Heralded amplification of path entangled quantum states
NASA Astrophysics Data System (ADS)
Monteiro, F.; Verbanis, E.; Caprara Vivoli, V.; Martin, A.; Gisin, N.; Zbinden, H.; Thew, R. T.
2017-06-01
Device-independent quantum key distribution (DI-QKD) represents one of the most fascinating challenges in quantum communication, exploiting concepts of fundamental physics, namely Bell tests of nonlocality, to ensure the security of a communication link. This requires the loophole-free violation of a Bell inequality, which is intrinsically difficult due to losses in fibre optic transmission channels. Heralded photon amplification (HPA) is a teleportation-based protocol that has been proposed as a means to overcome transmission loss for DI-QKD. Here we demonstrate HPA for path entangled states and characterise the entanglement before and after loss by exploiting a recently developed displacement-based detection scheme. We demonstrate that by exploiting HPA we are able to reliably maintain high fidelity entangled states over loss-equivalent distances of more than 50 km.
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.
Observing photonic de Broglie waves without the maximally-path-entangled |N,0>+|0,N> state
Kwon, Osung; Ra, Young-Sik; Kim, Yoon-Ho
2010-06-15
The photonic de Broglie wave, in which an ensemble of N identical photons with wavelength {lambda} reveals {lambda}/N interference fringes, has been known to be a unique feature exhibited by the photon-number-path-entangled |N,0>+|0,N> state or the N00N state. Here, we report the observation of the photonic de Broglie wave for a pair of photons, generated by spontaneous parametric down-conversion, that are not photon-number-path entangled. We also show that the photonic de Broglie wave can even be observed for a pair of photons that are completely separable (i.e., no entanglement in all degrees of freedom) and distinguishable. The experimental and theoretical results suggest that the photonic de Broglie wave is, in fact, not related to the entanglement of the photons, rather it is related to the indistinguishable pathways established by the measurement scheme. The phase sensitivity surpassing the standard quantum limit, however, is shown to be closely related to the N00N state.
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.
Quantum Entanglement Swapping between Two Multipartite Entangled States.
Su, Xiaolong; Tian, Caixing; Deng, Xiaowei; Li, Qiang; Xie, Changde; Peng, Kunchi
2016-12-09
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.
Entangling ability of a beam splitter in the presence of temporal which-path information
Velsen, J.L. van
2005-07-15
We calculate the amount of polarization-entanglement induced by two-photon interference at a lossless beam splitter. Entanglement and its witness are quantified, respectively, by concurrence and the Bell-Clauser-Horne-Shimony-Holt (CHSH) parameter. In the presence of a Mandel dip, the interplay of two kinds of which-path information--temporal and polarization--gives rise to the existence of entangled polarization states that cannot violate the Bell-CHSH inequality.
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.
A new method for quantifying entanglement of multipartite entangled states
NASA Astrophysics Data System (ADS)
Su, Pei-Yuan; Li, Wen-Dong; Ma, Xiao-Ping; Liu, Kai; Wang, Zhao-Ming; Gu, Yong-Jian
2017-08-01
We propose a new way for quantifying entanglement of multipartite entangled states which have a symmetrical structure and can be expressed as valence-bond-solid states. We put forward a new concept `unit.' The entangled state can be decomposed into a series of units or be reconstructed by multiplying the units successively, which simplifies the analyses of multipartite entanglement greatly. We compute and add up the generalized concurrence of each unit to quantify the entanglement of the whole state. We verify that the new method coincides with concurrence for two-partite pure states. We prove that the new method is a good entanglement measure obeying the three necessary conditions for all good entanglement quantification methods. Based on the method, we compute the entanglement of multipartite GHZ, cluster and AKLT states.
Local cloning of entangled states
NASA Astrophysics Data System (ADS)
Gheorghiu, Vlad; Yu, Li; Cohen, Scott M.
2010-08-01
We investigate the conditions under which a set S of pure bipartite quantum states on a D×D 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.
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 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…
Irreversibility for All Bound Entangled States
NASA Astrophysics Data System (ADS)
Yang, Dong; Horodecki, Michał; Horodecki, Ryszard; Synak-Radtke, Barbara
2005-11-01
We derive a new inequality for entanglement for a mixed four-partite state. Employing this inequality, we present a one-shot lower bound for entanglement cost and prove that entanglement cost is strictly larger than zero for any entangled state. We demonstrate that irreversibility occurs in the process of formation for all nondistillable entangled states. In this way we solve a long standing problem of how “real” is entanglement of bound entangled states. Using the new inequality we also prove the impossibility of local cloning of a known entangled 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.
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.
Mixtures of maximally entangled pure states
Flores, M.M. Galapon, E.A.
2016-09-15
We study the conditions when mixtures of maximally entangled pure states remain entangled. We found that the resulting mixed state remains entangled when the number of entangled pure states to be mixed is less than or equal to the dimension of the pure states. For the latter case of mixing a number of pure states equal to their dimension, we found that the mixed state is entangled provided that the entangled pure states to be mixed are not equally weighted. We also found that one can restrict the set of pure states that one can mix from in order to ensure that the resulting mixed state is genuinely entangled. Also, we demonstrate how these results could be applied as a way to detect entanglement in mixtures of the entangled pure states with noise.
Fickler, Robert; Lapkiewicz, Radek; Huber, Marcus; Lavery, Martin P J; Padgett, Miles J; Zeilinger, Anton
2014-07-30
Photonics has become a mature field of quantum information science, where integrated optical circuits offer a way to scale the complexity of the set-up as well as the dimensionality of the quantum state. On photonic chips, paths are the natural way to encode information. To distribute those high-dimensional quantum states over large distances, transverse spatial modes, like orbital angular momentum possessing Laguerre Gauss modes, are favourable as flying information carriers. Here we demonstrate a quantum interface between these two vibrant photonic fields. We create three-dimensional path entanglement between two photons in a nonlinear crystal and use a mode sorter as the quantum interface to transfer the entanglement to the orbital angular momentum degree of freedom. Thus our results show a flexible way to create high-dimensional spatial mode entanglement. Moreover, they pave the way to implement broad complex quantum networks where high-dimensionally entangled states could be distributed over distant photonic chips.
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.
Scattering of entangled two-photon states.
Schotland, John C; Cazé, A; Norris, Theodore B
2016-02-01
We consider the scattering of entangled two-photon states from collections of small particles. We also study the related Mie problem of scattering from a sphere. In both cases, we calculate the entropy of entanglement and investigate the influence of the entanglement of the incident field on the entanglement of the scattered field.
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.
Phase-Tuned Entangled State Generation between Distant Spin Qubits
NASA Astrophysics Data System (ADS)
Stockill, R.; Stanley, M. J.; Huthmacher, L.; Clarke, E.; Hugues, M.; Miller, A. J.; Matthiesen, C.; Le Gall, C.; Atatüre, M.
2017-07-01
Quantum entanglement between distant qubits is an important feature of quantum networks. Distribution of entanglement over long distances can be enabled through coherently interfacing qubit pairs via photonic channels. Here, we report the realization of optically generated quantum entanglement between electron spin qubits confined in two distant semiconductor quantum dots. The protocol relies on spin-photon entanglement in the trionic Λ system and quantum erasure of the Raman-photon path information. The measurement of a single Raman photon is used to project the spin qubits into a joint quantum state with an interferometrically stabilized and tunable relative phase. We report an average Bell-state fidelity for |ψ(+)⟩ and |ψ(-)⟩ states of 61.6 ±2.3 % and a record-high entanglement generation rate of 7.3 kHz between distant qubits.
Local copying of orthogonal entangled quantum states
NASA Astrophysics Data System (ADS)
Anselmi, Fabio; Chefles, Anthony; Plenio, Martin B.
2004-11-01
In classical information theory one can, in principle, produce a perfect copy of any input state. In quantum information theory, the no cloning theorem prohibits exact copying of non-orthogonal states. Moreover, if we wish to copy multiparticle entangled states and can perform only local operations and classical communication (LOCC), then further restrictions apply. We investigate the problem of copying orthogonal, entangled quantum states with an entangled blank state under the restriction to LOCC. Throughout, the subsystems have finite dimension D. We show that if all of the states to be copied are non-maximally entangled, then novel LOCC copying procedures based on entanglement catalysis are possible. We then study in detail the LOCC copying problem where both the blank state and at least one of the states to be copied are maximally entangled. For this to be possible, we find that all the states to be copied must be maximally entangled. We obtain a necessary and sufficient condition for LOCC copying under these conditions. For two orthogonal, maximally entangled states, we provide the general solution to this condition. We use it to show that for D = 2, 3, any pair of orthogonal, maximally entangled states can be locally copied using a maximally entangled blank state. However, we also show that for any D which is not prime, one can construct pairs of such states for which this is impossible.
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.
