert quantum states across a network composed of many atomic nodes. In this letter, we present the experimental demonstration of tripartite polarization entanglement described by Stokes operators of optical field. The tripartite entangled states of light at the frequency resonant with D1 line of Rubidium atoms are transformed into the continuous variable polarization entanglement among three bright optical beams via an optical beam splitter network. The obtained entanglement is confirmed by the extended criterion for polarization entanglement of multipartite quantized optical modes.
Entanglement and extreme spin squeezing of unpolarized states
NASA Astrophysics Data System (ADS)
Vitagliano, Giuseppe; Apellaniz, Iagoba; Kleinmann, Matthias; Lücke, Bernd; Klempt, Carsten; Tóth, Géza
2017-01-01
We present criteria to detect the depth of entanglement in macroscopic ensembles of spin-j particles using the variance and second moments of the collective spin components. The class of states detected goes beyond traditional spin-squeezed states by including Dicke states and other unpolarized states. The criteria derived are easy to evaluate numerically even for systems of very many particles and outperform past approaches, especially in practical situations where noise is present. We also derive analytic lower bounds based on the linearization of our criteria, which make it possible to define spin-squeezing parameters for Dicke states. In addition, we obtain spin squeezing parameters also from the condition derived in (Sørensen and Mølmer 2001 Phys. Rev. Lett. 86 4431). We also extend our results to systems with fluctuating number of particles.
Quantum memory for entangled continuous-variable states
NASA Astrophysics Data System (ADS)
Jensen, K.; Wasilewski, W.; Krauter, H.; Fernholz, T.; Nielsen, B. M.; Owari, M.; Plenio, M. B.; Serafini, A.; Wolf, M. M.; Polzik, E. S.
2011-01-01
A quantum memory for light is a key element for the realization of future quantum information networks. Requirements for a good quantum memory are versatility (allowing a wide range of inputs) and preservation of quantum information in a way unattainable with any classical memory device. Here we demonstrate such a quantum memory for continuous-variable entangled states, which play a fundamental role in quantum information processing. We store an extensive alphabet of two-mode 6.0dB squeezed states obtained by varying the orientation of squeezing and the displacement of the states. The two components of the entangled state are stored in two room-temperature cells separated by 0.5m, one for each mode, with a memory time of 1ms. The true quantum character of the memory is rigorously proved by showing that the experimental memory fidelity 0.52+/-0.02 significantly exceeds the benchmark of 0.45 for the best possible classical memory for a range of displacements.
NASA Astrophysics Data System (ADS)
Kröger, Martin
2005-06-01
We present an algorithm which returns a shortest path and related number of entanglements for a given configuration of a polymeric system in 2 or 3 dimensions. Rubinstein and Helfand, and later Everaers et al. introduced a concept to extract primitive paths for dense polymeric melts made of linear chains (a multiple disconnected multibead 'path'), where each primitive path is defined as a path connecting the (space-fixed) ends of a polymer under the constraint of non-interpenetration (excluded volume) between primitive paths of different chains, such that the multiple disconnected path fulfills a minimization criterion. The present algorithm uses geometrical operations and provides a—model independent—efficient approximate solution to this challenging problem. Primitive paths are treated as 'infinitely' thin (we further allow for finite thickness to model excluded volume), and tensionless lines rather than multibead chains, excluded volume is taken into account without a force law. The present implementation allows to construct a shortest multiple disconnected path (SP) for 2D systems (polymeric chain within spherical obstacles) and an optimal SP for 3D systems (collection of polymeric chains). The number of entanglements is then simply obtained from the SP as either the number of interior kinks, or from the average length of a line segment. Further, information about structure and potentially also the dynamics of entanglements is immediately available from the SP. We apply the method to study the 'concentration' dependence of the degree of entanglement in phantom chain systems. Program summaryTitle of program:Z Catalogue number:ADVG Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADVG Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Computer for which the program is designed and others on which it has been tested: Silicon Graphics (Irix), Sun (Solaris), PC (Linux) Operating systems or monitors under which the
NASA Astrophysics Data System (ADS)
Heo, Jino; Kang, Min-Sung; Hong, Chang-Ho; Yang, Hyeon; Choi, Seong-Gon
2017-01-01
We propose quantum information processing schemes based on cavity quantum electrodynamics (QED) for quantum communication. First, to generate entangled states (Bell and Greenberger-Horne-Zeilinger [GHZ] states) between flying photons and three-level atoms inside optical cavities, we utilize a controlled phase flip (CPF) gate that can be implemented via cavity QED). Subsequently, we present an entanglement swapping scheme that can be realized using single-qubit measurements and CPF gates via optical cavities. These schemes can be directly applied to construct an entanglement channel for a communication system between two users. Consequently, it is possible for the trust center, having quantum nodes, to accomplish the linked channel (entanglement channel) between the two separate long-distance users via the distribution of Bell states and entanglement swapping. Furthermore, in our schemes, the main physical component is the CPF gate between the photons and the three-level atoms in cavity QED, which is feasible in practice. Thus, our schemes can be experimentally realized with current technology.
Exchangeable, stationary, and entangled chains of Gaussian states
NASA Astrophysics Data System (ADS)
Parthasarathy, K. R.; Sengupta, Ritabrata
2015-10-01
We explore conditions on the covariance matrices of a consistent chain of mean zero finite mode Gaussian states in order that the chain may be exchangeable or stationary. For an exchangeable chain, our conditions are necessary and sufficient. Every stationary Gaussian chain admits an asymptotic entropy rate. Whereas an exchangeable chain admits a simple expression for its entropy rate, in our examples of stationary chains, the same admits an integral formula based on the asymptotic eigenvalue distribution for Toeplitz matrices. An example of a stationary entangled Gaussian chain is given.
Muon-fluorine entangled states in molecular magnets.
Lancaster, T; Blundell, S J; Baker, P J; Brooks, M L; Hayes, W; Pratt, F L; Manson, J L; Conner, M M; Schlueter, J A
2007-12-31
The information accessible from a muon-spin relaxation experiment can be limited due to a lack of knowledge of the precise muon stopping site. We demonstrate here the possibility of localizing a spin polarized muon in a known stopping state in a molecular material containing fluorine. The muon-spin precession that results from the entangled nature of the muon spin and surrounding nuclear spins is sensitive to the nature of the stopping site. We use this property to identify three classes of sites that occur in molecular magnets and describe the extent to which the muon distorts its surroundings.
Edge Theories in Projected Entangled Pair State Models
NASA Astrophysics Data System (ADS)
Yang, S.; Lehman, L.; Poilblanc, D.; Van Acoleyen, K.; Verstraete, F.; Cirac, J. I.; Schuch, N.
2014-01-01
We analyze the low energy excitations of spin lattice systems in two dimensions at zero temperature within the framework of projected entangled pair state models. Perturbations in the bulk give rise to physical excitations located at the edge. We identify the corresponding degrees of freedom, give a procedure to derive the edge Hamiltonian, and illustrate that it can exhibit a rich phase diagram. For topological models, the edge Hamiltonian is constrained by the topological order in the bulk, which gives rise to one-dimensional edge models with unconventional properties; for instance, a topologically ordered bulk can protect a ferromagnetic Ising chain at the edge against spontaneous symmetry breaking.
NASA Astrophysics Data System (ADS)
Sun, Wen-Yang; Wang, Dong; Shi, Jia-Dong; Ye, Liu
2017-02-01
In this work, there are two parties, Alice on Earth and Bob on the satellite, which initially share an entangled state, and some open problems, which emerge during quantum steering that Alice remotely steers Bob, are investigated. Our analytical results indicate that all entangled pure states and maximally entangled evolution states (EESs) are steerable, and not every entangled evolution state is steerable and some steerable states are only locally correlated. Besides, quantum steering from Alice to Bob experiences a “sudden death” with increasing decoherence strength. However, shortly after that, quantum steering experiences a recovery with the increase of decoherence strength in bit flip (BF) and phase flip (PF) channels. Interestingly, while they initially share an entangled pure state, all EESs are steerable and obey Bell nonlocality in PF and phase damping channels. In BF channels, all steerable states can violate Bell-CHSH inequality, but some EESs are unable to be employed to realize steering. However, when they initially share an entangled mixed state, the outcome is different from that of the pure state. Furthermore, the steerability of entangled mixed states is weaker than that of entangled pure states. Thereby, decoherence can induce the degradation of quantum steering, and the steerability of state is associated with the interaction between quantum systems and reservoirs.
Sun, Wen-Yang; Wang, Dong; Shi, Jia-Dong; Ye, Liu
2017-01-01
In this work, there are two parties, Alice on Earth and Bob on the satellite, which initially share an entangled state, and some open problems, which emerge during quantum steering that Alice remotely steers Bob, are investigated. Our analytical results indicate that all entangled pure states and maximally entangled evolution states (EESs) are steerable, and not every entangled evolution state is steerable and some steerable states are only locally correlated. Besides, quantum steering from Alice to Bob experiences a “sudden death” with increasing decoherence strength. However, shortly after that, quantum steering experiences a recovery with the increase of decoherence strength in bit flip (BF) and phase flip (PF) channels. Interestingly, while they initially share an entangled pure state, all EESs are steerable and obey Bell nonlocality in PF and phase damping channels. In BF channels, all steerable states can violate Bell-CHSH inequality, but some EESs are unable to be employed to realize steering. However, when they initially share an entangled mixed state, the outcome is different from that of the pure state. Furthermore, the steerability of entangled mixed states is weaker than that of entangled pure states. Thereby, decoherence can induce the degradation of quantum steering, and the steerability of state is associated with the interaction between quantum systems and reservoirs. PMID:28145467
Teleportation with insurance of an entangled atomic state via cavity decay
Chimczak, Grzegorz; Tanas, Ryszard; Miranowicz, Adam
2005-03-01
We propose a scheme to teleport an entangled state of two {lambda}-type three-level atoms via photons. The teleportation protocol involves the local redundant encoding protecting the initial entangled state and allowing for repeating the detection until quantum information transfer is successful. We also show how to manipulate a state of many {lambda}-type atoms trapped in a cavity.
Studying the thermally entangled state of a three-qubit Heisenberg XX ring via quantum teleportation
Yeo, Ye
2003-08-01
We consider quantum teleportation as a tool to investigate the thermally entangled state of a three-qubit Heisenberg XX ring. Our investigation reveals interesting aspects of quantum entanglement not reflected by the pairwise thermal concurrence of the state. In particular, two mixtures of different pairs of W states, which result in the same concurrence, could yield very different average teleportation fidelities.
Entanglement of three-qubit pure states in terms of teleportation capability
Lee, Soojoon; Joo, Jaewoo; Kim, Jaewan
2005-08-15
We define an entanglement measure, called the partial tangle, which represents the residual two-qubit entanglement of a three-qubit pure state. By its explicit calculations for three-qubit pure states, we show that the partial tangle is closely related to the faithfulness of a teleportation scheme over a three-qubit pure state.
Steady-state entanglement of a Bose-Einstein condensate and a nanomechanical resonator
Asjad, Muhammad; Saif, Farhan
2011-09-15
We analyze the steady-state entanglement between Bose-Einstein condensate trapped inside an optical cavity with a moving end mirror (nanomechanical resonator) driven by a single mode laser. The quantized laser field mediates the interaction between the Bose-Einstein condensate and nanomechanical resonator. In particular, we study the influence of temperature on the entanglement of the coupled system, and note that the steady-state entanglement is fragile with respect to temperature.
NASA Astrophysics Data System (ADS)
Shi, Ronghua; Su, Qian; Guo, Ying; Huang, Dazu
2013-02-01
We demonstrate an anonymous quantum communication (AQC) via the non-maximally entanglement state analysis (NESA) based on the dining cryptographer problem (DCP). The security of the present AQC is ensured due to the quantum-mechanical impossibility of local unitary transformations between non-maximally entanglement states, which provides random numbers for the secure AQC. The analysis shows that the DCP-based AQC can be performed without intractability through the NESA in the multi-photon entangled quantum system.
Entanglement analysis of two-mode Gaussian states in a parametric down-converter
NASA Astrophysics Data System (ADS)
Tahira, Rabia; Ge, Guoqin; Ikram, Manzoor
2017-04-01
Parametric down-conversion has been studied as a source of entangled radiation (Lee et al 2008 J. Phys. B: At. Mol. Opt. Phys. 41 145504). We investigate and quantify the entanglement of this system when the initial cavity modes are taken as two-mode Gaussian states. We study the effect of nonclassicality, purity, noise and leakage through the cavity modes on the two-mode Gaussian state entanglement.
Quantum secret sharing protocol based on four-dimensional three-particle entangled states
NASA Astrophysics Data System (ADS)
Xiang, Yi; Mo, Zhi Wen
2016-01-01
In this paper, we proposed a three-party quantum secret sharing (QSS) scheme using four-dimensional three-particle entangled states. In this QSS scheme, each agent can obtain a shadow of the secret key by performing single-particle measurements. Compared with the existing QSS protocol, this scheme has high efficiency and can resist the eavesdropping attack and entangle-measuring attack, which using three-particle entangled states are based on four-dimensional Hilbert space.
Comparison of qubit and qutrit like entangled squeezed and coherent states of light
NASA Astrophysics Data System (ADS)
Najarbashi, G.; Mirzaei, S.
2016-10-01
Squeezed state of light is one of the important subjects in quantum optics which is generated by optical nonlinear interactions. In this paper, we especially focus on qubit like entangled squeezed states (ESS's) generated by beam splitters, phase-shifter and cross Kerr nonlinearity. Moreover the Wigner function of two-mode qubit and qutrit like ESS are investigated. We will show that the distances of peaks of Wigner functions for two-mode ESS are entanglement sensitive and can be a witness for entanglement. Like the qubit cases, monogamy inequality is fulfilled for qutrit like ESS. These trends are compared with those obtained for qubit and qutrit like entangled coherent states (ECS).
Pattern classification using maximally entangled quantum states (MES)
NASA Astrophysics Data System (ADS)
Singh, Manu Pratap; Rajput, B. S.
2014-04-01
Pattern classifications have been performed by employing the method of Grover's iteration on Bell's MES and Singh-Rajput MES in a two-qubit system and it has been demonstrated that, for any pattern classification, in a two-qubit system the maximally entangled states of Singh-Rajput eigenbasis provide the most suitable choice of search states while, in no case, any of Bell's states is suitable for such pattern classifications. Applying the method of Grover's iterate on three different superpositions in a three-qubit system, it has been shown that the choice of exclusive superposition, as the search state, is the most suitable one for the desired pattern classifications based on Grover's iterative search algorithm.
A revisit to non-maximally entangled mixed states: teleportation witness, noisy channel and discord
NASA Astrophysics Data System (ADS)
Roy, Sovik; Ghosh, Biplab
2017-04-01
We constructed a class of non-maximally entangled mixed states (Adhikari et al. in Quantum Inf Comput 10:0398, 2010) and extensively studied their entanglement properties and also their usefulness as teleportation channels. In this article, we have revisited our constructed state and have studied it from three different perspectives. Since every entangled state is associated with a witness operator, we have found a suitable entanglement as well as teleportation witness operator for our non-maximally entangled mixed states. We considered the noisy channel's effects on our constructed states to see how much it affects the states' capacities as teleportation channels. For this purpose, we have mainly focussed on amplitude damping channel. A comparative study on concurrence and quantum discord of our constructed state of Adhikari et al. (2010) has also been carried out here.
Generating multipartite entangled states of qubits distributed in different cavities
NASA Astrophysics Data System (ADS)
He, Xiao-Ling; Su, Qi-Ping; Zhang, Feng-Yang; Yang, Chui-Ping
2014-06-01
Cavity-based large-scale quantum information processing (QIP) needs a large number of qubits, and placing all of them in a single cavity quickly runs into many fundamental and practical problems such as the increase in cavity decay rate and decrease in qubit-cavity coupling strength. Therefore, future QIP most likely will require quantum networks consisting of a large number of cavities, each hosting and coupled to multiple qubits. In this work, we propose a way to prepare a -class entangled state of spatially separated multiple qubits in different cavities, which are connected to a coupler qubit. Because no cavity photon is excited, decoherence caused by the cavity decay is greatly suppressed during the entanglement preparation. This proposal needs only one coupler qubit and one operational step, and does not require using a classical pulse, so that the engineering complexity is much reduced and the operation is greatly simplified. As an example of the experimental implementation, we further give a numerical analysis, which shows that high-fidelity generation of the state using three superconducting phase qubits each embedded in a one-dimensional transmission line resonator is feasible within the present circuit QED technique. The proposal is quite general and can be applied to accomplish the same task with other types of qubits such as superconducting flux qubits, charge qubits, quantum dots, nitrogen-vacancy centers, and atoms.
Grothendieck's constant and local models for noisy entangled quantum states
Acin, Antonio; Gisin, Nicolas; Toner, Benjamin
2006-06-15
We relate the nonlocal properties of noisy entangled states to Grothendieck's constant, a mathematical constant appearing in Banach space theory. For two-qubit Werner states {rho}{sub p}{sup W}=p|{psi}{sup -}><{psi}{sup -}|+(1-p)1/4, we show that there is a local model for projective measurements if and only if p{<=}1/K{sub G}(3), where K{sub G}(3) is Grothendieck's constant of order 3. Known bounds on K{sub G}(3) prove the existence of this model at least for p < or approx. 0.66, quite close to the current region of Bell violation, p{approx}0.71. We generalize this result to arbitrary quantum states.
Entanglement and communication-reducing properties of noisy N-qubit states
Laskowski, Wieslaw; Paterek, Tomasz; Brukner, Caslav; Zukowski, Marek
2010-04-15
We consider properties of states of many qubits, which arise after sending certain entangled states via various noisy channels (white noise, colored noise, local depolarization, dephasing, and amplitude damping). Entanglement of these states and their ability to violate certain classes of Bell inequalities are studied. States which violate them allow a higher than classical efficiency in solving related distributed computational tasks with constrained communication. This is a direct property of such states--not requiring their further modification via stochastic local operations and classical communication such as entanglement purification or distillation procedures. We identify families of multiparticle states which are entangled but nevertheless allow the local realistic description of specific Bell experiments. For some of them, the 'gap' between the critical values for entanglement and violation of Bell inequality remains finite even in the limit of infinitely many qubits.
Kunkri, Samir; Choudhary, Sujit K.; Ahanj, Ali; Joag, Pramod
2006-02-15
Here we deal with a nonlocality argument proposed by Cabello, which is more general than Hardy's nonlocality argument, but still maximally entangled states do not respond. However, for most of the other entangled states, maximum probability of success of this argument is more than that of the Hardy's argument.
Quantum computation and entangled state generation through a cavity output process
NASA Astrophysics Data System (ADS)
Xia, Yan; Hu, Chun; Song, Jie; Song, He-Shan
2011-10-01
We propose a protocol to realize quantum phase gates and generate entangled states between two atoms trapped in one cavity. In Lamb-Dick limits, it is not necessary to require coincidence detections, which will relax the conditions for the experimental realization. The protocol can be generalized to generate N-atom entangled states.
GENERAL: Steady State Entanglement and Saturation Effects in Correlated Spontaneous Emission Lasers
NASA Astrophysics Data System (ADS)
Wang, Fei; Hu, Xiang-Ming; Shi, Wen-Xing
2009-08-01
It has recently been shown that correlated spontaneous emission lasers (CEL) exhibit transient entanglement in the linear regime. Here we re-examine the quantum correlations in two-photon CEL and explore the saturation effects on continuous variable entanglement. It is shown that the steady state entanglement is obtainable in the weak or moderate saturation regime, while is washed out in the deep saturation regime.
Trail, Collin M; Madhok, Vaibhav; Deutsch, Ivan H
2008-10-01
We study the dynamical generation of entanglement as a signature of chaos in a system of periodically kicked coupled tops, where chaos and entanglement arise from the same physical mechanism. The long-time-averaged entanglement as a function of the position of an initially localized wave packet very closely correlates with the classical phase space surface of section--it is nearly uniform in the chaotic sea, and reproduces the detailed structure of the regular islands. The uniform value in the chaotic sea is explained by the random state conjecture. As classically chaotic dynamics take localized distributions in phase space to random distributions, quantized versions take localized coherent states to pseudorandom states in Hilbert space. Such random states are highly entangled, with an average value near that of the maximally entangled state. For a map with global chaos, we derive that value based on analytic results for the entropy of random states. For a mixed phase space, we use the Percival conjecture to identify a "chaotic subspace" of the Hilbert space. The typical entanglement, averaged over the unitarily invariant Haar measure in this subspace, agrees with the long-time-averaged entanglement for initial states in the chaotic sea. In all cases the dynamically generated entanglement is that of a random complex vector, even though the system is time-reversal invariant, and the Floquet operator is a member of the circular orthogonal ensemble.
NASA Astrophysics Data System (ADS)
Adesso, Gerardo; Giampaolo, Salvatore M.; Illuminati, Fabrizio
2007-10-01
We present a geometric approach to the characterization of separability and entanglement in pure Gaussian states of an arbitrary number of modes. The analysis is performed adapting to continuous variables a formalism based on single subsystem unitary transformations that has been recently introduced to characterize separability and entanglement in pure states of qubits and qutrits [S. M. Giampaolo and F. Illuminati, Phys. Rev. A 76, 042301 (2007)]. In analogy with the finite-dimensional case, we demonstrate that the 1×M bipartite entanglement of a multimode pure Gaussian state can be quantified by the minimum squared Euclidean distance between the state itself and the set of states obtained by transforming it via suitable local symplectic (unitary) operations. This minimum distance, corresponding to a , uniquely determined, extremal local operation, defines an entanglement monotone equivalent to the entropy of entanglement, and amenable to direct experimental measurement with linear optical schemes.
Adesso, Gerardo; Giampaolo, Salvatore M.; Illuminati, Fabrizio
2007-10-15
We present a geometric approach to the characterization of separability and entanglement in pure Gaussian states of an arbitrary number of modes. The analysis is performed adapting to continuous variables a formalism based on single subsystem unitary transformations that has been recently introduced to characterize separability and entanglement in pure states of qubits and qutrits [S. M. Giampaolo and F. Illuminati, Phys. Rev. A 76, 042301 (2007)]. In analogy with the finite-dimensional case, we demonstrate that the 1xM bipartite entanglement of a multimode pure Gaussian state can be quantified by the minimum squared Euclidean distance between the state itself and the set of states obtained by transforming it via suitable local symplectic (unitary) operations. This minimum distance, corresponding to a, uniquely determined, extremal local operation, defines an entanglement monotone equivalent to the entropy of entanglement, and amenable to direct experimental measurement with linear optical schemes.
Joo, Jaewoo; Ginossar, Eran
2016-01-01
We propose a deterministic scheme for teleporting an unknown qubit state through continuous-variable entangled states in superconducting circuits. The qubit is a superconducting two-level system and the bipartite quantum channel is a microwave photonic entangled coherent state between two cavities. A Bell-type measurement performed on the hybrid state of solid and photonic states transfers a discrete-variable unknown electronic state to a continuous-variable photonic cat state in a cavity mode. In order to facilitate the implementation of such complex protocols we propose a design for reducing the self-Kerr nonlinearity in the cavity. The teleporation scheme enables quantum information processing operations with circuit-QED based on entangled coherent states. These include state verification and single-qubit operations with entangled coherent states. These are shown to be experimentally feasible with the state of the art superconducting circuits. PMID:27245775
NASA Astrophysics Data System (ADS)
Joo, Jaewoo; Ginossar, Eran
2016-06-01
We propose a deterministic scheme for teleporting an unknown qubit state through continuous-variable entangled states in superconducting circuits. The qubit is a superconducting two-level system and the bipartite quantum channel is a microwave photonic entangled coherent state between two cavities. A Bell-type measurement performed on the hybrid state of solid and photonic states transfers a discrete-variable unknown electronic state to a continuous-variable photonic cat state in a cavity mode. In order to facilitate the implementation of such complex protocols we propose a design for reducing the self-Kerr nonlinearity in the cavity. The teleporation scheme enables quantum information processing operations with circuit-QED based on entangled coherent states. These include state verification and single-qubit operations with entangled coherent states. These are shown to be experimentally feasible with the state of the art superconducting circuits.
Joo, Jaewoo; Ginossar, Eran
2016-06-01
We propose a deterministic scheme for teleporting an unknown qubit state through continuous-variable entangled states in superconducting circuits. The qubit is a superconducting two-level system and the bipartite quantum channel is a microwave photonic entangled coherent state between two cavities. A Bell-type measurement performed on the hybrid state of solid and photonic states transfers a discrete-variable unknown electronic state to a continuous-variable photonic cat state in a cavity mode. In order to facilitate the implementation of such complex protocols we propose a design for reducing the self-Kerr nonlinearity in the cavity. The teleporation scheme enables quantum information processing operations with circuit-QED based on entangled coherent states. These include state verification and single-qubit operations with entangled coherent states. These are shown to be experimentally feasible with the state of the art superconducting circuits.
NASA Astrophysics Data System (ADS)
Zhao, Jie; Zheng, Chun-Hong; Shi, Peng; Ren, Chun-Nian; Gu, Yong-Jian
2014-07-01
We present schemes for deterministically generating multi-qubit electron-spin entangled cluster states by the giant circular birefringence, induced by the interface between the spin of a photon and the spin of an electron confined in a quantum dot embedded in a double-sided microcavity. Based on this interface, we construct the controlled phase flip (CPF) gate deterministically which is performed on electron-spin qubits and is the essential component of the cluster-state generation. As one of the universal gates, the CPF gate constructed can also be utilized in achieving scalable quantum computing. Besides, we propose the entanglement concentration protocol to reconstruct a partially entangled cluster state into a maximally entangled one, resorting to the projection measurement on an ancillary photon. By iterating the concentration scheme several times, the maximum success probability can be achieved. The fidelities and experimental feasibilities are analyzed with respect to currently available techniques, indicating that our schemes can work well in both the strong and weak (Purcell) coupling regimes.
Entangling qubit registers via many-body states of ultracold atoms
NASA Astrophysics Data System (ADS)
Melko, R. G.; Herdman, C. M.; Iouchtchenko, D.; Roy, P.-N.; Del Maestro, A.
2016-04-01
Inspired by the experimental measurement of the Rényi entanglement entropy in a lattice of ultracold atoms by Islam et al. [Nature (London) 528, 77 (2015), 10.1038/nature15750], we propose a method to entangle two spatially separated qubits using the quantum many-body state as a resource. Through local operations accessible in an experiment, entanglement is transferred to a qubit register from atoms at the ends of a one-dimensional chain. We compute the operational entanglement, which bounds the entanglement physically transferable from the many-body resource to the register, and discuss a protocol for its experimental measurement. Finally, we explore measures for the amount of entanglement available in the register after transfer, suitable for use in quantum information applications.
Comparison of quantum discord and fully entangled fraction of two classes of d⊗ d^2 states
NASA Astrophysics Data System (ADS)
Behdani, Javad; Akhtarshenas, Seyed Javad; Sarbishaei, Mohsen
2017-01-01
The quantumness of a generic state is the resource of many applications in quantum information theory, and it is interesting to survey the measures which are able to detect its trace in the properties of the state. In this work, we study the quantum discord and fully entangled fraction of two classes of bipartite states and compare their behaviors. These classes are complements to the d⊗ d Werner and isotropic states, in the sense that each class possesses the same purification as the corresponding complemental class of states. Our results show that maximally entangled mixed states are also maximally discordant states, leading to a generalization of the well-known fact that all maximally entangled pure states have also maximum quantum discord. Moreover, it is shown that the separability-entanglement boundary of a Werner or isotropic state is manifested as an inflection point in the diagram of quantum discord of the corresponding complemental state.
Entangled Biphoton Virtual-State Spectroscopy of the A(exp 2)Sigma(sup +)-X(exp 2)Pi System of OH
NASA Technical Reports Server (NTRS)
Kojima, Jun; Nguyen, Quang-Viet
2004-01-01
This Letter describes the first application of entanglement-induced virtual-state spectroscopy to a molecular system. Non-classical, non-monotonic behavior in a two-photon absorption cross section of the OH A-X system, induced by an entangled biphoton state is theoretically demonstrated. A Fourier transform analysis of the biphoton cross section permits access to the energy eigenvalues of intermediate rovibronic states with a fixed excitation photon energy. The dependence of the Fourier spectrum on the tuning range of the entanglement time (T(sub e)) and the relative path delay (tau(sub e)) is discussed. Our analysis reveals that the implementation of molecular virtual-state spectroscopy for the OH A-X system requires the tuning of tau(sub e) over a pico-second range with femto-second resolution.
Entangled Biphoton Virtual-State Spectroscopy of the A(exp 2)Sigma(+) - X(exp 2)Pi System of OH
NASA Technical Reports Server (NTRS)
Kojima, Jun; Nguyen, Quang-Viet
2004-01-01
This Letter describes the first application of entanglement-induced virtual-state spectroscopy to a molecular system. Non-classical, non-monotonic behavior in a two-photon absorption cross section of the OH A-X system, induced by an entangled biphoton state is theoretically demonstrated. A Fourier transform analysis of the biphoton cross section permits access to the energy eigenvalues of intermediate rovibronic states with a fixed excitation photon energy. The dependence of the Fourier spectrum on the tuning range of the entanglement time T(sub e), and the relative path delay tau(sub e) is discussed. Our analysis reveals that the implementation of molecular virtual-state spectroscopy for the OH A-X system requires the tuning of tau(sub e) over a pico-second range with femto-second resolution.
Entanglement generation from deformed spin coherent states using a beam splitter
NASA Astrophysics Data System (ADS)
Berrada, K.; El Baz, M.; Saif, F.; Hassouni, Y.; Mnia, S.
2009-07-01
Using the linear entropy as a measure of entanglement, we investigate the effect of a beam splitter on the Perelomov coherent states for the q-deformed Uq(su(2)) algebra. We distinguish two cases: in the classical q → 1 limit, we find that the states become Glauber coherent states as the spin tends to infinity; whereas for q ≠ 1, the states, contrary to the earlier case, become entangled as they pass through a beam splitter. The entanglement strongly depends on the q-deformation parameter and the amplitude Z of the state.
Generating Entangled Spin States for Quantum Metrology by Single-Photon Detection
NASA Astrophysics Data System (ADS)
McConnell, Robert; Zhang, Hao; Cuk, Senka; Hu, Jiazhong; Schleier-Smith, Monika; Vuletic, Vladan
2014-05-01
We present a proposal and latest experimental results on a probabilistic but heralded scheme to generate non-Gaussian entangled states of collective spin in large atomic ensembles by means of single-photon detection. One photon announces the preparation of a Dicke state, while two or more photons announce Schrödinger cat states. The entangled states thus produced allow interferometry below the Standard Quantum Limit (SQL). The method produces nearly pure states even for finite photon detection efficiency and weak atom-photon coupling. The entanglement generation can be made quasi-deterministic by means of repeated trial and feedback.
Generation of four-photon polarization entangled states with cross-Kerr nonlinearity
NASA Astrophysics Data System (ADS)
Wang, Meiyu; Yan, Fengli
2015-05-01
We show how to prepare three different types of four-photon polarization entangled states among four modes. The scheme only use cross-Kerr medium, polarization beam splitters and X homodyne measurements on coherent light fields, which can be efficiently implemented in quantum optical laboratories. GHZ states and symmetric Dick states can be generated in deterministic way based on the scheme. With the possible availability of suitable strong Kerr nonlinearity, another type of entangled state called genuine four-photon entangled state can be realized as well.
Harsij, Zeynab Mirza, Behrouz
2014-12-15
A helicity entangled tripartite state is considered in which the degree of entanglement is preserved in non-inertial frames. It is shown that Quantum Entanglement remains observer independent. As another measure of quantum correlation, Quantum Discord has been investigated. It is explicitly shown that acceleration has no effect on the degree of quantum correlation for the bipartite and tripartite helicity entangled states. Geometric Quantum Discord as a Hilbert–Schmidt distance is computed for helicity entangled states. It is shown that living in non-inertial frames does not make any influence on this distance, either. In addition, the analysis has been extended beyond single mode approximation to show that acceleration does not have any impact on the quantum features in the limit beyond the single mode. As an interesting result, while the density matrix depends on the right and left Unruh modes, the Negativity as a measure of Quantum Entanglement remains constant. Also, Quantum Discord does not change beyond single mode approximation. - Highlights: • The helicity entangled states here are observer independent in non-inertial frames. • It is explicitly shown that Quantum Discord for these states is observer independent. • Geometric Quantum Discord is also not affected by acceleration increase. • Extending to beyond single mode does not change the degree of entanglement. • Beyond single mode approximation the degree of Quantum Discord is also preserved.
NASA Astrophysics Data System (ADS)
Shan, Chuan-Jia; Chen, Tao; Liu, Ji-Bing; Cheng, Wei-Wen; Liu, Tang-Kun; Huang, Yan-Xia; Li, Hong
2010-06-01
In this paper, we investigate the dynamical behaviour of entanglement in terms of concurrence in a bipartite system subjected to an external magnetic field under the action of dissipative environments in the extended Werner-like initial state. The interesting phenomenon of entanglement sudden death as well as sudden birth appears during the evolution process. We analyse in detail the effect of the purity of the initial entangled state of two qubits via Heisenberg XY interaction on the apparition time of entanglement sudden death and entanglement sudden birth. Furthermore, the conditions on the conversion of entanglement sudden death and entanglement sudden birth can be generalized when the initial entangled state is not pure. In particular, a critical purity of the initial mixed entangled state exists, above which entanglement sudden birth vanishes while entanglement sudden death appears. It is also noticed that stable entanglement, which is independent of different initial states of the qubits (pure or mixed state), occurs even in the presence of decoherence. These results arising from the combination of the extended Werner-like initial state and dissipative environments suggest an approach to control and enhance the entanglement even after purity induced sudden birth, death and revival.
Optically Excited Entangled States in Organic Molecules Illuminate the Dark.
Upton, L; Harpham, M; Suzer, O; Richter, M; Mukamel, S; Goodson, T
2013-06-20
We utilize quantum entangled photons to carry out nonlinear optical spectroscopy in organic molecules with an extremely small number of photons. For the first time, fluorescence is reported as a result of entangled photon absorption in organic nonlinear optical molecules. Selectivity of the entangled photon absorption process is also observed and a theoretical model of this process is provided. Through these experiments and theoretical modeling it is found that while some molecules may not have strong classical nonlinear optical properties due to their excitation pathways; these same excitation pathways may enhance the entangled photon processes. It is found that the opposite is also true. Some materials with weak classical nonlinear optical effects may exhibit strong non-classical nonlinear optical effects. Our entangled photon fluorescence results provide the first steps in realizing and demonstrating the viability of entangled two-photon microscopy, remote sensing, and optical communications.
NASA Astrophysics Data System (ADS)
Du, Fang-Fang; Long, Gui-Lu
2017-01-01
We present a refined entanglement concentration protocol (ECP) for an arbitrary unknown less-entangled four-electron-spin cluster state by exploring the optical selection rules derived from the quantum-dot spins in one-sided optical microcavities. In our ECP, the parties obtain not only the four-electron-spin systems in the partial entanglement with two unknown parameters, but also the less-entangled two-electron-spin systems in the first step. Utilizing the above preserved systems as the resource for the second step of our ECP, the parties can obtain a standard cluster state by keeping the robust odd-parity instances with two parity-check gates. Meanwhile, the systems in the rest three instances can be used as the resource in the next round of our ECP. The success probability of our ECP is largely increased by iteration of the ECP process. Moreover, all the coefficients of our ECP are unknown for the parties without assistance of extra single electron-spin, so our ECP maybe has good applications in quantum communication network in the future.
Improvement on "Quantum Key Agreement Protocol with Maximally Entangled States"
NASA Astrophysics Data System (ADS)
Chong, Song-Kong; Tsai, Chia-Wei; Hwang, Tzonelih
2011-06-01
Recently, Hsueh and Chen [in Proceedings of the 14th Information Security Conference, National Taiwan University of Science and Technology, Taipei, pp. 236-242, 2004] proposed a quantum key agreement (QKA) protocol with maximally entangled states. Their protocol allows two users to negotiate a secret key in such a way that no one can predetermine the shared key alone. This study points out two security flaws in their protocol: (1) a legitimate but malicious user can fully control the shared key alone; (2) an eavesdropper can obtain the shared key without being detected. A possible solution is presented to avoid these attacks and also Tsai et al.'s CNOT attack [in Proceedings of the 20th Cryptology and Information Security Conference, National Chiao Tung University, Hsinchu, pp. 210-213, 2010] on Hsueh and Chen protocol to obtain the shared key without being detected.