Maximally entangled states of four nonbinary particles
NASA Astrophysics Data System (ADS)
Gaeta, Mario; Klimov, Andrei; Lawrence, Jay
2015-01-01
Systems of four nonbinary particles, with each particle having d ≥3 internal states, exhibit maximally entangled states that are inaccessible to four qubits. This breaks the pattern of two- and three-particle systems, in which the existing graph states are equally accessible to binary and nonbinary systems alike. We compare the entanglement properties of these special states (called P states) with those of the more familiar Greenberger-Horne-Zeilinger (GHZ) and cluster states accessible to qubits. The comparison includes familiar entanglement measures, the "steering" of states by projective measurements, and the probability that two such measurements, chosen at random, leave the remaining particles in a Bell state. These comparisons demonstrate not only that P -state entanglement is stronger than the other types but also that it is maximal in a well-defined sense. We prove that GHZ, cluster, and P states represent all possible entanglement classes of four-particle graph states with prime d ≥3 .
Partially entangled states bridge in quantum teleportation
NASA Astrophysics Data System (ADS)
Cai, Xiao-Fei; Yu, Xu-Tao; Shi, Li-Hui; Zhang, Zai-Chen
2014-10-01
The traditional method for information transfer in a quantum communication system using partially entangled state resource is quantum distillation or direct teleportation. In order to reduce the waiting time cost in hop-by-hop transmission and execute independently in each node, we propose a quantum bridging method with partially entangled states to teleport quantum states from source node to destination node. We also prove that the designed specific quantum bridging circuit is feasible for partially entangled states teleportation across multiple intermediate nodes. Compared to two traditional ways, our partially entanglement quantum bridging method uses simpler logic gates, has better security, and can be used in less quantum resource situation.
Detecting multiparticle entanglement of Dicke states.
Lücke, Bernd; Peise, Jan; Vitagliano, Giuseppe; Arlt, Jan; Santos, Luis; Tóth, Géza; Klempt, Carsten
2014-04-18
Recent experiments demonstrate the production of many thousands of neutral atoms entangled in their spin degrees of freedom. We present a criterion for estimating the amount of entanglement based on a measurement of the global spin. It outperforms previous criteria and applies to a wider class of entangled states, including Dicke states. Experimentally, we produce a Dicke-like state using spin dynamics in a Bose-Einstein condensate. Our criterion proves that it contains at least genuine 28-particle entanglement. We infer a generalized squeezing parameter of -11.4(5) dB.
Entanglement classification with matrix product states
NASA Astrophysics Data System (ADS)
Sanz, M.; Egusquiza, I. L.; di Candia, R.; Saberi, H.; Lamata, L.; Solano, E.
2016-07-01
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 .
Quantum states prepared by realistic entanglement swapping
Scherer, Artur; Howard, Regina B.; Sanders, Barry C.; Tittel, Wolfgang
2009-12-15
Entanglement swapping between photon pairs is a fundamental building block in schemes using quantum relays or quantum repeaters to overcome the range limits of long-distance quantum key distribution. We develop a closed-form solution for the actual quantum states prepared by realistic entanglement swapping, which takes into account experimental deficiencies due to inefficient detectors, detector dark counts, and multiphoton-pair contributions of parametric down-conversion sources. We investigate how the entanglement present in the final state of the remaining modes is affected by the real-world imperfections. To test the predictions of our theory, comparison with previously published experimental entanglement swapping is provided.
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.
PPT states and measures of entanglement
NASA Astrophysics Data System (ADS)
Majewski, Władysław A.
2011-10-01
Entanglement is one of the most important concepts in Quantum Information. But, mathematically one of the most hard task in quantum theory is to describe entanglement. Although the progress in this field is remarkable, still the theory is not complete. In this lecture we describe some aspects of the theory of positive maps, then the full characterization of PPT states will be given. Finally, we show how far we are able to classify quantum entanglement.
Entanglement verification of noisy NOON states
NASA Astrophysics Data System (ADS)
Bohmann, M.; Sperling, J.; Vogel, W.
2017-07-01
Entangled quantum states, such as NOON states, are of major importance for quantum technologies due to their quantum-enhanced performance. At the same time, their quantum correlations are relatively vulnerable when they are subjected to imperfections. Therefore, it is crucial to determine under which circumstances their distinct quantum features can be exploited. In this paper, we study the entanglement property of noisy NOON states. This class of states is a generalization of NOON states including various attenuation effects, such as mixing, constant or fluctuating losses, and dephasing. To verify their entanglement, we pursue two strategies: detection-based entanglement witnesses and entanglement quasiprobabilities. Both methods result from our solution of so-called separability eigenvalue equations. In particular, the entanglement quasiprobabilities allow for a full entanglement characterization. As examples of our general treatment, the cases of NOON states subjected to Gaussian dephasing and fluctuating atmospheric losses are explicitly studied. In any correlated fluctuating loss channel, entanglement is found to survive for nonzero transmissivity. In addition, an extension of our approach to multipartite systems is given, and the relation to the quantum-optical nonclassicality in phase space is discussed.
Entanglement witnesses and characterizing entanglement properties of some PPT states
NASA Astrophysics Data System (ADS)
Jafarizadeh, M. A.; Behzadi, N.; Akbari, Y.
2009-10-01
On the basis of linear programming, new sets of entanglement witnesses (EWs) for 3⊗3 and 4⊗4 systems are constructed. In both cases, the constructed EWs correspond to the hyper-planes contacting, without intersecting, the related feasible regions at line segments and restricted planes respectively. Due to the special property of the contacting area between the hyper-planes and the feasible regions, the corresponding hyper-planes can be turned around the contacting area throughout a bounded interval and hence create an infinite number of EWs. As these EWs are able to detect entanglement of some PPT states, they are non-decomposable (nd-EWs).
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.
Bell states and entanglement dynamics on two coupled quantum molecules
Oliveira, P.A.; Sanz, L.
2015-05-15
This work provides a complete description of entanglement properties between electrons inside coupled quantum molecules, nanoestructures which consist of two quantum dots. Each electron can tunnel between the two quantum dots inside the molecule, being also coupled by Coulomb interaction. First, it is shown that Bell states act as a natural basis for the description of this physical system, defining the characteristics of the energy spectrum and the eigenstates. Then, the entanglement properties of the eigenstates are discussed, shedding light on the roles of each physical parameters on experimental setup. Finally, a detailed analysis of the dynamics shows the path to generate states with a high degree of entanglement, as well as physical conditions associated with coherent oscillations between separable and Bell states.
Symmetric states: Their nonlocality and entanglement
Wang, Zizhu; Markham, Damian
2014-12-04
The nonlocality of permutation symmetric states of qubits is shown via an extension of the Hardy paradox and the extension of the associated inequality. This is achieved by using the Majorana representation, which is also a powerful tool in the study of entanglement properties of symmetric states. Through the Majorana representation, different nonlocal properties can be linked to different entanglement properties of a state, which is useful in determining the usefulness of different states in different quantum information processing tasks.
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.
Construction of bound entangled states based on permutation operators
NASA Astrophysics Data System (ADS)
Zhao, Hui; Guo, Sha; Jing, Naihuan; Fei, Shaoming
2016-04-01
We present a construction of new bound entangled states from given bound entangled states for arbitrary dimensional bipartite systems. One way to construct bound entangled states is to show that these states are positive partial transpose (PPT) and violate the range criterion at the same time. By applying certain operators to given bound entangled states or to one of the subsystems of the given bound entangled states, we obtain a set of new states which are both PPT and violate the range criterion. We show that the derived bound entangled states are not local unitary equivalent to the original bound entangled states by detail examples.
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.
Maximally Entangled Set of Multipartite Quantum States
NASA Astrophysics Data System (ADS)
de Vicente, J. I.; Spee, C.; Kraus, B.
2013-09-01
Entanglement is a resource in quantum information theory when state manipulation is restricted to local operations assisted by classical communication (LOCC). It is therefore of paramount importance to decide which LOCC transformations are possible and, particularly, which states are maximally useful under this restriction. While the bipartite maximally entangled state is well known (it is the only state that cannot be obtained from any other and, at the same time, it can be transformed to any other by LOCC), no such state exists in the multipartite case. In order to cope with this fact, we introduce here the notion of the maximally entangled set (MES) of n-partite states. This is the set of states which are maximally useful under LOCC manipulation; i.e., any state outside of this set can be obtained via LOCC from one of the states within the set and no state in the set can be obtained from any other state via LOCC. We determine the MES for states of three and four qubits and provide a simple characterization for them. In both cases, infinitely many states are required. However, while the MES is of measure zero for 3-qubit states, almost all 4-qubit states are in the MES. This is because, in contrast to the 3-qubit case, deterministic LOCC transformations are almost never possible among fully entangled four-partite states. We determine the measure-zero subset of the MES of LOCC convertible states. This is the only relevant class of states for entanglement manipulation.