NASA Astrophysics Data System (ADS)
Cao, Cong; Fan, Ling; Chen, Xi; Duan, Yu-Wen; Wang, Tie-Jun; Zhang, Ru; Wang, Chuan
2017-04-01
We propose an efficient entanglement concentration protocol (ECP) for nonlocal three-atom systems in an arbitrary unknown less-entangled W state, resorting to the Faraday rotation of photonic polarization in cavity quantum electrodynamics and the systematic concentration method. In the first step of the present ECP, one party in quantum communication performs a parity-check measurement on her two atoms in two three-atom systems for dividing the composite six-atom systems into two groups. In the first group, the three parties will obtain some three-atom systems in a less-entangled state with two unknown coefficients. In the second group, they will obtain some less-entangled two-atom systems. In the second step of the ECP, the three parties can obtain a subset of three-atom systems in the standard maximally entangled W state by exploiting the above three-atom and two-atom systems. Moreover, the preserved systems in the failed instances can be used as the resource for the entanglement concentration in the next round. The total success probability of the ECP can therefore be largely increased by iterating the entanglement concentration process several rounds. The distinct feature of our ECP is that we can concentrate arbitrary unknown atomic entangled W states via photonic Faraday rotation, and thus it may be universal and useful for entanglement concentration in future quantum communication network.
Probabilistic teleportation of a three-particle state via three pairs of entangled particles
Fang Jianxing; Lin Yinsheng; Zhu Shiqun; Chen Xianfeng
2003-01-01
A scheme for teleporting an arbitrary three-particle state is proposed when three pairs of entangled particles are used as quantum channels. Quantum teleportation can be successfully realized with a certain probability if the receiver adopts an appropriate unitary-reduction strategy. The probability of successful teleportation is determined by the smallest coefficients of the three entangled pairs.
General Method for Constructing Local Hidden Variable Models for Entangled Quantum States
NASA Astrophysics Data System (ADS)
Cavalcanti, D.; Guerini, L.; Rabelo, R.; Skrzypczyk, P.
2016-11-01
Entanglement allows for the nonlocality of quantum theory, which is the resource behind device-independent quantum information protocols. However, not all entangled quantum states display nonlocality. A central question is to determine the precise relation between entanglement and nonlocality. Here we present the first general test to decide whether a quantum state is local, and show that the test can be implemented by semidefinite programing. This method can be applied to any given state and for the construction of new examples of states with local hidden variable models for both projective and general measurements. As applications, we provide a lower-bound estimate of the fraction of two-qubit local entangled states and present new explicit examples of such states, including those that arise from physical noise models, Bell-diagonal states, and noisy Greenberger-Horne-Zeilinger and W states.
Superposition and entanglement of mesoscopic squeezed vacuum states in cavity QED
Chen Changyong; Feng Mang; Gao Kelin
2006-03-15
We propose a scheme to generate superposition and entanglement between the mesoscopic squeezed vacuum states by considering the two-photon interaction of N two-level atoms in a cavity with high quality factor, assisted by a strong driving field. By virtue of specific choices of the cavity detuning, a number of multiparty entangled states can be prepared, including the entanglement between the atomic and the squeezed vacuum cavity states and between the squeezed vacuum states and the coherent states of the cavities. We also present how to prepare entangled states and 'Schroedinger cats' states regarding the squeezed vacuum states of the cavity modes. The possible extension and application of our scheme are discussed. Our scheme is close to the reach with current cavity QED techniques.
A Criterion for Maximally Six-Qubit Entangled States via Coefficient Matrix
NASA Astrophysics Data System (ADS)
Yu, Yan; Zha, Xin Wei; Li, Wei
2017-03-01
In a recent paper (J. Phys. A: Math. Theor 45, 075308 (2012)), Li et al. established the coefficient matrix of six-qubit entangled states. With an emphasis on six qubits, we present a new criterion for maximally six-qubit entangled states via those coefficient matrices. By calculating the determinants of coefficient matrix, one use the criterion that characterize these states. Moreover, the criterion via the coefficient matrices gives rise to the combination of maximally multi-qubit entangled state(MMES) and matrix, and we believe that the new criterion can play an important role in quantum information.
Comment on 'Teleportation of entangled states without Bell-state measurement'
Zela, F. de
2006-08-15
We consider a protocol recently proposed by Cardoso et al. for teleporting entangled photon states from a bimodal cavity to another one. It is shown that the proposed protocol can afford full fidelity instead of the 97% fidelity that the authors ascribed to their scheme.
Random pure states: Quantifying bipartite entanglement beyond the linear statistics.
Vivo, Pierpaolo; Pato, Mauricio P; Oshanin, Gleb
2016-05-01
We analyze the properties of entangled random pure states of a quantum system partitioned into two smaller subsystems of dimensions N and M. Framing the problem in terms of random matrices with a fixed-trace constraint, we establish, for arbitrary N≤M, a general relation between the n-point densities and the cross moments of the eigenvalues of the reduced density matrix, i.e., the so-called Schmidt eigenvalues, and the analogous functionals of the eigenvalues of the Wishart-Laguerre ensemble of the random matrix theory. This allows us to derive explicit expressions for two-level densities, and also an exact expression for the variance of von Neumann entropy at finite N,M. Then, we focus on the moments E{K^{a}} of the Schmidt number K, the reciprocal of the purity. This is a random variable supported on [1,N], which quantifies the number of degrees of freedom effectively contributing to the entanglement. We derive a wealth of analytical results for E{K^{a}} for N=2 and 3 and arbitrary M, and also for square N=M systems by spotting for the latter a connection with the probability P(x_{min}^{GUE}≥sqrt[2N]ξ) that the smallest eigenvalue x_{min}^{GUE} of an N×N matrix belonging to the Gaussian unitary ensemble is larger than sqrt[2N]ξ. As a by-product, we present an exact asymptotic expansion for P(x_{min}^{GUE}≥sqrt[2N]ξ) for finite N as ξ→∞. Our results are corroborated by numerical simulations whenever possible, with excellent agreement.
Random pure states: Quantifying bipartite entanglement beyond the linear statistics
NASA Astrophysics Data System (ADS)
Vivo, Pierpaolo; Pato, Mauricio P.; Oshanin, Gleb
2016-05-01
We analyze the properties of entangled random pure states of a quantum system partitioned into two smaller subsystems of dimensions N and M . Framing the problem in terms of random matrices with a fixed-trace constraint, we establish, for arbitrary N ≤M , a general relation between the n -point densities and the cross moments of the eigenvalues of the reduced density matrix, i.e., the so-called Schmidt eigenvalues, and the analogous functionals of the eigenvalues of the Wishart-Laguerre ensemble of the random matrix theory. This allows us to derive explicit expressions for two-level densities, and also an exact expression for the variance of von Neumann entropy at finite N ,M . Then, we focus on the moments E {Ka} of the Schmidt number K , the reciprocal of the purity. This is a random variable supported on [1 ,N ] , which quantifies the number of degrees of freedom effectively contributing to the entanglement. We derive a wealth of analytical results for E {Ka} for N =2 and 3 and arbitrary M , and also for square N =M systems by spotting for the latter a connection with the probability P (xminGUE≥√{2 N }ξ ) that the smallest eigenvalue xminGUE of an N ×N matrix belonging to the Gaussian unitary ensemble is larger than √{2 N }ξ . As a by-product, we present an exact asymptotic expansion for P (xminGUE≥√{2 N }ξ ) for finite N as ξ →∞ . Our results are corroborated by numerical simulations whenever possible, with excellent agreement.
Photonic Four-qubit Entangled Decoherence-free States Assisted by Cavity-QED System
NASA Astrophysics Data System (ADS)
Chen, Chao
2016-11-01
We propose an efficient preparation of photonic four-qubit entangled decoherence-free states assisted by the cavity-QED system. By using the optical selection rule derived by a single electron charged self-assembled GaAs/InAs quantum dot in a micropillar resonator, two photons are used to generate four-qubit entangled decoherence-free states. Compared with previous entanglement based photonic protocols, the present one requires single-photon resources and is deterministic. These states may be applied to long-distance communications because only two photons are transmitted.
Entanglement of periodic states, the quantum Fourier transform, and Shor's factoring algorithm
Most, Yonatan; Biham, Ofer; Shimoni, Yishai
2010-05-15
The preprocessing stage of Shor's algorithm generates a class of quantum states referred to as periodic states, on which the quantum Fourier transform is applied. Such states also play an important role in other quantum algorithms that rely on the quantum Fourier transform. Since entanglement is believed to be a necessary resource for quantum computational speedup, we analyze the entanglement of periodic states and the way it is affected by the quantum Fourier transform. To this end, we derive a formula that evaluates the Groverian entanglement measure for periodic states. Using this formula, we explain the surprising result that the Groverian entanglement of the periodic states built up during the preprocessing stage is only slightly affected by the quantum Fourier transform.
Continuous-variable entanglement distillation of non-Gaussian mixed states
Dong Ruifang; Lassen, Mikael; Heersink, Joel; Marquardt, Christoph; Leuchs, Gerd; Andersen, Ulrik L.
2010-07-15
Many different quantum-information communication protocols such as teleportation, dense coding, and entanglement-based quantum key distribution are based on the faithful transmission of entanglement between distant location in an optical network. The distribution of entanglement in such a network is, however, hampered by loss and noise that is inherent in all practical quantum channels. Thus, to enable faithful transmission one must resort to the protocol of entanglement distillation. In this paper we present a detailed theoretical analysis and an experimental realization of continuous variable entanglement distillation in a channel that is inflicted by different kinds of non-Gaussian noise. The continuous variable entangled states are generated by exploiting the third order nonlinearity in optical fibers, and the states are sent through a free-space laboratory channel in which the losses are altered to simulate a free-space atmospheric channel with varying losses. We use linear optical components, homodyne measurements, and classical communication to distill the entanglement, and we find that by using this method the entanglement can be probabilistically increased for some specific non-Gaussian noise channels.
NASA Astrophysics Data System (ADS)
Tanaka, Yoshiharu; Asano, Masanari; Ohya, Masanori
2012-02-01
In this paper, we constmct a teleportation model with nonmaximal entangled state. This model, called the m-level teleportation, is discussed on the basis of the Kossakowski and Ohya teleportation scheme. For this study, we define a generalized Bell state in terms of Latn square, by which we derive a general form of appropriate nonmaximal entangled state for a perfect m-level teleportation.
Carving Complex Many-Atom Entangled States by Single-Photon Detection
NASA Astrophysics Data System (ADS)
Chen, Wenlan; Hu, Jiazhong; Duan, Yiheng; Braverman, Boris; Zhang, Hao; Vuletic, Vladan
2016-05-01
We propose a versatile and efficient method to generate a broad class of complex entangled states of many atoms via the detection of a single photon. For an atomic ensemble contained in a strongly coupled optical cavity illuminated by weak single- or multifrequency light, the atom-light interaction entangles the frequency spectrum of a transmitted photon with the collective spin of the atomic ensemble. Simple time-resolved detection of the transmitted photon then projects the atomic ensemble into a desired pure entangled state. This method can be implemented with existing technology, yields high success probability per trial, and can generate complex entangled states such as mesoscopic superposition states of coherent spin states with high fidelity.
Generating arbitrary photon-number entangled states for continuous-variable quantum informatics.
Lee, Su-Yong; Park, Jiyong; Lee, Hai-Woong; Nha, Hyunchul
2012-06-18
We propose two experimental schemes that can produce an arbitrary photon-number entangled state (PNES) in a finite dimension. This class of entangled states naturally includes non-Gaussian continuous-variable (CV) states that may provide some practical advantages over the Gaussian counterparts (two-mode squeezed states). We particularly compare the entanglement characteristics of the Gaussian and the non-Gaussian states in view of the degree of entanglement and the Einstein-Podolsky-Rosen correlation, and further discuss their applications to the CV teleportation and the nonlocality test. The experimental imperfection due to the on-off photodetectors with nonideal efficiency is also considered in our analysis to show the feasibility of our schemes within existing technologies.
Characterizing entanglement of an artificial atom and a cavity cat state with Bell's inequality
NASA Astrophysics Data System (ADS)
Vlastakis, Brian; Petrenko, Andrei; Ofek, Nissim; Sun, Luyan; Leghtas, Zaki; Sliwa, Katrina; Liu, Yehan; Hatridge, Michael; Blumoff, Jacob; Frunzio, Luigi; Mirrahimi, Mazyar; Jiang, Liang; Devoret, M. H.; Schoelkopf, R. J.
2015-11-01
The Schrodinger's cat thought experiment highlights the counterintuitive concept of entanglement in macroscopically distinguishable systems. The hallmark of entanglement is the detection of strong correlations between systems, most starkly demonstrated by the violation of a Bell inequality. No violation of a Bell inequality has been observed for a system entangled with a superposition of coherent states, known as a cat state. Here we use the Clauser-Horne-Shimony-Holt formulation of a Bell test to characterize entanglement between an artificial atom and a cat state, or a Bell-cat. Using superconducting circuits with high-fidelity measurements and real-time feedback, we detect correlations that surpass the classical maximum of the Bell inequality. We investigate the influence of decoherence with states up to 16 photons in size and characterize the system by introducing joint Wigner tomography. Such techniques demonstrate that information stored in superpositions of coherent states can be extracted efficiently, a crucial requirement for quantum computing with resonators.
Grover's search algorithm with an entangled database state
NASA Astrophysics Data System (ADS)
Alsing, Paul M.; McDonald, Nathan
2011-05-01
Grover's oracle based unstructured search algorithm is often stated as "given a phone number in a directory, find the associated name." More formally, the problem can be stated as "given as input a unitary black box Uf for computing an unknown function f:{0,1}n ->{0,1}find x=x0 an element of {0,1}n such that f(x0) =1, (and zero otherwise). The crucial role of the externally supplied oracle Uf (whose inner workings are unknown to the user) is to change the sign of the solution 0 x , while leaving all other states unaltered. Thus, Uf depends on the desired solution x0. This paper examines an amplitude amplification algorithm in which the user encodes the directory (e.g. names and telephone numbers) into an entangled database state, which at a later time can be queried on one supplied component entry (e.g. a given phone number t0) to find the other associated unknown component (e.g. name x0). For N=2n names x with N associated phone numbers t , performing amplitude amplification on a subspace of size N of the total space of size N2 produces the desired state 0 0 x t in √N steps. We discuss how and why sequential (though not concurrent parallel) searches can be performed on multiple database states. Finally, we show how this procedure can be generalized to databases with more than two correlated lists (e.g. x t s r ...).
Quantum Cloning of an Unknown 2-Atom State via Entangled Cluster States
NASA Astrophysics Data System (ADS)
Yu, L.-z.; Zhong, F.
2016-06-01
This paper presented a scheme for cloning a 2-atom state in the QED cavity with the help of Victor who is the state's preparer. The cloning scheme has two steps. In the first step, the scheme requires probabilistic teleportation of a 2-atom state that is unknown in advance, and uses a 4-atom cluster state as quantum channel. In the second step, perfect copies of the 2-atom entangled state may be realized with the assistance of Victor. The finding is that our scheme has two outstanding advantages: it is not sensitive to the cavity decay, and Bell state is easy to identify.
Entanglement of Photon-Added Nonlinear Coherent States Via a Beam Splitter
NASA Astrophysics Data System (ADS)
Honarasa, Gholamreza; Bagheri, Alireza; Gharaati, Abdolrasoul
2016-10-01
Nonlinear coherent states, photon-added coherent states and photon-added nonlinear coherent states are three of the important generalizations of standard coherent states. In this article, a photon-added nonlinear coherent state and a vacuum state are injected on two input modes of a beam splitter and the entanglement of the output state is investigated using linear entropy as the measure. Then, the impact of nonclassicality of the photon-added nonlinear coherent state on entanglement of the output state is studied.
Room-temperature steady-state optomechanical entanglement on a chip
Zou Changling; Zou Xubo; Sun Fangwen; Han Zhengfu; Guo Guangcan
2011-09-15
A potential experimental system, based on high-stress stoichiometric silicon nitride (Si{sub 3}N{sub 4}), is proposed to generate steady-state optomechanical entanglement at room temperature. In the proposed structure, a nanostring interacts dispersively and reactively with a microdisk cavity via the evanescent field. We study the role of both dispersive and reactive couplings in generating optomechanical entanglement, and show that the room-temperature entanglement can be effectively obtained through the dispersive couplings under the reasonable experimental parameters. In particular, in the limits of high temperature (T) and high mechanical quality factor (Q{sub m}), we find that the logarithmic entanglement depends only on the ratio T/Q{sub m}. This indicates that improvements of the material quantity and structure design may lead to more efficient generation of stationary high-temperature entanglement.
Room-temperature steady-state optomechanical entanglement on a chip
NASA Astrophysics Data System (ADS)
Zou, Chang-Ling; Zou, Xu-Bo; Sun, Fang-Wen; Han, Zheng-Fu; Guo, Guang-Can
2011-09-01
A potential experimental system, based on high-stress stoichiometric silicon nitride (Si3N4), is proposed to generate steady-state optomechanical entanglement at room temperature. In the proposed structure, a nanostring interacts dispersively and reactively with a microdisk cavity via the evanescent field. We study the role of both dispersive and reactive couplings in generating optomechanical entanglement, and show that the room-temperature entanglement can be effectively obtained through the dispersive couplings under the reasonable experimental parameters. In particular, in the limits of high temperature (T) and high mechanical quality factor (Qm), we find that the logarithmic entanglement depends only on the ratio T/Qm. This indicates that improvements of the material quantity and structure design may lead to more efficient generation of stationary high-temperature entanglement.
Entangled states decoherence in coupled molecular spin clusters
NASA Astrophysics Data System (ADS)
Troiani, Filippo; Szallas, Attila; Bellini, Valerio; Affronte, Marco
2010-03-01
Localized electron spins in solid-state systems are widely investigated as potential building blocks of quantum devices and computers. While most efforts in the field have been focused on semiconductor low-dimensional structures, molecular antiferromagnets were recently recognized as alternative implementations of effective few-level spin systems. Heterometallic, Cr-based spin rings behave as effective spin-1/2 systems at low temperature and show long decoherence times [1]; besides, they can be chemically linked and magnetically coupled in a controllable fascion [2]. Here, we theoretically investigate the decoherence of the Bell states in such ring dimers, resulting from hyperfine interactions with nuclear spins. Based on a microscopic description of the molecules [3], we simulate the effect of inhomogeneous broadening, spectral diffusion and electron-nuclear entanglement on the electron-spin coherence, estimating the role of the different nuclei (and of possible chemical substitutions), as well as the effect of simple spin-echo sequences. References: [1] F. Troiani, et al., Phys. Rev. Lett. 94, 207208 (2005). [2] G. A. Timco, S: Carretta, F. Troiani et al., Nature Nanotech. 4, 173 (2009). [3] F. Troiani, V. Bellini, and M. Affronte, Phys. Rev. B 77, 054428 (2008).
Teleportation of a two-atom entangled state with a thermal cavity
Jin Lihua; Jin Xingri; Zhang Shou
2005-08-15
We present a scheme to teleport an unknown atomic entangled state in driven cavity QED. In our scheme, the success probability can reach 1.0. In addition, the scheme is insensitive to the cavity decay and the thermal field.
Paraan, Francis N. C.; Korepin, Vladimir E.; Molina-Vilaplana, Javier; Bose, Sougato
2011-09-15
We quantify the extractable entanglement of excited states of a Lieb-Liniger gas that are obtained from coarse-grained measurements on the ground state in which the boson number in one of two complementary contiguous partitions of the gas is determined. Numerically exact results obtained from the coordinate Bethe ansatz show that the von Neumann entropy of the resulting bipartite pure state increases monotonically with the strength of repulsive interactions and saturates to the impenetrable-boson limiting value. We also present evidence indicating that the largest amount of entanglement can be extracted from the most probable projected state having half the number of bosons in a given partition. Our study points to a fundamental difference between the nature of the entanglement in free-bosonic and free-fermionic systems, with the entanglement in the former being zero after projection, while that in the latter (corresponding to the impenetrable-boson limit) being nonzero.
Entanglement concentration for two-mode Gaussian states in non-inertial frames
NASA Astrophysics Data System (ADS)
Di Noia, Maurizio; Giraldi, Filippo; Petruccione, Francesco
2017-04-01
Entanglement creation and concentration by means of a beam splitter (BS) is analysed for a generic two-mode bipartite Gaussian state in a relativistic framework. The total correlations, the purity and the entanglement in terms of logarithmic negativity are analytically studied for observers in an inertial state and in a non-inertial state of uniform acceleration. The dependence of entanglement on the BS transmissivity due to the Unruh effect is analysed in the case when one or both observers undergo uniform acceleration. Due to the Unruh effect, depending on the initial Gaussian state parameters and observed accelerations, the best condition for entanglement generation limited to the two modes of the observers in their regions is not always a balanced beam splitter, as it is for the inertial case.
Chen Zeqian
2004-08-01
Maximally entangled states should maximally violate the Bell inequality. It is proved that all two-qubit states that maximally violate the Bell-Clauser-Horne-Shimony-Holt inequality are exactly Bell states and the states obtained from them by local transformations. The proof is obtained by using the certain algebraic properties that Pauli's matrices satisfy. The argument is extended to the three-qubit system. Since all states obtained by local transformations of a maximally entangled state are equally valid entangled states, we thus give the characterizations of maximally entangled states in both the two-qubit and three-qubit systems in terms of the Bell inequality.
Entanglement monogamy in a three-qubit state
NASA Astrophysics Data System (ADS)
Huang, Jie-Hui; Zhu, Shi-Yao
2008-07-01
We investigate the monogamy nature of entanglement in a three-qubit system. A monogamy inequality is presented to describe the exclusive relation between the A-B two-qubit concurrence CAB and the AB-C three-qubit concurrence C(AB)C , which represents the entanglement between qubits A and B as a whole and the third qubit C . It is found that the entanglement between any two qubits in a three-qubit system is limited by the entanglement between these two qubits and another qubit. As a consequence, we present the upper bounds for the concurrence CAB , when the concurrence between qubits A and C (CAC) and the concurrence between qubits B and C (CBC) are both given or one of the two is provided.
A Multipli-entangled Photon Source for Cluster State Generation
2012-04-01
interferometric stability for any associated feed-forward methods required in photon-based quantum logic circuitry. 15. SUBJECT TERMS Quantum , entangled photons...required in photon-based quantum logic circuitry. Key Words: quantum , entangled photons, spontaneous parametric down-conversion 2. INTRODUCTION Photon...based quantum bits (qubits) continue to serve as one of the leading technologies for the demonstration of quantum computation. This is in part due to
Practical single-photon-assisted remote state preparation with non-maximally entanglement
NASA Astrophysics Data System (ADS)
Wang, Dong; Huang, Ai-Jun; Sun, Wen-Yang; Shi, Jia-Dong; Ye, Liu
2016-08-01
Remote state preparation (RSP) and joint remote state preparation (JRSP) protocols for single-photon states are investigated via linear optical elements with partially entangled states. In our scheme, by choosing two-mode instances from a polarizing beam splitter, only the sender in the communication protocol needs to prepare an ancillary single-photon and operate the entanglement preparation process in order to retrieve an arbitrary single-photon state from a photon pair in partially entangled state. In the case of JRSP, i.e., a canonical model of RSP with multi-party, we consider that the information of the desired state is split into many subsets and in prior maintained by spatially separate parties. Specifically, with the assistance of a single-photon state and a three-photon entangled state, it turns out that an arbitrary single-photon state can be jointly and remotely prepared with certain probability, which is characterized by the coefficients of both the employed entangled state and the target state. Remarkably, our protocol is readily to extend to the case for RSP and JRSP of mixed states with the all optical means. Therefore, our protocol is promising for communicating among optics-based multi-node quantum networks.
NASA Astrophysics Data System (ADS)
Steenbakkers, Rudi J. A.; Tzoumanekas, Christos; Li, Ying; Liu, Wing Kam; Kröger, Martin; Schieber, Jay D.
2014-01-01
We present a method to map the full equilibrium distribution of the primitive-path (PP) length, obtained from multi-chain simulations of polymer melts, onto a single-chain mean-field ‘target’ model. Most previous works used the Doi-Edwards tube model as a target. However, the average number of monomers per PP segment, obtained from multi-chain PP networks, has consistently shown a discrepancy of a factor of two with respect to tube-model estimates. Part of the problem is that the tube model neglects fluctuations in the lengths of PP segments, the number of entanglements per chain and the distribution of monomers among PP segments, while all these fluctuations are observed in multi-chain simulations. Here we use a recently proposed slip-link model, which includes fluctuations in all these variables as well as in the spatial positions of the entanglements. This turns out to be essential to obtain qualitative and quantitative agreement with the equilibrium PP-length distribution obtained from multi-chain simulations. By fitting this distribution, we are able to determine two of the three parameters of the model, which govern its equilibrium properties. This mapping is executed for four different linear polymers and for different molecular weights. The two parameters are found to depend on chemistry, but not on molecular weight. The model predicts a constant plateau modulus minus a correction inversely proportional to molecular weight. The value for well-entangled chains, with the parameters determined ab initio, lies in the range of experimental data for the materials investigated.
Quantum communication for satellite-to-ground networks with partially entangled states
NASA Astrophysics Data System (ADS)
Chen, Na; Quan, Dong-Xiao; Pei, Chang-Xing; Yang-Hong
2015-02-01
To realize practical wide-area quantum communication, a satellite-to-ground network with partially entangled states is developed in this paper. For efficiency and security reasons, the existing method of quantum communication in distributed wireless quantum networks with partially entangled states cannot be applied directly to the proposed quantum network. Based on this point, an efficient and secure quantum communication scheme with partially entangled states is presented. In our scheme, the source node performs teleportation only after an end-to-end entangled state has been established by entanglement swapping with partially entangled states. Thus, the security of quantum communication is guaranteed. The destination node recovers the transmitted quantum bit with the help of an auxiliary quantum bit and specially defined unitary matrices. Detailed calculations and simulation analyses show that the probability of successfully transferring a quantum bit in the presented scheme is high. In addition, the auxiliary quantum bit provides a heralded mechanism for successful communication. Based on the critical components that are presented in this article an efficient, secure, and practical wide-area quantum communication can be achieved. Project supported by the National Natural Science Foundation of China (Grant Nos. 61072067 and 61372076), the 111 Project (Grant No. B08038), the Fund from the State Key Laboratory of Integrated Services Networks (Grant No. ISN 1001004), and the Fundamental Research Funds for the Central Universities (Grant Nos. K5051301059 and K5051201021).
Optomechanically induced transparency associated with steady-state entanglement
NASA Astrophysics Data System (ADS)
He, Yong
2015-01-01
We theoretically investigate a two-cavity optomechanical system in which a cavity (cavity a ) couples to a mechanical resonator via radiation pressure and to another cavity (cavity c ) via a common waveguide. In the excitation of a strong pump filed to cavity a , the steady-state entanglement between cavity a and c , as a quantum channel, can be generated, which provides an indirect optical pathway to excite cavity c by means of the pump filed. Quantum interference between the direct and indirect optical pathways gives rise to an optomechanically induced transparency appearing in the probe transmission of cavity c . Unlike in a typical optomechanically induced transparency effect, the electromagnetical control of the transmission is implemented by resorting to the quantum channel. Furthermore, the coupling strength of the two cavities is an important factor of the quantum channel, which can influence the width of the transparency window and the bistable behavior of the mean photon number in cavity a . We also illustrate that the electromagnetical control via quantum channel can be exploited to implement the optical switch and the slow light.
NASA Astrophysics Data System (ADS)
Ota, Yukihiro; Mikami, Shuji; Yoshida, Motoyuki; Ohba, Ichiro
2007-11-01
Yu, Brown and Chuang investigated the entanglement attainable from unitary transformed thermal states in liquid-state nuclear magnetic resonance (NMR). Their research gave insight into the role of entanglement in a liquid-state NMR quantum computer. However, they assumed that the Zeeman energy of each nuclear spin which corresponds to a qubit takes a common value for all; there is no chemical shift. In this paper, we research a model with chemical shifts and analytically derive the physical parameter region where unitary transformed thermal states are entangled, by employing the positive partial transposition (PPT) criterion with respect to any bipartition. The analysis taking account of the chemical shift reveals how the difference between quantum gates reflects on the physical parameter region where unitary transformed thermal states are entangled. In addition, we examine the distillability of unitary transformed thermal states and the effect of the chemical shifts on the boundary between the separability and the nonseparability.
Distillation of mixed-state continuous-variable entanglement by photon subtraction
Zhang Shengli; Loock, Peter van
2010-12-15
We present a detailed theoretical analysis for the distillation of one copy of a mixed two-mode continuous-variable entangled state using beam splitters and coherent photon-detection techniques, including conventional on-off detectors and photon-number-resolving detectors. The initial Gaussian mixed-entangled states are generated by transmitting a two-mode squeezed state through a lossy bosonic channel, corresponding to the primary source of errors in current approaches to optical quantum communication. We provide explicit formulas to calculate the entanglement in terms of logarithmic negativity before and after distillation, including losses in the channel and the photon detection, and show that one-copy distillation is still possible even for losses near the typical fiber channel attenuation length. A lower bound for the transmission coefficient of the photon-subtraction beam splitter is derived, representing the minimal value that still allows to enhance the entanglement.
NASA Astrophysics Data System (ADS)
Li, Hui; Wang, Shuhao; Cui, Jianlian; Long, Guilu
2013-04-01
The entanglement quantification and classification of multipartite quantum states are two important research fields in quantum information. In this work, we study the entanglement of arbitrary-dimensional multipartite pure states by looking at the averaged partial entropies of various bipartite partitions of the system, namely, the so-called Manhattan distance (l1 norm) of averaged partial entropies (MAPE), and it is proved to be an entanglement measure for pure states. We connected the MAPE with the coefficient matrices, which are important tools in entanglement classification and reexpressed the MAPE for arbitrary-dimensional multipartite pure states by the nonzero singular values of the coefficient matrices. The entanglement properties of the n-qubit Dicke states, arbitrary-dimensional Greenberger-Horne-Zeilinger states, and D3n states are investigated in terms of the MAPE, and the relation between the rank of the coefficient matrix and the degree of entanglement is demonstrated for symmetric states by two examples.
Podoshvedov, S. A.
2008-03-15
We study a teleportation protocol of an unknown macroscopic qubit by means of a quantum channel composed of the displaced vacuum and single-photon states. The scheme is based on linear optical devices such as a beam splitter and photon number resolving detectors. A method based on conditional measurement is used to generate both the macroscopic qubit and entangled state composed from displaced vacuum and single-photon states. We show that such a qubit has both macroscopic and microscopic properties. In particular, we investigate a quantum teleportation protocol from a macroscopic object to a microscopic state.
Quantum entanglement at ambient conditions in a macroscopic solid-state spin ensemble.
Klimov, Paul V; Falk, Abram L; Christle, David J; Dobrovitski, Viatcheslav V; Awschalom, David D
2015-11-01
Entanglement is a key resource for quantum computers, quantum-communication networks, and high-precision sensors. Macroscopic spin ensembles have been historically important in the development of quantum algorithms for these prospective technologies and remain strong candidates for implementing them today. This strength derives from their long-lived quantum coherence, strong signal, and ability to couple collectively to external degrees of freedom. Nonetheless, preparing ensembles of genuinely entangled spin states has required high magnetic fields and cryogenic temperatures or photochemical reactions. We demonstrate that entanglement can be realized in solid-state spin ensembles at ambient conditions. We use hybrid registers comprising of electron-nuclear spin pairs that are localized at color-center defects in a commercial SiC wafer. We optically initialize 10(3) identical registers in a 40-μm(3) volume (with [Formula: see text] fidelity) and deterministically prepare them into the maximally entangled Bell states (with 0.88 ± 0.07 fidelity). To verify entanglement, we develop a register-specific quantum-state tomography protocol. The entanglement of a macroscopic solid-state spin ensemble at ambient conditions represents an important step toward practical quantum technology.
Quantum entanglement at ambient conditions in a macroscopic solid-state spin ensemble
Klimov, Paul V.; Falk, Abram L.; Christle, David J.; Dobrovitski, Viatcheslav V.; Awschalom, David D.
2015-01-01
Entanglement is a key resource for quantum computers, quantum-communication networks, and high-precision sensors. Macroscopic spin ensembles have been historically important in the development of quantum algorithms for these prospective technologies and remain strong candidates for implementing them today. This strength derives from their long-lived quantum coherence, strong signal, and ability to couple collectively to external degrees of freedom. Nonetheless, preparing ensembles of genuinely entangled spin states has required high magnetic fields and cryogenic temperatures or photochemical reactions. We demonstrate that entanglement can be realized in solid-state spin ensembles at ambient conditions. We use hybrid registers comprising of electron-nuclear spin pairs that are localized at color-center defects in a commercial SiC wafer. We optically initialize 103 identical registers in a 40-μm3 volume (with 0.95−0.07+0.05 fidelity) and deterministically prepare them into the maximally entangled Bell states (with 0.88 ± 0.07 fidelity). To verify entanglement, we develop a register-specific quantum-state tomography protocol. The entanglement of a macroscopic solid-state spin ensemble at ambient conditions represents an important step toward practical quantum technology. PMID:26702444
Fusion of entangled coherent W and GHZ states in cavity QED
NASA Astrophysics Data System (ADS)
Zang, Xue-Ping; Yang, Ming; Song, Wei; Cao, Zhuo-Liang
2016-07-01
Efficient preparation of W and GHZ states encoded in various degrees of freedom of quantum particles is vital in quantum information science. So far, most of the studies have focused on polarization encoded photonic W and GHZ states. In this paper, we focus on W- and GHZ-class entangled coherent states, and propose schemes to fuse small W- and GHZ-entangled coherent states into larger ones. Based on successive detuned interactions between optical modes and an ancilla atom, an (N + M - 2)-mode entangled coherent W state can be probabilistically prepared from an N-mode and an M-mode entangled coherent W states. This fusion scheme applies to entangled coherent GHZ states too, and it can succeed in a deterministic way. The ancilla atom only interacts with a single optical mode, which avoids the problem of synchronizing many atoms in the previous cavity QED based fusion schemes. The detuning property of the interaction makes the current fusion scheme more feasible that the ones based on resonant atom-light interactions. In addition, the two levels of the ancilla atom for encoding quantum information are two degenerate ground states, and the excited state is adiabatically eliminated during the fusion process, so the atomic decay from excited states does not affect the quality of the fusion process.
Hamada, Mitsuru
2003-07-01
The teleportation channel associated with an arbitrary bipartite state denotes the map that represents the change suffered by a teleported state when the bipartite state is used instead of the ideal maximally entangled state for teleportation. This work presents and proves an explicit expression of the teleportation channel for teleportation using Weyl's projective unitary representation of (Z/dZ){sup 2n} for integers d{>=}2, n{>=}1, which has been known for n=1. This formula allows any correlation among the n bipartite mixed states, and an application shows the existence of reliable schemes for distillation of entanglement from a sequence of mixed states with correlation.
Wang, Meiyu; Yan, Fengli; Gao, Ting
2016-01-01
We propose a theoretical protocol for preparing four-photon polarization entangled decoherence-free states, which are immune to the collective noise. With the assistance of the cross-Kerr nonlinearities, a two-photon spatial entanglement gate, two controlled-NOT gates, a four-photon polarization entanglement gate are inserted into the circuit, where X homodyne measurements are aptly applied. Combined with some swap gates and simple linear optical elements, four-photon polarization entangled decoherence-free states which can be utilized to represent two logical qubits, |0〉L and |1〉L are achieved at the output ports of the circuit. This generation scheme may be implemented with current experimental techniques. PMID:27901116
Protocol using kicked Ising dynamics for generating states with maximal multipartite entanglement
NASA Astrophysics Data System (ADS)
Mishra, Sunil K.; Lakshminarayan, Arul; Subrahmanyam, V.
2015-02-01
We present a solvable model of iterating cluster state protocols that lead to entanglement production, between contiguous blocks, of 1 ebit per iteration. This continues until the blocks are maximally entangled, at which stage an unravelling begins at the same rate until the blocks are unentangled. The model is a variant of the transverse-field Ising model and can be implemented with controlled-not and single-qubit gates. The interqubit entanglement as measured by the concurrence is shown to be zero for periodic chain realizations, while for open boundaries there are very specific instances at which these can develop. Thus we introduce a class of simply produced states with very large multipartite entanglement content of potential use in measurement-based quantum computing.
All-order dispersion cancellation and energy-time entangled state.
Ryu, Jinsoo; Cho, Kiyoung; Oh, Cha-Hwan; Kang, Hoonsoo
2017-01-23
Dispersion cancellation with an energy-time entangled photon pair in Hong-Ou-Mandel (HOM) interference is one phenomenon that reveals the nonclassical nature of the entangled photon pair. This phenomenon has been observed in materials with very weak dispersions. If the higher-order dispersion coefficient is non-negligible, then the experiment must be modified to realize dispersion cancellation. All-order dispersion cancellation using balanced dispersion was suggested by Steinberg. However, the same phenomenon is expected to occur even if a photon pair is not entangled. This behaviour can be explained by path indistinguishability with identical dispersion. To achieve an all-order dispersion experiment that cannot be explained classically, we modified the experiment and performed another all-order dispersion cancellation experiment that cannot be explained by identical dispersion. This is the first demonstration of nonclassical all-order dispersion cancellation.
Entangled-state engineering of vibrational modes in a multimembrane optomechanical system
NASA Astrophysics Data System (ADS)
Xu, Xun-Wei; Zhao, Yan-Jun; Liu, Yu-xi
2013-08-01
We propose an efficient method to generate entangled states of vibrational modes of membranes which are coupled to a single-mode cavity field via the radiation pressure. By using sideband excitations, we show that arbitrary entangled states of vibrational modes in different membranes can be produced in principle by sequentially applying a series of classical pulses with desired frequencies, phases, and durations. As examples, we show how to synthesize several typical entangled states, such as Bell states, NOON states, Greenberger-Horne-Zeilinger states, and W states. The environmental effect, information leakage, and experimental feasibility are briefly discussed. Our proposal can be applied to different setups of optomechanical systems, in which vibrating modes of many mechanical resonators are coupled to a single-mode cavity.
Controlled Remote Preparation of an Arbitrary Four-Qubit χ State Via Partially Entangled Channel
NASA Astrophysics Data System (ADS)
Ma, Song-Ya; Chen, Wei-Lin; Qu, Zhi-Guo; Tang, Ping
2017-02-01
By constructing sets of ingenious measurement bases at the sender's and the controller's locations, we devise two schemes to realize the controlled remote preparation of an arbitrary four-qubit χ-state via partially entangled quantum resource. The success probabilities of the proposed schemes are 50 % and 100 %, respectively. It means that the success probabilities are independent of the coefficients of the entangled channel.
Entanglement and purity of two-mode Gaussian states in noisy channels
Serafini, Alessio; Illuminati, Fabrizio; De Siena, Silvio; Paris, Matteo G.A.
2004-02-01
We study the evolution of purity, entanglement, and total correlations of general two-mode continuous variable Gaussian states in arbitrary uncorrelated Gaussian environments. The time evolution of purity, von Neumann entropy, logarithmic negativity, and mutual information is analyzed for a wide range of initial conditions. In general, we find that a local squeezing of the bath leads to a faster degradation of purity and entanglement, while it can help to preserve the mutual information between the modes.
Wu, Jin-Lei; Ji, Xin; Zhang, Shou
2017-01-01
We propose a dressed-state scheme to achieve shortcuts to adiabaticity in atom-cavity quantum electrodynamics for speeding up adiabatic two-atom quantum state transfer and maximum entanglement generation. Compared with stimulated Raman adiabatic passage, the dressed-state scheme greatly shortens the operation time in a non-adiabatic way. By means of some numerical simulations, we determine the parameters which can guarantee the feasibility and efficiency both in theory and experiment. Besides, numerical simulations also show the scheme is robust against the variations in the parameters, atomic spontaneous emissions and the photon leakages from the cavity.
Bidirectional Controlled Joint Remote State Preparation via a Seven-Qubit Entangled State
NASA Astrophysics Data System (ADS)
Wang, Xiao-yu; Mo, Zhi-wen
2017-04-01
A new protocol for implementing five-party bidirectional controlled joint remote state preparation is proposed by using a seven-qubit entangled state as the quantum channel. It can be shown that two distant senders can simultaneously and deterministically exchange their states with the other senders under the control of the supervisor, and it cannot be succeed without permission of the controller. Only pauli operation and single-qubit measurement are used in our scheme, so the scheme with five-party is feasible within the reach of current technologies.
NASA Astrophysics Data System (ADS)
Guo, Rui; Zhou, Lan; Gu, Shi-Pu; Wang, Xing-Fu; Sheng, Yu-Bo
2017-03-01
The concatenated Greenberger-Horne-Zeilinger (C-GHZ) state is a new type of multipartite entangled state, which has potential application in future quantum information. In this paper, we propose a protocol of constructing arbitrary C-GHZ entangled state approximatively. Different from previous protocols, each logic qubit is encoded in the coherent state. This protocol is based on the linear optics, which is feasible in experimental technology. This protocol may be useful in quantum information based on the C-GHZ state.
Entanglement entropy scaling in solid-state spin arrays via capacitance measurements
NASA Astrophysics Data System (ADS)
Banchi, Leonardo; Bayat, Abolfazl; Bose, Sougato
2016-12-01
Solid-state spin arrays are being engineered in varied systems, including gated coupled quantum dots and interacting dopants in semiconductor structures. Beyond quantum computation, these arrays are useful integrated analog simulators for many-body models. As entanglement between individual spins is extremely short ranged in these models, one has to measure the entanglement entropy of a block in order to truly verify their many-body entangled nature. Remarkably, the characteristic scaling of entanglement entropy, predicted by conformal field theory, has yet to be measured. Here, we show that with as few as two replicas of a spin array, and capacitive double-dot singlet-triplet measurements on neighboring spin pairs, the above scaling of the entanglement entropy can be verified. This opens up the controlled simulation of quantum field theories, as we exemplify with uniform chains and Kondo-type impurity models, in engineered solid-state systems. Our procedure remains effective even in the presence of typical imperfections of realistic quantum devices and can be used for thermometry, and to bound entanglement and discord in mixed many-body states.
Quantum teleportation and entanglement swapping of matter qubits with coherent multiphoton states
NASA Astrophysics Data System (ADS)
Torres, J. M.; Bernád, J. Z.; Alber, G.
2014-07-01
Protocols for probabilistic entanglement-assisted quantum teleportation and for entanglement swapping of material qubits are presented. They are based on a protocol for postselective Bell- state projection which is capable of projecting two material qubits onto a Bell state with the help of ancillary coherent multiphoton states and postselection by balanced homodyne photodetection. Provided this photonic postselection is successful, we explore the theoretical possibilities of realizing unit-fidelity quantum teleportation and entanglement swapping with 25% success probability. This photon-assisted Bell projection is generated by coupling almost resonantly the two material qubits to single modes of the radiation field in two separate cavities in a Ramsey-type interaction sequence and by measuring the emerged field states in a balanced homodyne detection scenario. As these quantum protocols require basic tools of quantum state engineering of coherent multiphoton states and balanced homodyne photodetection, they may offer interesting perspectives in particular for current quantum optical applications in quantum information processing.
NASA Astrophysics Data System (ADS)
Qian, Jing; Zhang, Weiping
2017-03-01
We develop a scheme for deterministic generation of an entangled state between two atoms on different Rydberg states via a chirped adiabatic passage, which directly connects the initial ground and target entangled states and also does not request the normally needed blockade effect. The occupancy of intermediate states suffers from a strong reduction via two pulses with proper time-dependent detunings and the electromagnetically induced transparency condition. By solving the analytical expressions of eigenvalues and eigenstates of a two-atom system, we investigate the optimal parameters for guaranteeing the adiabatic condition. We present a detailed study for the effect of pulse duration, changing rate, different Rydberg interactions on the fidelity of the prepared entangled state with experimentally feasible parameters, which reveals a good agreement between the analytic and full numerical results.
Tomography of the quantum state of photons entangled in high dimensions
Agnew, Megan; Leach, Jonathan; McLaren, Melanie; Roux, F. Stef; Boyd, Robert W.
2011-12-15
Systems entangled in high dimensions have recently been proposed as important tools for various quantum information protocols, such as multibit quantum key distribution and loophole-free tests of nonlocality. It is therefore important to have precise knowledge of the nature of such entangled quantum states. We tomographically reconstruct the quantum state of the two photons produced by parametric downconversion that are entangled in a d-dimensional orbital angular momentum basis. We determine exactly the density matrix of the entangled two-qudit state with d ranging from 2 to 8. The recording of higher-dimensional states is limited only by the number of data points required and therefore the length of time needed to complete the measurements. We find all the measured states to have fidelities and linear entropies that satisfy the criteria required for a violation of the appropriate high-dimensional Bell inequality. Our results therefore precisely characterize the nature of the entanglement, thus establishing the suitability of such states for applications in quantum information science.
Algorithmic Construction of Local Hidden Variable Models for Entangled Quantum States.
Hirsch, Flavien; Quintino, Marco Túlio; Vértesi, Tamás; Pusey, Matthew F; Brunner, Nicolas
2016-11-04
Constructing local hidden variable (LHV) models for entangled quantum states is a fundamental problem, with implications for the foundations of quantum theory and for quantum information processing. It is, however, a challenging problem, as the model should reproduce quantum predictions for all possible local measurements. Here we present a simple method for building LHV models, applicable to any entangled state and considering continuous sets of measurements. This leads to a sequence of tests which, in the limit, fully captures the set of quantum states admitting a LHV model. Similar methods are developed for local hidden state models. We illustrate the practical relevance of these methods with several examples.
Algorithmic Construction of Local Hidden Variable Models for Entangled Quantum States
NASA Astrophysics Data System (ADS)
Hirsch, Flavien; Quintino, Marco Túlio; Vértesi, Tamás; Pusey, Matthew F.; Brunner, Nicolas
2016-11-01
Constructing local hidden variable (LHV) models for entangled quantum states is a fundamental problem, with implications for the foundations of quantum theory and for quantum information processing. It is, however, a challenging problem, as the model should reproduce quantum predictions for all possible local measurements. Here we present a simple method for building LHV models, applicable to any entangled state and considering continuous sets of measurements. This leads to a sequence of tests which, in the limit, fully captures the set of quantum states admitting a LHV model. Similar methods are developed for local hidden state models. We illustrate the practical relevance of these methods with several examples.
NASA Astrophysics Data System (ADS)
Orús, Román
2014-10-01
This is a partly non-technical introduction to selected topics on tensor network methods, based on several lectures and introductory seminars given on the subject. It should be a good place for newcomers to get familiarized with some of the key ideas in the field, specially regarding the numerics. After a very general introduction we motivate the concept of tensor network and provide several examples. We then move on to explain some basics about Matrix Product States (MPS) and Projected Entangled Pair States (PEPS). Selected details on some of the associated numerical methods for 1d and 2d quantum lattice systems are also discussed.
Tripartite entanglement in single-neutron interferometer experiments
Erdösi, Daniel; Hasegawa, Yuji; Huber, Marcus; Hiesmayr, Beatrix C.
2014-12-04
We present experimental evidence of the generation of distinct types of genuine multipartite entanglement between the spin, energy, and path degrees of freedom within single-neutron quantum systems. This is achieved via the development of new spin manipulation apparatuses for neutron interferometry and the entanglement is detected via appropriately designed and optimized non-linear witnesses. We demonstrate the extraordinarily high controllability and fidelity of the generated entangled states.
Entanglement of two-electron spin states in a double quantum dot
NASA Astrophysics Data System (ADS)
Bagrov, V. G.; Gitman, D. M.; Levin, A. D.; Meireles, M. S.
Recently, an implementation of a universal set of one- and two-quantum-bit gates for quantum computation using spin states of coupled single-electron quantum dots was proposed. It was demonstrated that it is possible to execute a coherent control of a quantum system based on two-electron spin states in a double quantum dot, allowing state preparation, coherent manipulation, and projective readout. This possibility is based on rapid electrical control of the spin exchange interaction. These results motivated us to develop a formal theoretical study of the corresponding model of two coupled spins placed in a magnetic field and subjected to a time-dependent mutual Heisenberg interaction. Using possible exact solutions of the corresponding quantum problem, we study entangling of different separable initial states in this model. It is demonstrated that the entanglement due to a time-dependent Heisenberg interaction is dominating in comparison with the entanglement due to the action of an external magnetic field.
Superoperator analysis of entanglement in a four-qubit cluster state
NASA Astrophysics Data System (ADS)
Weinstein, Yaakov S.; Feldman, Jay; Robins, Jacob; Zukus, Jason; Gilbert, Gerald
2012-03-01
In this paper we utilize superoperator formalism to explore the entanglement evolution of four-qubit cluster states in a number of decohering environments. A four-qubit cluster state is a resource for the performance of an arbitrary single-logical-qubit rotation via measurement-based cluster-state quantum computation. We are specifically interested in the relationship between entanglement evolution and the fidelity with which the arbitrary single-logical-qubit rotation can be implemented in the presence of decoherence as this will have important experimental ramifications. We also note the exhibition of entanglement sudden death (ESD) and ask how severely its onset affects the utilization of the cluster state as a means of implementing an arbitrary single-logical-qubit rotation.
NASA Astrophysics Data System (ADS)
Dahlsten, Oscar C. O.; Lupo, Cosmo; Mancini, Stefano; Serafini, Alessio
2014-09-01
We provide a summary of both seminal and recent results on typical entanglement. By ‘typical’ values of entanglement, we refer here to values of entanglement quantifiers that (given a reasonable measure on the manifold of states) appear with arbitrarily high probability for quantum systems of sufficiently high dimensionality. We shall focus on pure states and work within the Haar measure framework for discrete quantum variables, where we report on results concerning the average von Neumann and linear entropies as well as arguments implying the typicality of such values in the asymptotic limit. We then proceed to discuss the generation of typical quantum states with random circuitry. Different phases of entanglement, and the connection between typical entanglement and thermodynamics are discussed. We also cover approaches to measures on the non-compact set of Gaussian states of continuous variable quantum systems.
NASA Astrophysics Data System (ADS)
Wei, Zhao-Hui; Zha, Xin-Wei; Yu, Yan
2017-01-01
Remote state preparation is increasingly becoming attractive in recent years, people have already started theoretical and experimental research, and have made valuable research results. Recently, a scheme for probabilistic remote preparation of a four-particle cluster-type was proposed Wang (Int. J. Theor. Phys. 55, 4371-4383 (2016)). In this paper we present a modified scheme for probabilistic remote preparation of four-particle cluster-type states using non-maximally entangled states as quantum channel. Compared with the previous schemes,the advantage of our schemes is that the total success probability of remote state preparation is increased from (b 1 b 2)2 to 4(b 1 b 2)2.
NASA Astrophysics Data System (ADS)
Wei, Zhao-Hui; Zha, Xin-Wei; Yu, Yan
2017-04-01
Remote state preparation is increasingly becoming attractive in recent years, people have already started theoretical and experimental research, and have made valuable research results. Recently, a scheme for probabilistic remote preparation of a four-particle cluster-type was proposed Wang (Int. J. Theor. Phys. 55, 4371-4383 (2016)). In this paper we present a modified scheme for probabilistic remote preparation of four-particle cluster-type states using non-maximally entangled states as quantum channel. Compared with the previous schemes,the advantage of our schemes is that the total success probability of remote state preparation is increased from ( b 1 b 2)2 to 4( b 1 b 2)2.
NASA Astrophysics Data System (ADS)
Hu, Yao-Hua; Tao, Ya-Ping; Tan, Yong-Gang; Yang, Hai-Feng
2017-02-01
Considering X-states the density matrixes of which look like the letter X, we propose a weak measurement-based entanglement protection protocol of two-qubit X-states under local amplitude damping channels using weak measurement and reversal operation. It is shown that, with increase of the decoherence parameter, the entanglement attenuates rapidly owing to the amplitude damping noise and even experiences entanglement sudden death (ESD). However, the entanglement under the weak measurement and reversal operation is always much stronger than the entanglement undergoing the amplitude damping decoherence. These results reflect that entanglement of two-qubit X-states from amplitude damping decoherence can be protected, and ESD can be circumvented by increasing the weak measurement strength.
Influence of classic noise on entangled state formation in parametric systems
NASA Astrophysics Data System (ADS)
Martynov, V. O.; Mironov, V. A.; Smirnov, L. A.
2017-04-01
A study of ‘high temperature’ entangled states in a system of two parametrically coupled quantum oscillators placed into independent thermal baths is performed taking into account partially coherent parametric pump. Processes in an open system are considered based on the Heisenberg–Langevin formalism. We obtain a closed system of equations for the averaged quadratic correlation functions in quantum stochastic problem as a result of Markov processes approximation. On the basis of numerical calculations the dynamics of the logarithmic negativity, which is the measure of entanglement in the system, is investigated. It is shown that the partial coherence of the parametric pump makes the lifetime of the entangled states finite. The threshold characteristics of the formation and existence of these states are specified.
Lo Franco, R.; Compagno, G.; Messina, A.; Napoli, A.
2005-11-15
We consider the entanglement of orthogonal generalized Bernoulli states in two separate single-mode high-Q cavities. The expectation values and the correlations of the electric field in the cavities are obtained. We then define, in each cavity, a dichotomic operator expressible in terms of the field states which can be, in principle, experimentally measured by a probe atom that 'reads' the field. Using the quantum correlations of couples of these operators, we construct a Bell's inequality which is shown to be violated for a wide range of the degree of entanglement and which can be tested in a simple way. Thus the cavity fields directly show quantum nonlocal properties. A scheme is also sketched to generate entangled orthogonal generalized Bernoulli states in the two separate cavities.
Li Zhenni; Jin Jiasen; Yu Changshui
2011-01-15
We present schemes for a type of one-parameter bipartite quantum state to probe quantum entanglement, quantum discord, the classical correlation, and the quantum state based on cavity QED. It is shown that our detection does not influence all these measured quantities. We also discuss how the spontaneous emission introduced by our probe atom influences our detection.
Decay and storage of multiparticle entangled states of atoms in collective thermostat
Basharov, A. M.; Gorbachev, V. N.; Rodichkina, A. A.
2006-10-15
We derive a master equation describing the collective decay of two-level atoms inside a single mode cavity in the dispersive limit. By considering atomic decay in the collective thermostat, we found a decoherence-free subspace of the multiparticle entangled states of the W-like class. We present a scheme for writing and storing these states in collective thermostat.
Concurrent remote entanglement with continuous variables
NASA Astrophysics Data System (ADS)
Zalys-Geller, E.; Narla, A.; Shankar, S.; Hatridge, M.; Silveri, M.; Sliwa, K. M.; Mundhada, S. O.; Girvin, S. M.; Devoret, M. H.
A necessary ingredient for large scale quantum information processing is the ability to entangle distant qubits on demand. In the field of superconducting quantum information, this process can be achieved by entangling stationary superconducting qubits with flying coherent states of microwave light, which are then co-amplified by a Josephson Parametric Converter (JPC). The JPC also serves as a which-path information eraser, causing the probabilistic continuous measurement process to concurrently entangle the qubits. We discuss the sensitivity of the experiment to the loss of quantum information during the flight of the coherent states, as well as strategies to improve which-path information erasure and reduce information loss to the degree required for entanglement generation. Work supported by ARO, AFOSR, NSF, and YINQE.
GHZ argument for four-qubit entangled states in the presence of white and colored noise
NASA Astrophysics Data System (ADS)
Shi, Ming-jun; Ren, Chang-liang; Chong, Bo; Du, Jiang-feng
2008-04-01
Greenberger-Horn-Zeilinger (GHZ) argument of nonlocality without inequalities is extended to the case of four-qubit mixed states. Three different kinds of entangled states are analyzed in presence of white and colored noise. The nonlocality properties of these states will be weakened and destroyed by the noise. We found that all these states have the same ability to resist the influence of white noise, while the cluster state is the most robust against colored noise.
Efficient quantum secret sharing scheme with two-particle entangled states
NASA Astrophysics Data System (ADS)
Zhu, Zhen-Chao; Zhang, Yu-Qing; Fu, An-Min
2011-04-01
This paper proposes a protocol for multi-party quantum secret sharing utilizing four non-orthogonal two-particle entangled states following some ideas in the schemes proposed by Liu et al. (2006 Chin. Phys. Lett. 23 3148) and Zhang et al. (2009 Chin. Phys. B 18 2149) respectively. The theoretical efficiency for qubits of the new protocol is improved from 50% to approaching 100%. All the entangled states can be used for generating the private key except those used for the eavesdropping check. The validity of a probable attack called opaque cheat attack to this kind of protocols is considered in the paper for the first time.
Generation of multiphoton entangled quantum states by means of integrated frequency combs.
Reimer, Christian; Kues, Michael; Roztocki, Piotr; Wetzel, Benjamin; Grazioso, Fabio; Little, Brent E; Chu, Sai T; Johnston, Tudor; Bromberg, Yaron; Caspani, Lucia; Moss, David J; Morandotti, Roberto
2016-03-11
Complex optical photon states with entanglement shared among several modes are critical to improving our fundamental understanding of quantum mechanics and have applications for quantum information processing, imaging, and microscopy. We demonstrate that optical integrated Kerr frequency combs can be used to generate several bi- and multiphoton entangled qubits, with direct applications for quantum communication and computation. Our method is compatible with contemporary fiber and quantum memory infrastructures and with chip-scale semiconductor technology, enabling compact, low-cost, and scalable implementations. The exploitation of integrated Kerr frequency combs, with their ability to generate multiple, customizable, and complex quantum states, can provide a scalable, practical, and compact platform for quantum technologies.
NASA Astrophysics Data System (ADS)
Volynets, M. V.; Gorbachev, V. N.; Zhulis, A. V.; Kazakov, A. Ya; Sakharova, G. P.
2007-12-01
The geometrical measure of entanglement of the W states is introduced and exact analytic expressions are obtained for it. Based on numerical calculations, the degree of entanglement is considered for some states of this class which are used as a quantum channel in problems of quantum theory of information.
Compressively Characterizing High-Dimensional Entangled States with Complementary, Random Filtering
NASA Astrophysics Data System (ADS)
Howland, Gregory A.; Knarr, Samuel H.; Schneeloch, James; Lum, Daniel J.; Howell, John C.
2016-04-01
The resources needed to conventionally characterize a quantum system are overwhelmingly large for high-dimensional systems. This obstacle may be overcome by abandoning traditional cornerstones of quantum measurement, such as general quantum states, strong projective measurement, and assumption-free characterization. Following this reasoning, we demonstrate an efficient technique for characterizing high-dimensional, spatial entanglement with one set of measurements. We recover sharp distributions with local, random filtering of the same ensemble in momentum followed by position—something the uncertainty principle forbids for projective measurements. Exploiting the expectation that entangled signals are highly correlated, we use fewer than 5000 measurements to characterize a 65,536-dimensional state. Finally, we use entropic inequalities to witness entanglement without a density matrix. Our method represents the sea change unfolding in quantum measurement, where methods influenced by the information theory and signal-processing communities replace unscalable, brute-force techniques—a progression previously followed by classical sensing.
Controllable high-fidelity quantum state transfer and entanglement generation in circuit QED.
Xu, Peng; Yang, Xu-Chen; Mei, Feng; Xue, Zheng-Yuan
2016-01-25
We propose a scheme to realize controllable quantum state transfer and entanglement generation among transmon qubits in the typical circuit QED setup based on adiabatic passage. Through designing the time-dependent driven pulses applied on the transmon qubits, we find that fast quantum sate transfer can be achieved between arbitrary two qubits and quantum entanglement among the qubits also can also be engineered. Furthermore, we numerically analyzed the influence of the decoherence on our scheme with the current experimental accessible systematical parameters. The result shows that our scheme is very robust against both the cavity decay and qubit relaxation, the fidelities of the state transfer and entanglement preparation process could be very high. In addition, our scheme is also shown to be insensitive to the inhomogeneous of qubit-resonator coupling strengths.
Two-Party Quantum Private Comparison with Five-Qubit Entangled States
NASA Astrophysics Data System (ADS)
Ye, Tian-Yu; Ji, Zhao-Xu
2017-01-01
In this paper, a two-party quantum private comparison (QPC) protocol is proposed by using five-qubit entangled states as the quantum resource. The proposed protocol needs the help from a semi-honest third party (TP), who is allowed to misbehave on his own but not allowed to conspire with the adversary including the dishonest user. The proposed protocol has the following distinct features: (1) One five-qubit entangled state can be used to achieve the equality comparison of two bits in each round of comparison; (2) Neither unitary operations nor quantum entanglement swapping technology is needed, both of which may consume expensive quantum devices; (3) Only Bell measurements and single-particle measurements are employed, both of which can be realized with current quantum technologies; (4) The security toward both the outside attack and the participant attack can be guaranteed; (5) The private information of two parties is not leaked out to TP.
Arkhipov, Ievgen I.; Peřina Jr., Jan; Haderka, Ondřej; Allevi, Alessia; Bondani, Maria
2016-01-01
Multipartite entanglement and nonclassicality of four-mode Gaussian states generated in two simultaneous nonlinear processes involving parametric down-conversion and frequency up-conversion are analyzed assuming the vacuum as the initial state. Suitable conditions for the generation of highly entangled states are found. Transfer of the entanglement from the down-converted modes into the up-converted ones is also suggested. The analysis of the whole set of states reveals that sub-shot-noise intensity correlations between the equally-populated down-converted modes, as well as the equally-populated up-converted modes, uniquely identify entangled states. They represent a powerful entanglement identifier also in other cases with arbitrarily populated modes. PMID:27658508
Unity fidelity multiple teleportation using partially entangled states
NASA Astrophysics Data System (ADS)
Rigolin, Gustavo
2009-12-01
We show that the multiple teleportation protocol (MTP) given in reference (J Modławska and A Grudka 2008 Phys. Rev. Lett. 100 110503) is not restricted to the Knill-Laflamme-Milburn (KLM) framework. Rather, we show that MTP can be implemented using any teleportation scheme. We also present two new MTPs which, under certain situations, are more efficient than the original one, requiring half of the number of its teleportations to achieve at least the same probability of success (\\mathcal {P}_suc). One of the protocols, however, uses less entanglement than the others yielding, surprisingly, the greatest \\mathcal {P}_suc.
Quantum entanglement at high temperatures? Bosonic systems in nonequilibrium steady state
NASA Astrophysics Data System (ADS)
Hsiang, Jen-Tsung; Hu, B. L.
2015-11-01
This is the second of a series of three papers examining how viable it is for entanglement to be sustained at high temperatures for quantum systems in thermal equilibrium (Case A), in nonequilibrium (Case B) and in nonequilibrium steady state (NESS) conditions (Case C). The system we analyze here consists of two coupled quantum harmonic oscillators each interacting with its own bath described by a scalar field, set at temperatures T 1 > T 2. For constant bilinear inter-oscillator coupling studied here (Case C1) owing to the Gaussian nature, the problem can be solved exactly at arbitrary temperatures even for strong coupling. We find that the valid entanglement criterion in general is not a function of the bath temperature difference, in contrast to thermal transport in the same NESS setting [1]. Thus lowering the temperature of one of the thermal baths does not necessarily help to safeguard the entanglement between the oscillators. Indeed, quantum entanglement will disappear if any one of the thermal baths has a temperature higher than the critical temperature T c, defined as the temperature above which quantum entanglement vanishes. With the Langevin equations derived we give a full display of how entanglement dynamics in this system depends on T 1, T 2, the inter-oscillator coupling and the system-bath coupling strengths. For weak oscillator-bath coupling the critical temperature T c is about the order of the inverse oscillator frequency, but for strong oscillator-bath coupling it will depend on the bath cutoff frequency. We conclude that in most realistic circumstances, for bosonic systems in NESS with constant bilinear coupling, `hot entanglement' is largely a fiction.
Characterizing entanglement of an artificial atom and a cavity cat state with Bell's inequality
Vlastakis, Brian; Petrenko, Andrei; Ofek, Nissim; Sun, Luyan; Leghtas, Zaki; Sliwa, Katrina; Liu, Yehan; Hatridge, Michael; Blumoff, Jacob; Frunzio, Luigi; Mirrahimi, Mazyar; Jiang, Liang; Devoret, M. H.; Schoelkopf, R. J.
2015-01-01
The Schrodinger's cat thought experiment highlights the counterintuitive concept of entanglement in macroscopically distinguishable systems. The hallmark of entanglement is the detection of strong correlations between systems, most starkly demonstrated by the violation of a Bell inequality. No violation of a Bell inequality has been observed for a system entangled with a superposition of coherent states, known as a cat state. Here we use the Clauser–Horne–Shimony–Holt formulation of a Bell test to characterize entanglement between an artificial atom and a cat state, or a Bell-cat. Using superconducting circuits with high-fidelity measurements and real-time feedback, we detect correlations that surpass the classical maximum of the Bell inequality. We investigate the influence of decoherence with states up to 16 photons in size and characterize the system by introducing joint Wigner tomography. Such techniques demonstrate that information stored in superpositions of coherent states can be extracted efficiently, a crucial requirement for quantum computing with resonators. PMID:26611724
NASA Astrophysics Data System (ADS)
Akulin, V. M.; Kabatiansky, G. A.; Mandilara, A.
2015-10-01
Using geometric means, we first consider a density matrix decomposition of a multipartite quantum system of a finite dimension into two density matrices: a separable one, also known as the best separable approximation, and an essentially entangled one, which contains no product state components. We show that this convex decomposition can be achieved in practice with the help of a linear programming algorithm that scales in the general case polynomially with the system dimension. We illustrate the algorithm implementation with an example of a composite system of dimension 12 that undergoes a loss of coherence due to classical noise and we trace the time evolution of its essentially entangled component. We suggest a "geometric" description of entanglement dynamics and demonstrate how it explains the well-known phenomena of sudden death and revival of multipartite entanglements. For a statistical weight loss of the essentially entangled component with time, its average entanglement content is not affected by the coherence loss.
Ground-state fidelity and bipartite entanglement in the Bose-Hubbard model.
Buonsante, P; Vezzani, A
2007-03-16
We analyze the quantum phase transition in the Bose-Hubbard model borrowing two tools from quantum-information theory, i.e., the ground-state fidelity and entanglement measures. We consider systems at unitary filling comprising up to 50 sites and show for the first time that a finite-size scaling analysis of these quantities provides excellent estimates for the quantum critical point. We conclude that fidelity is particularly suited for revealing a quantum phase transition and pinning down the critical point thereof, while the success of entanglement measures depends on the mechanisms governing the transition.
Compressively Characterizing High-Dimensional Entangled States with Complementary, Random Filtering
2016-06-30
22 December 2015; published 12 May 2016) The resources needed to conventionally characterize a quantum system are overwhelmingly large for high...dimensional systems. This obstacle may be overcome by abandoning traditional cornerstones of quantum measurement, such as general quantum states, strong...entanglement without a density matrix. Our method represents the sea change unfolding in quantum measurement, where methods influenced by the
NASA Astrophysics Data System (ADS)
Carlini, A.; Hosoya, A.
2001-02-01
Grover's quantum algorithm for an unstructured search problem and the COUNT algorithm by Brassard et al. are generalized to the case when the initial state is arbitrarily and maximally entangled. This ansatz might be relevant with quantum subroutines, when the computational qubits and the environment are coupled, and in general when the control over the quantum system is partial.
Deterministic Quantum Key Distribution Using Two Non-orthogonal Entangled States
NASA Astrophysics Data System (ADS)
Guo, Ying; Zeng, Gui-Hua
2007-03-01
A deterministic quantum key distribution scheme using two non-orthogonal entangled states is proposed. In the proposed scheme, communicators share key information by exchanging one travelling photon with two random and secret polarization angles. The security of the distributed key is guaranteed by three checking phases in three-way channel and the communicators' secret polarization angles.
Di Lisi, Antonio; De Siena, Silvio; Illuminati, Fabrizio; Vitali, David
2005-09-15
We introduce an efficient, quasideterministic scheme to generate maximally entangled states of two atomic ensembles. The scheme is based on quantum nondemolition measurements of total atomic populations and on adiabatic quantum feedback conditioned by the measurements outputs. The high efficiency of the scheme is tested and confirmed numerically for ideal photodetection as well as in the presence of losses.
Generating two-photon entangled states in a driven two-atom system
Almutairi, Khulud; Tanas, Ryszard; Ficek, Zbigniew
2011-07-15
We describe a mechanism for a controlled generation of a pure Bell state with correlated atoms that involve two or zero excitations. The mechanism inhibits transitions into singly excited collective states of a two-atom system by shifting them from their unperturbed energies. The shift is accomplished by the dipole-dipole interaction between the atoms. The creation of the Bell state is found to be dependent on the relaxation of the atomic excitation. When the relaxation is not present or can be ignored, the state of the system evolves harmonically between a separable to the maximally entangled state. We follow the temporal evolution of the state and find that the concurrence can be different from zero only in the presence of the dipole-dipole interaction. Furthermore, in the limit of a large dipole-dipole interaction, the concurrence reduces to that predicted for an X state of the system. A general inequality is found which shows that the concurrence of an X-state system is a lower bound for the concurrence of the two-atom system. With the relaxation present, the general state of the system is a mixed state that under a strong dipole-dipole interaction reduces the system to an X-state form. We find that mixed states admit of lower level of entanglement, and the entanglement may occur over a finite range of time. A simple analytical expression is obtained for the steady-state concurrence which shows that there is a threshold value for the dipole-dipole interaction relative to the Rabi frequency of the driving field above which the atoms can be entangled over the entire time of the evolution.
Teleportation of a qubit using entangled non-orthogonal states: a comparative study
NASA Astrophysics Data System (ADS)
Sisodia, Mitali; Verma, Vikram; Thapliyal, Kishore; Pathak, Anirban
2017-03-01
The effect of non-orthogonality of an entangled non-orthogonal state-based quantum channel is investigated in detail in the context of the teleportation of a qubit. Specifically, average fidelity, minimum fidelity and minimum assured fidelity (MASFI) are obtained for teleportation of a single-qubit state using all the Bell-type entangled non-orthogonal states known as quasi-Bell states. Using Horodecki criterion, it is shown that the teleportation scheme obtained by replacing the quantum channel (Bell state) of the usual teleportation scheme by a quasi-Bell state is optimal. Further, the performance of various quasi-Bell states as teleportation channel is compared in an ideal situation (i.e., in the absence of noise) and under different noise models (e.g., amplitude and phase damping channels). It is observed that the best choice of the quasi-Bell state depends on the amount non-orthogonality, both in noisy and noiseless case. A specific quasi-Bell state, which was found to be maximally entangled in the ideal conditions, is shown to be less efficient as a teleportation channel compared to other quasi-Bell states in particular cases when subjected to noisy channels. It has also been observed that usually the value of average fidelity falls with an increase in the number of qubits exposed to noisy channels (viz., Alice's, Bob's and to be teleported qubits), but the converse may be observed in some particular cases.
New Maximally Entangled States and Pattern Classification in Two-Qubit System
NASA Astrophysics Data System (ADS)
Singh, Manu Pratap; Rajput, B. S.
2014-09-01
Pattern classifications have been performed by employing the method of Grover's iteration on Bell's MES and Singh-Rajput MES in two-qubit system and it has been demonstrated that for any pattern classification in a two-qubit system the maximally entangled states of Singh-Rajput eigen basis provide the most suitable choice of search states while in no case any of Bell's states is suitable for such pattern classifications.
Wu Chunfeng; Chen Jingling; Oh, C.H.; Kwek, L.C.; Xue Kang
2005-02-01
We construct an explicit Wigner function for the N-mode squeezed state. Based on a previous observation that the Wigner function describes correlations in the joint measurement of the phase-space displaced parity operator, we investigate the nonlocality of the multipartite entangled state by the violation of the Zukowski-Brukner N-qubit Bell inequality. We find that quantum predictions for such a squeezed state violate these inequalities by an amount that grows with the number N.
Quantum state regeneration in entanglement based quantum key distribution protocols
NASA Astrophysics Data System (ADS)
Erdmann, Reinhard
2014-05-01
Quantum Key Distribution (QKD) has been shown to be provably secure when certain idealized conditions are met in a physical realization. All implementations of QKD to date require non-orthogonal basis measurements to implement it; making it commonly assumed that measurement basis variation is fundamental to making QKD protocols secure from eavesdropping. We show here that in particular physical conditions this assumption is incorrect, and that provable security can be achieved without use of multiple bases. Basis setting information can in fact be shared with all potential eavesdroppers, as they are unable to use it to acquire or influence any part of the encryption key generation. Furthermore the key generation efficiency is limited to 100 % as compared with an inherent 50 % limit for alternating bases in BB84 or Entangled Ekert protocols.
NASA Astrophysics Data System (ADS)
Yi, Xiao-jie
2017-04-01
We study quantum entanglement and phase-sensitivity of a Mach-Zehnder interferometer for the coherent spin state input. It's shown that entanglement and the Heisenberg limit of phase-sensitivity can be obtained adjusting the phase shift and increasing the total photons' number.
NASA Astrophysics Data System (ADS)
Wang, Fei; Nie, Wei; Feng, Xunli; Oh, C. H.
2016-07-01
The correlated emission lasing (CEL) is experimentally demonstrated in harmonic oscillators coupled via a single three-level artificial atom [Phys. Rev. Lett. 115, 223603 (2015), 10.1103/PhysRevLett.115.223603] in which two-mode entanglement only exists in a certain time period when the harmonic oscillators are resonant with the atomic transitions. Here we examine this system and show that it is possible to obtain the steady-state entanglement when the two harmonic oscillators are resonant with Rabi sidebands. Applying dressed atomic states and Bogoliubov-mode transformation, we obtain the analytical results of the variance sum of a pair of Einstein-Podolsky-Rosen (EPR)-like operators. The stable entanglement originates from the dissipation process of the Bogoliubov modes because the atomic system can act as a reservoir in dressed state representation. We also show that the entanglement is robust against the dephasing rates of the superconducing atom, which is expected to have important applications in quantum information processing.
Generation of a macroscopic entangled coherent state using quantum memories in circuit QED
Liu, Tong; Su, Qi-Ping; Xiong, Shao-Jie; Liu, Jin-Ming; Yang, Chui-Ping; Nori, Franco
2016-01-01
W-type entangled states can be used as quantum channels for, e.g., quantum teleportation, quantum dense coding, and quantum key distribution. In this work, we propose a way to generate a macroscopic W-type entangled coherent state using quantum memories in circuit QED. The memories considered here are nitrogen-vacancy center ensembles (NVEs), each located in a different cavity. This proposal does not require initially preparing each NVE in a coherent state instead of a ground state, which should significantly reduce its experimental difficulty. For most of the operation time, each cavity remains in a vacuum state, thus decoherence caused by the cavity decay and the unwanted inter-cavity crosstalk are greatly suppressed. Moreover, only one external-cavity coupler qubit is needed, which simplifies the circuit. PMID:27562055
Generation of a macroscopic entangled coherent state using quantum memories in circuit QED.