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
Lazy states, discordant states and entangled states for 2-qubit systems
NASA Astrophysics Data System (ADS)
Xu, Jianwei
2015-06-01
We investigate the lazy states, entangled states and discordant states for 2-qubit systems. We show that many lazy states are discordant, many lazy states are entangled, and many mixed entangled states are not lazy. With these investigations, we provide a laziness-discord-entanglement hierarchy diagram for 2-qubit quantum correlations.
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.
Entangled states of trapped atomic ions.
Blatt, Rainer; Wineland, David
2008-06-19
To process information using quantum-mechanical principles, the states of individual particles need to be entangled and manipulated. One way to do this is to use trapped, laser-cooled atomic ions. Attaining a general-purpose quantum computer is, however, a distant goal, but recent experiments show that just a few entangled trapped ions can be used to improve the precision of measurements. If the entanglement in such systems can be scaled up to larger numbers of ions, simulations that are intractable on a classical computer might become possible.
Quantum Entanglement in Neural Network States
NASA Astrophysics Data System (ADS)
Deng, Dong-Ling; Li, Xiaopeng; Das Sarma, S.
2017-04-01
Machine learning, one of today's most rapidly growing interdisciplinary fields, promises an unprecedented perspective for solving intricate quantum many-body problems. Understanding the physical aspects of the representative artificial neural-network states has recently become highly desirable in the applications of machine-learning techniques to quantum many-body physics. In this paper, we explore the data structures that encode the physical features in the network states by studying the quantum entanglement properties, with a focus on the restricted-Boltzmann-machine (RBM) architecture. We prove that the entanglement entropy of all short-range RBM states satisfies an area law for arbitrary dimensions and bipartition geometry. For long-range RBM states, we show by using an exact construction that such states could exhibit volume-law entanglement, implying a notable capability of RBM in representing quantum states with massive entanglement. Strikingly, the neural-network representation for these states is remarkably efficient, in the sense that the number of nonzero parameters scales only linearly with the system size. We further examine the entanglement properties of generic RBM states by randomly sampling the weight parameters of the RBM. We find that their averaged entanglement entropy obeys volume-law scaling, and the meantime strongly deviates from the Page entropy of the completely random pure states. We show that their entanglement spectrum has no universal part associated with random matrix theory and bears a Poisson-type level statistics. Using reinforcement learning, we demonstrate that RBM is capable of finding the ground state (with power-law entanglement) of a model Hamiltonian with a long-range interaction. In addition, we show, through a concrete example of the one-dimensional symmetry-protected topological cluster states, that the RBM representation may also be used as a tool to analytically compute the entanglement spectrum. Our results uncover the
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.
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.
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.
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.
Generation of Counterpropagating Path-Entangled Photon Pairs in a Single Periodic Waveguide
NASA Astrophysics Data System (ADS)
Saravi, Sina; Pertsch, Thomas; Setzpfandt, Frank
2017-05-01
We propose the use of nonlinear periodic waveguides for direct and fully integrated generation of counterpropagating photon pairs by spontaneous parametric down-conversion. Using the unique properties of Bloch modes in such periodic structures, we furthermore show that two counterpropagating phase-matching conditions can be fulfilled simultaneously, allowing for the generation of path-entangled Bell states in a single periodic waveguide. To demonstrate the feasibility of our proposal, we design a photonic crystal slab waveguide made of lithium niobate and numerically demonstrate Bell-state generation.
Entangled states with strong positive partial transpose
Ha, Kil-Chan
2010-06-15
Chruscinski, Jurkowski, and Kossakowski [Phys. Rev. A 77, 022113 (2008)] studied quantum states with strong positive partial transpose (SPPT) and conjectured that all SPPT states are separable. We construct a two-parameter class of 3 x 3 entangled SPPT states, so the conjecture does not hold true for general SPPT states.
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.
Searching for highly entangled multi-qubit states
NASA Astrophysics Data System (ADS)
Brown, Iain D. K.; Stepney, Susan; Sudbery, Anthony; Braunstein, Samuel L.
2005-02-01
We present a simple numerical optimization procedure to search for highly entangled states of 2, 3, 4 and 5 qubits. We develop a computationally tractable entanglement measure based on the negative partial transpose criterion, which can be applied to quantum systems of an arbitrary number of qubits. The search algorithm attempts to optimize this entanglement cost function to find the maximal entanglement in a quantum system. We present highly entangled 4-qubit and 5-qubit states discovered by this search. We show that the 4-qubit state is not quite as entangled, according to two separate measures, as the conjectured maximally entangled Higuchi-Sudbery state. Using this measure, these states are more highly entangled than the 4-qubit and 5-qubit GHZ states. We also present a conjecture about the NPT measure, inspired by some of our numerical results, that the single-qubit reduced states of maximally entangled states are all totally mixed.
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.
Lugani, Jasleen; Ghosh, Sankalpa; Thyagarajan, K.
2011-06-15
Integrated optical devices are expected to play a promising role in the field of quantum information science and technology. In this paper we propose a scheme for the generation of nondegenerate, copolarized, modal, and path-entangled photons using a directional coupler and an asymmetric Y-coupler geometry in type-0 phase-matched domain-engineered lithium niobate (LN) waveguide. The nonlinearity in LN is tailored in such a way that quasi-phase-matching conditions for two different spontaneous parametric down-conversion processes are obeyed simultaneously, leading to a modal and path-entangled state at the output. Assuming typical values of various parameters, we show, through numerical simulations, that an almost maximally entangled state is achievable over a wide range of waveguide parameters. For the degenerate case, the proposed scheme gives a NOON state for N = 2. The generated entangled photon pairs should have potential applications in quantum information schemes and also in quantum metrology. By appropriate domain engineering and component designing, the idea can be further extended to generate hyperentangled and two-photon multipath-entangled states, which may have further applications in quantum computation protocols.
All Entangled States can Demonstrate Nonclassical Teleportation
NASA Astrophysics Data System (ADS)
Cavalcanti, Daniel; Skrzypczyk, Paul; Šupić, Ivan
2017-09-01
Quantum teleportation, the process by which Alice can transfer an unknown quantum state to Bob by using preshared entanglement and classical communication, is one of the cornerstones of quantum information. The standard benchmark for certifying quantum teleportation consists in surpassing the maximum average fidelity between the teleported and the target states that can be achieved classically. According to this figure of merit, not all entangled states are useful for teleportation. Here we propose a new benchmark that uses the full information available in a teleportation experiment and prove that all entangled states can implement a quantum channel which cannot be reproduced classically. We introduce the idea of nonclassical teleportation witness to certify if a teleportation experiment is genuinely quantum and discuss how to quantify this phenomenon. Our work provides new techniques for studying teleportation that can be immediately applied to certify the quality of quantum technologies.
Bell Inequalities Tailored to Maximally Entangled States
NASA Astrophysics Data System (ADS)
Salavrakos, Alexia; Augusiak, Remigiusz; Tura, Jordi; Wittek, Peter; Acín, Antonio; Pironio, Stefano
2017-07-01
Bell inequalities have traditionally been used to demonstrate that quantum theory is nonlocal, in the sense that there exist correlations generated from composite quantum states that cannot be explained by means of local hidden variables. With the advent of device-independent quantum information protocols, Bell inequalities have gained an additional role as certificates of relevant quantum properties. In this work, we consider the problem of designing Bell inequalities that are tailored to detect maximally entangled states. We introduce a class of Bell inequalities valid for an arbitrary number of measurements and results, derive analytically their tight classical, nonsignaling, and quantum bounds and prove that the latter is attained by maximally entangled states. Our inequalities can therefore find an application in device-independent protocols requiring maximally entangled states.
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.
NASA Astrophysics Data System (ADS)
Liu, Cunjin; Jia, Fang; Gong, Lihua; Guo, Qin
2017-09-01
A scheme for teleporting an arbitrary tripartite entangled state is proposed when three bipartite entangled states (| η〉) with continuous variables are used as quantum channels. Quantum teleportation can be carried out successfully if the receiver adopts an appropriate unitary transformation. The calculation is greatly simplified by virtue of the Schmidt decompositions of both tripartite entangled state | p t , χ 2, χ 3〉 and | η〉. Any tripartite state which can be expanded in terms of | p t , χ 2, χ 3〉 may be teleported in this way due to the completeness of | p t , χ 2, χ 3〉.
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.
Entanglement classification of four-partite states under the SLOCC
NASA Astrophysics Data System (ADS)
Zangi, S. M.; Li, Jun-Li; Qiao, Cong-Feng
2017-08-01
We present a practical classification scheme for the four-partite entangled states under stochastic local operations and classical communication (SLOCC). By transforming a four-partite state into a triple-state set composed of two tripartite states and a bipartite state, the entanglement classification is reduced to the classification of tripartite and bipartite entanglements. This reduction method has the merit of involving only the linear constrains, and meanwhile provides an insight into the entanglement character of the subsystems.
Entanglement and symmetry in permutation-symmetric states
Markham, Damian J. H.