Liu, Tong; Su, Qi-Ping; Xiong, Shao-Jie; Liu, Jin-Ming; Yang, Chui-Ping; Nori, Franco
2016-08-26
W-type entangled states can be used as quantum channels for, e.g., quantum teleportation, quantum dense coding, and quantum key distribution. In this work, we propose a way to generate a macroscopic W-type entangled coherent state using quantum memories in circuit QED. The memories considered here are nitrogen-vacancy center ensembles (NVEs), each located in a different cavity. This proposal does not require initially preparing each NVE in a coherent state instead of a ground state, which should significantly reduce its experimental difficulty. For most of the operation time, each cavity remains in a vacuum state, thus decoherence caused by the cavity decay and the unwanted inter-cavity crosstalk are greatly suppressed. Moreover, only one external-cavity coupler qubit is needed, which simplifies the circuit.
Generation of a macroscopic entangled coherent state using quantum memories in circuit QED
NASA Astrophysics Data System (ADS)
Liu, Tong; Su, Qi-Ping; Xiong, Shao-Jie; Liu, Jin-Ming; Yang, Chui-Ping; Nori, Franco
2016-08-01
W-type entangled states can be used as quantum channels for, e.g., quantum teleportation, quantum dense coding, and quantum key distribution. In this work, we propose a way to generate a macroscopic W-type entangled coherent state using quantum memories in circuit QED. The memories considered here are nitrogen-vacancy center ensembles (NVEs), each located in a different cavity. This proposal does not require initially preparing each NVE in a coherent state instead of a ground state, which should significantly reduce its experimental difficulty. For most of the operation time, each cavity remains in a vacuum state, thus decoherence caused by the cavity decay and the unwanted inter-cavity crosstalk are greatly suppressed. Moreover, only one external-cavity coupler qubit is needed, which simplifies the circuit.
Path Flow Estimation Using Time Varying Coefficient State Space Model
NASA Astrophysics Data System (ADS)
Jou, Yow-Jen; Lan, Chien-Lun
2009-08-01
The dynamic path flow information is very crucial in the field of transportation operation and management, i.e., dynamic traffic assignment, scheduling plan, and signal timing. Time-dependent path information, which is important in many aspects, is nearly impossible to be obtained. Consequently, researchers have been seeking estimation methods for deriving valuable path flow information from less expensive traffic data, primarily link traffic counts of surveillance systems. This investigation considers a path flow estimation problem involving the time varying coefficient state space model, Gibbs sampler, and Kalman filter. Numerical examples with part of a real network of the Taipei Mass Rapid Transit with real O-D matrices is demonstrated to address the accuracy of proposed model. Results of this study show that this time-varying coefficient state space model is very effective in the estimation of path flow compared to time-invariant model.
Hyperspherical Bloch Vectors with Applications to Entanglement and Quantum State Tomography
NASA Astrophysics Data System (ADS)
Hedemann, Samuel R.
Since the birth of quantum mechanics, it has become apparent that the density operator gives the most complete description of quantum states, both pure and mixed. However, Bloch vectors are also capable of describing all quantum states, with the added bonus that they are real-valued geometrical objects. While Bloch vectors are widely used in many fields such as quantum information and quantum measurement, they are often avoided and may be occasionally misused due to the lack of a complete, centralized theory describing Bloch vectors in depth. Therefore, the purpose of this work is to give a compact, complete introduction to a standard formalism of quantum mechanics for discrete systems in the language of Bloch vectors expressed using hyperspherical parameterizations. The subject matter covers representations of pure and mixed states, unipartite and multipartite systems, closed-form description of Bloch-vector physicality, reductions of state, new investigations of multipartite entanglement, rotations of state, quantum measurements, state and process tomography, quantum operations, and state dynamics in both closed and open quantum systems. A new multipartite entanglement monotone is also developed, with the benefit of being automatically normalized for all possible systems, and it is extended to mixed states with convex roof extension. Emphasis is placed on geometrical interpretations and parameterizations, and on applying the theory to common applications, particularly those related to entanglement and tomography.
Two-party quantum key agreement protocol with four-particle entangled states
NASA Astrophysics Data System (ADS)
He, Yefeng; Ma, Wenping
2016-09-01
Based on four-particle entangled states and the delayed measurement technique, a two-party quantum key agreement protocol is proposed in this paper. In the protocol, two participants can deduce the measurement results of each other’s initial quantum states in terms of the measurement correlation property of four-particle entangled states. According to the corresponding initial quantum states deduced by themselves, two parties can extract the secret keys of each other by using the publicly announced value or by performing the delayed measurement, respectively. This guarantees the fair establishment of a shared key. Since each particle in quantum channel is transmitted only once, the protocol is congenitally free from the Trojan horse attacks. The security analysis shows that the protocol not only can resist against both participant and outsider attacks but also has no information leakage problem. Moreover, it has high qubit efficiency.
Seevinck, Michael; Uffink, Jos
2007-10-15
By introducing a quantitative 'degree of commutativity' in terms of the angle between spin observables we present two tight quantitative trade-off relations in the case of two qubits. First, for entangled states, between the degree of commutativity of local observables and the maximal amount of violation of the Bell inequality: if both local angles increase from zero to {pi}/2 (i.e., the degree of local commutativity decreases), the maximum violation of the Bell inequality increases. Secondly, a converse trade-off relation holds for separable states: if both local angles approach {pi}/2 the maximal value obtainable for the correlations in the Bell inequality decreases and thus the non-violation increases. As expected, the extremes of these relations are found in the case of anticommuting local observables where, respectively, the bounds of 2{radical}(2) and {radical}(2) hold for the expectation value of the Bell operator. The trade-off relations show that noncommmutativity gives 'a more than classical result' for entangled states, whereas 'a less than classical result' is obtained for separable states. The experimental relevance of the trade-off relation for separable states is that it provides an experimental test for two qubit entanglement. Its advantages are twofold: in comparison to violations of Bell inequalities it is a stronger criterion and in comparison to entanglement witnesses it needs to make less strong assumptions about the observables implemented in the experiment.
Quantum nonlocality of generic family of four-qubit entangled pure states
NASA Astrophysics Data System (ADS)
Ding, Dong; He, Ying-Qiu; Yan, Feng-Li; Gao, Ting
2015-07-01
We directly introduce a Bell-type inequality for four-qubit systems. Using the inequality we investigate quantum nonlocality of a generic family of states |Gabcd> [Phys. Rev. A 65 052112 (2002)] and several canonical four-qubit entangled states. It has been demonstrated that the inequality is maximally violated by the so called “four-qubit the maximally entangled state |Gm>” and it is also violated by four-qubit W state and a special family of states |Gab00>. Moreover, a useful entanglement-nonlocality relationship for the family of states |Gab00> is derived. Finally, we present a scheme of preparation of the state |Gm> with linear optics and cross-Kerr nonlinearities. Project supported by the National Natural Science Foundation of China (Grant Nos. 11475054 and 11371005), Hebei Natural Science Foundation of China (Grant Nos. A2012205013 and A2014205060), the Fundamental Research Funds for the Central Universities of Ministry of Education of China (Grant Nos. 3142014068 and 3142014125), and Langfang Key Technology Research and Development Program of China (Grant No. 2014011002).
NASA Astrophysics Data System (ADS)
Poddubny, Alexander N.; Sukhorukov, Andrey A.
2015-09-01
The practical development of quantum plasmonic circuits incorporating non-classical interference [1] and sources of entangled states calls for a versatile quantum theoretical framework which can fully describe the generation and detection of entangled photons and plasmons. However, majority of the presently used theoretical approaches are typically limited to the toy models assuming loss-less and nondispersive elements or including just a few resonant modes. Here, we present a rigorous Green function approach describing entangled photon-plasmon state generation through spontaneous wave mixing in realistic metal-dielectric nanostructures. Our approach is based on the local Huttner-Barnett quantization scheme [2], which enables problem formulation in terms of a Hermitian Hamiltonian where the losses and dispersion are fully encoded in the electromagnetic Green functions. Hence, the problem can be addressed by the standard quantum mechanical perturbation theory, overcoming mathematical difficulties associated with other quantization schemes. We derive explicit expressions with clear physical meaning for the spatially dependent two-photon detection probability, single-photon detection probability and single-photon density matrix. In the limiting case of low-loss nondispersive waveguides our approach reproduces the previous results [3,4]. Importantly, our technique is far more general and can quantitatively describe generation and detection of spatially-entangled photons in arbitrary metal-dielectric structures taking into account actual losses and dispersion. This is essential to perform the design and optimization of plasmonic structures for generation and control of quantum entangled states. [1] J.S. Fakonas, H. Lee, Y.A. Kelaita and H.A. Atwater, Nature Photonics 8, 317(2014) [2] W. Vogel and D.-G. Welsch, Quantum Optics, Wiley (2006). [3] D.A. Antonosyan, A.S. Solntsev and A.A. Sukhorukov, Phys. Rev. A 90 043845 (2014) [4] L.-G. Helt, J.E. Sipe and M.J. Steel, ar
Generation and purification of maximally entangled atomic states in optical cavities
Lougovski, P.; Walther, H.; Solano, E.
2005-01-01
We present a probabilistic scheme for generating and purifying maximally entangled states of two atoms inside an optical cavity via no-photon detection at the cavity output, where ideal detectors are not required. The intermediate mixed states can be continuously purified so as to violate Bell inequalities in a parametrized manner. The scheme relies on an additional strong-driving field that realizes, atypically, simultaneous Jaynes-Cummings and anti-Jaynes-Cummings interactions.
NASA Astrophysics Data System (ADS)
Zhang, Binbin; Liu, Yu
2009-09-01
We present a novel protocol for teleportation of arbitrary bipartite pure and mixed state with shared cluster entanglement in this paper. By employing Bell-state measurement on the teleported state and the shared cluster state twice, a sender could transmit the arbitrary bipartite state to a distant receiver. We show the good feature of the cluster state channel, with which it can realize the deterministic teleportation rather than probabilistic one. Moreover, since we require less particles to be shared and need no auxiliary qubit in our protocol, it is more efficient and applicable than the previous schemes.
Deterministic LOCC transformation of three-qubit pure states and entanglement transfer
NASA Astrophysics Data System (ADS)
Tajima, Hiroyasu
2013-02-01
A necessary and sufficient condition of the possibility of a deterministic local operations and classical communication (LOCC) transformation of three-qubit pure states is given. The condition shows that the three-qubit pure states are a partially ordered set parametrized by five well-known entanglement parameters and a novel parameter; the five are the concurrences CAB, CAC, CBC, the tangle τABC and the fifth parameter J5 of Acín et al. (2000) Ref. [19], while the other new one is the entanglement charge Qe. The order of the partially ordered set is defined by the possibility of a deterministic LOCC transformation from a state to another state. In this sense, the present condition is an extension of Nielsen's work (Nielsen (1999) [14]) to three-qubit pure states. We also clarify the rules of transfer and dissipation of the entanglement which is caused by deterministic LOCC transformations. Moreover, the minimum number of times of measurements to reproduce an arbitrary deterministic LOCC transformation between three-qubit pure states is given.
Self-healing of quantum entanglement after an obstruction
NASA Astrophysics Data System (ADS)
McLaren, Melanie; Mhlanga, Thandeka; Padgett, Miles J.; Roux, Filippus S.; Forbes, Andrew
2014-02-01
Quantum entanglement between photon pairs is fragile and can easily be masked by losses in transmission path and noise in the detection system. When observing the quantum entanglement between the spatial states of photon pairs produced by parametric down-conversion, the presence of an obstruction introduces losses that can mask the correlations associated with the entanglement. Here we show that we can overcome these losses by measuring in the Bessel basis, thus once again revealing the entanglement after propagation beyond the obstruction. We confirm that, for the entanglement of orbital angular momentum, measurement in the Bessel basis is more robust to these losses than measuring in the usually employed Laguerre-Gaussian basis. Our results show that appropriate choice of measurement basis can overcome some limitations of the transmission path, perhaps offering advantages in free-space quantum communication or quantum processing systems.
NASA Astrophysics Data System (ADS)
Dong, Li; Wang, Jun-Xi; Li, Qing-Yang; Dong, Hai-Kuan; Xiu, Xiao-Ming; Gao, Ya-Jun
2016-07-01
Employing a polarization-entangled χ state, which is a four-photon genuine entangled state, we propose a protocol teleporting a general two-photon polarization state. Firstly, the sender needs to perform one Controlled-NOT gate, one Hadamard gate, and one Controlled-NOT gate on the state to be teleported in succession. Secondly, the sender performs local nondemolition parity analyses based on cross-Kerr nonlinearities and publicizes the achieved outcomes. Finally, conditioned on the sender's analysis outcomes, the receiver executes the single-photon unitary transformation operations on his own photons to obtain the state originally sit in the sender's location. Due to the employment of nondemolition parity analyses rather than four-qubit joint measurement, it can be realized more feasible with currently available technologies. Moreover, the resources of Bell states can be achieved because the nondestructive measurement is exploited, which facilitates other potential tasks of quantum information processing.
Entanglement Entropy of the ν =1 /2 Composite Fermion Non-Fermi Liquid State
NASA Astrophysics Data System (ADS)
Shao, Junping; Kim, Eun-Ah; Haldane, F. D. M.; Rezayi, Edward H.
2015-05-01
The so-called "non-Fermi liquid" behavior is very common in strongly correlated systems. However, its operational definition in terms of "what it is not" is a major obstacle for the theoretical understanding of this fascinating correlated state. Recently there has been much interest in entanglement entropy as a theoretical tool to study non-Fermi liquids. So far explicit calculations have been limited to models without direct experimental realizations. Here we focus on a two-dimensional electron fluid under magnetic field and filling fraction ν =1 /2 , which is believed to be a non-Fermi liquid state. Using a composite fermion wave function which captures the ν =1 /2 state very accurately, we compute the second Rényi entropy using the variational Monte Carlo technique. We find the entanglement entropy scales as L log L with the length of the boundary L as it does for free fermions, but has a prefactor twice that of free fermions.
NASA Astrophysics Data System (ADS)
Gao, W. B.; Imamoglu, A.; Bernien, H.; Hanson, R.
2015-06-01
Realization of a quantum interface between stationary and flying qubits is a requirement for long-distance quantum communication and distributed quantum computation. The prospects for integrating many qubits on a single chip render solid-state spins promising candidates for stationary qubits. Certain solid-state systems, including quantum dots and nitrogen-vacancy centres in diamond, exhibit spin-state-dependent optical transitions, allowing for fast initialization, manipulation and measurement of the spins using laser excitation. Recent progress has brought spin photonics research in these materials into the quantum realm, allowing the demonstration of spin-photon entanglement, which in turn has enabled distant spin entanglement as well as quantum teleportation. Advances in the fabrication of photonic nanostructures hosting spin qubits suggest that chips incorporating a high-efficiency spin-photon interface in a quantum photonic network are within reach.
Entanglement and nonlocality of one- and two-mode combination squeezed state
NASA Astrophysics Data System (ADS)
Hu, Li-yun; Xu, Xue-xiang; Guo, Qin; Fan, Hong-yi
2010-12-01
We investigate the entanglement and nonlocality properties of one- and two-mode combination squeezed vacuum state (OTCSS, with two-parameter λ and γ) by analyzing the logarithmic negativity and the Bell's inequality. It is found that this state exhibits larger entanglement than that of the usual two-mode squeezed vacuum state (TSVS), and that in a certain regime of λ, the violation of Bell's inequality becomes more obvious, which indicates that the nonlocality of OTCSS can be stronger than that of TSVS. As an application of OTCSS, the quantum teleportation is examined, which shows that there is a region spanned by λ and γin which the fidelity of OTCSS channel is larger than that of TSVS.
Optimum Mixed-State Discrimination for Noisy Entanglement-Enhanced Sensing
NASA Astrophysics Data System (ADS)
Zhuang, Quntao; Zhang, Zheshen; Shapiro, Jeffrey H.
2017-01-01
Quantum metrology utilizes nonclassical resources, such as entanglement or squeezed light, to realize sensors whose performance exceeds that afforded by classical-state systems. Environmental loss and noise, however, easily destroy nonclassical resources and, thus, nullify the performance advantages of most quantum-enhanced sensors. Quantum illumination (QI) is different. It is a robust entanglement-enhanced sensing scheme whose 6 dB performance advantage over a coherent-state sensor of the same average transmitted photon number survives the initial entanglement's eradication by loss and noise. Unfortunately, an implementation of the optimum quantum receiver that would reap QI's full performance advantage has remained elusive, owing to its having to deal with a huge number of very noisy optical modes. We show how sum-frequency generation (SFG) can be fruitfully applied to optimum multimode Gaussian-mixed-state discrimination. Applied to QI, our analysis and numerical evaluations demonstrate that our SFG receiver saturates QI's quantum Chernoff bound. Moreover, augmenting our SFG receiver with a feedforward (FF) mechanism pushes its performance to the Helstrom bound in the limit of low signal brightness. The FF-SFG receiver, thus, opens the door to optimum quantum-enhanced imaging, radar detection, state and channel tomography, and communication in practical Gaussian-state situations.
Safe Maritime Autonomous Path Planning in a High Sea State
NASA Technical Reports Server (NTRS)
Ono, Masahiro; Quadrelli, Marco; Huntsberger, Terrance L.
2014-01-01
This paper presents a path planning method for sea surface vehicles that prevents capsizing and bow-diving in a high sea-state. A key idea is to use response amplitude operators (RAOs) or, in control terminology, the transfer functions from a sea state to a vessel's motion, in order to find a set of speeds and headings that results in excessive pitch and roll oscillations. This information is translated to arithmetic constraints on the ship's velocity, which are passed to a model predictive control (MPC)-based path planner to find a safe and optimal path that achieves specified goals. An obstacle avoidance capability is also added to the path planner. The proposed method is demonstrated by simulations.
Quantum Authencryption with Two-Photon Entangled States for Off-Line Communicants
NASA Astrophysics Data System (ADS)
Ye, Tian-Yu
2016-02-01
In this paper, a quantum authencryption protocol is proposed by using the two-photon entangled states as the quantum resource. Two communicants Alice and Bob share two private keys in advance, which determine the generation of two-photon entangled states. The sender Alice sends the two-photon entangled state sequence encoded with her classical bits to the receiver Bob in the manner of one-step quantum transmission. Upon receiving the encoded quantum state sequence, Bob decodes out Alice's classical bits with the two-photon joint measurements and authenticates the integrity of Alice's secret with the help of one-way hash function. The proposed protocol only uses the one-step quantum transmission and needs neither a public discussion nor a trusted third party. As a result, the proposed protocol can be adapted to the case where the receiver is off-line, such as the quantum E-mail systems. Moreover, the proposed protocol provides the message authentication to one bit level with the help of one-way hash function and has an information-theoretical efficiency equal to 100 %.
NASA Astrophysics Data System (ADS)
Bashkirov, E. K.; Mastyugin, M. S.
2014-02-01
The influence of dipole-dipole interaction on the entanglement between two Δ-type artificial atoms interacting with two-mode field via non-degenerate two-photon transitions has been investigated. The atom-field system is assumed to be prepared in four-partite atom-field entangled state. The results show that the entanglement between two atoms can be increased by means of dipole-dipole interaction and for some initial states the entanglement sudden death effect can be weakened.
Discussion on Quantum Proxy Group Signature Scheme with χ-TYPE Entangled State
NASA Astrophysics Data System (ADS)
Zuo, Hui-Juan; Qin, Su-Juan; Song, Ting-Ting
2013-06-01
Recently, Yin et al. (Int. J. Quantum Inform. 10 (2012) 1250041) proposed a quantum proxy group signature scheme with χ-type entangled states. The scheme combines the properties of group signature and proxy signature. The study points out that the semi-honest Trent can give the forged signature under the assumption of this scheme. And, we find that even if the three parties honestly perform the scheme, the signature still cannot be realized with high efficiency.
A New Quantum Proxy Multi-signature Scheme Using Maximally Entangled Seven-Qubit States
NASA Astrophysics Data System (ADS)
Cao, Hai-Jing; Zhang, Jia-Fu; Liu, Jian; Li, Zeng-You
2016-02-01
In this paper, we propose a new secure quantum proxy multi-signature scheme using seven-qubit entangled quantum state as quantum channels, which may have applications in e-payment system, e-government, e-business, etc. This scheme is based on controlled quantum teleportation. The scheme uses the physical characteristics of quantum mechanics to guarantee its anonymity, verifiability, traceability, unforgetability and undeniability.
Quantum dialogue protocols over collective noise using entanglement of GHZ state
NASA Astrophysics Data System (ADS)
Chang, Chih-Hung; Yang, Chun-Wei; Hzu, Geng-Rong; Hwang, Tzonelih; Kao, Shih-Hung
2016-07-01
In this paper, two quantum dialogue (QD) protocols based on the entanglement of GHZ states are proposed to resist the collective noise. Besides, two new coding functions are designed for each of the proposed protocols, which can resist two types of collective noise: collective-dephasing noise and collective-rotation noise, respectively. Furthermore, it is also argued that these QD protocols are also free from the Trojan horse attacks and the information leakage problem.
Nonlocality without inequalities for almost all entangled states of any quantum system
Ghirardi, GianCarlo; Marinatto, Luca
2005-07-15
It is shown that it is possible to rule out all local and stochastic hidden variable models accounting for the quantum mechanical predictions implied by almost any entangled quantum state vector of any number of particles whose Hilbert spaces have arbitrary dimensions, without resorting to Bell-type inequalities. The present proof makes use of the mathematically precise notion of Bell locality and it involves only simple set theoretic arguments.
Preparation of free-travelling three-mode W-type entangled squeezed vacuum states
NASA Astrophysics Data System (ADS)
Wen, Jing-Ji; Yeon, Kyu-Hwang; Wang, Hong-Fu; Zhang, Shou
2016-02-01
A scheme is proposed to prepare W-type entangled squeezed vacuum states (ESVSs) via free-travelling optical fields with simple linear optical devices, photo detectors and cross-Kerr medium. We investigate the influence of an inexact nonlinear phase factor between two modes on the fidelity of the prepared three-mode W-type ESVSs. By adjusting the appropriate reflectivity, the scheme can be extended to create 2n+1-mode W-type ESVSs.
Three-observer Bell inequality violation on a two-qubit entangled state
NASA Astrophysics Data System (ADS)
Schiavon, Matteo; Calderaro, Luca; Pittaluga, Mirko; Vallone, Giuseppe; Villoresi, Paolo
2017-03-01
Bipartite Bell inequalities can simultaneously be violated by two different pairs of observers when weak measurements and signalling is employed. Here, we experimentally demonstrate the violation of two simultaneous CHSH inequalities by exploiting a two-photon polarisation maximally entangled state. Our results demonstrate that large double violation is experimentally achievable. Our demonstration may have impact for Quantum Key Distribution or certification of Quantum Random Number generators based on weak measurements.
Quantum Information Splitting of a Two-qubit Bell State Using a Five-qubit Entangled State
NASA Astrophysics Data System (ADS)
Wang, Rui-jin; Li, Dong-fen; Deng, Fu-hu
2015-09-01
A scheme for quantum information splitting of a two-qubit Bell state using a five-qubit entangled state as quantum channel is proposed. In the scheme,a genuine five-qubit entangled can be used as the quantum channel. Assume that the sender is called Alice, the receiver is called Bob and the controller id called Charlie. Alice, Bob and Charlie share a five-qubit quantum entangled state. The sender Alice sends the quantum information to the receiver Bob, anyone can not obtain the quantum information, unless they cooperate with each other. Alice first performs Bell-state measurements on her qubit paris (A, 1) (B, 5) respectively and then tells Charlie and Bob measurement results via a classical channel. It is impossible for Bob to reconstruct the original state with local operation, if Charlie allows Bob to reconstruct the original states, he needs to perform a single-qubit measurement on his qubit and tells Bob the results. According to the information from Alice and Charlie, Bob can reconstruct the original state with an appropriate unitary operation of his qubits 3, 4. We also consider the problem of security attacks. This protocol is considered to be secure.
NASA Astrophysics Data System (ADS)
Pouranvari, Mohammad
In this thesis, we study the entanglement properties of quantum systems to characterize quantum phases and phase transitions. We focus on the free fermion lattice systems and we use numerical calculation to verify our ideas. Behavior of the entanglement entropy is used to distinguish different phases, in addition the area law of the entanglement entropy is studied. We propose that beside the entanglement entropy, there is physical information in the entanglement Hamiltonian of the reduced density matrix of a chosen subsystem. We verify our ideas by studying different free fermion models. The verification is made by comparing the results we obtain from studying the behavior of the entanglement Hamiltonian with the known previous results. As starting point, to show that entanglement Hamiltonian eigenmodes have physical information, we employ the XX spin chain model. Real space renormalization group method predicts that the ground state is the product state of singlet states and thus those singlet that cross the boundary make the entanglement. We use the entanglement Hamiltonian to show that its single particle eigenmode shows the location of the entangled singlet spins. This is done in the case of ground state at T = 0. We also studied the entanglement properties of the highly excited eigenstate of the system. We use modified version of real space renormalization group for excited state and we show that in T ≠ 0 case where singlet and triplet state with total SZ = 0 make entanglement, entanglement Hamiltonian eigenmode shows the location of the entangled spins. We distinguish one eigenmode of the entanglement Hamiltonian as the maximally entangled mode. This mode corresponds to the smallest entanglement energy and thus contributes the most to the entanglement entropy. In addition, we use two one-dimensional free fermion models, namely the random dimer model and power law random banded model to show that for a localized-delocalized phase transition, behavior of the
Fortes, Raphael; Rigolin, Gustavo
2013-09-15
We push the limits of the direct use of partially pure entangled states to perform quantum teleportation by presenting several protocols in many different scenarios that achieve the optimal efficiency possible. We review and put in a single formalism the three major strategies known to date that allow one to use partially entangled states for direct quantum teleportation (no distillation strategies permitted) and compare their efficiencies in real world implementations. We show how one can improve the efficiency of many direct teleportation protocols by combining these techniques. We then develop new teleportation protocols employing multipartite partially entangled states. The three techniques are also used here in order to achieve the highest efficiency possible. Finally, we prove the upper bound for the optimal success rate for protocols based on partially entangled Bell states and show that some of the protocols here developed achieve such a bound. -- Highlights: •Optimal direct teleportation protocols using directly partially entangled states. •We put in a single formalism all strategies of direct teleportation. •We extend these techniques for multipartite partially entangle states. •We give upper bounds for the optimal efficiency of these protocols.
NASA Astrophysics Data System (ADS)
Liao, Qing-Hong; Zhang, Qi; Xu, Juan; Yan, Qiu-Rong; Liu, Ye; Chen, An
2016-06-01
We have studied the dynamics and transfer of the entanglement of the two identical atoms simultaneously interacting with vacuum field by employing the dressed-state representation. The two atoms are driven by classical fields. The influence of the initial entanglement degree of two atoms, the coupling strength between the atom and the classical field and the detuning between the atomic transition frequency and the frequency of classical field on the entanglement and atomic linear entropy is discussed. The initial entanglement of the two atoms can be transferred into the entanglement between the atom and cavity field when the dissipation is neglected. The maximally entangled state between the atoms and cavity field can be obtained under some certain conditions. The time of disentanglement of two atoms can be controlled and manipulated by adjusting the detuning and classical driving fields. Moreover, the larger the cavity decay rate is, the more quickly the entanglement of the two atoms decays. Supported by National Natural Science Foundation of China under Grant Nos. 11247213, 61368002, 11304010, 11264030, 61168001, China Postdoctoral Science Foundation under Grant No. 2013M531558, Jiangxi Postdoctoral Research Project under Grant No. 2013KY33, the Natural Science Foundation of Jiangxi Province under Grant No. 20142BAB217001, the Foundation for Young Scientists of Jiangxi Province (Jinggang Star) under Grant No. 20122BCB23002, the Research Foundation of the Education Department of Jiangxi Province under Grant Nos. GJJ13051, GJJ13057, and the Graduate Innovation Special Fund of Nanchang University under Grant No. cx2015137
Gaussian entanglement of formation
Wolf, M.M.; Giedke, G.; Krueger, O.; Werner, R. F.; Cirac, J.I.
2004-05-01
We introduce a Gaussian version of the entanglement of formation adapted to bipartite Gaussian states by considering decompositions into pure Gaussian states only. We show that this quantity is an entanglement monotone under Gaussian operations and provide a simplified computation for states of arbitrary many modes. For the case of one mode per site the remaining variational problem can be solved analytically. If the considered state is in addition symmetric with respect to interchanging the two modes, we prove additivity of the considered entanglement measure. Moreover, in this case and considering only a single copy, our entanglement measure coincides with the true entanglement of formation.
Tripartite operation sharing with a six-particle maximally entangled state
NASA Astrophysics Data System (ADS)
Peng, Jian
2015-11-01
A three-party quantum operation-sharing scheme is proposed that uses a six-particle maximally entangled state, the same state used in Helwig et al.'s quantum secret sharing scheme. The security of the proposed scheme is analyzed, and the essential role of the six-particle state in this quantum task is explained. Also, a symmetry feature for sharers and the scheme determinancy is identified. Finally, the experimental feasibility of the proposed protocol is discussed and confirmed, and the protocol is compared with competing protocols.
NASA Astrophysics Data System (ADS)
Hua, Congyi; Chen, Yi-Xin
2016-11-01
We propose a deterministic remote state preparation (RSP) scheme for preparing an arbitrary (including pure and mixed) qubit, where a partially entangled state and finite classical communication are used. To our knowledge, our scheme is the first RSP scheme that fits into this category. One other RSP scheme proposed by Berry shares close features, but can only be used to prepare an arbitrary pure qubit. Even so, our scheme saves classical communication by approximate 1 bit per prepared qubit under equal conditions. When using a maximally entangled state, the classical communication for our scheme is 2 bits, which agrees with Lo's conjecture on the resource cost. Furthermore Alice can switch between our RSP scheme and a standard teleportation scheme without letting Bob know, which makes the quantum channel multipurpose.
NASA Astrophysics Data System (ADS)
Castro, E.; Gómez, R.; Ladera, C. L.; Zambrano, A.
2013-11-01
Among many applications quantum weak measurements have been shown to be important in exploring fundamental physics issues, such as the experimental violation of the Heisenberg uncertainty relation and the Hardy paradox, and have also technological implications in quantum optics, quantum metrology and quantum communications, where the precision of the measurement is as important as the precision of quantum state preparation. The theory of weak measurement can be formulated using the pre-and post-selected quantum systems, as well as using the weak measurement operator formalism. In this work, we study the quantum discord (QD) of quasi-Werner mixed states based on bipartite entangled coherent states using the weak measurements operator, instead of the projective measurement operators. We then compare the quantum discord for both kinds of measurement operators, in terms of the entanglement quality, the latter being measured using the concept of concurrence. It's found greater quantum correlations using the weak measurement operators.
Entanglement and the ground state of fermions trapped in optical lattices
NASA Astrophysics Data System (ADS)
Silva-Valencia, J.; Franco, R.; Figueira, M. S.
2009-10-01
Using White's density matrix renormalization group technique we calculate entanglement of fermions confined in a one-dimensional trap with an underlying lattice. The system is modeled using a repulsive Hubbard model plus a quadratic potential. Due to the confining potential, metallic and Mott-insulating domains coexist in the system. The entanglement is measured by the on-site entropy and the block entropy, and these quantities are calculated as a function of the local repulsion and the curvature of the trap. We found that local entropy decreases with the curvature for a fixed on-site repulsion. As a function of the on-site repulsion the local entropy first increases and then diminishes. Our most important goal is to show that local and block entropy are useful tools for characterization of the ground states of fermions trapped in optical lattices.
Higher-point conformal blocks and entanglement entropy in heavy states
NASA Astrophysics Data System (ADS)
Banerjee, Pinaki; Datta, Shouvik; Sinha, Ritam
2016-05-01
We consider conformal blocks of two heavy operators and an arbitrary number of light operators in a (1+1)- d CFT with large central charge. Using the monodromy method, these higher-point conformal blocks are shown to factorize into products of 4-point conformal blocks in the heavy-light limit for a class of OPE channels. This result is reproduced by considering suitable worldline configurations in the bulk conical defect geometry. We apply the CFT results to calculate the entanglement entropy of an arbitrary number of disjoint intervals for heavy states. The corresponding holographic entanglement entropy calculated via the minimal area prescription precisely matches these results from CFT. Along the way, we briefly illustrate the relation of these conformal blocks to Riemann surfaces and their associated moduli space.
NASA Astrophysics Data System (ADS)
Mishmash, Ryan V.; Motrunich, Olexei I.
2016-08-01
Quantum phases characterized by surfaces of gapless excitations are known to violate the otherwise ubiquitous boundary law of entanglement entropy in the form of a multiplicative log correction: S ˜Ld -1logL . Using variational Monte Carlo, we calculate the second Rényi entropy for a model wave function of the ν =1 /2 composite Fermi liquid (CFL) state defined on the two-dimensional triangular lattice. By carefully studying the scaling of the total Rényi entropy and, crucially, its contributions from the modulus and sign of the wave function on various finite-size geometries, we argue that the prefactor of the leading L logL term is equivalent to that in the analogous free fermion wave function. In contrast to the recent results of Shao et al. [Phys. Rev. Lett. 114, 206402 (2015), 10.1103/PhysRevLett.114.206402], we thus conclude that the "Widom formula" holds even in this non-Fermi liquid CFL state. More generally, our results further elucidate—and place on a more quantitative footing—the relationship between nontrivial wave function sign structure and S ˜L logL entanglement scaling in such highly entangled gapless phases.
More on the rainbow chain: entanglement, space-time geometry and thermal states
NASA Astrophysics Data System (ADS)
Rodríguez-Laguna, Javier; Dubail, Jérôme; Ramírez, Giovanni; Calabrese, Pasquale; Sierra, Germán
2017-04-01
The rainbow chain is an inhomogenous exactly solvable local spin model that, in its ground state, displays a half-chain entanglement entropy growing linearly with the system size. Although many exact results about the rainbow chain are known, the structure of the underlying quantum field theory has not yet been unraveled. Here we show that the universal scaling features of this model are captured by a massless Dirac fermion in a curved space-time with constant negative curvature R = ‑h 2 (h is the amplitude of the inhomogeneity). This identification allows us to use recently developed techniques to study inhomogeneous conformal systems and to analytically characterise the entanglement entropies of more general bipartitions. These results are carefully tested against exact numerical calculations. Finally, we study the entanglement entropies of the rainbow chain in thermal states, and find that there is a non-trivial interplay between the rainbow effective temperature T R and the physical temperature T.
Dong, Li; Xiu, Xiao-Ming; Ren, Yuan-Peng; Gao, Ya-Jun; Yi, X. X.
2013-01-15
We propose a protocol transferring an arbitrary unknown two-qubit state using the quantum channel of a four-qubit genuine entangled state. Simplifying the four-qubit joint measurement to the combination of Bell-state measurements, it can be realized more easily with currently available technologies.
NASA Astrophysics Data System (ADS)
Xu, Shu-Jiang; Chen, Xiu-Bo; Wang, Lian-Hai; Ding, Qing-Yan; Zhang, Shu-Hui
2016-06-01
In 2011, Qu et al. proposed a quantum information hiding protocol based on the entanglement swapping of χ-type quantum states. Because a χ-type state can be described by the 4-particle cat states which have good symmetry, the possible output results of the entanglement swapping between a given χ-type state and all of the 16 χ-type states are divided into 8 groups instead of 16 groups of different results when the global phase is not considered. So it is difficult to read out the secret messages since each result occurs twice in each line (column) of the secret messages encoding rule for the original protocol. In fact, a 3-bit instead of a 4-bit secret message can be encoded by performing two unitary transformations on 2 particles of a χ-type quantum state in the original protocol. To overcome this defect, we propose an improved quantum information hiding protocol based on the general term formulas of the entanglement swapping among χ-type states. Supported by the National Natural Science Foundation of China under Grant Nos. 61572297, 61303199, 61272514, and 61373131, the Shandong Provincial Natural Science Foundation of China under Grant Nos. ZR2013FM025, ZR2013FQ001, ZR2014FM003, and ZY2015YL018, the Shandong Provincial Outstanding Research Award Fund for Young Scientists of China under Grant Nos. BS2015DX006 and BS2014DX007, the National Development Foundation for Cryptological Research, China under Grant No. MMJJ201401012, the Priority Academic Program Development of Jiangsu Higher Education Institutions and Jiangsu Collaborative Innovation Center on Atmospheric Environment and Equipment Technology Funds, and the Shandong Academy of Sciences Youth Fund Project, China under Grant Nos. 2015QN003 and 2013QN007
NASA Astrophysics Data System (ADS)
Adesso, Gerardo; Illuminati, Fabrizio
2008-10-01
We investigate the structural aspects of genuine multipartite entanglement in Gaussian states of continuous variable systems. Generalizing the results of Adesso and Illuminati [Phys. Rev. Lett. 99, 150501 (2007)], we analyze whether the entanglement shared by blocks of modes distributes according to a strong monogamy law. This property, once established, allows us to quantify the genuine N -partite entanglement not encoded into 2,…,K,…,(N-1) -partite quantum correlations. Strong monogamy is numerically verified, and the explicit expression of the measure of residual genuine multipartite entanglement is analytically derived, by a recursive formula, for a subclass of Gaussian states. These are fully symmetric (permutation-invariant) states that are multipartitioned into blocks, each consisting of an arbitrarily assigned number of modes. We compute the genuine multipartite entanglement shared by the blocks of modes and investigate its scaling properties with the number and size of the blocks, the total number of modes, the global mixedness of the state, and the squeezed resources needed for state engineering. To achieve the exact computation of the block entanglement, we introduce and prove a general result of symplectic analysis: Correlations among K blocks in N -mode multisymmetric and multipartite Gaussian states, which are locally invariant under permutation of modes within each block, can be transformed by a local (with respect to the partition) unitary operation into correlations shared by K single modes, one per block, in effective nonsymmetric states where N-K modes are completely uncorrelated. Due to this theorem, the above results, such as the derivation of the explicit expression for the residual multipartite entanglement, its nonnegativity, and its scaling properties, extend to the subclass of non-symmetric Gaussian states that are obtained by the unitary localization of the multipartite entanglement of symmetric states. These findings provide strong
Local reversibility and entanglement structure of many-body ground states
NASA Astrophysics Data System (ADS)
Kuwahara, Tomotaka; Arad, Itai; Amico, Luigi; Vedral, Vlatko
2017-03-01
The low-temperature physics of quantum many-body systems is largely governed by the structure of their ground states. Minimizing the energy of local interactions, ground states often reflect strong properties of locality such as the area law for entanglement entropy and the exponential decay of correlations between spatially separated observables. Here, we present a novel characterization of quantum states, which we call ‘local reversibility’. It characterizes the type of operations that are needed to reverse the action of a general disturbance on the state. We prove that unique ground states of gapped local Hamiltonian are locally reversible. This way, we identify new universal features of many-body ground states, which cannot be derived from the aforementioned properties. We use local reversibility to distinguish between states enjoying microscopic and macroscopic quantum phenomena. To demonstrate the potential of our approach, we prove specific properties of ground states, which are relevant both to critical and non-critical theories.
NASA Astrophysics Data System (ADS)
López-Rosa, S.; Esquivel, R. O.; Plastino, A. R.; Dehesa, J. S.
2015-09-01
In this work we have performed state-of-the-art configuration-interaction (CI) calculations to determine the linear and von Neumann entanglement entropies for the helium-like systems with varying nuclear charge Z in the range 1≤slant Z≤slant 10. The focus of the work resides on determining accurate entanglement values for 2-electron systems with the lowest computational cost through compact CI-wave functions. Our entanglement results for the helium atom fully agree with the results obtained with higher quality wave functions of the Kinoshita type (Dehesa [5]). We find that the correlation energy is linearly related to the entanglement measures associated with the linear and von Neumann entropies of the single-particle reduced density matrizes, which sheds new light on the physical implications of entanglement in helium-like systems. Moreover, we report CI-wave-function-based benchmark results for the entanglement values for all members of the helium isoelectronic series with an accuracy similar to that of Kinoshita-type wave functions. Finally, we give parametric expressions of the linear and von Neumann entanglement measures for two-electron systems as Z varies from 1 to 10.
Deng Fuguo
2005-09-15
The multipartite state in the Rigolin's protocol [Phys. Rev. A 71, 032303 (2005)] for teleporting an arbitrary two-qubit state is just a product state of N Einstein-Podolsky-Rosen pairs in essence, not a genuine multipartite entangled state, and this protocol in principle is equivalent to the Yang-Guo protocol [Chin. Phys. Lett. 17, 162 (2000)].
Bitwise Bell-inequality violations for an entangled state involving 2N ions
Pope, D.T.; Milburn, G.J.
2004-05-01
Following on from previous work [J.-A ring . Larsson, Phys. Rev. A 67, 022108 (2003)], Bell inequalities based on correlations between binary digits are considered for a particular entangled state involving 2N trapped ions. These inequalities involve applying displacement operations to half of the ions and then measuring correlations between pairs of corresponding bits in the binary representations of the number of center-of-mass phonons of N particular ions. It is shown that the state violates the inequalities and thus displays nonclassical correlations. It is also demonstrated that it violates a Bell inequality when the displacements are replaced by squeezing operations.
Pure valley- and spin-entangled states in a MoS2-based bipolar transistor
NASA Astrophysics Data System (ADS)
Bai, Chunxu; Zou, Yonglian; Lou, Wen-Kai; Chang, Kai
2014-11-01
In this study, we show that the local Andreev reflection not only can be tuned largely by the type of the normal metal electrode, it also is related to the electrostatic potential in the superconductor region in a MoS2-based n (p ) -type metal/superconductor junction. In a MoS2-based n -type metal/n (p ) -type superconductor/p -type metal (n Sp ) transistor, nonlocal pure valley- and spin-entangled current can be tuned by the length and local gate voltage of a superconductor region. In particular, switching the quasiparticle type in both structures results in a series of intriguing features. Such an effect is not attainable in a graphene-based junction where the electron-hole symmetry enables the symmetry results to be observed. Besides, we have shown that the crossed Andreev reflection exhibits a maximum around ξ /2 instead of the exponential decay behavior in conventional superconductors and a maximum around ξ in the graphene material. The proposed straightforward experimental design and pure valley- and spin-entangled state can pave the way for a wider use in the entanglement based on material group-VI dichalcogenides.
Spee, C; de Vicente, J I; Sauerwein, D; Kraus, B
2017-01-27
We consider generic pure n-qubit states and a general class of pure states of arbitrary dimensions and arbitrarily many subsystems. We characterize those states which can be reached from some other state via local operations assisted by finitely many rounds of classical communication (LOCC_{N}). For n qubits with n>3, we show that this set of states is of measure zero, which implies that the maximally entangled set is generically of full measure if restricted to the practical scenario of LOCC_{N}. Moreover, we identify a class of states for which any LOCC_{N} protocol can be realized via a concatenation of deterministic steps. We show, however, that in general there exist state transformations which require a probabilistic step within the protocol, which highlights the difference between bipartite and multipartite LOCC.
Realignment criteria for recognizing multipartite entanglement of quantum states
NASA Astrophysics Data System (ADS)
Zhang, Yan-Hua; Lu, Yuan-Yuan; Wang, Guang-Bin; Shen, Shu-Qian
2017-04-01
By multiple realignments of density matrices, we present a new separability criterion for the multipartite quantum state, which includes the computable cross-norm or realignment criterion and the multipartite partial realignment criterion as special cases. An example is used to show that the new criterion can be more efficient than the corresponding multipartite realignment criteria given in Horodecki et al. (Open Syst Inf Dyn 13:103-111, 2006) and Shen et al. (Phys Rev A 92:042332, 2015).
Measurement-based quantum communication with resource states generated by entanglement purification
NASA Astrophysics Data System (ADS)
Wallnöfer, J.; Dür, W.
2017-01-01
We investigate measurement-based quantum communication with noisy resource states that are generated by entanglement purification. We consider the transmission of encoded information via noisy quantum channels using a measurement-based implementation of encoding, error correction, and decoding. We show that such an approach offers advantages over direct transmission, gate-based error correction, and measurement-based schemes with direct generation of resource states. We analyze the noise structure of resource states generated by entanglement purification and show that a local error model, i.e., noise acting independently on all qubits of the resource state, is a good approximation in general, and provides an exact description for Greenberger-Horne-Zeilinger states. The latter are resources for a measurement-based implementation of error-correction codes for bit-flip or phase-flip errors. This provides an approach to link the recently found very high thresholds for fault-tolerant measurement-based quantum information processing based on local error models for resource states with error thresholds for gate-based computational models.
Boche, H. Janßen, G.
2014-08-01
We consider one-way quantum state merging and entanglement distillation under compound and arbitrarily varying source models. Regarding quantum compound sources, where the source is memoryless, but the source state an unknown member of a certain set of density matrices, we continue investigations begun in the work of Bjelaković et al. [“Universal quantum state merging,” J. Math. Phys. 54, 032204 (2013)] and determine the classical as well as entanglement cost of state merging. We further investigate quantum state merging and entanglement distillation protocols for arbitrarily varying quantum sources (AVQS). In the AVQS model, the source state is assumed to vary in an arbitrary manner for each source output due to environmental fluctuations or adversarial manipulation. We determine the one-way entanglement distillation capacity for AVQS, where we invoke the famous robustification and elimination techniques introduced by Ahlswede. Regarding quantum state merging for AVQS we show by example that the robustification and elimination based approach generally leads to suboptimal entanglement as well as classical communication rates.
Cao, Cong; Wang, Chuan; He, Ling-Yan; Zhang, Ru
2013-02-25
We investigate an atomic entanglement purification protocol based on the coherent state input-output process by working in low-Q cavity in the atom-cavity intermediate coupling region. The information of entangled states are encoded in three-level configured single atoms confined in separated one-side optical micro-cavities. Using the coherent state input-output process, we design a two-qubit parity check module (PCM), which allows the quantum nondemolition measurement for the atomic qubits, and show its use for remote parities to distill a high-fidelity atomic entangled ensemble from an initial mixed state ensemble nonlocally. The proposed scheme can further be used for unknown atomic states entanglement concentration. Also by exploiting the PCM, we describe a modified scheme for atomic entanglement concentration by introducing ancillary single atoms. As the coherent state input-output process is robust and scalable in realistic applications, and the detection in the PCM is based on the intensity of outgoing coherent state, the present protocols may be widely used in large-scaled and solid-based quantum repeater and quantum information processing.
NASA Astrophysics Data System (ADS)
Adesso, Gerardo; Serafini, Alessio; Illuminati, Fabrizio
2006-03-01
We present a complete analysis of the multipartite entanglement of three-mode Gaussian states of continuous-variable systems. We derive standard forms which characterize the covariance matrix of pure and mixed three-mode Gaussian states up to local unitary operations, showing that the local entropies of pure Gaussian states are bound to fulfill a relationship which is stricter than the general Araki-Lieb inequality. Quantum correlations can be quantified by a proper convex roof extension of the squared logarithmic negativity, the continuous-variable tangle, or contangle. We review and elucidate in detail the proof that in multimode Gaussian states the contangle satisfies a monogamy inequality constraint [G. Adesso and F. Illuminati, New J. Phys8, 15 (2006)]. The residual contangle, emerging from the monogamy inequality, is an entanglement monotone under Gaussian local operations and classical communications and defines a measure of genuine tripartite entanglements. We determine the analytical expression of the residual contangle for arbitrary pure three-mode Gaussian states and study in detail the distribution of quantum correlations in such states. This analysis yields that pure, symmetric states allow for a promiscuous entanglement sharing, having both maximum tripartite entanglement and maximum couplewise entanglement between any pair of modes. We thus name these states GHZ/W states of continuous-variable systems because they are simultaneous continuous-variable counterparts of both the GHZ and the W states of three qubits. We finally consider the effect of decoherence on three-mode Gaussian states, studying the decay of the residual contangle. The GHZ/W states are shown to be maximally robust against losses and thermal noise.
Adesso, Gerardo; Serafini, Alessio; Illuminati, Fabrizio
2006-03-15
We present a complete analysis of the multipartite entanglement of three-mode Gaussian states of continuous-variable systems. We derive standard forms which characterize the covariance matrix of pure and mixed three-mode Gaussian states up to local unitary operations, showing that the local entropies of pure Gaussian states are bound to fulfill a relationship which is stricter than the general Araki-Lieb inequality. Quantum correlations can be quantified by a proper convex roof extension of the squared logarithmic negativity, the continuous-variable tangle, or contangle. We review and elucidate in detail the proof that in multimode Gaussian states the contangle satisfies a monogamy inequality constraint [G. Adesso and F. Illuminati, New J. Phys8, 15 (2006)]. The residual contangle, emerging from the monogamy inequality, is an entanglement monotone under Gaussian local operations and classical communications and defines a measure of genuine tripartite entanglements. We determine the analytical expression of the residual contangle for arbitrary pure three-mode Gaussian states and study in detail the distribution of quantum correlations in such states. This analysis yields that pure, symmetric states allow for a promiscuous entanglement sharing, having both maximum tripartite entanglement and maximum couplewise entanglement between any pair of modes. We thus name these states GHZ/W states of continuous-variable systems because they are simultaneous continuous-variable counterparts of both the GHZ and the W states of three qubits. We finally consider the effect of decoherence on three-mode Gaussian states, studying the decay of the residual contangle. The GHZ/W states are shown to be maximally robust against losses and thermal noise.
NASA Astrophysics Data System (ADS)
Hwang, Myung-Joong; Choi, Mahn-Soo
2013-03-01
We study the effect of ultrastrong cavity-qubit coupling on the low-lying excitations of a chain of coupled circuit quantum electrodynamic (QED) systems. We show that, in the presence of the onsite ultrastrong coupling, the photon hopping between cavities can be mapped to the Ising interaction between the lowest two levels of individual circuit QED of the chain. Based on our mapping, we predict two nearly degenerate ground states whose wave functions involve maximal entanglement between the macroscopic quantum states of the cavities and the states of qubits and identify that they are mathematically equivalent to Majorana bound states. Further, we devise a scheme for the dispersive measurement of the ground states using an additional resonator attached to one end of the circuit QED chain. Finally, we discuss the effects of disorders and local noises on the coherence of the ground states.
2014-06-19
the number of possible paths within a program grows exponentially with respect to loops and conditionals. New techniques are needed to address the path...increasing the code coverage. Each algorithm is tested over 66 of the GNU COREUTILS utilities. State merging combined with state pruning outperforms...30 3.6.1 GNU COREUTILS . . . . . . . . . . . . . . . . . . . . . . . . . . 30 3.7 Performance Metrics
Charged topological entanglement entropy
NASA Astrophysics Data System (ADS)
Matsuura, Shunji; Wen, Xueda; Hung, Ling-Yan; Ryu, Shinsei
2016-05-01
A charged entanglement entropy is a new measure which probes quantum entanglement between different charge sectors. We study symmetry-protected topological (SPT) phases in (2+1)-dimensional space-time by using this charged entanglement entropy. SPT phases are short-range entangled states without topological order and hence cannot be detected by the topological entanglement entropy. We demonstrate that the universal part of the charged entanglement entropy is nonzero for nontrivial SPT phases and therefore it is a useful measure to detect short-range entangled topological phases. We also discuss that the classification of SPT phases based on the charged topological entanglement entropy is related to that of the braiding statistics of quasiparticles.
Polarization entangled cluster state generation in a lithium niobate chip
NASA Astrophysics Data System (ADS)
Szep, Attila; Kim, Richard; Shin, Eunsung; Fanto, Michael L.; Osman, Joseph; Alsing, Paul M.
2016-10-01
We present a design of a quantum information processing C-phase (Controlled-phase) gate applicable for generating cluster states that has a form of integrated photonic circuits assembled with cascaded directional couplers on a Ti in-diffused Lithium Niobate (Ti-LN) platform where directional couplers as the integrated optical analogue of bulk beam splitters are used as fundamental building blocks. Based on experimentally optimized fabrication parameters of Ti-LN optical waveguides operating at an 810nm wavelength, an integrated Ti-LN quantum C-phase gate is designed and simulated. Our proposed C-phase gate consists of three tunable directional couplers cascaded together with having different weighted switching ratios for providing a tool of routing vertically- and horizontally-polarized photons independently. Its operation mechanism relies on selectively controlling the optical coupling of orthogonally polarized modes via the change in the index of refraction, and its operation is confirmed by the BPM simulation.
NASA Astrophysics Data System (ADS)
Corboz, Philippe; Orús, Román; Bauer, Bela; Vidal, Guifré
2010-04-01
We explain how to implement, in the context of projected entangled-pair states (PEPSs), the general procedure of fermionization of a tensor network introduced in P. Corboz and G. Vidal, Phys. Rev. B 80, 165129 (2009). The resulting fermionic PEPS, similar to previous proposals, can be used to study the ground state of interacting fermions on a two-dimensional lattice. As in the bosonic case, the cost of simulations depends on the amount of entanglement in the ground state and not directly on the strength of interactions. The present formulation of fermionic PEPS leads to a straightforward numerical implementation that allowed us to recycle much of the code for bosonic PEPS. We demonstrate that fermionic PEPS are a useful variational ansatz for interacting fermion systems by computing approximations to the ground state of several models on an infinite lattice. For a model of interacting spinless fermions, ground state energies lower than Hartree-Fock results are obtained, shifting the boundary between the metal and charge-density wave phases. For the t-J model, energies comparable with those of a specialized Gutzwiller-projected ansatz are also obtained.
Hikami, Kazuhiro
2008-07-15
We study topological properties of quasi-particle states in the non-Abelian quantum Hall states. We apply a skein-theoretic method to the Read-Rezayi state whose effective theory is the SU(2){sub K} Chern-Simons theory. As a generalization of the Pfaffian (K = 2) and the Fibonacci (K = 3) anyon states, we compute the braiding matrices of quasi-particle states with arbitrary spins. Furthermore we propose a method to compute the entanglement entropy skein-theoretically. We find that the entanglement entropy has a nontrivial contribution called the topological entanglement entropy which depends on the quantum dimension of non-Abelian quasi-particle intertwining two subsystems.
Direct measurement of the Concurrence of spin-entangled states in a cavity-quantum dot system
NASA Astrophysics Data System (ADS)
Dong, Ping; Liu, Jun; Zhang, Li-Hua; Cao, Zhuo-Liang
2016-08-01
A scheme for implementing the direct measurement of Concurrence is given in a cavity-quantum dot system. The scenario not only can directly measure the Concurrence of two-spin pure entangled state, but also suitable for the case of mixed state. More importantly, all of the operations are of geometric nature, which depend on the cavity-state-free evolution and can be robust against random operation errors. Our scheme provided an alternative method for directly measuring the degree of entanglement in solid-state system.
Deterministic Joint Remote Preparation of Asymmetric Five-Party Three-Qubit Entangled States
NASA Astrophysics Data System (ADS)
Ma, Peng-Cheng; Chen, Gui-Bin; Li, Xiao-Wei; Zhan, You-Bang
2017-04-01
We present two schemes for joint remote state preparation (JRSP) of asymmetric five-party three-qubit entangled states with complex coefficients via three three-qubit and (N+1)-qubit GHZ states as the quantum channel, respectively. In these schemes, two senders(or N senders) share the original state which they wish to help the receiver to remotely prepare. To complete the JRSP schemes, some novel sets of mutually orthogonal basis vectors are introduced. It is shown that, only if two senders(or N senders) collaborate with each other, and perform projective measurements under suitable measuring basis on their own qubits respectively, the receiver can reconstruct the original state by means of some appropriate unitary operations. The advantage of the present schemes is that the success probability in all the considered JRSP can reach 1.
Randomly distilling W-class states into general configurations of two-party entanglement
Cui, W.; Chitambar, E.; Lo, H. K.
2011-11-15
In this article we obtain results for the task of converting a single N-qubit W-class state (of the form {radical}(x{sub 0})|00...0>+{radical}(x{sub 1})|10...0>+{center_dot}{center_dot}{center_dot}+{radical}(x{sub N})|00...1>) into maximum entanglement shared between two random parties. Previous studies in random distillation have not considered how the particular choice of target pairs affects the transformation, and here we develop a strategy for distilling into general configurations of target pairs. We completely solve the problem of determining the optimal distillation probability for all three-qubit configurations and most four-qubit configurations when x{sub 0}=0. Our proof involves deriving new entanglement monotones defined on the set of four-qubit W-class states. As an additional application of our results, we present new upper bounds for converting a generic W-class state into the standard W state |W{sub N}>={radical}((1/N))(|10...0>+{center_dot}{center_dot}{center_dot}+|00...1>).
Error Distributions on Large Entangled States with Non-Markovian Dynamics
NASA Astrophysics Data System (ADS)
McCutcheon, Dara P. S.; Lindner, Netanel H.; Rudolph, Terry
2014-12-01
We investigate the distribution of errors on a computationally useful entangled state generated via the repeated emission from an emitter undergoing strongly non-Markovian evolution. For emitter-environment coupling of pure-dephasing form, we show that the probability that a particular patten of errors occurs has a bound of Markovian form, and thus, accuracy threshold theorems based on Markovian models should be just as effective. Beyond the pure-dephasing assumption, though complicated error structures can arise, they can still be qualitatively bounded by a Markovian error model.
Entanglement manipulation of multipartite pure states with finite rounds of classical communication
NASA Astrophysics Data System (ADS)
de Vicente, J. I.; Spee, C.; Sauerwein, D.; Kraus, B.
2017-01-01
We studied pure state transformations using local operations assisted by finitely many rounds of classical communication (LOCCIN) [C. Spee, J. I. de Vicente, D. Sauerwein, and B. Kraus [Phys. Rev. Lett. (to be published)], arXiv:1606.04418]. Here, we present the details of some of the proofs and generalize the construction of examples of state transformations via LOCCIN which require a probabilistic step. However, we also present explicit examples of SLOCC classes where any separable transformation can be realized by a protocol in which each step is deterministic (all-det-LOCCIN). Such transformations can be considered as natural generalizations of bipartite transformations. Furthermore, we provide examples of pure state transformations which are possible via separable transformations, but not via LOCCIN. We also analyze an interesting genuinely multipartite effect which we call locking or unlocking the power of other parties. This means that one party can prevent or enable the implementation of LOCC transformations by other parties. Moreover, we investigate the maximally entangled set restricted to LOCCIN and show how easily computable bounds on some entanglement measures can be derived by restricting to LOCCIN.
Twisted injectivity in projected entangled pair states and the classification of quantum phases
Buerschaper, Oliver
2014-12-15
We introduce a class of projected entangled pair states (PEPS) which is based on a group symmetry twisted by a 3-cocycle of the group. This twisted symmetry is expressed as a matrix product operator (MPO) with bond dimension greater than 1 and acts on the virtual boundary of a PEPS tensor. We show that it gives rise to a new standard form for PEPS from which we construct a family of local Hamiltonians which are gapped, frustration-free and include fixed points of the renormalization group flow. Based on this insight, we advance the classification of 2D gapped quantum spin systems by showing how this new standard form for PEPS determines the emergent topological order of these local Hamiltonians. Specifically, we identify their universality class as DIJKGRAAF–WITTEN topological quantum field theory (TQFT). - Highlights: • We introduce a new standard form for projected entangled pair states via a twisted group symmetry which is given by nontrivial matrix product operators. • We construct a large family of gapped, frustration-free Hamiltonians in two dimensions from this new standard form. • We rigorously show how this new standard form for low energy states determines the emergent topological order.
Entanglement Entropy of the ν=1/2 Composite Fermion Non-Fermi Liquid State.
Shao, Junping; Kim, Eun-Ah; Haldane, F D M; Rezayi, Edward H
2015-05-22
The so-called "non-Fermi liquid" behavior is very common in strongly correlated systems. However, its operational definition in terms of "what it is not" is a major obstacle for the theoretical understanding of this fascinating correlated state. Recently there has been much interest in entanglement entropy as a theoretical tool to study non-Fermi liquids. So far explicit calculations have been limited to models without direct experimental realizations. Here we focus on a two-dimensional electron fluid under magnetic field and filling fraction ν=1/2, which is believed to be a non-Fermi liquid state. Using a composite fermion wave function which captures the ν=1/2 state very accurately, we compute the second Rényi entropy using the variational Monte Carlo technique. We find the entanglement entropy scales as LlogL with the length of the boundary L as it does for free fermions, but has a prefactor twice that of free fermions.
High-dimensional quantum key distribution with the entangled single-photon-added coherent state
NASA Astrophysics Data System (ADS)
Wang, Yang; Bao, Wan-Su; Bao, Hai-Ze; Zhou, Chun; Jiang, Mu-Sheng; Li, Hong-Wei
2017-04-01
High-dimensional quantum key distribution (HD-QKD) can generate more secure bits for one detection event so that it can achieve long distance key distribution with a high secret key capacity. In this Letter, we present a decoy state HD-QKD scheme with the entangled single-photon-added coherent state (ESPACS) source. We present two tight formulas to estimate the single-photon fraction of postselected events and Eve's Holevo information and derive lower bounds on the secret key capacity and the secret key rate of our protocol. We also present finite-key analysis for our protocol by using the Chernoff bound. Our numerical results show that our protocol using one decoy state can perform better than that of previous HD-QKD protocol with the spontaneous parametric down conversion (SPDC) using two decoy states. Moreover, when considering finite resources, the advantage is more obvious.
Zhao, Yan-Jun; Wang, Changqing; Zhu, Xiaobo; Liu, Yu-xi
2016-01-01
It has been shown that there are not only transverse but also longitudinal couplings between microwave fields and a superconducting qubit with broken inversion symmetry of the potential energy. Using multiphoton processes induced by longitudinal coupling fields and frequency matching conditions, we design a universal algorithm to produce arbitrary superpositions of two-mode photon states of microwave fields in two separated transmission line resonators, which are coupled to a superconducting qubit. Based on our algorithm, we analyze the generation of evenly-populated states and NOON states. Compared to other proposals with only single-photon process, we provide an efficient way to produce entangled microwave photon states when the interactions between superconducting qubits and microwave fields are in the strong and ultrastrong regime. PMID:27033558
Tripartite entanglement in qudit stabilizer states and application in quantum error correction
Looi, Shiang Yong; Griffiths, Robert B.
2011-11-15
Consider a stabilizer state on n qudits, each of dimension D with D being a prime or squarefree integer, divided into three mutually disjoint sets or parts. Generalizing a result of Bravyi et al.[J. Math. Phys. 47, 062106 (2006)] for qubits (D=2), we show that up to local unitaries, the three parts of the state can be written as tensor product of unentangled signle-qudit states, maximally entangled Einstein-Podolsky-Rosen (EPR) pairs, and tripartite Greenberger-Horne-Zeilinger (GHZ) states. We employ this result to obtain a complete characterization of the properties of a class of channels associated with stabilizer error-correcting codes, along with their complementary channels.
Projected Entangled Pair States with non-Abelian gauge symmetries: An SU(2) study
NASA Astrophysics Data System (ADS)
Zohar, Erez; Wahl, Thorsten B.; Burrello, Michele; Cirac, J. Ignacio
2016-11-01
Over the last years, Projected Entangled Pair States have demonstrated great power for the study of many body systems, as they naturally describe ground states of gapped many body Hamiltonians, and suggest a constructive way to encode and classify their symmetries. The PEPS study is not only limited to global symmetries, but has also been extended and applied for local symmetries, allowing to use them for the description of states in lattice gauge theories. In this paper we discuss PEPS with a local, SU(2) gauge symmetry, and demonstrate the use of PEPS features and techniques for the study of a simple family of many body states with a non-Abelian gauge symmetry. We present, in particular, the construction of fermionic PEPS able to describe both two-color fermionic matter and the degrees of freedom of an SU(2) gauge field with a suitable truncation.
Evolution of entanglements in crazing of glassy polymers
NASA Astrophysics Data System (ADS)
Hoy, Robert S.
2005-03-01
Highly entangled polymer glasses often fail via crazing [1]. The polymer expands by a large factor λ from an initial dense state to a craze network of fibrils and voids. The value of λ is found to correlate with the chemical distance between entanglements in both experiments [1] and simulations [2], indicating that the entanglements act like chemical bonds in limiting the expansion. We have applied the primitive path analysis method developed by Everaers et. al. [3] to follow the real space structure of entanglements in model polymer glasses during crazing. A wide range of initial states corresponding to melts with different Kuhn lengths and entanglement lengths was studied. In each case the primitive paths deform affinely and the number of entanglements remains constant during craze formation. Straining the craze past λ leads to a gradual reduction in the number of entanglements, and ultimately to craze fracture.1. E. Kramer and L. L. Berger, Adv. Polym. Sci. 91/92, 1 (1990).2. J. Rottler and M. O. Robbins, Phys. Rev. E 68, 011801 (2003).3. R. Everaers, et al., Science 203, 823 (2004).
Long distance entanglement distribution
NASA Astrophysics Data System (ADS)
Broadfoot, Stuart Graham
Developments in the interdisciplinary field of quantum information open up previously impossible abilities in the realms of information processing and communication. Quantum entanglement has emerged as one property of quantum systems that acts as a resource for quantum information processing and, in particular, enables teleportation and secure cryptography. Therefore, the creation of entangled resources is of key importance for the application of these technologies. Despite a great deal of research the efficient creation of entanglement over long distances is limited by inevitable noise. This problem can be overcome by creating entanglement between nodes in a network and then performing operations to distribute the entanglement over a long distance. This thesis contributes to the field of entanglement distribution within such quantum networks. Entanglement distribution has been extensively studied for one-dimensional networks resulting in "quantum repeater" protocols. However, little work has been done on higher dimensional networks. In these networks a fundamentally different scaling, called "long distance entanglement distribution", can appear between the resources and the distance separating the systems to be entangled. I reveal protocols that enable long distance entanglement distribution for quantum networks composed of mixed state and give a few limitations to the capabilities of entanglement distribution. To aid in the implementation of all entanglement distribution protocols I finish by introducing a new system, composed of an optical nanofibre coupled to a carbon nanotube, that may enable new forms of photo-detectors and quantum memories.
Geometric measures of entanglement
Uyanik, K.; Turgut, S.
2010-03-15
The geometric measure of entanglement, which expresses the minimum distance to product states, has been generalized to distances to sets that remain invariant under the stochastic reducibility relation. For each such set, an associated entanglement monotone can be defined. The explicit analytical forms of these measures are obtained for bipartite entangled states. Moreover, the three-qubit case is discussed and it is argued that the distance to the W states is a new monotone.
NASA Astrophysics Data System (ADS)
Xiu, Xiao-Ming; Li, Qing-Yang; Lin, Yan-Fang; Dong, Hai-Kuan; Dong, Li; Gao, Ya-Jun
2016-10-01
With the assistance of weak cross-Kerr nonlinearities, we present a preparation scheme of four-photon polarization-entangled decoherence-free states, which can be used to construct the minimal optical decoherence-free subspaces where a logical qubit is fully protected against collective decoherence. To complete the preparation task, one spatial entanglement process, two polarization entanglement processes, and one detecting process are applied. The fulfillments of the above processes are contributed by a cross-Kerr nonlinear interaction between the signal photons and a coherent state via Kerr media. Exploiting the available single-photon resource and simple linear optics elements, this scheme is feasible and desirable to be extended to the construction of multiphoton decoherence-free states against the collective decoherence.
NASA Astrophysics Data System (ADS)
Bich Cao, Thi; Hop Nguyen, Van; Nguyen, Ba An
2016-06-01
Transferring a quantum state from one location to another without physically sending the state itself through open space is a special global task that can only be carried out thanks to the laws of nature, namely the principles of quantum mechanics. In this work, we devise protocols for two senders to jointly prepare the most general two-qubit state for a receiver under the supervision of a controller by using three different types of quantum channels, all of which are non-maximally entangled. First, we propose the schemes to produce the quantum channels concerned, and then we present the concrete steps required to execute the protocols, highlighting the issue of why shared non-maximal entanglement is intentionally used instead of maximal entanglement.
Quantum Storage of Orbital Angular Momentum Entanglement in an Atomic Ensemble
NASA Astrophysics Data System (ADS)
Ding, Dong-Sheng; Zhang, Wei; Zhou, Zhi-Yuan; Shi, Shuai; Xiang, Guo-Yong; Wang, Xi-Shi; Jiang, Yun-Kun; Shi, Bao-Sen; Guo, Guang-Can
2015-02-01
Constructing a quantum memory for a photonic entanglement is vital for realizing quantum communication and network. Because of the inherent infinite dimension of orbital angular momentum (OAM), the photon's OAM has the potential for encoding a photon in a high-dimensional space, enabling the realization of high channel capacity communication. Photons entangled in orthogonal polarizations or optical paths had been stored in a different system, but there have been no reports on the storage of a photon pair entangled in OAM space. Here, we report the first experimental realization of storing an entangled OAM state through the Raman protocol in a cold atomic ensemble. We reconstruct the density matrix of an OAM entangled state with a fidelity of 90.3 % ±0.8 % and obtain the Clauser-Horne-Shimony-Holt inequality parameter S of 2.41 ±0.06 after a programed storage time. All results clearly show the preservation of entanglement during the storage.
Quantum dual signature scheme based on coherent states with entanglement swapping
NASA Astrophysics Data System (ADS)
Liu, Jia-Li; Shi, Rong-Hua; Shi, Jin-Jing; Lv, Ge-Li; Guo, Ying
2016-08-01
A novel quantum dual signature scheme, which combines two signed messages expected to be sent to two diverse receivers Bob and Charlie, is designed by applying entanglement swapping with coherent states. The signatory Alice signs two different messages with unitary operations (corresponding to the secret keys) and applies entanglement swapping to generate a quantum dual signature. The dual signature is firstly sent to the verifier Bob who extracts and verifies the signature of one message and transmits the rest of the dual signature to the verifier Charlie who verifies the signature of the other message. The transmission of the dual signature is realized with quantum teleportation of coherent states. The analysis shows that the security of secret keys and the security criteria of the signature protocol can be greatly guaranteed. An extensional multi-party quantum dual signature scheme which considers the case with more than three participants is also proposed in this paper and this scheme can remain secure. The proposed schemes are completely suited for the quantum communication network including multiple participants and can be applied to the e-commerce system which requires a secure payment among the customer, business and bank. Project supported by the National Natural Science Foundation of China (Grant Nos. 61272495, 61379153, and 61401519) and the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20130162110012).
Spin-orbital entangled molecular jeff states in lacunar spinel compounds.
Kim, Heung-Sik; Im, Jino; Han, Myung Joon; Jin, Hosub
2014-06-03
The entanglement of the spin and orbital degrees of freedom through the spin-orbit coupling has been actively studied in condensed matter physics. In several iridium oxide systems, the spin-orbital entangled state, identified by the effective angular momentum jeff, can host novel quantum phases. Here we show that a series of lacunar spinel compounds, GaM4X8 (M=Nb, Mo, Ta and W and X=S, Se and Te), gives rise to a molecular jeff state as a new spin-orbital composite on which the low-energy effective Hamiltonian is based. A wide range of electron correlations is accessible by tuning the bandwidth under external and/or chemical pressure, enabling us to investigate the cooperation between spin-orbit coupling and electron correlations. As illustrative examples, a two-dimensional topological insulating phase and an anisotropic spin Hamiltonian are investigated in the weak and strong coupling regimes, respectively. Our finding can provide an ideal platform for exploring jeff physics and the resulting emergent phenomena.
Dechoum, K.; Hahn, M. D.; Khoury, A. Z.
2010-04-15
We derive the steady-state solution of the Fokker-Planck equation that describes the dynamics of the nondegenerate optical parametric oscillator in the truncated Wigner representation of the density operator. We assume that the pump mode is strongly damped, which permits its adiabatic elimination. When the elimination is correctly executed, the resulting stochastic equations contain multiplicative noise terms and do not admit a potential solution. However, we develop a heuristic scheme leading to a satisfactory steady-state solution. This provides a clear view of the intracavity two-mode entangled state valid in all operating regimes of the optical parametric oscillator. A non-Gaussian distribution is obtained for the above threshold solution.
Quantum secret sharing and random hopping: Using single states instead of entanglement
NASA Astrophysics Data System (ADS)
Karimipour, V.; Asoudeh, M.
2015-09-01
Quantum secret sharing (QSS) protocols between N players, for sharing classical secrets, either use multipartite entangled states or use sequential manipulation of single d -level states only when d is prime (A. Tavakoli et al., arXiv:1501.05582). We propose a sequential scheme which is valid for any value of d . In contrast to A. Tavakoli et al. whose efficiency (number of valid rounds) is 1/d , the efficiency of our scheme is 1/2 for any d . This, together with the fact that in the limit d ⟶∞ the scheme can be implemented by continuous variable optical states, brings the scheme into the domain of present day technology.
Ran, Du; Hu, Chang-Sheng; Yang, Zhen-Biao
2016-01-01
We study the entanglement transfer from a two-mode continuous variable system (initially in the two-mode SU(2) cat states) to a couple of discrete two-state systems (initially in an arbitrary mixed state), by use of the resonant Jaynes-Cummings (JC) interaction. We first quantitatively connect the entanglement transfer to non-Gaussianity of the two-mode SU(2) cat states and find a positive correlation between them. We then investigate the behaviors of the entanglement transfer and find that it is dependent on the initial state of the discrete systems. We also find that the largest possible value of the transferred entanglement exhibits a variety of behaviors for different photon number as well as for the phase angle of the two-mode SU(2) cat states. We finally consider the influences of the noise on the transferred entanglement. PMID:27553881
NASA Astrophysics Data System (ADS)
Pakniat, R.; Tavassoly, M. K.; Zandi, M. H.