2011-04-15
We investigate the relationship between multipartite entanglement and symmetry, focusing on permutation symmetric states. We give a highly intuitive geometric interpretation to entanglement via the Majorana representation, where these states correspond to points on a unit sphere. We use this to show how various entanglement properties are determined by the symmetry properties of the states. The geometric measure of entanglement is thus phrased entirely as a geometric optimization and a condition for the equivalence of entanglement measures written in terms of point symmetries. Finally, we see that different symmetries of the states correspond to different types of entanglement with respect to interconvertibility under stochastic local operations and classical communication.
Entangled qubits in a non-Gaussian quantum state
Kiesel, T.; Vogel, W.; Hage, B.; Schnabel, R.
2011-06-15
We experimentally generate and tomographically characterize a mixed, genuinely non-Gaussian bipartite continuous-variable entangled state. By testing entanglement in 2x2-dimensional two-qubit subspaces, entangled qubits are localized within the density matrix, which, first, proves the distillability of the state and, second, is useful to estimate the efficiency and test the applicability of distillation protocols. In our example, the entangled qubits are arranged in the density matrix in an asymmetric way, i.e., entanglement is found between diverse qubits composed of different photon number states, although the entangled state is symmetric under exchanging the modes.
Entanglement bound for multipartite pure states based on local measurements
Jiang Lizhen; Chen Xiaoyu; Ye Tianyu
2011-10-15
An entanglement bound based on local measurements is introduced for multipartite pure states. It is the upper bound of the geometric measure and the relative entropy of entanglement. It is the lower bound of the minimal-measurement entropy. For pure bipartite states, the bound is equal to the entanglement entropy. The bound is applied to pure tripartite qubit states and the exact tripartite relative entropy of entanglement is obtained for a wide class of states.
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.
NASA Astrophysics Data System (ADS)
Shi, Jin
2017-05-01
Two-photon four-dimensional spatial modes partially entangled Dicke state can be compactly generated from six concurrent spontaneous parametric down-conversion processes by cascading poling domain structures in 5% MgO-doped poled lithium niobate bulk crystal. Entanglement concentration of the two-photon four-dimensional spatial modes partially entangled Dicke state can be realized by using quantum nondestructive detection of nonlinear Kerr medium, optical beam splitter, and quantum gate operation.
Entanglement of Convex Linear Combination and Construction of Ppt Entangled States
NASA Astrophysics Data System (ADS)
Cheng, Wei; Xu, Fang; Li, Hua; Wang, Gang
2013-02-01
Given two bipartite quantum states and the convex linear combination of them, we discuss the relation between the entanglement of the convex linear combination state and the entanglement of states being combined. This is achieved by characterizing quantum states quantitatively via the positive partial transpose (PPT) criterion and the computable cross-norm or realignment (CCNR) criterion. Inspired by the Horodecki's 3 ⊗ 3 quantum states, we also give explicit examples to illustrate all possible cases of convex linear combination. Finally, as an application of this method, we show how to construct new bipartite PPT entangled states from known PPT entangled states by convex linear combination.
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.
Entangled quantum states as direction indicators.
Peres, A; Scudo, P F
2001-04-30
We consider the use of N spin-1/2 particles for indicating a direction in space. If N>2, their optimal state is entangled. For large N, the mean square error decreases as N-2 (rather than N-1 for parallel spins).
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.
Increasing entanglement between Gaussian states by coherent photon subtraction.
Ourjoumtsev, Alexei; Dantan, Aurélien; Tualle-Brouri, Rosa; Grangier, Philippe
2007-01-19
We experimentally demonstrate that the entanglement between Gaussian entangled states can be increased by non-Gaussian operations. Coherent subtraction of single photons from Gaussian quadrature-entangled light pulses, created by a nondegenerate parametric amplifier, produces delocalized states with negative Wigner functions and complex structures more entangled than the initial states in terms of negativity. The experimental results are in very good agreement with the theoretical predictions.
Entangled exciton states in quantum dot molecules
NASA Astrophysics Data System (ADS)
Bayer, Manfred
2002-03-01
Currently there is strong interest in quantum information processing(See, for example, The Physics of Quantum Information, eds. D. Bouwmeester, A. Ekert and A. Zeilinger (Springer, Berlin, 2000).) in a solid state environment. Many approaches mimic atomic physics concepts in which semiconductor quantum dots are implemented as artificial atoms. An essential building block of a quantum processor is a gate which entangles the states of two quantum bits. Recently a pair of vertically aligned quantum dots has been suggested as optically driven quantum gate(P. Hawrylak, S. Fafard, and Z. R. Wasilewski, Cond. Matter News 7, 16 (1999).)(M. Bayer, P. Hawrylak, K. Hinzer, S. Fafard, M. Korkusinski, Z.R. Wasilewski, O. Stern, and A. Forchel, Science 291, 451 (2001).): The quantum bits are individual carriers either on dot zero or dot one. The different dot indices play the same role as a "spin", therefore we call them "isospin". Quantum mechanical tunneling between the dots rotates the isospin and leads to superposition of these states. The quantum gate is built when two different particles, an electron and a hole, are created optically. The two particles form entangled isospin states. Here we present spectrocsopic studies of single self-assembled InAs/GaAs quantum dot molecules that support the feasibility of this proposal. The evolution of the excitonic recombination spectrum with varying separation between the dots allows us to demonstrate coherent tunneling of carriers across the separating barrier and the formation of entangled exciton states: Due to the coupling between the dots the exciton states show a splitting that increases with decreasing barrier width. For barrier widths below 5 nm it exceeds the thermal energy at room temperature. For a given barrier width, we find only small variations of the tunneling induced splitting demonstrating a good homogeneity within a molecule ensemble. The entanglement may be controlled by application of electromagnetic field. For
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.
Measurement-device-independent entanglement witnesses for all entangled quantum states.
Branciard, Cyril; Rosset, Denis; Liang, Yeong-Cherng; Gisin, Nicolas
2013-02-08
The problem of demonstrating entanglement is central to quantum information processing applications. Resorting to standard entanglement witnesses requires one to perfectly trust the implementation of the measurements to be performed on the entangled state, which may be an unjustified assumption. Inspired by the recent work of F. Buscemi [Phys. Rev. Lett. 108, 200401 (2012)], we introduce the concept of measurement-device-independent entanglement witnesses (MDI-EWs), which allow one to demonstrate entanglement of all entangled quantum states with untrusted measurement apparatuses. We show how to systematically obtain such MDI-EWs from standard entanglement witnesses. Our construction leads to MDI-EWs that are loss tolerant and can be implemented with current technology.
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.
Operational multipartite entanglement classes for symmetric photonic qubit states
Kiesel, N.; Wieczorek, W.; Weinfurter, H.; Krins, S.; Bastin, T.; Solano, E.
2010-03-15
We present experimental schemes that allow us to study the entanglement classes of all symmetric states in multiqubit photonic systems. We compare the efficiency of the proposed schemes and highlight the relation between the entanglement properties of symmetric Dicke states and a recently proposed entanglement scheme for atoms. In analogy to the latter, we obtain a one-to-one correspondence between well-defined sets of experimental parameters and multiqubit entanglement classes inside the symmetric subspace of the photonic system.
Teleporting entanglements of cavity-field states
Pires, Geisa; Baseia, B.; Almeida, N.G. de; Avelar, A. T.
2004-08-01
We present a scheme to teleport an entanglement of zero- and one-photon states from one cavity to another. The scheme, which has 100% success probability, relies on two perfect and identical bimodal cavities, a collection of two kinds of two-level atoms, a three-level atom in a ladder configuration driven by a classical field, Ramsey zones, and selective atomic-state detectors.
Entanglement distillation between solid-state quantum network nodes.
Kalb, N; Reiserer, A A; Humphreys, P C; Bakermans, J J W; Kamerling, S J; Nickerson, N H; Benjamin, S C; Twitchen, D J; Markham, M; Hanson, R
2017-06-02
The impact of future quantum networks hinges on high-quality quantum entanglement shared between network nodes. Unavoidable imperfections necessitate a means to improve remote entanglement by local quantum operations. We realize entanglement distillation on a quantum network primitive of distant electron-nuclear two-qubit nodes. The heralded generation of two copies of a remote entangled state is demonstrated through single-photon-mediated entangling of the electrons and robust storage in the nuclear spins. After applying local two-qubit gates, single-shot measurements herald the distillation of an entangled state with increased fidelity that is available for further use. The key combination of generating, storing, and processing entangled states should enable the exploration of multiparticle entanglement on an extended quantum network. Copyright © 2017, American Association for the Advancement of Science.
Entanglement distillation between solid-state quantum network nodes
NASA Astrophysics Data System (ADS)
Kalb, N.; Reiserer, A. A.; Humphreys, P. C.; Bakermans, J. J. W.; Kamerling, S. J.; Nickerson, N. H.; Benjamin, S. C.; Twitchen, D. J.; Markham, M.; Hanson, R.
2017-06-01
The impact of future quantum networks hinges on high-quality quantum entanglement shared between network nodes. Unavoidable imperfections necessitate a means to improve remote entanglement by local quantum operations. We realize entanglement distillation on a quantum network primitive of distant electron-nuclear two-qubit nodes. The heralded generation of two copies of a remote entangled state is demonstrated through single-photon-mediated entangling of the electrons and robust storage in the nuclear spins. After applying local two-qubit gates, single-shot measurements herald the distillation of an entangled state with increased fidelity that is available for further use. The key combination of generating, storing, and processing entangled states should enable the exploration of multiparticle entanglement on an extended quantum network.
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.
Usefulness of classical communication for local cloning of entangled states
NASA Astrophysics Data System (ADS)
Demkowicz-Dobrzański, Rafał; Lewenstein, Maciej; Sen(de), Aditi; Sen, Ujjwal; Bruß, Dagmar
2006-03-01
We solve the problem of the optimal cloning of pure entangled two-qubit states with a fixed degree of entanglement using local operations and classical communication. We show that, amazingly, classical communication between the parties can improve the fidelity of local cloning if and only if the initial entanglement is higher than a certain critical value. It is completely useless for weakly entangled states. We also show that bound entangled states with positive partial transpose are not useful as a resource to improve the best local cloning fidelity.
Entanglement conditions for two-mode states: Applications
Hillery, Mark; Zubairy, M. Suhail
2006-09-15
We examine the implications of several recently derived conditions [Hillery and Zubairy, Phys. Rev. Lett. 96, 050503 (2006)] for determining when a two-mode state is entangled. We first find examples of non-Gaussian states that satisfy these conditions. We then apply the entanglement conditions to the study of several linear devices, the beam splitter, the parametric amplifier, and the linear phase-insensitive amplifier. For the first two, we find conditions on the input states that guarantee that the output states are entangled. For the linear amplifier, we determine in the limit of high and no gain, when an entangled input leads to an entangled output. Finally, we show how application of two two-mode entanglement conditions to a three-mode state can serve as a test of genuine three-mode entanglement.
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.
Quantum Communication Using Macroscopic Phase Entangled States
2015-12-10
goals of our program was to investigate several different ways in which to implement the Kerr medium that allows a single photon to change the phase ...E7(/(3+21(180%(5 ,QFOXGHDUHDFRGH 1 i. Quantum Communication Using Macroscopic Phase Entangled States Final Report Reporting...media that can produce a shift in the phase of a laser pulse provided that a single photon from another source and at a different frequency is also
Searching for extremal PPT entangled states
NASA Astrophysics Data System (ADS)
Augusiak, Remigiusz; Grabowski, Janusz; Kuś, Marek; Lewenstein, Maciej
2010-03-01
We study extremality in various sets of states that have positive partial transposes. One of the tools we use for this purpose is the recently formulated criterion allowing to judge if a given state is extremal in the set of PPT states. First we investigate qubit-ququart states and show that the only candidates for extremal PPT entangled states (PPTES) have ranks of the state and its partial transposition (5, 5) or (5, 6) (equivalently (6, 5)). Then, examples of extremal states of (5, 5) type and the so-called edge states of type (5, 6) are provided. We also make an attempt to explore the set of PPT states with ranks (5, 6). Finally, we discuss what are the possible configurations of ranks of density matrices and their respective partial transposition in general three-qubit and four-qubit symmetric states for which there may exist extremal entangled PPT states. For instance in the first case we show that the only possibilities are (4, 4, 4) and (4, 4, 5).
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.
Bound entangled states with extremal properties
NASA Astrophysics Data System (ADS)
BadziaÂģ, Piotr; Horodecki, Karol; Horodecki, Michał; Jenkinson, Justin; Szarek, Stanisław J.
2014-07-01
Following recent work of Beigi and Shor, we investigate positive partial transpose (PPT) states that are "heavily entangled." We first exploit volumetric methods to show that in a randomly chosen direction, there are PPT states whose distance in trace norm from separable states is (asymptotically) at least 1/4. We then provide explicit examples of PPT states which are nearly as far from separable ones as possible. To obtain a distance of 2-ɛ from the separable states, we need a dimension of 2poly [log(1/ɛ)], as opposed to 2poly (1/ɛ) given by the construction of Beigi and Shor [J. Math. Phys. 51, 042202 (2010), 10.1063/1.3364793]. We do so by exploiting the so-called private states, introduced earlier in the context of quantum cryptography. We also provide a lower bound for the distance between private states and PPT states and investigate the distance between pure states and the set of PPT states.
Teleportation of continuous variable multimode Greeberger Horne Zeilinger entangled states
NASA Astrophysics Data System (ADS)
He, Guangqiang; Zhang, Jingtao; Zeng, Guihua
2008-11-01
Quantum teleportation protocols of continuous variable (CV) Greeberger-Horne-Zeilinger (GHZ) and Einstein-Podolsky-Rosen (EPR) entangled states are proposed, and are generalized to teleportation of arbitrary multimode GHZ entangled states described by Van Loock and Braunstein (2000 Phys. Rev. Lett. 84 3482). Each mode of a multimode entangled state is teleported using a CV EPR entangled pair and classical communication. The analytical expression of fidelity for the multimode Gaussian states which evaluates the teleportation quality is presented. The analytical results show that the fidelity is a function of both the squeezing parameter r, which characterizes the multimode entangled state to be teleported, and the channel parameter p, which characterizes the EPR pairs shared by Alice and Bob. The fidelity increases with increasing p, but decreases with increasing r, i.e., it is more difficult to teleport the more perfect multimode entangled states. The entanglement degree of the teleported multimode entangled states increases with increasing both r and p. In addition, the fact is proved that our teleportation protocol of EPR entangled states using parallel EPR pairs as quantum channels is the best case of the protocol using four-mode entangled states (Adhikari et al 2008 Phys. Rev. A 77 012337).
Excited state entanglement in homogeneous fermionic chains
NASA Astrophysics Data System (ADS)
Ares, F.; Esteve, J. G.; Falceto, F.; Sánchez-Burillo, E.
2014-06-01
We study the Rényi entanglement entropy of an interval in a periodic fermionic chain for a general eigenstate of a free, translational invariant Hamiltonian. In order to analytically compute the entropy we use two technical tools. The first is used to logarithmically reduce the complexity of the problem and the second to compute the Rényi entropy of the chosen subsystem. We introduce new strategies to perform the computations, derive new expressions for the entropy of these general states and show the perfect agreement of the analytical computations and the numerical outcome. Finally we discuss the physical interpretation of our results and generalize them to compute the entanglement entropy for a fragment of a fermionic ladder.
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.
Entangled state fusion with Rydberg atoms
NASA Astrophysics Data System (ADS)
Ji, Y. Q.; Dai, C. M.; Shao, X. Q.; Yi, X. X.
2017-10-01
We propose a scheme for preparation of large-scale entangled GHZ states and W states with neutral Rydberg atoms. The scheme mainly depends on Rydberg antiblockade effect, i.e., as the Rydberg-Rydberg interaction strength and the detuning between the atom transition frequency and the classical laser frequency satisfies some certain conditions, the effective Rabi oscillation between the two ground states and the two excitation Rydberg states would be generated. The prominent advantage is that both two multiparticle GHZ states and two multiparticle W states can be fused in this model, especially the success probability for fusion of GHZ states can reach unit. In addition, the imperfections induced by the spontaneous emission is also discussed through numerical simulation.
Multiple state transition path sampling
NASA Astrophysics Data System (ADS)
Rogal, Jutta; Bolhuis, Peter G.
2008-12-01
We developed a multiple state transition path sampling (TPS) approach in which it is possible to simultaneously sample pathways connecting a number of different stable states. Based on the original formulation of the TPS we have extended the path ensemble to include trajectories connecting not only two distinct stable states but any two states defined within a system. The multiple state TPS approach is useful in complex systems exhibiting a number of intermediate stable states that are interconnected in phase space. Combining this approach with transition interface sampling we can also directly obtain an expression for the rate constants of all possible transitions within the system.
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.
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.
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.
Entangled States of Atoms upon Interaction with Narrowband Light
Gorbachev, V.N.; Zhiliba, A.I.; Rodichkina, A.A.; Trubilko, A.I.
2005-08-15
The process of resonant interaction of light with two-level atoms in the absence of relaxation is considered. For a special form of initial conditions, simple and exact solutions are found that describe coherent processes leading to the appearance of many-particle entangled W-class states. These processes can be used for preparation and transformation of entangled states, in particular, for problems of quantum memory and generation of entangled atomic chains.
Multi-Particle Interferometry Based on Double Entangled States
NASA Technical Reports Server (NTRS)
Pittman, Todd B.; Shih, Y. H.; Strekalov, D. V.; Sergienko, A. V.; Rubin, M. H.
1996-01-01
A method for producing a 4-photon entangled state based on the use of two independent pair sources is discussed. Of particular interest is that each of the pair sources produces a two-photon state which is simultaneously entangled in both polarization and space-time variables. Performing certain measurements which exploit this double entanglement provides an opportunity for verifying the recent demonstration of nonlocality by Greenberger, Horne, and Zeilinger.