2017-01-01
In this paper, we outline a scheme for entanglement swapping based on the concept of cavity QED. The atom-field entangled state in our study is produced in the nonlinear regime. In this scheme, the exploited cavities are prepared in a hybrid entangled state (a combination of coherent and number states) and the swapping process is investigated using two different methods, i.e., detecting and Bell-state measurement methods through the cavity QED. Then, we make use of the atom-field entangled state obtained by detecting method to show that how the atom-atom entanglement as well as atomic and field states teleportation can be achieved with complete fidelity.
Kuang Leman; Zhou Lan
2003-10-01
In this paper, we present a method to generate continuous-variable-type entangled states between photons and atoms in atomic Bose-Einstein condensate (BEC). The proposed method involves an atomic BEC with three internal states, a weak quantized probe laser, and a strong classical coupling laser, which form a three-level {lambda}-shaped BEC system. We consider a situation where the BEC is in electromagnetically induced transparency with the coupling laser being much stronger than the probe laser. In this case, the upper and intermediate levels are unpopulated, so that their adiabatic elimination enables an effective two-mode model involving only the atomic field at the lowest internal level and the quantized probe laser field. Atom-photon quantum entanglement is created through laser-atom and interatomic interactions, and two-photon detuning. We show how to generate atom-photon entangled coherent states and entangled states between photon (atom) coherent states and atom-(photon-) macroscopic quantum superposition (MQS) states, and between photon-MQS and atom-MQS states.
Entanglement negativity in the multiverse
Kanno, Sugumi; Soda, Jiro E-mail: jonathan.shock@uct.ac.za
2015-03-01
We explore quantum entanglement between two causally disconnected regions in the multiverse. We first consider a free massive scalar field, and compute the entanglement negativity between two causally separated open charts in de Sitter space. The qualitative feature of it turns out to be in agreement with that of the entanglement entropy. We then introduce two observers who determine the entanglement between two causally disconnected de Sitter spaces. When one of the observers remains constrained to a region of the open chart in a de Sitter space, we find that the scale dependence enters into the entanglement. We show that a state which is initially maximally entangled becomes more entangled or less entangled on large scales depending on the mass of the scalar field and recovers the initial entanglement in the small scale limit. We argue that quantum entanglement may provide some evidence for the existence of the multiverse.
Entanglement negativity in the multiverse
Kanno, Sugumi; Shock, Jonathan P.; Soda, Jiro
2015-03-10
We explore quantum entanglement between two causally disconnected regions in the multiverse. We first consider a free massive scalar field, and compute the entanglement negativity between two causally separated open charts in de Sitter space. The qualitative feature of it turns out to be in agreement with that of the entanglement entropy. We then introduce two observers who determine the entanglement between two causally disconnected de Sitter spaces. When one of the observers remains constrained to a region of the open chart in a de Sitter space, we find that the scale dependence enters into the entanglement. We show that a state which is initially maximally entangled becomes more entangled or less entangled on large scales depending on the mass of the scalar field and recovers the initial entanglement in the small scale limit. We argue that quantum entanglement may provide some evidence for the existence of the multiverse.
NASA Astrophysics Data System (ADS)
Cao, Cong; Chen, Xi; Duan, YuWen; Fan, Ling; Zhang, Ru; Wang, TieJun; Wang, Chuan
2016-10-01
Entanglement plays an important role in quantum information science, especially in quantum communications. Here we present an efficient entanglement concentration protocol (ECP) for nonlocal atom systems in the partially entangled W-class states, using the single-photon input-output process regarding low- Q cavity and linear optical elements. Compared with previously published ECPs for the concentration of non-maximally entangled atomic states, our protocol is much simpler and more efficient as it employs the Faraday rotation in cavity quantum electrodynamics (QED) and the parameter-splitting method. The Faraday rotation requires the cavity with low- Q factor and weak coupling to the atom, which makes the requirement for entanglement concentration much less stringent than the previous methods, and achievable with current cavity QED techniques. The parameter-splitting method resorts to linear-optical elements only. This ECP has high efficiency and fidelity in realistic experiments, and some imperfections during the experiment can be avoided efficiently with currently available techniques.
NASA Astrophysics Data System (ADS)
Gerry, Christopher C.; Benmoussa, Adil
2005-06-01
Recently, Markham and Vedral [Phys. Rev. A 67, 042113 (2003)] investigated the effect of beam splitting on the spin, or SU(2), coherent states for a single mode field. The spin coherent state is a binomial coherent state related to the Holstein-Primakoff realization of the su(2) Lie algebra given in terms of a set of single mode bose annihilation and creation operators. Upon beam splitting, the ordinary (or Glauber) coherent states merely split into products of ordinary coherent states with reduced amplitudes without becoming entangled, as one would expect for a classical-like field. The above authors expected the spin coherent states to go over to the ordinary coherent states in the limit of high spin, j→∞ , and thus to become product states after beam splitting. But this expectation was not confirmed through numerical calculation of the entropy which, instead of going to zero, leveled off with increasing spin. In this paper we find similar behavior for SU(1,1) coherent states of the Perelomov type for large Bargman index k , but also find that the Barut-Girardello SU(1,1) coherent states appear to rapidly become product states after beam splitting for increasing k . We explain these results by showing that, in reality, neither the spin coherent states nor the Perelomov SU(1,1) coherent states go over to ordinary coherent states in the limits of large j or k , and that the Barut-Girardello coherent states merely go over to the vacuum in the large k limit. Finally, we examine the correct limiting procedure for obtaining separable states (i.e., products of coherent states) upon beam splitting by performing contractions of the su(2) and su(1,1) Lie algebras and of their associated coherent states.
Gerry, Christopher C.; Benmoussa, Adil
2005-06-15
Recently, Markham and Vedral [Phys. Rev. A 67, 042113 (2003)] investigated the effect of beam splitting on the spin, or SU(2), coherent states for a single mode field. The spin coherent state is a binomial coherent state related to the Holstein-Primakoff realization of the su(2) Lie algebra given in terms of a set of single mode bose annihilation and creation operators. Upon beam splitting, the ordinary (or Glauber) coherent states merely split into products of ordinary coherent states with reduced amplitudes without becoming entangled, as one would expect for a classical-like field. The above authors expected the spin coherent states to go over to the ordinary coherent states in the limit of high spin, j{yields}{infinity}, and thus to become product states after beam splitting. But this expectation was not confirmed through numerical calculation of the entropy which, instead of going to zero, leveled off with increasing spin. In this paper we find similar behavior for SU(1,1) coherent states of the Perelomov type for large Bargman index k, but also find that the Barut-Girardello SU(1,1) coherent states appear to rapidly become product states after beam splitting for increasing k. We explain these results by showing that, in reality, neither the spin coherent states nor the Perelomov SU(1,1) coherent states go over to ordinary coherent states in the limits of large j or k, and that the Barut-Girardello coherent states merely go over to the vacuum in the large k limit. Finally, we examine the correct limiting procedure for obtaining separable states (i.e., products of coherent states) upon beam splitting by performing contractions of the su(2) and su(1,1) Lie algebras and of their associated coherent states.
NASA Astrophysics Data System (ADS)
Cohen, Guy Z.; Di Ventra, Massimiliano
2013-01-01
We study a system of two nanomechanical resonators embedded in a dc superconducting quantum interference device (SQUID). We show that the inductively coupled resonators can be treated as two entangled quantum memory elements with states that can be read from, or written on, by employing the SQUID as a displacement detector or switching additional external magnetic fields, respectively. We present a scheme to squeeze the even mode of the state of the resonators and, consequently, reduce the noise in the measurement of the magnetic flux threading the SQUID. We finally analyze the effect of dissipation on the squeezing using the quantum master equation, and show the qualitatively different behavior for the weak and strong damping regimes. Our predictions can be tested using current experimental capabilities.
A characterization of positive linear maps and criteria of entanglement for quantum states
NASA Astrophysics Data System (ADS)
Hou, Jinchuan
2010-09-01
Let H and K be (finite- or infinite-dimensional) complex Hilbert spaces. A characterization of positive completely bounded normal linear maps from {\\mathcal B}(H) into {\\mathcal B}(K) is given, which particularly gives a characterization of positive elementary operators including all positive linear maps between matrix algebras. This characterization is then applied to give a representation of quantum channels (operations) between infinite-dimensional systems. A necessary and sufficient criterion of separability is given which shows that a state ρ on HotimesK is separable if and only if (ΦotimesI)ρ >= 0 for all positive finite-rank elementary operators Φ. Examples of NCP and indecomposable positive linear maps are given and are used to recognize some entangled states that cannot be recognized by the PPT criterion and the realignment criterion.
Two-circles theorem, q-periodic functions and entangled qubit states
NASA Astrophysics Data System (ADS)
Pashaev, Oktay K.
2014-03-01
For arbitrary hydrodynamic flow in circular annulus we introduce the two circle theorem, allowing us to construct the flow from a given one in infinite plane. Our construction is based on q-periodic analytic functions for complex potential, leading to fixed scale-invariant complex velocity, where q is determined by geometry of the region. Self-similar fractal structure of the flow with q-periodic modulation as solution of q-difference equation is studied. For one point vortex problem in circular annulus by fixing singular points we find solution in terms of q-elementary functions. Considering image points in complex plane as a phase space for qubit coherent states we construct Fibonacci and Lucas type entangled N-qubit states. Complex Fibonacci curve related to this construction shows reach set of geometric patterns.
Gradient methods for variational optimization of projected entangled-pair states
NASA Astrophysics Data System (ADS)
Vanderstraeten, Laurens; Haegeman, Jutho; Corboz, Philippe; Verstraete, Frank
2016-10-01
We present a conjugate-gradient method for the ground-state optimization of projected entangled-pair states (PEPS) in the thermodynamic limit, as a direct implementation of the variational principle within the PEPS manifold. Our optimization is based on an efficient and accurate evaluation of the gradient of the global energy functional by using effective corner environments, and is robust with respect to the initial starting points. It has the additional advantage that physical and virtual symmetries can be straightforwardly implemented. We provide the tools to compute static structure factors directly in momentum space, as well as the variance of the Hamiltonian. We benchmark our method on Ising and Heisenberg models, and show a significant improvement on the energies and order parameters as compared to algorithms based on imaginary-time evolution.
Efficient three-qubit entangling (Toffoli) gates via excited states in qubit-cavity systems.
NASA Astrophysics Data System (ADS)
Reinecke, Thomas; Economou, Sophia; Solenov, Dmitry
2014-03-01
Efficient multi-qubit quantum operations are crucial for further development of quantum information processing using available physical designs. We report our results on efficient three-qubit entangling operations in qubit-cavity systems. The proposed gate design is based on non-commutativity of single-qubit pulse controls that can be achieved for systems in which auxiliary states above the qubit subspace are available. It does not rely on dynamical tuning of energy states, and, unlike traditional decomposition approaches, it provides efficiency comparable to that of a single control-NOT operation. We will focus on the transmon qubit systems, which have recently demonstrated coherence times suitable for multi-qubit computation. Other systems will also be discussed.
Optimal Control for Fast and Robust Generation of Entangled States in Anisotropic Heisenberg Chains
NASA Astrophysics Data System (ADS)
Zhang, Xiong-Peng; Shao, Bin; Zou, Jian
2017-02-01
Motivated by some recent results of the optimal control (OC) theory, we study anisotropic XXZ Heisenberg spin-1/2 chains with control fields acting on a single spin, with the aim of exploring how maximally entangled state can be prepared. To achieve the goal, we use a numerical optimization algorithm (e.g., the Krotov algorithm, which was shown to be capable of reaching the quantum speed limit) to search an optimal set of control parameters, and then obtain OC pulses corresponding to the target fidelity. We find that the minimum time for implementing our target state depending on the anisotropy parameter Δ of the model. Finally, we analyze the robustness of the obtained results for the optimal fidelities and the effectiveness of the Krotov method under some realistic conditions.
Entanglement scaling of excited states in large one-dimensional many-body localized systems
NASA Astrophysics Data System (ADS)
Kennes, D. M.; Karrasch, C.
2016-06-01
We study the properties of excited states in one-dimensional many-body localized (MBL) systems using a matrix product state algorithm. First, the method is tested for a large disordered noninteracting system, where for comparison we compute a quasiexact reference solution via a Monte Carlo sampling of the single-particle levels. Thereafter, we present extensive data obtained for large interacting systems of L ˜100 sites and large bond dimensions χ ˜1700 , which allows us to quantitatively analyze the scaling behavior of the entanglement S in the system. The MBL phase is characterized by a logarithmic growth S (L )˜log(L ) over a large scale separating the regimes where volume and area laws hold. We check the validity of the eigenstate thermalization hypothesis. Our results are consistent with the existence of a mobility edge.
Evaluation of ground-state entanglement in spin systems with the random phase approximation
NASA Astrophysics Data System (ADS)
Matera, J. M.; Rossignoli, R.; Canosa, N.
2010-11-01
We discuss a general treatment based on the mean field plus random-phase approximation (RPA) for the evaluation of subsystem entropies and negativities in ground states of spin systems. The approach leads to a tractable general method that becomes straightforward in translationally invariant arrays. The method is examined in arrays of arbitrary spin with XYZ couplings of general range in a uniform transverse field, where the RPA around both the normal and parity-breaking mean-field state, together with parity-restoration effects, is discussed in detail. In the case of a uniformly connected XYZ array of arbitrary size, the method is shown to provide simple analytic expressions for the entanglement entropy of any global bipartition, as well as for the negativity between any two subsystems, which become exact for large spin. The limit case of a spin s pair is also discussed.
A Quantum Multi-proxy Multi-blind-signature Scheme Based on Genuine Six-Qubit Entangled State
NASA Astrophysics Data System (ADS)
Shao, Ai-Xia; Zhang, Jian-Zhong; Xie, Shu-Cui
2016-12-01
In this paper, a very efficient and secure multi-proxy multi-blind-signature scheme is proposed which is based on controlled quantum teleportation. Genuine six-qubit entangled state functions as quantum channel. The scheme uses the physical characteristics of quantum mechanics to guarantee its unforgeability, undeniability, blindness and unconditional security.
NASA Astrophysics Data System (ADS)
Xiao, Yunlong; Jing, Naihuan; Li-Jost, Xianqing; Fei, Shao-Ming
2016-08-01
We present several criteria for genuine multipartite entanglement from universal uncertainty relations based on majorization theory. Under non-negative Schur-concave functions, the vector-type uncertainty relation generates a family of infinitely many detectors to check genuine multipartite entanglement. We also introduce the concept of k-separable circles via geometric distance for probability vectors, which include at most ( k-1)-separable states. The entanglement witness is also generalized to a universal entanglement witness which is able to detect the k-separable states more accurately.
Protecting single-photon entangled state from photon loss with noiseless linear amplification
NASA Astrophysics Data System (ADS)
Zhang, ShengLi; Yang, Song; Zou, XuBo; Shi, BaoSen; Guo, GuangCan
2012-09-01
Single-photon entanglement provides a valuable resource for quantum communication and quantum repeaters. However, single-photon entanglement is sensitive to photon loss. In this Brief Report, we show that a noiseless linear amplifier is an efficient tool for protecting single-photon entanglement. The performance of ideal noiseless linear amplification as well as the nonideal amplification with on-off detectors and heralded single photons are also investigated.
NASA Astrophysics Data System (ADS)
Fan, Hong-yi; Lu, Hai-liang; Fan, Yue
2006-02-01
Newton-Leibniz integration rule only applies to commuting functions of continuum variables, while operators made of Dirac's symbols (ket versus bra, e.g., | q>< q| of continuous parameter q) in quantum mechanics are usually not commutative. Therefore, integrations over the operators of type |><| cannot be directly performed by Newton-Leibniz rule. We invented an innovative technique of integration within an ordered product (IWOP) of operators that made the integration of non-commutative operators possible. The IWOP technique thus bridges this mathematical gap between classical mechanics and quantum mechanics, and further reveals the beauty and elegance of Dirac's symbolic method and transformation theory. Various applications of the IWOP technique, including constructing the entangled state representations and their applications, are presented.
NASA Astrophysics Data System (ADS)
Sen, Arnab; Nandy, Sourav; Sengupta, K.
2016-12-01
We study a class of periodically driven d -dimensional integrable models and show that after n drive cycles with frequency ω , pure states with non-area-law entanglement entropy Sn(l ) ˜lα (n ,ω ) are generated, where l is the linear dimension of the subsystem, and d -1 ≤α (n ,ω )≤d . The exponent α (n ,ω ) eventually approaches d (volume law) for large enough l when n →∞ . We identify and analyze the crossover phenomenon from an area (S ˜ld -1 for d ≥1 ) to a volume (S ˜ld ) law and provide a criterion for their occurrence which constitutes a generalization of Hastings's theorem to driven integrable systems in one dimension. We also find that Sn generically decays to S∞ as (ω/n ) (d +2 )/2 for fast and (ω/n ) d /2 for slow periodic drives; these two dynamical phases are separated by a topological transition in the eigenspectrum of the Floquet Hamiltonian. This dynamical transition manifests itself in the temporal behavior of all local correlation functions and does not require a critical point crossing during the drive. We find that these dynamical phases show a rich re-entrant behavior as a function of ω for d =1 models and also discuss the dynamical transition for d >1 models. Finally, we study entanglement properties of the steady state and show that singular features (cusps and kinks in d =1 ) appear in S∞ as a function of ω whenever there is a crossing of the Floquet bands. We discuss experiments which can test our theory.
NASA Astrophysics Data System (ADS)
Rojas, M.; de Souza, S. M.; Rojas, Onofre
2017-02-01
The quantum teleportation plays an important role in quantum information process, in this sense, the quantum entanglement properties involving an infinite chain structure is quite remarkable because real materials could be well represented by an infinite chain. We study the teleportation of an entangled state through a couple of quantum channels, composed by Heisenberg dimers in an infinite Ising-Heisenberg diamond chain, the couple of chains are considered sufficiently far away from each other to be ignored the any interaction between them. To teleporting a couple of qubits through the quantum channel, we need to find the average density operator for Heisenberg spin dimers, which will be used as quantum channels. Assuming the input state as a pure state, we can apply the concept of fidelity as a useful measurement of teleportation performance of a quantum channel. Using the standard teleportation protocol, we have derived an analytical expression for the output concurrence, fidelity, and average fidelity. We study in detail the effects of coupling parameters, external magnetic field and temperature dependence of quantum teleportation. Finally, we explore the relations between entanglement of the quantum channel, the output entanglement and the average fidelity of the system. Through a kind of phase diagram as a function of Ising-Heisenberg diamond chain model parameters, we illustrate where the quantum teleportation will succeed and a region where the quantum teleportation could fail.
Quantum Trajectories and Their Statistics for Remotely Entangled Quantum Bits
NASA Astrophysics Data System (ADS)
Chantasri, Areeya; Kimchi-Schwartz, Mollie E.; Roch, Nicolas; Siddiqi, Irfan; Jordan, Andrew N.
2016-10-01
We experimentally and theoretically investigate the quantum trajectories of jointly monitored transmon qubits embedded in spatially separated microwave cavities. Using nearly quantum-noise-limited superconducting amplifiers and an optimized setup to reduce signal loss between cavities, we can efficiently track measurement-induced entanglement generation as a continuous process for single realizations of the experiment. The quantum trajectories of transmon qubits naturally split into low and high entanglement classes. The distribution of concurrence is found at any given time, and we explore the dynamics of entanglement creation in the state space. The distribution exhibits a sharp cutoff in the high concurrence limit, defining a maximal concurrence boundary. The most-likely paths of the qubits' trajectories are also investigated, resulting in three probable paths, gradually projecting the system to two even subspaces and an odd subspace, conforming to a "half-parity" measurement. We also investigate the most-likely time for the individual trajectories to reach their most entangled state, and we find that there are two solutions for the local maximum, corresponding to the low and high entanglement routes. The theoretical predictions show excellent agreement with the experimental entangled-qubit trajectory data.
NASA Astrophysics Data System (ADS)
Wang, Jingtao; Li, Lixiang; Peng, Haipeng; Yang, Yixian
2017-02-01
In this study, we propose the concept of judgment space to investigate the quantum-secret-sharing scheme based on local distinguishability (called LOCC-QSS). Because of the proposing of this conception, the property of orthogonal mutiqudit entangled states under restricted local operation and classical communication (LOCC) can be described more clearly. According to these properties, we reveal that, in the previous (k ,n )-threshold LOCC-QSS scheme, there are two required conditions for the selected quantum states to resist the unambiguous attack: (i) their k -level judgment spaces are orthogonal, and (ii) their (k -1 )-level judgment spaces are equal. Practically, if k
Jeong, Hyunseok; Ralph, Timothy C.
2007-10-15
We study characteristics of superpositions and entanglement of thermal states at high temperatures and discuss their applications to quantum-information processing. We introduce thermal-state qubits and thermal-Bell states, which are a generalization of pure-state qubits and Bell states to thermal mixtures. A scheme is then presented to discriminate between the four thermal-Bell states without photon number resolving detection but with Kerr nonlinear interactions and two single-photon detectors. This enables one to perform quantum teleportation and gate operations for quantum computation with thermal-state qubits.
Decoherence of entangled states by colored noise: application to precision measurements
NASA Astrophysics Data System (ADS)
Andre, Axel; Sorensen, Anders; Lukin, Mikhail; van der Wal, Caspar
2003-05-01
Controlled manipulation of quantum systems can lead to a number of exciting new applications in quantum information science, from quantum computation to applications in precision measurements. In many such applications, decoherence is a key factor to take into account and ultimately determines the feasibility or usefulness of the proposal. The decoherence of quantum mechanical degrees of freedom is usually modeled through their interaction with a bath consisting of a large number of harmonic oscillators. The separation of energy scales between the energy of the oscillators and the interaction energy leads to separation of time scales so that the decoherence process can be modeled effectively by a markovian process (infinitely short reservoir correlation time). Low-lying state are long-lived and are therefore ideally suited for storage of quantum information and long-lived quantum memory. Due to their long lifetime, these states are sensitive to the low frequency noise of the environment. In particular 1/f noise is dominating at low frequencies and this changes the form of the decoherence. In this case, non-exponential decay is to be expected so that the importance of decoherence depends on the time-scale. We consider the accuracy of frequency measurements using the Ramsey technique when the ensemble of atoms is subject to colored noise during the measurement. It has been shown that the use of entangled states of atomic ensembles (so-called spin squeezed states) may lead to an improvement in the accuracy of frequency measurements when the system is noiseless [1]. To assess the usefulness in a real setup decoherence has to be taken into account. It has been shown that for white noise spectra the net improvement is very small [2], this conclusion is however changed significantly when the system is influenced by colored noise. We study phase noise of the reference oscillator in frequency measurements and show that for non-white noise spectra (e.g. when the noise power
Path toward a high-energy solid-state laser
NASA Astrophysics Data System (ADS)
Wood, Gary L.; Merkle, Larry D.; Dubinskii, Mark; Zandi, Bahram
2004-04-01
Lasers have come a long way since the first demonstration by Maiman of a ruby crystal laser in 1960. Lasers are used as scientific tools as well as for a wide variety of applications for both commercial industry and the military. Today lasers come in all types, shapes and sizes depending on their application. The solid-state laser has some distinct advantages in that it can be rugged, compact, and self contained, making it reliable over long periods of time. With the advent of diode laser pumping a ten times increase in overall laser efficiency has been realized. This significant event, and others, is changing the way solid-state lasers are applied and allows new possibilities. One of those new areas of exploration is the high energy laser. Solid-state lasers for welding are already developed and yield energies in the 0.5 to 6 kilojoule range. These lasers are at the forefront of what is possible in terms of high energy solid-state lasers. It is possible to achieve energies of greater than 100 kJ. These sorts of energies would allow applications, in addition to welding, such as directed energy weapons, extremely remote sensing, power transfer, propulsion, biological and chemical agent neutralization and unexploded and mine neutralization. This article will review these new advances in solid-state lasers and the different paths toward achieving a high energy laser. The advantages and challenges of each approach will be highlighted.
NASA Astrophysics Data System (ADS)
Dai, Yan-Wei; Cho, Sam Young; Batchelor, Murray T.; Zhou, Huan-Qiang
2017-01-01
The von Neumann entanglement entropy is used to estimate the critical point hc/J ≃0.143 (3 ) of the mixed ferro-antiferromagnetic three-state quantum Potts model H =∑i[J (XiXi+1 2+Xi2Xi +1) -h Ri] , where Xi and Ri are standard three-state Potts spin operators and J >0 is the antiferromagnetic coupling parameter. This critical point value gives improved estimates for two Kosterlitz-Thouless transition points in the antiferromagnetic (β <0 ) region of the Δ -β phase diagram of the three-state quantum chiral clock model, where Δ and β are, respectively, the chirality and coupling parameters in the clock model. These are the transition points βc≃-0.143 (3 ) at Δ =1/2 between incommensurate and commensurate phases and βc≃-7.0 (1 ) at Δ =0 between disordered and incommensurate phases. The von Neumann entropy is also used to calculate the central charge c of the underlying conformal field theory in the massless phase h ≤hc . The estimate c ≃1 in this phase is consistent with the known exact value at the particular point h /J =-1 corresponding to the purely antiferromagnetic three-state quantum Potts model. The algebraic decay of the Potts spin-spin correlation in the massless phase is used to estimate the continuously varying critical exponent η .
Path integral Monte Carlo on a lattice. II. Bound states
NASA Astrophysics Data System (ADS)
O'Callaghan, Mark; Miller, Bruce N.
2016-07-01
The equilibrium properties of a single quantum particle (qp) interacting with a classical gas for a wide range of temperatures that explore the system's behavior in the classical as well as in the quantum regime is investigated. Both the qp and the atoms are restricted to sites on a one-dimensional lattice. A path integral formalism developed within the context of the canonical ensemble is utilized, where the qp is represented by a closed, variable-step random walk on the lattice. Monte Carlo methods are employed to determine the system's properties. To test the usefulness of the path integral formalism, the Metropolis algorithm is employed to determine the equilibrium properties of the qp in the context of a square well potential, forcing the qp to occupy bound states. We consider a one-dimensional square well potential where all atoms on the lattice are occupied with one atom with an on-site potential except for a contiguous set of sites of various lengths centered at the middle of the lattice. Comparison of the potential energy, the energy fluctuations, and the correlation function are made between the results of the Monte Carlo simulations and the numerical calculations.
NASA Astrophysics Data System (ADS)
Pakniat, R.; Tavassoly, M. K.; Zandi, M. H.
2016-10-01
We outline a scheme for entanglement swapping based on cavity QED as well as quasi-Bell state measurement (quasi-BSM) methods. The atom-field interaction in the cavity QED method is performed in small and large detuning regimes. We assume two atoms are initially entangled together and, distinctly two cavities are prepared in an entangled coherent-coherent state. In this scheme, we want to transform entanglement to the atom-field system. It is observed that, the fidelities of the swapped entangled state in the quasi-BSM method can be compatible with those obtained in the small and large detuning regimes in the cavity QED method (the condition of this compatibility will be discussed). In addition, in the large detuning regime, the swapped entangled state is obtained by detecting and quasi-BSM approaches. In the continuation, by making use of the atom-field entangled state obtained in both approaches in a large detuning regime, we show that the atomic as well as field states teleportation with complete fidelity can be achieved.
Ultrabright source of entangled photon pairs.
Dousse, Adrien; Suffczyński, Jan; Beveratos, Alexios; Krebs, Olivier; Lemaître, Aristide; Sagnes, Isabelle; Bloch, Jacqueline; Voisin, Paul; Senellart, Pascale
2010-07-08
A source of triggered entangled photon pairs is a key component in quantum information science; it is needed to implement functions such as linear quantum computation, entanglement swapping and quantum teleportation. Generation of polarization entangled photon pairs can be obtained through parametric conversion in nonlinear optical media or by making use of the radiative decay of two electron-hole pairs trapped in a semiconductor quantum dot. Today, these sources operate at a very low rate, below 0.01 photon pairs per excitation pulse, which strongly limits their applications. For systems based on parametric conversion, this low rate is intrinsically due to the Poissonian statistics of the source. Conversely, a quantum dot can emit a single pair of entangled photons with a probability near unity but suffers from a naturally very low extraction efficiency. Here we show that this drawback can be overcome by coupling an optical cavity in the form of a 'photonic molecule' to a single quantum dot. Two coupled identical pillars-the photonic molecule-were etched in a semiconductor planar microcavity, using an optical lithography method that ensures a deterministic coupling to the biexciton and exciton energy states of a pre-selected quantum dot. The Purcell effect ensures that most entangled photon pairs are emitted into two cavity modes, while improving the indistinguishability of the two optical recombination paths. A polarization entangled photon pair rate of 0.12 per excitation pulse (with a concurrence of 0.34) is collected in the first lens. Our results open the way towards the fabrication of solid state triggered sources of entangled photon pairs, with an overall (creation and collection) efficiency of 80%.
Matched witness for multipartite entanglement
NASA Astrophysics Data System (ADS)
Chen, Xiao-yu; Jiang, Li-zhen; Xu, Zhu-an
2017-04-01
Entanglement criteria for multipartite entangled states are obtained by matching witnesses to multipartite entangled states. The necessary and sufficient criterion of separability for three qubit X states is given as an example to illustrate the procedure of finding a criterion. The result is utilized to obtain the noise tolerance of W state. The necessary and sufficient criteria of three partite separability and full separability for four qubit noisy cluster states, three partite separability for four qubit noisy GHZ states are obtained.
NASA Astrophysics Data System (ADS)
Bose, Soumyakanti; Kumar, M. Sanjay
2017-01-01
Continuous-variable beam-splitter (BS)-generated entanglement from single-mode optical states generated by a single nonclassicality (NC)-inducing operation has been found to be immensely important in several information processing tasks. There exists a broader class of optical states, generated from successive action of multiple different NC-inducing operations, which show many intriguing nonclassical properties; however, the BS conversion of the NC for such states remains unexplored. In this work we have critically analyzed the BS-generated entanglement from such nonclassical optical states at input. Here we present a scenario where BS output entanglement becomes nonmonotonic with the input NC parameters, accessible experimentally (e.g., number of photon excitation and squeezing strength), in contrast to the previous results with states comprising a single NC-inducing operation. We explain this counterintuitive feature in terms of the competition between these two NC-inducing operations as manifest in the contours of the Q functions associated with these states.
Detecting entanglement with Jarzynski's equality
Hide, Jenny; Vedral, Vlatko
2010-06-15
We present a method for detecting the entanglement of a state using nonequilibrium processes. A comparison of relative entropies allows us to construct an entanglement witness. The relative entropy can further be related to the quantum Jarzynski equality, allowing nonequilibrium work to be used in entanglement detection. To exemplify our results, we consider two different spin chains.
Estimating concurrence via entanglement witnesses
Jurkowski, Jacek; Chruscinski, Dariusz
2010-05-15
We show that each entanglement witness detecting a given bipartite entangled state provides an estimation of its concurrence. We illustrate our result with several well-known examples of entanglement witnesses and compare the corresponding estimation of concurrence with other estimations provided by the trace norm of partial transposition and realignment.
Quantum Entanglement Molecular Absorption Spectrum Simulator
NASA Technical Reports Server (NTRS)
Nguyen, Quang-Viet; Kojima, Jun
2006-01-01
Quantum Entanglement Molecular Absorption Spectrum Simulator (QE-MASS) is a computer program for simulating two photon molecular-absorption spectroscopy using quantum-entangled photons. More specifically, QE-MASS simulates the molecular absorption of two quantum-entangled photons generated by the spontaneous parametric down-conversion (SPDC) of a fixed-frequency photon from a laser. The two-photon absorption process is modeled via a combination of rovibrational and electronic single-photon transitions, using a wave-function formalism. A two-photon absorption cross section as a function of the entanglement delay time between the two photons is computed, then subjected to a fast Fourier transform to produce an energy spectrum. The program then detects peaks in the Fourier spectrum and displays the energy levels of very short-lived intermediate quantum states (or virtual states) of the molecule. Such virtual states were only previously accessible using ultra-fast (femtosecond) laser systems. However, with the use of a single-frequency continuous wave laser to produce SPDC photons, and QEMASS program, these short-lived molecular states can now be studied using much simpler laser systems. QE-MASS can also show the dependence of the Fourier spectrum on the tuning range of the entanglement time of any externally introduced optical-path delay time. QE-MASS can be extended to any molecule for which an appropriate spectroscopic database is available. It is a means of performing an a priori parametric analysis of entangled photon spectroscopy for development and implementation of emerging quantum-spectroscopic sensing techniques. QE-MASS is currently implemented using the Mathcad software package.
Phase sensitivity of two nonlinear interferometers with inputting entangled coherent states
NASA Astrophysics Data System (ADS)
Wei, Chao-Ping; Xiao-Yu, Hu; Ya-Fei, Yu; Zhi-Ming, Zhang
2016-04-01
We investigate the phase sensitivity of the SU(1,1) interfereometer [SU(1,1)I] and the modified Mach-Zehnder interferometer (MMZI) with the entangled coherent states (ECS) as inputs. We consider the ideal case and the situations in which the photon losses are taken into account. We find that, under ideal conditions, the phase sensitivity of both the MMZI and the SU(1,1)I can beat the shot-noise limit (SNL) and approach the Heisenberg limit (HL). In the presence of photon losses, the ECS can beat the coherent and squeezed states as inputs in the SU(1,1)I, and the MMZI is more robust against internal photon losses than the SU(1,1)I. Project supported by the Major Research Plan of the National Natural Science Foundation of China (Grant No. 91121023), the National Natural Science Foundation of China (Grant Nos. 11574092, 61378012, and 60978009), the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20124407110009), the National Basic Research Program of China (Grant Nos. 2011CBA00200 and 2013CB921804), and the Program for Innovative Research Team in University (Grant No. IRT1243).
Huber, Marcus; Erker, Paul; Schimpf, Hans; Gabriel, Andreas; Hiesmayr, Beatrix
2011-04-15
We construct a set of criteria detecting genuine multipartite entanglement in arbitrary dimensional multipartite systems. These criteria are optimally suited for detecting multipartite entanglement in n-qubit Dicke states with m excitations, as shown in exemplary cases. Furthermore, they can be employed to detect multipartite entanglement in different states related to quantum cloning, decoherence-free communication, and quantum secret sharing. In a detailed analysis, we show that the criteria are also more robust to noise than any other criterion known so far, especially with increasing system size. Furthermore, it is shown that the number of required local observables scales only polynomially with size, thus making the criteria experimentally feasible.
NASA Astrophysics Data System (ADS)
Bartkiewicz, Karol; Chimczak, Grzegorz; Lemr, Karel
2017-02-01
We describe a direct method for experimental determination of the negativity of an arbitrary two-qubit state with 11 measurements performed on multiple copies of the two-qubit system. Our method is based on the experimentally accessible sequences of singlet projections performed on up to four qubit pairs. In particular, our method permits the application of the Peres-Horodecki separability criterion to an arbitrary two-qubit state. We explicitly demonstrate that measuring entanglement in terms of negativity requires three measurements more than detecting two-qubit entanglement. The reported minimal set of interferometric measurements provides a complete description of bipartite quantum entanglement in terms of two-photon interference. This set is smaller than the set of 15 measurements needed to perform a complete quantum state tomography of an arbitrary two-qubit system. Finally, we demonstrate that the set of nine Makhlin's invariants needed to express the negativity can be measured by performing 13 multicopy projections. We demonstrate both that these invariants are a useful theoretical concept for designing specialized quantum interferometers and that their direct measurement within the framework of linear optics does not require performing complete quantum state tomography.
NASA Astrophysics Data System (ADS)
Yang, Yu-Feng; Chen, Ye-Hong; Wu, Qi-Cheng; Kang, Yi-Hao; Huang, Bi-Hua; Xia, Yan
2017-01-01
We present an efficient protocol to rapidly generate a three-dimensional entangled state for two atoms trapped in a cavity with quantum Zeno dynamics and Lewis-Riesenfeld invariants. The required time for the protocol is much shorter than that with adiabatic passage. The influence of various decoherence processes such as atomic spontaneous emission and photon loss on the fidelity of the three-dimensional entangled state is investigated. Numerical simulation demonstrates that the protocol is robust against both the atomic spontaneous emission and cavity decay. Different from Lin et al. (J Opt Soc Am B 33(4):519-524, 2016), the three-dimensional entangled state can be fast generated with only one step. Furthermore, the protocol can be generalized to generate N-dimensional entanglement state. Therefore, we hope the protocol may be useful in quantum information field.
Excited-State Decay Paths in Tetraphenylethene Derivatives.
Gao, Yuan-Jun; Chang, Xue-Ping; Liu, Xiang-Yang; Li, Quan-Song; Cui, Ganglong; Thiel, Walter
2017-04-06
The photophysical properties of tetraphenylethene (TPE) compounds may differ widely depending on the substitution pattern, for example, with regard to the fluorescence quantum yield ϕf and the propensity to exhibit aggregation-induced emission (AIE). We report combined electronic structure calculations and nonadiabatic dynamics simulations to study the excited-state decay mechanisms of two TPE derivatives with four methyl substituents, either in the meta position (TPE-4mM, ϕf = 0.1%) or in the ortho position (TPE-4oM, ϕf = 64.3%). In both cases, two excited-state decay pathways may be relevant, namely, photoisomerization around the central ethylenic double bond and photocyclization involving two adjacent phenyl rings. In TPE-4mM, the barrierless S1 cyclization is favored; it is responsible for the ultralow fluorescence quantum yield observed experimentally. In TPE-4oM, both the S1 photocyclization and photoisomerization paths are blocked by non-negligible barriers, and fluorescence is thus feasible. Nonadiabatic dynamics simulations with more than 1000 surface hopping trajectories show ultrafast cyclization upon photoexcitation of TPE-4mM, whereas TPE-4oM remains unreactive during the 1 ps simulations. We discuss the chances for spectroscopic detection of the postulated cyclic photoproduct of TPE-4mM and the relevance of our findings for the AIE process.