Macroscopic entanglement in many-particle quantum states
NASA Astrophysics Data System (ADS)
Tichy, Malte C.; Park, Chae-Yeun; Kang, Minsu; Jeong, Hyunseok; Mølmer, Klaus
2016-04-01
We elucidate the relationship between Schrödinger-cat-like macroscopicity and geometric entanglement and argue that these quantities are not interchangeable. While both properties are lost due to decoherence, we show that macroscopicity is rare in uniform and in so-called random physical ensembles of pure quantum states, despite possibly large geometric entanglement. In contrast, permutation-symmetric pure states feature rather low geometric entanglement and strong and robust macroscopicity.
Highly Entangled Ground States in Tripartite Qubit Systems
NASA Astrophysics Data System (ADS)
Röthlisberger, Beat; Lehmann, Jörg; Saraga, D. S.; Traber, Philipp; Loss, Daniel
2008-03-01
We investigate the creation of highly entangled ground states in a system of three exchange-coupled qubits arranged in a ring geometry. Suitable magnetic field configurations yielding approximate Greenberger-Horne-Zeilinger and exact W ground states are identified. The entanglement in the system is studied at finite temperature in terms of the mixed-state tangle τ. By generalizing a conjugate gradient optimization algorithm originally developed to evaluate the entanglement of formation, we demonstrate that τ can be calculated efficiently and with high precision. We identify the parameter regime for which the equilibrium entanglement of the tripartite system reaches its maximum.
Asymptotic entanglement in quantum walks from delocalized initial states
NASA Astrophysics Data System (ADS)
Orthey, Alexandre C.; Amorim, Edgard P. M.
2017-09-01
We study the entanglement between the internal (spin) and external (position) degrees of freedom of the one-dimensional discrete time quantum walk starting from local and delocalized initial states whose time evolution is driven by Hadamard and Fourier coins. We obtain the dependence of the asymptotic entanglement with the initial dispersion of the state and establish a way to connect the asymptotic entanglement between local and delocalized states. We find out that the delocalization of the state increases the number of initial spin states which achieves maximal entanglement from two states (local) to a continuous set of spin states (delocalized) given by a simple relation between the angles of the initial spin state. We also carry out numerical simulations of the average entanglement along the time to confront with our analytical results.
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.
Distinguishability and cloning of entangled states by LOCC
NASA Astrophysics Data System (ADS)
Kar, Guruprasad
2006-11-01
There exist sets of multipartite orthogonal states which can not be distinguished by local operation and classical communication (LOCC). The simplest example is the set of four Bell states. The problem of characterizing a set in terms of distinguishability is a hard problem in general. For maximally entangled states, some results are known. Local cloning of entangled states by supplying necessary entanglement in the blank state is another idea that was introduced very recently. Interestingly there are sets of orthogonal entangled states which can be distinguished locally but can not be copied by local operation (even if necessary entanglement is supplied in the blank state) contrary to the fact that happens in the case of global operation.
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.
Improving entanglement concentration of Gaussian states by local displacements
Fiurasek, Jaromir
2011-07-15
We investigate entanglement concentration of continuous-variable Gaussian states by local single-photon subtractions combined with local Gaussian operations. We first analyze the local squeezing-enhanced entanglement-concentration protocol proposed very recently by Zhang and van Loock [arXiv:1103.4500] and discuss the mechanism by which local squeezing before photon subtraction helps to increase the entanglement of the output state of the protocol. We next show that a similar entanglement improvement can be achieved by using local coherent displacements instead of single-mode squeezing.
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.
Conditional preparation of X{sup (2)} macroscopic entangled states
Podoshvedov, S. A.
2006-04-15
Two experimental arrangements consisting of coupled spontaneous parametric down-converters with type-I phase matching pumped simultaneously by a powerful optical field in a coherent state through a balanced beam splitter and linear optical elements are proposed for conditional preparation of macroscopic entangled states in output pumping modes of the studied system. Successful generation of the macroscopic entangled state in the pumping modes is unambiguously heralded by coincident detection of two photons in the generated signal and idler modes of the system. We calculate the amount of entanglement and probabilities of successfully observing the X{sup (2)} macroscopic entangled states in the total wavefunction. We show that the proposed schemes can be used to obtain a new type of macroscopic entangled 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.
NASA Astrophysics Data System (ADS)
Deng, Li; Chen, Ai-Xi; Zhang, Jian-Song
2011-11-01
We provide a scheme with which the transfer of the entangled state and the entanglement swapping can be realized in a system of neutral atoms via the Rydberg blockade. Our idea can be extended to teleport an unknown atomic state. According to the latest theoretical research of the Rydberg excitation and experimental reports of the Rydberg blockade effect in quantum information processing, we discuss the experimental feasibility of our scheme.
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.
Quantum entanglement swapping of two arbitrary biqubit pure states
NASA Astrophysics Data System (ADS)
Xie, ChuanMei; Liu, YiMin; Chen, JianLan; Yin, XiaoFeng; Zhang, ZhanJun
2016-10-01
In this paper, the issue of swapping quantum entanglements in two arbitrary biqubit pure states via a local bipartite entangledstate projective measure in the middle node is studied in depth, especially with regard to quantitative aspects. Attention is mainly focused on the relation between the measure and the final entanglement obtained via swapping. During the study, the entanglement of formation (EoF) is employed as a quantifier to characterize and quantify the entanglements present in all involved states. All concerned EoFs are expressed analytically; thus, the relation between the final entanglement and the measuring state is established. Through concrete analyses, the measure demands for getting a certain amount of a final entanglement are revealed. It is found that a maximally entangled final state can be obtained from any two given initial entangled states via swapping with a certain probability; however, a peculiar measure should be performed. Moreover, some distinct properties are revealed and analyzed. Such a study will be useful in quantum information processes.
Cluster-type entangled coherent states: Generation and application
NASA Astrophysics Data System (ADS)
An, Nguyen Ba; Kim, Jaewan
2009-10-01
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.
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.
Entanglement Concentration of Partially Entangled Multi-electron Spin W States with CNOT Gates
NASA Astrophysics Data System (ADS)
Gu, Bin; Huang, Yugai; Fang, Xia; Wang, Haibin
2014-04-01
We propose a novel entanglement concentration protocol (ECP) for nonlocal N-electron systems in a partially entangled W state, resorting to an ancillary single electron and controlled-not gates. Compared with other ECPs for W states, our ECP has some illustrious advantages. First, each N-electron entangled system can be used to complete the entanglement concentration with only an ancillary electron. It does not require that there are two copies of N-electron entangled systems in each round of entanglement concentration. Second, only one of the users, say Charlie, needs to perform the protocol, while all parties should perform the same operations as Charlie in other ECPs for W-class states. Third, only Charlie asks other parities to retain or discard their electrons, and they do not need to check their measurement results, which greatly simplifies the complication of classical communication. Fourth, our ECP has a higher success probability than other ECPs for W-class states as its success probability equals to the limit value of an ECP for a W state in theory. These advantages maybe make our ECP more useful in practical applications.
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.
Generating entangled states of two ququarts using linear optical elements
Baek, So-Young; Kim, Yoon-Ho
2007-03-15
We propose linear optical schemes for generating entangled states of two ququarts (four-dimensional quantum systems) in which the single-ququart state is constructed with frequency-nondegenerate biphoton polarization states of spontaneous parametric down-conversion. We show explicitly that it is possible to generate various two-ququart entangled states by interfering two ququarts at a linear optical beam splitter (an ordinary 50-50 beam splitter, a polarizing beam splitter, or a dichroic beam splitter)
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.
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.
Zhang, Zhi-Chao; Gao, Fei; Cao, Tian-Qing; Qin, Su-Juan; Wen, Qiao-Yan
2016-07-26
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
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
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.
Heralded entangled coherent states between spatially separated massive resonators
NASA Astrophysics Data System (ADS)
Asadian, Ali; Abdi, Mehdi
2016-05-01
We put forward an experimentally feasible scheme for heralded entanglement generation between two distant macroscopic mechanical resonators. The protocol exploits a hybrid quantum device, a qubit interacting with a mechanical resonator as well as a cavity mode, for each party. The cavity modes interfere on a beam splitter followed by suitable heralding detections, which postselect a hybrid entangled state with success probability 1/2. Subsequently, by local measurements on the qubits, a mechanically entangled coherent state can be achieved. The mechanical entanglement can be further verified via monitoring the entanglement of the qubit pair. The setup is envisioned as a test bed for sensing gravitational effects on the quantum dynamics of gravitationally coupled massive objects. As a concrete example, we illustrate the implementation of our protocol using the current circuit QED architectures.
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.
High-fidelity entangled Bell states via shortcuts to adiabaticity
NASA Astrophysics Data System (ADS)
Paul, Koushik; Sarma, Amarendra K.
2016-11-01
We present a couple of protocols based on shortcut to adiabaticity techniques for rapid generation of robust entangled Bell states in a pair of two-state systems. Our protocol relies on the so-called transitionless quantum driving (TQD) algorithm and Lewis-Riesenfeld invariant (LRI) method. Both TQD and LRI methods result in high fidelity in population transfer. Our study shows that it is possible to prepare an entangled state in extremely short time without losing robustness and efficiency.
Multi-state Quantum Teleportation via One Entanglement State
NASA Astrophysics Data System (ADS)
Guo, Ying; Zeng, Gui-Hua; Moon Ho, Lee
2008-08-01
A multi-sender-controlled quantum teleportation scheme is proposed to teleport several secret quantum states from different senders to a distance receiver based on only one Einstein Podolsky Rosen (EPR) pair with controlled-NOT (CNOT) gates. In the present scheme, several secret single-qubit quantum states are encoded into a multi-qubit entangled quantum state. Two communication modes, i.e., the detecting mode and the message mode, are employed so that the eavesdropping can be detected easily and the teleported message may be recovered efficiently. It has an advantage over teleporting several different quantum states for one scheme run with more efficiency than the previous quantum teleportation schemes.
Polarization entanglement purification for concatenated Greenberger-Horne-Zeilinger state
NASA Astrophysics Data System (ADS)
Zhou, Lan; Sheng, Yu-Bo
2017-10-01
Entanglement purification plays a fundamental role in long-distance quantum communication. In the paper, we put forward the first polarization entanglement purification protocol (EPP) for one type of nonlocal logic-qubit entanglement, i.e., concatenated Greenberger-Horne-Zeilinger (C-GHZ) state, resorting to the photon-atom interaction in low-quality (Q) cavity. In contrast to existing EPPs, this protocol can purify the bit-flip error and phase-flip error in both physic and logic level. Instead of measuring the photons directly, this protocol only requires to measure the atom states to judge whether the protocol is successful. In this way, the purified logic entangled states can be preserved for further application. Moreover, it makes this EPP repeatable so as to obtain a higher fidelity of logic entangled states. As the logic-qubit entanglement utilizes the quantum error correction (QEC) codes, which has an inherent stability against noise and decoherence, this EPP combined with the QEC codes may provide a double protection for the entanglement from the channel noise and may have potential applications in long-distance quantum communication.
Manipulation of Entangled States for Quantum Information Processing
NASA Astrophysics Data System (ADS)
Bose, S.; Huelga, S. F.; Jonathan, D.; Knight, P. L.; Murao, M.; Plenio, M. B.; Vedral, V.
Entanglement manipulation, and especially Entanglement Swapping is at the heart of current work on quantum information processing, purification and quantum teleportation. We will discuss how it may be generalized to multiparticle systems and how this enables multi-user quantum cryptographic protocols to be developed. Our scheme allows us to establish multiparticle entanglement between particles which belong to distant users in a communication network through a prior distribution of Bell state singlets followed by local measurements. We compare our method for generating entanglement with existing schemes using simple quantum networks, and highlight the advantages and applications in cryptographic conferencing and in reading messages from more than one source through a single quantum measurement. We also discuss how entanglement leads to the idea of `telecloning', in which a teleportation-like protocol can be found which reproduces the output of an optimal quantum cloning machine.
Toward Heisenberg-limited spectroscopy with multiparticle entangled states.
Leibfried, D; Barrett, M D; Schaetz, T; Britton, J; Chiaverini, J; Itano, W M; Jost, J D; Langer, C; Wineland, D J
2004-06-04
The precision in spectroscopy of any quantum system is fundamentally limited by the Heisenberg uncertainty relation for energy and time. For N systems, this limit requires that they be in a quantum-mechanically entangled state. We describe a scalable method of spectroscopy that can potentially take full advantage of entanglement to reach the Heisenberg limit and has the practical advantage that the spectroscopic information is transferred to states with optimal protection against readout noise. We demonstrate our method experimentally with three beryllium ions. The spectroscopic sensitivity attained is 1.45(2) times as high as that of a perfect experiment with three non-entangled particles.
Operational entanglement families of symmetric mixed N -qubit states
NASA Astrophysics Data System (ADS)
Bastin, T.; Mathonet, P.; Solano, E.
2015-02-01
We introduce an operational entanglement classification of symmetric mixed states for an arbitrary number of qubits based on stochastic local operations assisted with classical communication (SLOCC operations). We define families of SLOCC entanglement classes successively embedded into each other, we prove that they are of nonzero measure, and we construct witness operators to distinguish them. Moreover, we discuss how arbitrary symmetric mixed states can be realized in the laboratory via a one-to-one correspondence between well-defined sets of controllable parameters and the corresponding entanglement families.
All entangled pure quantum states violate the bilocality inequality
NASA Astrophysics Data System (ADS)
Gisin, Nicolas; Mei, Quanxin; Tavakoli, Armin; Renou, Marc Olivier; Brunner, Nicolas
2017-08-01
The nature of quantum correlations in networks featuring independent sources of entanglement remains poorly understood. Here, focusing on the simplest network of entanglement swapping, we start a systematic characterization of the set of quantum states leading to violation of the so-called "bilocality" inequality. First, we show that all possible pairs of entangled pure states can violate the inequality. Next, we derive a general criterion for violation for arbitrary pairs of mixed two-qubit states. Notably, this reveals a strong connection between the Clauser-Horne-Shimony-Holt (CHSH) Bell inequality and the bilocality inequality, namely, that any entangled state violating CHSH also violates the bilocality inequality. We conclude with a list of open questions.
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.
Direct transfer of classical non-separable states into hybrid entangled two photon states.
Jabir, M V; Apurv Chaitanya, N; Mathew, Manoj; Samanta, G K
2017-08-04
Hybrid entangled states, having entanglement between different degrees-of-freedom (DoF) of a particle pair, are of great interest for quantum information science and communication protocols. Among different DoFs, the hybrid entangled states encoded with polarization and orbital angular momentum (OAM) allow the generation of qubit-qudit entangled states, macroscopic entanglement with very high quanta of OAM and improvement in angular resolution in remote sensing. Till date, such hybrid entangled states are generated by using a high-fidelity polarization entangled states and subsequent imprinting of chosen amount of OAM using suitable mode converters such as spatial light modulator in complicated experimental schemes. Given that the entangled sources have feeble number of photons, loss of photons during imprinting of OAM using diffractive optical elements limits the use of such hybrid states for practical applications. Here we report, on a simple generic experimental scheme to generate hybrid entangled states in polarization and OAM through direct transfer of classical non-separable states of the pump beam in parametric down conversion process. As a proof of principle, using local non-separable pump states of OAM mode l = 3, we have produced quantum hybrid entangled states with entanglement witness parameter of ~1.25 ± 0.03 violating by 8 standard deviation.
NASA Astrophysics Data System (ADS)
Chen, Hui-Na; Liu, Jin-Ming
2009-10-01
We present an optical scheme to almost completely teleport a bipartite entangled coherent state using a four-partite cluster-type entangled coherent state as quantum channel. The scheme is based on optical elements such as beam splitters, phase shifters, and photon detectors. We also obtain the average fidelity of the teleportation process. It is shown that the average fidelity is quite close to unity if the mean photon number of the coherent state is not too small.
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.
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.
Comment on "Multipartite Entanglement in Four-qubit Graph States"
NASA Astrophysics Data System (ADS)
Haddadi, Saeed
2017-09-01
The following comment is based on an article by Jafarpour and Assadi (Eur. Phys. J. D 70, 62 2016) which with an exploitation of Scott measure (or generalized Meyer-Wallach measure) the entanglement quantity of four-qubit graph states has been calculated. We are to reveal that a 2-2 partition necessarily always does not provide a stronger entanglement than a 3-1 partition in all the graph states.
All entangled pure states violate a single Bell's inequality.
Yu, Sixia; Chen, Qing; Zhang, Chengjie; Lai, C H; Oh, C H
2012-09-21
We show that a single Bell's inequality with two dichotomic observables for each observer, which originates from Hardy's nonlocality proof without inequalities, is violated by all entangled pure states of a given number of particles, each of which may have a different number of energy levels. Thus Gisin's theorem is proved in its most general form from which it follows that for pure states Bell's nonlocality and quantum entanglement are equivalent.
NASA Astrophysics Data System (ADS)
Hu, Juju; Xu, Lin
2015-07-01
We demonstrate the controllable generation of entangled coherent states in circuit quantum electrodynamics (circuit QED). In our scheme, the easy integration of solid-state quantum circuit is exploited. In particular, through manipulating the external capacitor or external classical microwave impulse, the coupling between superconducting qubits and cavity can be manipulated, the entanglement effect between qubit and field modes can be enhanced and the decoherence effect can be effectively suppressed. We further discuss the correspondence between quantum entanglement and some non-classical effects such as the squeezing of entangled coherent state field, the anti-buching effect. The results show that the time evolution of the quantum entanglement between field modes is always accompanied by the synchronous changes of certain non-classical effect. When the quantum entanglement reaches maximum, the anti-bunching (or compression effect) almost reaches maximum synchronously. Once entanglement sudden death occurs, the non-classical effects disappear.