Excited-State Decay Paths in Tetraphenylethene Derivatives
2017-01-01
The photophysical properties of tetraphenylethene (TPE) compounds may differ widely depending on the substitution pattern, for example, with regard to the fluorescence quantum yield ϕf and the propensity to exhibit aggregation-induced emission (AIE). We report combined electronic structure calculations and nonadiabatic dynamics simulations to study the excited-state decay mechanisms of two TPE derivatives with four methyl substituents, either in the meta position (TPE-4mM, ϕf = 0.1%) or in the ortho position (TPE-4oM, ϕf = 64.3%). In both cases, two excited-state decay pathways may be relevant, namely, photoisomerization around the central ethylenic double bond and photocyclization involving two adjacent phenyl rings. In TPE-4mM, the barrierless S1 cyclization is favored; it is responsible for the ultralow fluorescence quantum yield observed experimentally. In TPE-4oM, both the S1 photocyclization and photoisomerization paths are blocked by non-negligible barriers, and fluorescence is thus feasible. Nonadiabatic dynamics simulations with more than 1000 surface hopping trajectories show ultrafast cyclization upon photoexcitation of TPE-4mM, whereas TPE-4oM remains unreactive during the 1 ps simulations. We discuss the chances for spectroscopic detection of the postulated cyclic photoproduct of TPE-4mM and the relevance of our findings for the AIE process. PMID:28318255
Jeong, Hyunseok; Nguyen Ba An
2006-08-15
We study Greenberger-Horne-Zeilinger-type (GHZ-type) and W-type three-mode entangled coherent states. Both types of entangled coherent states violate Mermin's version of the Bell inequality with threshold photon detection (i.e., without photon counting). Such an experiment can be performed using linear optics elements and threshold detectors with significant Bell violations for GHZ-type entangled coherent states. However, to demonstrate Bell-type inequality violations for W-type entangled coherent states, additional nonlinear interactions are needed. We also propose an optical scheme to generate W-type entangled coherent states in free-traveling optical fields. The required resources for the generation are a single-photon source, a coherent state source, beam splitters, phase shifters, photodetectors, and Kerr nonlinearities. Our scheme does not necessarily require strong Kerr nonlinear interactions; i.e., weak nonlinearities can be used for the generation of the W-type entangled coherent states. Furthermore, it is also robust against inefficiencies of the single-photon source and the photon detectors.
Dong Li; Xiu Xiaoming; Gao Yajun; Yi, X. X.
2011-10-15
Using three-photon polarization-entangled GHZ states or W states, we propose controlled quantum key distribution protocols for circumventing two main types of collective noise, collective dephasing noise, or collective rotation noise. Irrespective of the number of controllers, a three-photon state can generate a one-bit secret key. The storage technique of quantum states is dispensable for the controller and the receiver, and it therefore allows performing the process in a more convenient mode. If the photon cost in a security check is disregarded, then the efficiency theoretically approaches unity.
NASA Astrophysics Data System (ADS)
Parra-Murillo, Carlos A.; Muñoz-Arias, Manuel H.; Madroñero, Javier; Wimberger, Sandro
2017-03-01
A many-body Wannier-Stark system coupled to an effective reservoir is studied within a non-Hermitian approach in the presence of a periodic driving. We show how the interplay of dissipation and driving dynamically induces a subspace of states which are very robust against dissipation. We numerically probe the structure of these asymptotic states and their robustness to imperfections in the initial-state preparation and to the size of the system. Moreover, the asymptotic states are found to be strongly entangled making them interesting for further applications.
Entanglement generation by qubit scattering in three dimensions
NASA Astrophysics Data System (ADS)
Hida, Yuichiro; Nakazato, Hiromichi; Yuasa, Kazuya; Omar, Yasser
2009-07-01
A qubit (a spin-1/2 particle) prepared in the up state is scattered by local spin-flipping potentials produced by the two target qubits (two fixed spins), both prepared in the down state, to generate an entangled state in the latter when the former is found in the down state after scattering. The scattering process is analyzed in three dimensions, both to lowest order and in full order in perturbation, with an appropriate renormalization for the latter. The entanglement is evaluated in terms of the concurrence as a function of the incident and scattering angles, the size of the incident wave packet, and the detector resolution to clarify the key elements for obtaining an entanglement with high quality. The characteristics of the results are also discussed in the context of (in)distinguishability of alternative paths for a quantum particle.
Exploiting Many-Body Bus States for Multi-Qubit Entanglement
2013-06-06
effective long- range interactions. In this project, our efforts were divided between three main tasks: (1) to develop multi-qubit entangling... effective interactions and the ability to mediate long-range entanglement differs significantly for chains of opposite parity. In Ref. [1], we contrast...the characters of even and odd-size chains when they are coupled to external qubits. Additional parity effects emerge in both cases, depending on the
NASA Astrophysics Data System (ADS)
Anshu, Anurag; Arad, Itai; Jain, Aditya
2016-11-01
Two-dimensional tensor networks such as projected entangled pairs states (PEPS) are generally hard to contract. This is arguably the main reason why variational tensor network methods in two dimensions are still not as successful as in one dimension. However, this is not necessarily the case if the tensor network represents a gapped ground state of a local Hamiltonian; such states are subject to many constraints and contain much more structure. In this paper, we introduce an approach for approximating the expectation value of a local observable in ground states of local Hamiltonians that are represented by PEPS tensor networks. Instead of contracting the full tensor network, we try to estimate the expectation value using only a local patch of the tensor network around the observable. Surprisingly, we demonstrate that this is often easier to do when the system is frustrated. In such case, the spanning vectors of the local patch are subject to nontrivial constraints that can be utilized via a semidefinite program to calculate rigorous lower and upper bounds on the expectation value. We test our approach in one-dimensional systems, where we show how the expectation value can be calculated up to at least 3 or 4 digits of precision, even when the patch radius is smaller than the correlation length.
Mazzarella, G.; Toigo, F.; Salasnich, L.; Parola, A.
2011-05-15
We consider a bosonic Josephson junction made of N ultracold and dilute atoms confined by a quasi-one-dimensional double-well potential within the two-site Bose-Hubbard model framework. The behavior of the system is investigated at zero temperature by varying the interatomic interaction from the strongly attractive regime to the repulsive one. We show that the ground state exhibits a crossover from a macroscopic Schroedinger-cat state to a separable Fock state through an atomic coherent regime. By diagonalizing the Bose-Hubbard Hamiltonian we characterize the emergence of the macroscopic cat states by calculating the Fisher information F, the coherence by means of the visibility {alpha} of the interference fringes in the momentum distribution, and the quantum correlations by using the entanglement entropy S. Both Fisher information and visibility are shown to be related to the ground-state energy by employing the Hellmann-Feynman theorem. This result, together with a perturbative calculation of the ground-state energy, allows simple analytical formulas for F and {alpha} to be obtained over a range of interactions, in excellent agreement with the exact diagonalization of the Bose-Hubbard Hamiltonian. In the attractive regime the entanglement entropy attains values very close to its upper limit for a specific interaction strength lying in the region where coherence is lost and self-trapping sets in.
Rajabi, Fereshteh; Houde, Martin
2017-03-01
We apply Dicke's theory of superradiance (introduced in 1954) to the 6.7-GHz methanol and 22-GHz water spectral lines, often detected in molecular clouds as signposts for the early stages of the star formation process. We suggest that superradiance, characterized by burst-like features taking place over a wide range of time scales, may provide a natural explanation for the recent observations of periodic and seemingly alternating methanol and water maser flares in G107.298+5.639. Although these observations would be very difficult to explain within the context of maser theory, we show that these flares may result from simultaneously initiated 6.7-GHz methanol and 22-GHz water superradiant bursts operating on different time scales, thus providing a natural mechanism for their observed durations and time ordering. The evidence of superradiance in this source further suggests the existence of entangled quantum mechanical states, involving a very large number of molecules, over distances of up to a few kilometers in the interstellar medium.
Explaining recurring maser flares in the ISM through large-scale entangled quantum mechanical states
Rajabi, Fereshteh; Houde, Martin
2017-01-01
We apply Dicke’s theory of superradiance (introduced in 1954) to the 6.7-GHz methanol and 22-GHz water spectral lines, often detected in molecular clouds as signposts for the early stages of the star formation process. We suggest that superradiance, characterized by burst-like features taking place over a wide range of time scales, may provide a natural explanation for the recent observations of periodic and seemingly alternating methanol and water maser flares in G107.298+5.639. Although these observations would be very difficult to explain within the context of maser theory, we show that these flares may result from simultaneously initiated 6.7-GHz methanol and 22-GHz water superradiant bursts operating on different time scales, thus providing a natural mechanism for their observed durations and time ordering. The evidence of superradiance in this source further suggests the existence of entangled quantum mechanical states, involving a very large number of molecules, over distances of up to a few kilometers in the interstellar medium. PMID:28378015
NASA Astrophysics Data System (ADS)
Ye, Tian-Yu
2015-04-01
In this paper, using the quantum entanglement swapping technologies under the collective-dephasing noise and the collective-rotation noise, two robust quantum dialogue protocols are proposed, respectively. The logical Bell states are used as the traveling states to combat the collective noise. The auxiliary logical Bell state is shared privately between two participants through the manner of direct transmission first. After encoded with the receiver's secret messages, it swaps entanglement with its adjacent logical Bell state. In this way, the information leakage problem is avoided. Moreover, Eve's active attacks can be detected with the help of decoy photon technology. For decoding, the Bell state measurements rather than the four-qubit joint measurements are needed.
Goyal, Sandeep K.; Ghosh, Sibasish
2010-10-15
Entanglement sudden death (ESD) in spatially separated two-mode Gaussian states coupled to local thermal and squeezed thermal baths is studied by mapping the problem to that of the quantum-to-classical transition. Using Simon's criterion concerning the characterization of classicality in Gaussian states, the time to ESD is calculated by analyzing the covariance matrices of the system. The results for the two-mode system at T=0 and T>0 for the two types of bath states are generalized to n modes, and are shown to be similar in nature to the results for the general discrete n-qubit system.
Cooper, W Grant
2009-08-01
Evidence requiring transcriptase quantum processing is identified and elementary quantum methods are used to qualitatively describe origins and consequences of time-dependent coherent proton states populating informational DNA base pair sites in T4 phage, designated by G-C-->G'-C', G-C-->*G-*C and AT-->*A-*T. Coherent states at these 'point' DNA lesions are introduced as consequences of hydrogen bond arrangement, keto-amino-->enol-imine, where product protons are shared between two sets of indistinguishable electron lone-pairs, and thus, participate in coupled quantum oscillations at frequencies of approximately 10(13) s(-1). This quantum mixing of proton energy states introduces stability enhancements of approximately 0.25-7 kcal/mole. Transcriptase genetic specificity is determined by hydrogen bond components contributing to the formation of complementary interstrand hydrogen bonds which, in these cases, is variable due to coupled quantum oscillations of coherent enol-imine protons. The transcriptase deciphers and executes genetic specificity instructions by implementing measurements on superposition proton states at G'-C', *G-*C and *A-*T sites in an interval Deltat<10(-13) s. After initiation of transcriptase measurement, model calculations indicate proton decoherence time, tau(D), satisfies the relation Deltat
Witnessing entanglement without entanglement witness operators
Pezzè, Luca; Li, Yan; Li, Weidong; Smerzi, Augusto
2016-01-01
Quantum mechanics predicts the existence of correlations between composite systems that, although puzzling to our physical intuition, enable technologies not accessible in a classical world. Notwithstanding, there is still no efficient general method to theoretically quantify and experimentally detect entanglement of many qubits. Here we propose to detect entanglement by measuring the statistical response of a quantum system to an arbitrary nonlocal parametric evolution. We witness entanglement without relying on the tomographic reconstruction of the quantum state, or the realization of witness operators. The protocol requires two collective settings for any number of parties and is robust against noise and decoherence occurring after the implementation of the parametric transformation. To illustrate its user friendliness we demonstrate multipartite entanglement in different experiments with ions and photons by analyzing published data on fidelity visibilities and variances of collective observables. PMID:27681625
Witnessing entanglement without entanglement witness operators
NASA Astrophysics Data System (ADS)
Pezzè, Luca; Li, Yan; Li, Weidong; Smerzi, Augusto
2016-10-01
Quantum mechanics predicts the existence of correlations between composite systems that, although puzzling to our physical intuition, enable technologies not accessible in a classical world. Notwithstanding, there is still no efficient general method to theoretically quantify and experimentally detect entanglement of many qubits. Here we propose to detect entanglement by measuring the statistical response of a quantum system to an arbitrary nonlocal parametric evolution. We witness entanglement without relying on the tomographic reconstruction of the quantum state, or the realization of witness operators. The protocol requires two collective settings for any number of parties and is robust against noise and decoherence occurring after the implementation of the parametric transformation. To illustrate its user friendliness we demonstrate multipartite entanglement in different experiments with ions and photons by analyzing published data on fidelity visibilities and variances of collective observables.
Otsuka, K; Chu, S-C; Lin, C-C; Tokunaga, K; Ohtomo, T
2009-11-23
To provide the underlying physical mechanism for formations of spatial- and polarization-entangled lasing patterns (namely, SPEPs), we performed experiments using a c-cut Nd:GdVO(4) microchip laser with off-axis laser-diode pumping. This extends recent work on entangled lasing pattern generation from an isotropic laser, where such a pattern was explained only in terms of generalized coherent states (GCSs) formed by mathematical manipulation. Here, we show that polarization-resolved transverse patterns can be well explained by the transverse mode-locking of distinct orthogonal linearly polarized Ince-Gauss (IG) mode pairs rather than GCSs. Dynamic properties of SPEPs were experimentally examined in both free-running and modulated conditions to identify long-term correlations of IG mode pairs over time. The complete chaos synchronization among IG mode pairs subjected to external perturbation is also demonstrated.
Ultrafine Entanglement Witnessing
NASA Astrophysics Data System (ADS)
Shahandeh, Farid; Ringbauer, Martin; Loredo, Juan C.; Ralph, Timothy C.
2017-03-01
Entanglement witnesses are invaluable for efficient quantum entanglement certification without the need for expensive quantum state tomography. Yet, standard entanglement witnessing requires multiple measurements and its bounds can be elusive as a result of experimental imperfections. Here, we introduce and demonstrate a novel procedure for entanglement detection which simply and seamlessly improves any standard witnessing procedure by using additional available information to tighten the witnessing bounds. Moreover, by relaxing the requirements on the witness operators, our method removes the general need for the difficult task of witness decomposition into local observables. We experimentally demonstrate entanglement detection with our approach using a separable test operator and a simple fixed measurement device for each agent. Finally, we show that the method can be generalized to higher-dimensional and multipartite cases with a complexity that scales linearly with the number of parties.
Effect of Cavity QED on Entanglement
NASA Astrophysics Data System (ADS)
Rfifi, Saad; Siyouri, Fatimazahra
2016-11-01
We use a quantum electrodynamics model, to study the evolution of maximally entangled bipartite states (Bell states), as well as a maximally entangled tripartite states as a multipartite system. Furthermore, we study the entanglement behaviour of these output states in cavity QED as function of interaction time and the coupling strength. The present study discusses the separability and the entanglement limit of such states after interaction with a cavity QED.
Healing of polymer interfaces: Interfacial dynamics, entanglements, and strength
Ge, Ting; Robbins, Mark O.; Perahia, Dvora; ...
2014-07-25
Self-healing of polymer films often takes place as the molecules diffuse across a damaged region, above their melting temperature. Using molecular dynamics simulations we probe the healing of polymer films and compare the results with those obtained for thermal welding of homopolymer slabs. These two processes differ from each other in their interfacial structure since damage leads to increased polydispersity and more short chains. A polymer sample was cut into two separate films that were then held together in the melt state. The recovery of the damaged film was followed as time elapsed and polymer molecules diffused across the interface.more » The mass uptake and formation of entanglements, as obtained from primitive path analysis, are extracted and correlated with the interfacial strength obtained from shear simulations. We find that the diffusion across the interface is signifcantly faster in the damaged film compared to welding because of the presence of short chains. Though interfacial entanglements increase more rapidly for the damaged films, a large fraction of these entanglements are near chain ends. As a result, the interfacial strength of the healing film increases more slowly than for welding. For both healing and welding, the interfacial strength saturates as the bulk entanglement density is recovered across the interface. However, the saturation strength of the damaged film is below the bulk strength for the polymer sample. At saturation, cut chains remain near the healing interface. They are less entangled and as a result they mechanically weaken the interface. When the strength of the interface saturates, the number of interfacial entanglements scales with the corresponding bulk entanglement density. Chain stiffness increases the density of entanglements, which increases the strength of the interface. Our results show that a few entanglements across the interface are sufficient to resist interfacial chain pullout and enhance the mechanical
Healing of polymer interfaces: Interfacial dynamics, entanglements, and strength
Ge, Ting; Robbins, Mark O.; Perahia, Dvora; Grest, Gary S.
2014-07-25
Self-healing of polymer films often takes place as the molecules diffuse across a damaged region, above their melting temperature. Using molecular dynamics simulations we probe the healing of polymer films and compare the results with those obtained for thermal welding of homopolymer slabs. These two processes differ from each other in their interfacial structure since damage leads to increased polydispersity and more short chains. A polymer sample was cut into two separate films that were then held together in the melt state. The recovery of the damaged film was followed as time elapsed and polymer molecules diffused across the interface. The mass uptake and formation of entanglements, as obtained from primitive path analysis, are extracted and correlated with the interfacial strength obtained from shear simulations. We find that the diffusion across the interface is signifcantly faster in the damaged film compared to welding because of the presence of short chains. Though interfacial entanglements increase more rapidly for the damaged films, a large fraction of these entanglements are near chain ends. As a result, the interfacial strength of the healing film increases more slowly than for welding. For both healing and welding, the interfacial strength saturates as the bulk entanglement density is recovered across the interface. However, the saturation strength of the damaged film is below the bulk strength for the polymer sample. At saturation, cut chains remain near the healing interface. They are less entangled and as a result they mechanically weaken the interface. When the strength of the interface saturates, the number of interfacial entanglements scales with the corresponding bulk entanglement density. Chain stiffness increases the density of entanglements, which increases the strength of the interface. Our results show that a few entanglements across the interface are sufficient to resist interfacial chain pullout and enhance the mechanical strength.
Gaussian Intrinsic Entanglement
NASA Astrophysics Data System (ADS)
Mišta, Ladislav; Tatham, Richard
2016-12-01
We introduce a cryptographically motivated quantifier of entanglement in bipartite Gaussian systems called Gaussian intrinsic entanglement (GIE). The GIE is defined as the optimized mutual information of a Gaussian distribution of outcomes of measurements on parts of a system, conditioned on the outcomes of a measurement on a purifying subsystem. We show that GIE vanishes only on separable states and exhibits monotonicity under Gaussian local trace-preserving operations and classical communication. In the two-mode case, we compute GIE for all pure states as well as for several important classes of symmetric and asymmetric mixed states. Surprisingly, in all of these cases, GIE is equal to Gaussian Rényi-2 entanglement. As GIE is operationally associated with the secret-key agreement protocol and can be computed for several important classes of states, it offers a compromise between computable and physically meaningful entanglement quantifiers.
Entanglement Involved in Time Evolution of Two-Mode Squeezed State in Single-Mode Diffusion Channel
NASA Astrophysics Data System (ADS)
Xu, Xue-Fen; Fan, Hong-Yi
2017-02-01
We derive the evolution law of an initial two-mode squeezed vacuum state sech2λ e^{a^{dag }b^{dagger }tanh λ }\\vert 00rangle < 00\\vert e^{ab tanh λ } (a pure state) passing through an a-mode diffusion channel described by the master equation dρ ( t) /dt=-κ [ a^{dagger}aρ ( t) -a^{dagger}ρ ( t) a-aρ ( t) a^{dagger}+ρ ( t) aa^{dagger}] , since the two-mode squeezed state is simultaneously an entangled state, the final state which emerges from this channel is a two-mode mixed state. Performing partial trace over the b-mode of ρ(t) yields a new chaotic field, ρ a(t) = {sech2λ}/{1+κt sech2λ}:exp [ {-sech2λ}/{1+κt sech2λ }a^{dagger }a ] :, which exhibits higher temperature and more photon numbers, showing the diffusion effect. Besides, measuring a-mode of ρ(t) to find n photons will result in the collapse of the two-mode system to a new Laguerre polynomial-weighted chaotic state in b-mode, which also exhibits entanglement.
NASA Astrophysics Data System (ADS)
Hach, Edwin E.; Alsing, Paul M.; Gerry, Christopher C.
2016-04-01
We study the violation of the Bell-Clauser-Horne-Shimony-Holt (Bell-CHSH) inequality for entangled SU(1,1) coherent states of the form proposed by Perelomov. Specifically, we examine Bell-CHSH violations by such states in the case in which distant observers Alice and Bob perform local, noncompact, SU(1,1) transformations characterized by hyperbolic angles on each of the subsystems and subsequently measure dichotomic observables, namely SU(1,1) parity operators. We find significant violations over a broad range of hyperbolic angles.
Nonlinear cascades and concurrences for multipartite-entangled and non-Gaussian states of light
NASA Astrophysics Data System (ADS)
Pooser, Raphael
This thesis presents theoretical and experimental progress towards generating essential quantum optical building blocks for the implementation of quantum computing (QC) and quantum information (QI). Quantum optical systems such as Optical Parametric Oscillators (OPOs) provide a natural implementation of QC and QI by producing entanglement using nonlinear optical media. This dissertation covers the theoretical study of novel nonlinear optical systems such as concurrence- and cascade-based OPOs, in the spirit of developing them for use in QC and QI. The experimental research presents the first realizations of the novel nonlinear materials necessary to build these exotic OPOs. A further application of entanglement in quantum optics, Heisenberg-limited interferometry, is also discussed.
Large-Alphabet Quantum Key Distribution Using Energy-Time Entangled Bipartite States
NASA Astrophysics Data System (ADS)
Ali-Khan, Irfan; Broadbent, Curtis J.; Howell, John C.
2007-02-01
We present a protocol for large-alphabet quantum key distribution (QKD) using energy-time entangled biphotons. Binned, high-resolution timing measurements are used to generate a large-alphabet key with over 10 bits of information per photon pair, albeit with large noise. QKD with 5% bit error rate is demonstrated with 4 bits of information per photon pair, where the security of the quantum channel is determined by the visibility of Franson interference fringes. The protocol is easily generalizable to even larger alphabets, and utilizes energy-time entanglement which is robust to transmission over large distances in fiber.
Nonextensive statistics in stringy space-time foam models and entangled meson states
Mavromatos, Nick E.; Sarkar, Sarben
2009-05-15
The possibility of generation of nonextensive statistics, in the sense of Tsallis, due to space-time foam is discussed within the context of a particular kind of foam in string/brane theory, the D-particle foam model. The latter involves pointlike brane defects (D-particles), which provide the topologically nontrivial foamy structures of space-time. A stochastic Langevin equation for the velocity recoil of D-particles can be derived from the pinched approximation for a sum over genera in the calculation of the partition function of a bosonic string in the presence of heavy D-particles. The string coupling in standard perturbation theory is related to the exponential of the expectation of the dilaton. Inclusion of fluctuations of the dilaton itself and uncertainties in the string background will then necessitate fluctuations in g{sub s}. The fluctuation in the string coupling in the sum over genera typically leads to a generic structure of the Langevin equation where the coefficient of the noise term fluctuates owing to dependence on the string coupling g{sub s}. The positivity of g{sub s} leads naturally to a stochastic modeling of its distribution with a {chi} distribution. This then rigorously implies a Tsallis-type nonextensive or, more generally, a superstatistics distribution for the recoil velocity of D-particles. As a concrete and physically interesting application, we provide a rigorous estimate of an {omega}-like effect, pertinent to CPT violating modifications of the Einstein-Podolsky-Rosen correlators in entangled states of neutral kaons. In the case of D-particle foam fluctuations, which respect the Lorentz symmetry of the vacuum on average, we find that the {omega} effect may be within the range of sensitivity of future meson factories.
NASA Astrophysics Data System (ADS)
Wang, Shuai; Hou, Li-Li; Chen, Xian-Feng; Xu, Xue-Fen
2015-06-01
We theoretically analyze the Einstein-Podolsky-Rosen (EPR) correlation, the quadrature squeezing, and the continuous-variable quantum teleportation when considering non-Gaussian entangled states generated by applying multiple-photon subtraction and multiple-photon addition to a two-mode squeezed vacuum state (TMSVs). Our results indicate that in the case of the multiple-photon-subtracted TMSVs with symmetric operations, the corresponding EPR correlation, the two-mode squeezing degree, the sum squeezing, and the fidelity of teleporting a coherent state or a squeezed vacuum state can be enhanced for any squeezing parameter r and these enhancements increase with the number of subtracted photons in the low-squeezing regime, while asymmetric multiple-photon subtractions will generally reduce these quantities. For the multiple-photon-added TMSVs, although it holds stronger entanglement, its EPR correlation, two-mode squeezing, sum squeezing, and the fidelity of a coherent state are always smaller than that of the TMSVs. Only when considering the case of teleporting a squeezed vacuum state does the symmetric photon addition make somewhat of an improvement in the fidelity for large-squeezing parameters. In addition, we analytically prove that a one-mode multiple-photon-subtracted TMSVs is equivalent to that of the one-mode multiple-photon-added one. And one-mode multiple-photon operations will diminish the above four quantities for any squeezing parameter r .
Gualdi, Giulia; Giampaolo, Salvatore M; Illuminati, Fabrizio
2011-02-04
We introduce and discuss the concept of modular entanglement. This is the entanglement that is established between the end points of modular systems composed by sets of interacting moduli of arbitrarily fixed size. We show that end-to-end modular entanglement scales in the thermodynamic limit and rapidly saturates with the number of constituent moduli. We clarify the mechanisms underlying the onset of entanglement between distant and noninteracting quantum systems and its optimization for applications to quantum repeaters and entanglement distribution and sharing.
Minimal Entanglement Witness from Electrical Current Correlations
NASA Astrophysics Data System (ADS)
Brange, F.; Malkoc, O.; Samuelsson, P.
2017-01-01
Despite great efforts, an unambiguous demonstration of entanglement of mobile electrons in solid state conductors is still lacking. Investigating theoretically a generic entangler-detector setup, we here show that a witness of entanglement between two flying electron qubits can be constructed from only two current cross correlation measurements, for any nonzero detector efficiencies and noncollinear polarization vectors. We find that all entangled pure states, but not all mixed ones, can be detected with only two measurements, except the maximally entangled states, which require three. Moreover, detector settings for optimal entanglement witnessing are presented.
Recovering entanglement by local operations
D’Arrigo, A.; Lo Franco, R.; Benenti, G.; Paladino, E.; Falci, G.
2014-11-15
We investigate the phenomenon of bipartite entanglement revivals under purely local operations in systems subject to local and independent classical noise sources. We explain this apparent paradox in the physical ensemble description of the system state by introducing the concept of “hidden” entanglement, which indicates the amount of entanglement that cannot be exploited due to the lack of classical information on the system. For this reason this part of entanglement can be recovered without the action of non-local operations or back-transfer process. For two noninteracting qubits under a low-frequency stochastic noise, we show that entanglement can be recovered by local pulses only. We also discuss how hidden entanglement may provide new insights about entanglement revivals in non-Markovian dynamics.
Concentrating partial entanglement by local operations
NASA Astrophysics Data System (ADS)
Bennett, Charles H.; Bernstein, Herbert J.; Popescu, Sandu; Schumacher, Benjamin
1996-04-01
If two separated observers are supplied with entanglement, in the form of n pairs of particles in identical partly entangled pure states, one member of each pair being given to each observer, they can, by local actions of each observer, concentrate this entanglement into a smaller number of maximally entangled pairs of particles, for example, Einstein-Podolsky-Rosen singlets, similarly shared between the two observers. The concentration process asymptotically conserves entropy of entanglement-the von Neumann entropy of the partial density matrix seen by either observer-with the yield of singlets approaching, for large n, the base-2 entropy of entanglement of the initial partly entangled pure state. Conversely, any pure or mixed entangled state of two systems can be produced by two classically communicating separated observers, drawing on a supply of singlets as their sole source of entanglement.
Constructing optimal entanglement witnesses
Chruscinski, Dariusz; Pytel, Justyna; Sarbicki, Gniewomir
2009-12-15
We provide a class of indecomposable entanglement witnesses. In 4x4 case, it reproduces the well-known Breuer-Hall witness. We prove that these witnesses are optimal and atomic, i.e., they are able to detect the 'weakest' quantum entanglement encoded into states with positive partial transposition. Equivalently, we provide a construction of indecomposable atomic maps in the algebra of 2kx2k complex matrices. It is shown that their structural physical approximations give rise to entanglement breaking channels. This result supports recent conjecture by Korbicz et al. [Phys. Rev. A 78, 062105 (2008)].
Entanglement Dynamics of Electrons and Photons
NASA Astrophysics Data System (ADS)
Wu, Xiang-Yao; Liu, Xiao-Jing; Lu, Jing-Bin; Li, Tian-Shun; Zhang, Si-Qi; Liang, Yu; Ma, Ji; Li, Hong
2016-12-01
Entanglement is a fundamental feature of quantum theory as well as a key resource for quantum computing and quantum communication, but the entanglement mechanism has not been found at present. We think when the two subsystems exist interaction directly or indirectly, they can be in entanglement state. such as, in the Jaynes-Cummings model, the entanglement between the atom and the light field comes from their interaction. In this paper, we have studied the entanglement mechanism of electron-electron and photon-photon, which are from the spin-spin interaction. We found their total entanglement states are relevant both space state and spin state. When two electrons or two photons are far away, their entanglement states should be disappeared even if their spin state is entangled.
Entanglement Measure and Quantum Violation of Bell-Type Inequality
NASA Astrophysics Data System (ADS)
Ding, Dong; He, Ying-Qiu; Yan, Feng-Li; Gao, Ting
2016-10-01
By calculating entanglement measures and quantum violation of Bell-type inequality, we reveal the relationship between entanglement measure and the amount of quantum violation for a family of four-qubit entangled states. It has been demonstrated that the Bell-type inequality is completely violated by these four-qubit entangled states. The plot of entanglement measure as a function of the expectation value of Bell operator shows that entanglement measure first decreases and then increases smoothly with increasing quantum violation.
Secure Key from Bound Entanglement
NASA Astrophysics Data System (ADS)
Horodecki, Karol; Horodecki, Michał; Horodecki, Paweł; Oppenheim, Jonathan
2005-04-01
We characterize the set of shared quantum states which contain a cryptographically private key. This allows us to recast the theory of privacy as a paradigm closely related to that used in entanglement manipulation. It is shown that one can distill an arbitrarily secure key from bound entangled states. There are also states that have less distillable private keys than the entanglement cost of the state. In general, the amount of distillable key is bounded from above by the relative entropy of entanglement. Relationships between distillability and distinguishability are found for a class of states which have Bell states correlated to separable hiding states. We also describe a technique for finding states exhibiting irreversibility in entanglement distillation.
NASA Astrophysics Data System (ADS)
Singh, Manu Pratap; Rajput, Balwant S.
2017-04-01
New set of maximally entangled states (Singh-Rajput MES), constituting orthonormal eigen bases, has been revisited and its superiority and suitability in pattern-association (Quantum Associative Memory, QuAM) have been demonstrated. Using these MES as memory states in the evolutionary process of pattern storage in a two-qubit system, it has been shown that the first two states of Singh-Rajput MES are useful for storing the pattern |11> and the last two of these MES are useful in storing the pattern |10> Recall operations of quantum associate memory (QuAM) have been conducted through evolutionary process in terms of unitary operators by separately choosing Singh-Rajput MES and Bell's MES as memory states and it has been shown that Singh-Rajput MES as valid memory states for recalling the patterns in a two-qubit system are much more suitable than Bell's MES.
NASA Astrophysics Data System (ADS)
Lu, Chi-Ken; Chiou, Dah-Wei; Lin, Feng-Li
2015-08-01
We consider integer quantum Hall states and calculate the bulk entanglement spectrum by formulating the correlation matrix in the guiding center representation. Our analytical approach is based on the strategy of redefining the inner product of states in the Hilbert space, via a projection operator, to take care of the restriction imposed by the (rectangle-pixeled) checkerboard partition. The resultant correlation matrix contains various couplings between states of different guiding centers parameterized by the magnetic length and the pixel size. Given a fixed magnetic field, we find various patterns of band crossings by tuning the pixel size (quantified by the flux Φ threading each pixel) and by changing the filling factor ν ∈N (determined by the Fermi level). When ν =1 and Φ =2 π , or ν =2 and Φ =π , one Dirac band crossing is found. For ν =1 and Φ =π , the band crossings are in the form of a nodal line, enclosing the Brillouin zone. As for ν =2 and Φ =2 π , the doubled Dirac point, or the quadratic point, is seen. Additionally, we infer that the quadratic point is protected by the C4 symmetry of the pixel since it evolves into two separate Dirac points when the symmetry is lowered to C2. We also identify the emerging symmetries responsible for the symmetric bulk entanglement spectra, which are absent in the underlying quantum Hall states.
NASA Astrophysics Data System (ADS)
D'Ambrosio, Vincenzo; Carvacho, Gonzalo; Graffitti, Francesco; Vitelli, Chiara; Piccirillo, Bruno; Marrucci, Lorenzo; Sciarrino, Fabio
2016-09-01
Light beams having a vectorial field structure, or polarization, that varies over the transverse profile and a central optical singularity are called vector vortex (VV) beams and may exhibit specific properties such as focusing into "light needles" or rotation invariance. VV beams have already found applications in areas ranging from microscopy to metrology, optical trapping, nano-optics, and quantum communication. Individual photons in such beams exhibit a form of single-particle quantum entanglement between different degrees of freedom. On the other hand, the quantum states of two photons can be also entangled with each other. Here, we combine these two concepts and demonstrate the generation of quantum entanglement between two photons that are both in VV states: a form of entanglement between two complex vectorial fields. This result may lead to quantum-enhanced applications of VV beams as well as to quantum information protocols fully exploiting the vectorial features of light.
A Subsystem-Independent Generalization of Entanglement
NASA Astrophysics Data System (ADS)
Barnum, Howard; Knill, Emanuel; Ortiz, Gerardo; Somma, Rolando; Viola, Lorenza
2004-03-01
We present a generalization of entanglement based on the idea that entanglement is relative to a distinguished subspace of observables rather than a distinguished subsystem decomposition. A pure quantum state is entangled relative to such a subspace if its expectations are a proper mixture of those of other states. Many information-theoretic aspects of entanglement can be extended to this observable-based setting, suggesting new ways of measuring and classifying multipartite entanglement. By going beyond the distinguishable-subsystem framework, generalized entanglement also provides novel tools for probing quantum correlations in interacting many-body systems.
Reliable Entanglement Verification
NASA Astrophysics Data System (ADS)
Arrazola, Juan; Gittsovich, Oleg; Donohue, John; Lavoie, Jonathan; Resch, Kevin; Lütkenhaus, Norbert
2013-05-01
Entanglement plays a central role in quantum protocols. It is therefore important to be able to verify the presence of entanglement in physical systems from experimental data. In the evaluation of these data, the proper treatment of statistical effects requires special attention, as one can never claim to have verified the presence of entanglement with certainty. Recently increased attention has been paid to the development of proper frameworks to pose and to answer these type of questions. In this work, we apply recent results by Christandl and Renner on reliable quantum state tomography to construct a reliable entanglement verification procedure based on the concept of confidence regions. The statements made do not require the specification of a prior distribution nor the assumption of an independent and identically distributed (i.i.d.) source of states. Moreover, we develop efficient numerical tools that are necessary to employ this approach in practice, rendering the procedure ready to be employed in current experiments. We demonstrate this fact by analyzing the data of an experiment where photonic entangled two-photon states were generated and whose entanglement is verified with the use of an accessible nonlinear witness.
Higher-order quantum entanglement
NASA Technical Reports Server (NTRS)
Zeilinger, Anton; Horne, Michael A.; Greenberger, Daniel M.
1992-01-01
In quantum mechanics, the general state describing two or more particles is a linear superposition of product states. Such a superposition is called entangled if it cannot be factored into just one product. When only two particles are entangled, the stage is set for Einstein-Podolsky-Rosen (EPR) discussions and Bell's proof that the EPR viewpoint contradicts quantum mechanics. If more than two particles are involved, new possibilities and phenomena arise. For example, the Greenberger, Horne, and Zeilinger (GHZ) disproof of EPR applies. Furthermore, as we point out, with three or more particles even entanglement itself can be an entangled property.
NASA Astrophysics Data System (ADS)
Namiki, Ryo
2013-12-01
We consider the composability of quantum channels from a limited amount of entanglement via local oper-ations and classical communication (LOCC). We show that any k-partial-entanglement-breaking channel can be composed from an entangled state with a Schmidt number of k via one-way LOCC. From the entanglement-assisted construction we can reach an alternative definition of partial-entanglement-breaking channels.
Optimal Gaussian entanglement swapping
Hoelscher-Obermaier, Jason; Loock, Peter van
2011-01-15
We consider entanglement swapping with general mixed two-mode Gaussian states and calculate the optimal gains for a broad class of such states including those states most relevant in communication scenarios. We show that, for this class of states, entanglement swapping adds no additional mixedness; that is, the ensemble-average output state has the same purity as the input states. This implies that, by using intermediate entanglement swapping steps, it is, in principle, possible to distribute entangled two-mode Gaussian states of higher purity as compared to direct transmission. We then apply the general results on optimal Gaussian swapping to the problem of quantum communication over a lossy fiber and demonstrate that, in contrast to the negative conclusions in the literature, swapping-based schemes in fact often perform better than direct transmission for high input squeezing. However, an effective transmission analysis reveals that the hope for improved performance based on optimal Gaussian entanglement swapping is spurious since the swapping does not lead to an enhancement of the effective transmission. This implies that the same or better results can always be obtained using direct transmission in combination with, in general, less squeezing.
From entanglement witness to generalized Catalan numbers
Cohen, E.; Hansen, T.; Itzhaki, N.
2016-01-01
Being extremely important resources in quantum information and computation, it is vital to efficiently detect and properly characterize entangled states. We analyze in this work the problem of entanglement detection for arbitrary spin systems. It is demonstrated how a single measurement of the squared total spin can probabilistically discern separable from entangled many-particle states. For achieving this goal, we construct a tripartite analogy between the degeneracy of entanglement witness eigenstates, tensor products of SO(3) representations and classical lattice walks with special constraints. Within this framework, degeneracies are naturally given by generalized Catalan numbers and determine the fraction of states that are decidedly entangled and also known to be somewhat protected against decoherence. In addition, we introduce the concept of a “sterile entanglement witness”, which for large enough systems detects entanglement without affecting much the system’s state. We discuss when our proposed entanglement witness can be regarded as a sterile one. PMID:27461089
From entanglement witness to generalized Catalan numbers
NASA Astrophysics Data System (ADS)
Cohen, E.; Hansen, T.; Itzhaki, N.
2016-07-01
Being extremely important resources in quantum information and computation, it is vital to efficiently detect and properly characterize entangled states. We analyze in this work the problem of entanglement detection for arbitrary spin systems. It is demonstrated how a single measurement of the squared total spin can probabilistically discern separable from entangled many-particle states. For achieving this goal, we construct a tripartite analogy between the degeneracy of entanglement witness eigenstates, tensor products of SO(3) representations and classical lattice walks with special constraints. Within this framework, degeneracies are naturally given by generalized Catalan numbers and determine the fraction of states that are decidedly entangled and also known to be somewhat protected against decoherence. In addition, we introduce the concept of a “sterile entanglement witness”, which for large enough systems detects entanglement without affecting much the system’s state. We discuss when our proposed entanglement witness can be regarded as a sterile one.
Spatiotemporal multipartite entanglement
Kolobov, Mikhail I.; Patera, Giuseppe
2011-05-15
In this Rapid Communication, we propose, following the spirit of quantum imaging, to generalize the theory of multipartite entanglement for the continuous-variable Gaussian states by considering, instead of the global covariance matrix, the local correlation matrix at two different spatiotemporal points ({rho}-vector,t) and ({rho}-vector{sup '},t{sup '}), with {rho}-vector being the transverse coordinate. Our approach makes it possible to introduce the characteristic spatial length and the characteristic time of the multipartite entanglement, which in general depend on the number of 'parties' in the system. As an example, we consider tripartite entanglement in spontaneous parametric down-conversion with a spatially structured pump. We investigate spatiotemporal properties of such entanglement and calculate its characteristic spatial length and time.
Inter-Universal Quantum Entanglement
NASA Astrophysics Data System (ADS)
Robles-Pérez, S. J.; González-Díaz, P. F.
2015-01-01
The boundary conditions to be imposed on the quantum state of the whole multiverse could be such that the universes would be created in entangled pairs. Then, interuniversal entanglement would provide us with a vacuum energy for each single universe that might be fitted with observational data, making testable not only the multiverse proposal but also the boundary conditions of the multiverse. Furthermore, the second law of the entanglement thermodynamics would enhance the expansion of the single universes.
NASA Astrophysics Data System (ADS)
Mezzacapo, Fabio; Angelone, Adriano; Pupillo, Guido
2016-10-01
We show that the entangled-plaquette variational Ansatz can be adapted to study the two-dimensional t-J model in the presence of two mobile holes. Specifically, we focus on a square lattice comprising up to N =256 sites in the parameter range 0.4 ≤J /t ≤2.0 . Ground state energies are obtained via the optimization of a wave function in which the weight of a given configuration is expressed in terms of variational coefficients associated with square and linear entangled plaquettes. Our estimates are in excellent agreement with exact results available for the N =16 lattice. By extending our study to considerably larger systems we find, based on the analysis of the long-distance tail of the probability of finding two holes at spatial separation r , and on our computed two-hole binding energies, the existence of a two-hole bound state for all the values of J /t explored here. It is estimated that d -wave binding of the two holes does not occur for J /t
Spin-parity effect in violation of Bell’s inequalities for entangled states of parallel polarization
NASA Astrophysics Data System (ADS)
Zhang, Haifeng; Wang, Jianhua; Song, Zhigang; Liang, J.-Q.; Wei, L.-F.
2017-02-01
Bell’s inequalities (BIs) derived in terms of quantum probability statistics are extended to general bipartite-entangled states of arbitrary spins with parallel polarization. The original formula of Bell for the two-spin singlet is slightly modified in the parallel configuration, while the inequality formulated by Clauser-Horne-Shimony-Holt (CHSH) remains unchanged. The violation of BIs indeed resulted from the quantum nonlocal correlation for spin-1 2 case. However, the inequalities are always satisfied for the spin-1 entangled states regardless of parallel or antiparallel polarizations of two spins. The spin parity effect originally demonstrated with the antiparallel spin-polarizations (Z. Song, J.-Q. Liang and L.-F. Wei, Mod. Phys. Lett. B 28 (2013) 145004) still exists for the parallel case. The quantum nonlocality does not lead to the violation for integer spins due to the cancellation of nonlocal interference effects by the quantum statistical average. Again, the violation of BIs seems to be a result of the measurement-induced nontrivial Berry phase (BP) for half-integer spins.
NASA Astrophysics Data System (ADS)
Zhang, Dasen; Zhang, Zhiming
2017-02-01
We study the spatiotemporal structure of the biphoton entangled state generated by the four-wave mixing (FWM) process in a cold two-level atomic ensemble. We analyze, for the first time, the X-like shaped structure of the biphoton entangled state and the geometry of the biphoton correlation for different lengths and densities of the cold atomic ensemble. The propagation equations of the photon pairs generated from FWM process are derived in a spatiotemporal framework. By means of the input-output relations of the propagation equations, the biphoton amplitude function is obtained in a spatiotemporal domain. In the given frequency range, the biphoton amplitude displays an X-like shaped geometry, nonfactorizable in the space-time domain. Such an X-like shaped spatiotemporal structure is caused by the phase matching and the FWM gain. The former leads to the X-like shaped envelope of the biphoton correlation, while the latter gives rise to the oscillations around the X-like shaped envelope.
Zhang, Dasen; Zhang, Zhiming
2017-02-20
We study the spatiotemporal structure of the biphoton entangled state generated by the four-wave mixing (FWM) process in a cold two-level atomic ensemble. We analyze, for the first time, the X-like shaped structure of the biphoton entangled state and the geometry of the biphoton correlation for different lengths and densities of the cold atomic ensemble. The propagation equations of the photon pairs generated from FWM process are derived in a spatiotemporal framework. By means of the input-output relations of the propagation equations, the biphoton amplitude function is obtained in a spatiotemporal domain. In the given frequency range, the biphoton amplitude displays an X-like shaped geometry, nonfactorizable in the space-time domain. Such an X-like shaped spatiotemporal structure is caused by the phase matching and the FWM gain. The former leads to the X-like shaped envelope of the biphoton correlation, while the latter gives rise to the oscillations around the X-like shaped envelope.
Zhang, Dasen; Zhang, Zhiming
2017-01-01
We study the spatiotemporal structure of the biphoton entangled state generated by the four-wave mixing (FWM) process in a cold two-level atomic ensemble. We analyze, for the first time, the X-like shaped structure of the biphoton entangled state and the geometry of the biphoton correlation for different lengths and densities of the cold atomic ensemble. The propagation equations of the photon pairs generated from FWM process are derived in a spatiotemporal framework. By means of the input-output relations of the propagation equations, the biphoton amplitude function is obtained in a spatiotemporal domain. In the given frequency range, the biphoton amplitude displays an X-like shaped geometry, nonfactorizable in the space-time domain. Such an X-like shaped spatiotemporal structure is caused by the phase matching and the FWM gain. The former leads to the X-like shaped envelope of the biphoton correlation, while the latter gives rise to the oscillations around the X-like shaped envelope. PMID:28218235
Entanglement Entropy of Black Holes
NASA Astrophysics Data System (ADS)
Solodukhin, Sergey N.
2011-12-01
The entanglement entropy is a fundamental quantity, which characterizes the correlations between sub-systems in a larger quantum-mechanical system. For two sub-systems separated by a surface the entanglement entropy is proportional to the area of the surface and depends on the UV cutoff, which regulates the short-distance correlations. The geometrical nature of entanglement-entropy calculation is particularly intriguing when applied to black holes when the entangling surface is the black-hole horizon. I review a variety of aspects of this calculation: the useful mathematical tools such as the geometry of spaces with conical singularities and the heat kernel method, the UV divergences in the entropy and their renormalization, the logarithmic terms in the entanglement entropy in four and six dimensions and their relation to the conformal anomalies. The focus in the review is on the systematic use of the conical singularity method. The relations to other known approaches such as ’t Hooft’s brick-wall model and the Euclidean path integral in the optical metric are discussed in detail. The puzzling behavior of the entanglement entropy due to fields, which non-minimally couple to gravity, is emphasized. The holographic description of the entanglement entropy of the blackhole horizon is illustrated on the two- and four-dimensional examples. Finally, I examine the possibility to interpret the Bekenstein-Hawking entropy entirely as the entanglement entropy.
Quantum entanglement and the Bell matrix
NASA Astrophysics Data System (ADS)
Lai, Anna Chiara; Pedicini, Marco; Rognone, Silvia
2016-07-01
We present a class of maximally entangled states generated by a high-dimensional generalisation of the cnot gate. The advantage of our constructive approach is the simple algebraic structure of both entangling operator and resulting entangled states. In order to show that the method can be applied to any dimension, we introduce new sufficient conditions for global and maximal entanglement with respect to Meyer and Wallach's measure.
Chitanvis, S.M.
1998-09-01
We have developed a theory of polymer entanglement using an extended Cahn-Hilliard functional with two extra terms. One is a nonlocal attractive term, operating over mesoscales, which is interpreted as giving rise to entanglement, and the other is a local repulsive term indicative of excluded volume interactions. This functional can be derived using notions from gauge theory. We go beyond the Gaussian approximation, to the one-loop level, to show that the system exhibits a crossover to a state of entanglement as the average chain length between points of entanglement decreases. This crossover is marked by {ital critical} slowing down, as the effective diffusion constant goes to zero. We have also computed the tensile modulus of the system, and we find a corresponding crossover to a regime of high modulus. The single parameter in our theory is obtained by fitting to available experimental data on polystyrene melts of various chain lengths. Extrapolation of this fit yields a model for the crossover to entanglement. The need for additional experiments detailing the crossover to the entangled state is pointed out. {copyright} {ital 1998} {ital The American Physical Society}
NASA Astrophysics Data System (ADS)
Liu, Jiong; Zhou, Lan; Sheng, Yu-Bo
2015-07-01
We propose a protocol for directly measuring the concurrence of a two-qubit electronic pure entangled state. To complete this task, we first design a parity-check measurement (PCM) which is constructed by two polarization beam splitters (PBSs) and a charge detector. By using the PCM for three rounds, we can achieve the concurrence by calculating the total probability of picking up the odd parity states from the initial states. Since the conduction electron may be a good candidate for the realization of quantum computation, this protocol may be useful in future solid quantum computation. Project supported by the National Natural Science Foundation of China (Grant Nos. 11474168 and 61401222), the Qing Lan Project in Jiangsu Province, China, and the Priority Academic Development Program of Jiangsu Higher Education Institutions, China.
Human Rights in Southeast Asia: Choosing a Path for the United States
1995-01-01
95-E- 60 c. I NATIONAL DEFENSE UNWERSrN NATIONAL WAR COLLEGE IilUMAN RIGHTS N SOUTHEAST ASIA CHOOSING A PATH FOR THE UNITED STATES CORE COURSE...COVERED 00-00-1995 to 00-00-1995 4. TITLE AND SUBTITLE Human Rights in Southeast Asia Choosing a Path for the United States 5a. CONTRACT NUMBER...unclassified c. THIS PAGE unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 HUMAN RIGHTS IN SOUTHEAST ASIA CHOOSIXG A PATH
Multipartite entanglement for entanglement teleportation
Lee, Jinhyoung; Min, Hyegeun; Oh, Sung Dahm
2002-11-01
A scheme for entanglement teleportation is proposed to incorporate multipartite entanglement of four qubits as a quantum channel. Based on the invariance of entanglement teleportation under an arbitrary two-qubit unitary transformation, we derive relations for the separabilities of joint measurements at a sending station and of unitary operations at a receiving station. From the relations of the separabilities it is found that an inseparable quantum channel always leads to total teleportation of entanglement with an inseparable joint measurement and/or a nonlocal unitary operation.
High-dimensional entanglement certification
Huang, Zixin; Maccone, Lorenzo; Karim, Akib; Macchiavello, Chiara; Chapman, Robert J.; Peruzzo, Alberto
2016-01-01
Quantum entanglement is the ability of joint quantum systems to possess global properties (correlation among systems) even when subsystems have no definite individual property. Whilst the 2-dimensional (qubit) case is well-understood, currently, tools to characterise entanglement in high dimensions are limited. We experimentally demonstrate a new procedure for entanglement certification that is suitable for large systems, based entirely on information-theoretics. It scales more efficiently than Bell’s inequality and entanglement witness. The method we developed works for arbitrarily large system dimension d and employs only two local measurements of complementary properties. This procedure can also certify whether the system is maximally entangled. We illustrate the protocol for families of bipartite states of qudits with dimension up to 32 composed of polarisation-entangled photon pairs. PMID:27311935
Witnessing entanglement in hybrid systems
NASA Astrophysics Data System (ADS)
Borrelli, Massimo; Rossi, Matteo; Macchiavello, Chiara; Maniscalco, Sabrina
2014-08-01
We extend the definition of entanglement witnesses based on spin structure factors to the case of scatterers with quantum mechanical motion. We show that this allows for hybrid entanglement detection and specialize the witness for a chain of trapped ions. Within this framework, we also show how the collective vibronic state of the chain can act as an undesired quantum environment affecting the spin-spin-entanglement detection. Furthermore, we investigate several specific cases where these witness operators allow us to detect hybrid entanglement.
Collective decoherence of the superpositional entangled states in the quantum Shor algorithm
Berman, G.P.; Kamenev, D.I.; Tsifrinovich, V. I.
2005-03-01
We consider collective decoherence for the quantum Shor algorithm. A quantum computer which interacts with its environment is modeled by a spin-1/2 chain interacting with harmonic oscillators at a given temperature. We calculate the nondiagonal matrix elements of the density matrix which are important for implementation of the quantum Shor algorithm, and study the decay rate and the Lamb phase shift for these elements. It is shown that the probability of superdecoherence in the quantum Shor algorithm is extremely small. The conditions for preserving quantum entanglement are formulated.
Relative Entropy and Squashed Entanglement
NASA Astrophysics Data System (ADS)
Li, Ke; Winter, Andreas
2014-02-01
We are interested in the properties and relations of entanglement measures. Especially, we focus on the squashed entanglement and relative entropy of entanglement, as well as their analogues and variants. Our first result is a monogamy-like inequality involving the relative entropy of entanglement and its one-way LOCC variant. The proof is accomplished by exploring the properties of relative entropy in the context of hypothesis testing via one-way LOCC operations, and by making use of an argument resembling that by Piani on the faithfulness of regularized relative entropy of entanglement. Following this, we obtain a commensurate and faithful lower bound for squashed entanglement, in the form of one-way LOCC relative entropy of entanglement. This gives a strengthening to the strong subadditivity of von Neumann entropy. Our result improves the trace-distance-type bound derived in Brandão et al. (Commun Math Phys, 306:805-830, 2011), where faithfulness of squashed entanglement was first proved. Applying Pinsker's inequality, we are able to recover the trace-distance-type bound, even with slightly better constant factor. However, the main improvement is that our new lower bound can be much larger than the old one and it is almost a genuine entanglement measure. We evaluate exactly the relative entropy of entanglement under various restricted measurement classes, for maximally entangled states. Then, by proving asymptotic continuity, we extend the exact evaluation to their regularized versions for all pure states. Finally, we consider comparisons and separations between some important entanglement measures and obtain several new results on these, too.
NASA Astrophysics Data System (ADS)
Daneshmand, R. N.; Tavassoly, M. K.
2015-05-01
Following the approach of Solano et al (2003 Phys. Rev. Lett. 90 027903) we propose a scheme for a generation of a few classes of entangled (nonlinear) coherent states. To achieve this purpose, the interaction of a spatially narrow collection of two-level atoms with a quantized field in a high-Q factor cavity in the presence of a strong-driving classical field is studied. We perform appropriate Hamiltonians describing the atom-field interaction by focusing on two particular forms of intensity-dependent functions which are directly related to su(1, 1) and su(2) Lie algebras. It is shown that the dynamical evolution of the considered systems can generate bipartite, tripartite (nonlinear) and more complicated entangled states corresponding to the mentioned groups depending on the number of atoms in the cavity. In the processes of the abovementioned generation schemes, even and odd nonlinear coherent states are produced. In the end, in a particular circumstance with the two-mode quantized field we can turn easily from Jaynes-Cummings to anti-Jaynes-Cummings interactions which brings us to the maximally entangled number state. Finally, to quantify the degree of entanglement of the produced states, the measures of von Neumann and linear entropies are applied.
Modernizing the State Education Agency: Different Paths toward Performance Management
ERIC Educational Resources Information Center
Murphy, Patrick; Rainey, Lydia
2012-01-01
This project examines how eight state education agencies engaged the charge of improving their lowest-performing schools. The states examined are among the most active and intentional in this regard. In many ways, they are at the leading edge of what could eventually become 50 different experiments in performance management. By focusing on states…
Entanglement and nonclassicality: A mutual impression
NASA Astrophysics Data System (ADS)
Gholipour, H.; Shahandeh, F.
2016-06-01
We find a sufficient condition to imprint the single-mode bosonic phase-space nonclassicality onto a bipartite state as modal entanglement and vice versa using an arbitrary beam splitter. Surprisingly, the entanglement produced or detected in this way depends only on the nonclassicality of the marginal input or output states, regardless of their purity and separability. In this way, our result provides a sufficient condition for generating entangled states of arbitrary high temperature and arbitrary large number of particles. We also study the evolution of the entanglement within a lossy Mach-Zehnder interferometer and show that unless both modes are totally lost, the entanglement does not diminish.
Quantum entanglement of angular momentum states with quantum numbers up to 10,010
NASA Astrophysics Data System (ADS)
Fickler, Robert; Campbell, Geoff; Buchler, Ben; Lam, Ping Koy; Zeilinger, Anton
2016-11-01
Photons with a twisted phase front carry a quantized amount of orbital angular momentum (OAM) and have become important in various fields of optics, such as quantum and classical information science or optical tweezers. Because no upper limit on the OAM content per photon is known, they are also interesting systems to experimentally challenge quantum mechanical prediction for high quantum numbers. Here, we take advantage of a recently developed technique to imprint unprecedented high values of OAM, namely spiral phase mirrors, to generate photons with more than 10,000 quanta of OAM. Moreover, we demonstrate quantum entanglement between these large OAM quanta of one photon and the polarization of its partner photon. To our knowledge, this corresponds to entanglement with the largest quantum number that has been demonstrated in an experiment. The results may also open novel ways to couple single photons to massive objects, enhance angular resolution, and highlight OAM as a promising way to increase the information capacity of a single photon.
Quantum entanglement of angular momentum states with quantum numbers up to 10,010.
Fickler, Robert; Campbell, Geoff; Buchler, Ben; Lam, Ping Koy; Zeilinger, Anton
2016-11-29
Photons with a twisted phase front carry a quantized amount of orbital angular momentum (OAM) and have become important in various fields of optics, such as quantum and classical information science or optical tweezers. Because no upper limit on the OAM content per photon is known, they are also interesting systems to experimentally challenge quantum mechanical prediction for high quantum numbers. Here, we take advantage of a recently developed technique to imprint unprecedented high values of OAM, namely spiral phase mirrors, to generate photons with more than 10,000 quanta of OAM. Moreover, we demonstrate quantum entanglement between these large OAM quanta of one photon and the polarization of its partner photon. To our knowledge, this corresponds to entanglement with the largest quantum number that has been demonstrated in an experiment. The results may also open novel ways to couple single photons to massive objects, enhance angular resolution, and highlight OAM as a promising way to increase the information capacity of a single photon.
Multi-photon entanglement in high dimensions
NASA Astrophysics Data System (ADS)
Malik, Mehul; Erhard, Manuel; Huber, Marcus; Krenn, Mario; Fickler, Robert; Zeilinger, Anton
2016-04-01
Forming the backbone of quantum technologies today, entanglement has been demonstrated in physical systems as diverse as photons, ions and superconducting circuits. Although steadily pushing the boundary of the number of particles entangled, these experiments have remained in a two-dimensional space for each particle. Here we show the experimental generation of the first multi-photon entangled state where both the number of particles and dimensions are greater than two. Two photons in our state reside in a three-dimensional space, whereas the third lives in two dimensions. This asymmetric entanglement structure only appears in multiparticle entangled states with d > 2. Our method relies on combining two pairs of photons, high-dimensionally entangled in their orbital angular momentum. In addition, we show how this state enables a new type of ‘layered’ quantum communication protocol. Entangled states such as these serve as a manifestation of the complex dance of correlations that can exist within quantum mechanics.
Fermionic entanglement ambiguity in noninertial frames
Montero, Miguel; Martin-Martinez, Eduardo
2011-06-15
We analyze an ambiguity in previous works on entanglement of fermionic fields in noninertial frames. This ambiguity, related to the anticommutation properties of field operators, leads to nonunique results when computing entanglement measures for the same state. We show that the ambiguity disappears when we introduce detectors, which are in any case necessary as a means to probe the field entanglement.
SU(2) Coherent State Path Integrals Labeled by a Full Set of Euler Angles: Basic Formulation
NASA Astrophysics Data System (ADS)
Matsumoto, Masao
2012-11-01
We develop a basic formulation of the spin (SU(2)) coherent state path integrals based not on the conventional highest or lowest weight vectors but on arbitrary fiducial vectors. The coherent states, being defined on a 3-sphere, are specified by a full set of Euler angles. They are generally considered as states without classical analogues. The overcompleteness relation holds for the states, by which we obtain the time evolution of general systems in terms of the path integral representation; the resultant Lagrangian in the action has a monopole-type term à la Balachandran et al. as well as some additional terms, both of which depend on fiducial vectors in a simple way. The process of the discrete path integrals to the continuous ones is clarified. Complex variable forms of the states and path integrals are also obtained. During the course of all steps, we emphasize the analogies and correspondences to the general canonical coherent states and path integrals that we proposed some time ago. In this paper we concentrate on the basic formulation. The physical applications as well as criteria in choosing fiducial vectors for real Lagrangians, in relation to fictitious monopoles and geometric phases, will be treated in subsequent papers separately.
Cooper, W Grant
2011-06-01
Evolutionary pressures have selected quantum uncertainty limits -ΔxΔp ( x ) ≥ 1/2ħ-to operate on metastable amino DNA protons. This introduces a probability of molecular clock arrangement, keto-amino → enol-imine, where product protons are entangled and participate in coupled quantum oscillation at frequencies of ∼ 10(13) s(-1). The ket "seen by" the transcriptase, reading a coherent enol-imine G'-state, is |φ >= α| + + > +β|+- > +γ|-+ > +δ|-->. The transcriptase implements its measurement and generates an output qubit of observable genetic specificity information in an interval Δt ≪ 10(-13) s. These quantum measurements can specify the relative distribution of coherent G'-C' states at time of measurement. The ensuing quantum entanglement between coherent protons and transcriptase units is utilized as a resource to generate proper decoherence and introduce selected time-dependent substitutions, ts, and deletions, td. Topal-Fresco ts are G'202 → T, G'002 → C, *G020(0) → A and *C202(2) → T, whereas td are exhibited at coherent *A-*T sites. Variation in clock 'tic-rate' is a consequence of clock introduction of initiation codons - UUG, CUG, AUG, GUG - and stop codons, UAA, UAG, UGA. Using approximate quantum methods for times t < ∼ 100 y, the probability, P(t), of keto-amino → enolimine arrangement is P ( ρ )(t) = 1/2(γ ( ρ )/ħ)(2) t (2) where γ ( ρ ) is the energy shift. This introduces a quantum Darwinian evolution model which provides insight into biological consequences of coherent states populating human genes, including inherited (CAG)( n ) repeat tracts.
Purification of genuine multipartite entanglement
Huber, Marcus; Plesch, Martin
2011-06-15
In tasks where multipartite entanglement plays a central role, state purification is, due to inevitable noise, a crucial part of the procedure. We consider a scenario exploiting the multipartite entanglement in a straightforward multipartite purification algorithm and compare it to bipartite purification procedures combined with state teleportation. While complete purification requires an infinite amount of input states in both cases, we show that for an imperfect output fidelity the multipartite procedure exhibits a major advantage in terms of input states used.
Gerry, Christopher C.; Campos, R. A.
2003-08-01
We outline a procedure for Heisenberg-limited phase resolution between two Bose-Einstien condensates (BECs) defined as different hyperfine levels. The method involves first establishing a maximally entangled state using the ideas of nonlinear interferometry previously discussed in the optical domain [C. C. Gerry et al., Phys. Rev. A 66, 013804 (2002)]. In the case of the condensates, the nonlinear interactions are realized by the interatomic interactions within each condensate. Quarter cycle Raman pulses between hyperfine levels act as beam splitters. Parity measurements of one of the components of the BEC resolve the phase at the Heisenberg limit. We point out that parity measurements can be made by coupling the mode of interest with a third condensate where both components evolve under nonlinear interatomic interactions. After another Raman pulse, the components are populated according to parity. One need only determine which component is populated to determine the parity.
Perfect embezzlement of entanglement
NASA Astrophysics Data System (ADS)
Cleve, Richard; Liu, Li; Paulsen, Vern I.
2017-01-01
Van Dam and Hayden introduced a concept commonly referred to as embezzlement, where, for any entangled quantum state ϕ, there is an entangled catalyst state ψ, from which a high fidelity approximation of ϕ ⊗ ψ can be produced using only local operations. We investigate a version of this where the embezzlement is perfect (i.e., the fidelity is 1). We prove that perfect embezzlement is impossible in a tensor product framework, even with infinite-dimensional Hilbert spaces and infinite entanglement entropy. Then we prove that perfect embezzlement is possible in a commuting operator framework. We prove this using the theory of C*-algebras and we also provide an explicit construction. Next, we apply our results to analyze perfect versions of a nonlocal game introduced by Regev and Vidick. Finally, we analyze the structure of perfect embezzlement protocols in the commuting operator model, showing that they require infinite-dimensional Hilbert spaces.
Evolution of Quantum Entanglement in Open Systems
Isar, A.
2010-08-04
In the framework of the theory of open systems based on completely positive quantum dynamical semigroups, we give a description of the continuous-variable entanglement for a system consisting of two uncoupled harmonic oscillators interacting with a thermal environment. Using Peres-Simon necessary sufficient criterion for separability of two-mode Gaussian states, we show that for some values of diffusion coefficient, dissipation constant and temperature of the environment, the state keeps for all times its initial type: separable or entangled. In other cases, entanglement generation, entanglement sudden death or a periodic collapse revival of entanglement take place.
Global Qualitative Flow-Path Modeling for Local State Determination in Simulation and Analysis
NASA Technical Reports Server (NTRS)
Malin, Jane T. (Inventor); Fleming, Land D. (Inventor)
1998-01-01
For qualitative modeling and analysis, a general qualitative abstraction of power transmission variables (flow and effort) for elements of flow paths includes information on resistance, net flow, permissible directions of flow, and qualitative potential is discussed. Each type of component model has flow-related variables and an associated internal flow map, connected into an overall flow network of the system. For storage devices, the implicit power transfer to the environment is represented by "virtual" circuits that include an environmental junction. A heterogeneous aggregation method simplifies the path structure. A method determines global flow-path changes during dynamic simulation and analysis, and identifies corresponding local flow state changes that are effects of global configuration changes. Flow-path determination is triggered by any change in a flow-related device variable in a simulation or analysis. Components (path elements) that may be affected are identified, and flow-related attributes favoring flow in the two possible directions are collected for each of them. Next, flow-related attributes are determined for each affected path element, based on possibly conflicting indications of flow direction. Spurious qualitative ambiguities are minimized by using relative magnitudes and permissible directions of flow, and by favoring flow sources over effort sources when comparing flow tendencies. The results are output to local flow states of affected components.
Bayesian path specific frailty models for multi-state survival data with applications.
de Castro, Mário; Chen, Ming-Hui; Zhang, Yuanye
2015-09-01
Multi-state models can be viewed as generalizations of both the standard and competing risks models for survival data. Models for multi-state data have been the theme of many recent published works. Motivated by bone marrow transplant data, we propose a Bayesian model using the gap times between two successive events in a path of events experienced by a subject. Path specific frailties are introduced to capture the dependence structure of the gap times in the paths with two or more states. Under improper prior distributions for the parameters, we establish propriety of the posterior distribution. An efficient Gibbs sampling algorithm is developed for drawing samples from the posterior distribution. An extensive simulation study is carried out to examine the empirical performance of the proposed approach. A bone marrow transplant data set is analyzed in detail to further demonstrate the proposed methodology.
Bayesian Path Specific Frailty Models for Multi-state Survival Data with Applications
de Castro, Mário; Chen, Ming-Hui; Zhang, Yuanye
2015-01-01
Summary Multi-state models can be viewed as generalizations of both the standard and competing risks models for survival data. Models for multi-state data have been the theme of many recent published works. Motivated by bone marrow transplant data, we propose a Bayesian model using the gap times between two successive events in a path of events experienced by a subject. Path specific frailties are introduced to capture the dependence structure of the gap times in the paths with two or more states. Under improper prior distributions for the parameters, we establish propriety of the posterior distribution. An efficient Gibbs sampling algorithm is developed for drawing samples from the posterior distribution. An extensive simulation study is carried out to examine the empirical performance of the proposed approach. A bone marrow transplant data set is analyzed in detail to further demonstrate the proposed methodology. PMID:25762198
Diffraction of entangled particles by light gratings
Sancho, Pedro
2015-04-15
We analyze the diffraction regime of the Kapitza–Dirac effect for particles entangled in momentum. The detection patterns show two-particle interferences. In the single-mode case we identify a discontinuity in the set of joint detection probabilities, associated with the disconnected character of the space of non-separable states. For Gaussian multi-mode states we derive the diffraction patterns, providing an example of the dependence of the light–matter interaction on entanglement. When the particles are identical, we can explore the relation between exchange and entanglement effects. We find a complementary behavior between overlapping and Schmidt’s number. In particular, symmetric entanglement can cancel the exchange effects. - Highlights: • Kapitza–Dirac diffraction of entangled particles shows multiparticle interference. • There is a discontinuity in the set of joint detection patterns of entangled states. • We find a complementary behavior between overlapping and Schmidt’s number. • Symmetric entanglement can cancel the exchange effects.
Quantum Entanglement on a Hypersphere
NASA Astrophysics Data System (ADS)
Peters, James F.; Tozzi, Arturo
2016-08-01
A quantum entanglement's composite system does not display separable states and a single constituent cannot be fully described without considering the other states. We introduce quantum entanglement on a hypersphere - which is a 4D space undetectable by observers living in a 3D world -, derived from signals originating on the surface of an ordinary 3D sphere. From the far-flung branch of algebraic topology, the Borsuk-Ulam theorem states that, when a pair of opposite (antipodal) points on a hypersphere are projected onto the surface of 3D sphere, the projections have matching description. In touch with this theorem, we show that a separable state can be achieved for each of the entangled particles, just by embedding them in a higher dimensional space. We view quantum entanglement as the simultaneous activation of signals in a 3D space mapped into a hypersphere. By showing that the particles are entangled at the 3D level and un-entangled at the 4D hypersphere level, we achieved a composite system in which each local constituent is equipped with a pure state. We anticipate this new view of quantum entanglement leading to what are known as qubit information systems.
Chandrasekaran, Srinivas Niranj; Das, Jhuma; Dokholyan, Nikolay V.; Carter, Charles W.
2016-01-01
PATH rapidly computes a path and a transition state between crystal structures by minimizing the Onsager-Machlup action. It requires input parameters whose range of values can generate different transition-state structures that cannot be uniquely compared with those generated by other methods. We outline modifications to estimate these input parameters to circumvent these difficulties and validate the PATH transition states by showing consistency between transition-states derived by different algorithms for unrelated protein systems. Although functional protein conformational change trajectories are to a degree stochastic, they nonetheless pass through a well-defined transition state whose detailed structural properties can rapidly be identified using PATH. PMID:26958584
Entanglement versus energy in the entanglement transfer problem
Cavalcanti, Daniel; Oliveira, J. G. Jr.; Santos, Marcelo Franca; Peixoto de Faria, J. G.; Terra Cunha, Marcelo O.
2006-10-15
We study the relation between energy and entanglement in an entanglement transfer problem. We first analyze the general setup of two entangled qubits ('a' and 'b') exchanging this entanglement with two other independent qubits ('A' and 'B'). Qubit 'a' ('b') interacts with qubit 'A' ('B') via a spin-exchange-like unitary evolution. A physical realization of this scenario could be the problem of two-level atoms transferring entanglement to resonant cavities via independent Jaynes-Cummings interactions. We study the dynamics of entanglement and energy for the second pair of qubits (tracing out the originally entangled ones) and show that these quantities are closely related. For example, the allowed quantum states occupy a restricted area in a phase diagram entanglement vs energy. Moreover, the curve which bounds this area is exactly the one followed if both interactions are equal and the entire four qubit system is isolated. We also consider the case when the target pair of qubits is subjected to losses and can spontaneously decay.
The Path of Carbon in Photosynthesis XX. The Steady State
DOE R&D Accomplishments Database
Calvin, M.; Massini, Peter
1952-09-01
The separation of the phenomenon of photosynthesis in green plants into a photochemical reaction and into the light-dependent reduction of carbon dioxide is discussed, The reduction of carbon dioxide and the fate of the assimilated carbon were investigated with the help of the tracer technique (exposure of the planks to the radioactive C{sup 14}O{sub 2}) and of paper chromatography. A reaction cycle is proposed in which phosphoglyceric acid is the first isolable assimilations product. Analyses of the algal extracts which had assimilated radioactive carbon dioxide in a stationary condition ('steady-state' photosynthesis) for a long time provided further information concerning the proposed cycle and permitted the approximate estimation, for a number of compounds of what fraction of each compound was taking part in the cycle. The earlier supposition that light influences the respiration cycle was confirmed. The possibility of the assistance of {alpha}-lipoic acid, or of a related substance, in this influence and in the photosynthesis cycle, is discussed.
Qubit entanglement between ring-resonator photon-pair sources on a silicon chip
Silverstone, J. W.; Santagati, R.; Bonneau, D.; Strain, M. J.; Sorel, M.; O'Brien, J. L.; Thompson, M. G.
2015-01-01
Entanglement—one of the most delicate phenomena in nature—is an essential resource for quantum information applications. Scalable photonic quantum devices must generate and control qubit entanglement on-chip, where quantum information is naturally encoded in photon path. Here we report a silicon photonic chip that uses resonant-enhanced photon-pair sources, spectral demultiplexers and reconfigurable optics to generate a path-entangled two-qubit state and analyse its entanglement. We show that ring-resonator-based spontaneous four-wave mixing photon-pair sources can be made highly indistinguishable and that their spectral correlations are small. We use on-chip frequency demultiplexers and reconfigurable optics to perform both quantum state tomography and the strict Bell-CHSH test, both of which confirm a high level of on-chip entanglement. This work demonstrates the integration of high-performance components that will be essential for building quantum devices and systems to harness photonic entanglement on the large scale. PMID:26245267