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.
Dynamical generation of maximally entangled states in two identical cavities
Alexanian, Moorad
2011-11-15
The generation of entanglement between two identical coupled cavities, each containing a single three-level atom, is studied when the cavities exchange two coherent photons and are in the N=2,4 manifolds, where N represents the maximum number of photons possible in either cavity. The atom-photon state of each cavity is described by a qutrit for N=2 and a five-dimensional qudit for N=4. However, the conservation of the total value of N for the interacting two-cavity system limits the total number of states to only 4 states for N=2 and 8 states for N=4, rather than the usual 9 for two qutrits and 25 for two five-dimensional qudits. In the N=2 manifold, two-qutrit states dynamically generate four maximally entangled Bell states from initially unentangled states. In the N=4 manifold, two-qudit states dynamically generate maximally entangled states involving three or four states. The generation of these maximally entangled states occurs rather rapidly for large hopping strengths. The cavities function as a storage of periodically generated maximally entangled states.
Harnessing gauge fields for maximally entangled state generation
NASA Astrophysics Data System (ADS)
Reyes, S. A.; Morales-Molina, L.; Orszag, M.; Spehner, D.
2014-10-01
We study the generation of entanglement between two species of bosons living on a ring lattice, where each group of particles can be described by a d-dimensional Hilbert space (qudit). Gauge fields are exploited to create an entangled state between the pair of qudits. Maximally entangled eigenstates are found for well-defined values of the Aharonov-Bohm phase, which are zero-energy eigenstates of both the kinetic and interacting parts of the Bose-Hubbard Hamiltonian, making them quite exceptional and robust. We propose a protocol to reach the maximally entangled state (MES) by starting from an initially prepared ground state. Also, an indirect method to detect the MES by measuring the current of the particles is proposed.
Harnessing gauge fields for maximally entangled state generation
NASA Astrophysics Data System (ADS)
Reyes, Sebastian; Morales-Molina, Luis; Orszag, Miguel; Spehner, Dominique
2015-03-01
We study the generation of entanglement between two species of bosons living on a ring lattice, where each group of particles can be described by a d-dimensional Hilbert space (qudit). Gauge fields are exploited to create an entangled state between the pair of qudits. Maximally entangled eigenstates are found for well-defined values of the Aharonov-Bohm phase, which are zero-energy eigenstates of both the kinetic and interacting parts of the Bose-Hubbard Hamiltonian, making them quite exceptional. We propose a protocol to reach the maximally entangled state (MES) by starting from an initially prepared ground state. Also, an indirect method to detect the MES by measuring the current of the particles is proposed.
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.
Optimal estimation of parameters of an entangled quantum state
NASA Astrophysics Data System (ADS)
Virzì, S.; Avella, A.; Piacentini, F.; Gramegna, M.; Brida, G.; Degiovanni, I. P.; Genovese, M.
2017-05-01
Two-photon entangled quantum states are a fundamental tool for quantum information and quantum cryptography. A complete description of a generic quantum state is provided by its density matrix: the technique allowing experimental reconstruction of the density matrix is called quantum state tomography. Entangled states density matrix reconstruction requires a large number of measurements on many identical copies of the quantum state. An alternative way of certifying the amount of entanglement in two-photon states is represented by the estimation of specific parameters, e.g., negativity and concurrence. If we have a priori partial knowledge of our state, it’s possible to develop several estimators for these parameters that require lower amount of measurements with respect to full density matrix reconstruction. The aim of this work is to introduce and test different estimators for negativity and concurrence for a specific class of two-photon 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.
Genuinely entangled symmetric states with no N -partite correlations
NASA Astrophysics Data System (ADS)
Designolle, S.; Giraud, O.; Martin, J.
2017-09-01
We investigate genuinely entangled N -qubit states with no N -partite correlations in the case of symmetric states. Using a tensor representation for mixed symmetric states, we obtain a simple characterization of the absence of N -partite correlations. We show that symmetric states with no N -partite correlations cannot exist for an even number of qubits. We fully identify the set of genuinely entangled symmetric states with no N -partite correlations in the case of three qubits, and in the case of rank-2 states. We present a general procedure to construct families for an arbitrary odd number of qubits.
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.
Approximating local observables on projected entangled pair states
NASA Astrophysics Data System (ADS)
Schwarz, M.; Buerschaper, O.; Eisert, J.
2017-06-01
Tensor network states are for good reasons believed to capture ground states of gapped local Hamiltonians arising in the condensed matter context, states which are in turn expected to satisfy an entanglement area law. However, the computational hardness of contracting projected entangled pair states in two- and higher-dimensional systems is often seen as a significant obstacle when devising higher-dimensional variants of the density-matrix renormalization group method. In this work, we show that for those projected entangled pair states that are expected to provide good approximations of such ground states of local Hamiltonians, one can compute local expectation values in quasipolynomial time. We therefore provide a complexity-theoretic justification of why state-of-the-art numerical tools work so well in practice. We finally turn to the computation of local expectation values on quantum computers, providing a meaningful application for a small-scale quantum computer.
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
Multipartite Continuous-Variable Entanglement Distribution with Separable Gaussian States
NASA Astrophysics Data System (ADS)
Zhong, Daili; Wang, Yijun; Guo, Ying
2017-05-01
Entangling quantum systems at distant locations is a newly discovered counterintuitive phenomenon. However, the generation effect will be reduced by imperfections of practical devices. In this paper, we demonstrate a Gaussian process approach for the scheme design of multipartite continuous-variable (CV) entanglement generation and distribution by using separable Gaussian states, which are superimposed on the beam splitters with the single auxiliary state, rendering the desirable CV entangled states. The superimposing operation not only can avoid the complexity and imperfection of the practical state-superimposing operations, which defends the eavesdropper as the auxiliary mode which is separable, but also can be regulated flexibly by performing suitable displacements with the regulated parameter of the initial states before being sent to the beam splitters to optimize the performance.
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.
Chen Lixiang; She Weilong
2011-01-15
Twisted photons offer a high-dimensional Hilbert space with the degree of freedom of orbital angular momentum (OAM). Entanglement swapping allows entangling photons that never interact. We report in this paper the hybrid entanglement swapping from multiphoton spin-entangled states to multiphoton OAM entangled states with the aid of N-pair hybrid spin-OAM entangled photons. Our scheme provides a feasible method for creating the two-photon OAM Bell states (N=2) or multiphoton multidimensional OAM Greenberger-Horne-Zeilinger states (N{>=}3). We highlight the advantage of multiparticle, multidimensional entangled states in some applications of quantum information protocols.
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.
Super-resolving phase measurements with a multiphoton entangled state.
Mitchell, M W; Lundeen, J S; Steinberg, A M
2004-05-13
Interference phenomena are ubiquitous in physics, often forming the basis of demanding measurements. Examples include Ramsey interferometry in atomic spectroscopy, X-ray diffraction in crystallography and optical interferometry in gravitational-wave studies. It has been known for some time that the quantum property of entanglement can be exploited to perform super-sensitive measurements, for example in optical interferometry or atomic spectroscopy. The idea has been demonstrated for an entangled state of two photons, but for larger numbers of particles it is difficult to create the necessary multiparticle entangled states. Here we demonstrate experimentally a technique for producing a maximally entangled three-photon state from initially non-entangled photons. The method can in principle be applied to generate states of arbitrary photon number, giving arbitrarily large improvement in measurement resolution. The method of state construction requires non-unitary operations, which we perform using post-selected linear-optics techniques similar to those used for linear-optics quantum computing.
Controlled Teleportation of a Qudit State by Partially Entangled GHZ States
NASA Astrophysics Data System (ADS)
Wang, Jin-wei; Shu, Lan; Mo, Zhi-wen; Zhang, Zhi-hua
2014-08-01
In this paper, we propose a controlled teleportation scheme which communicates an arbitrary ququart state via two sets of partially entangled GHZ state. The necessary measurements and operations are given detailedly. Furthmore the scheme is generalized to teleport a qudit state via s sets of partially entangled GHZ state.
Identifying non-Abelian topological order through minimal entangled states.
Zhu, W; Gong, S S; Haldane, F D M; Sheng, D N
2014-03-07
The topological order is encoded in the pattern of long-range quantum entanglements, which cannot be measured by any local observable. Here we perform an exact diagonalization study to establish the non-Abelian topological order for topological band models through entanglement entropy measurement. We focus on the quasiparticle statistics of the non-Abelian Moore-Read and Read-Rezayi states on the lattice models with bosonic particles. We identify multiple independent minimal entangled states (MESs) in the ground state manifold on a torus. The extracted modular S matrix from MESs faithfully demonstrates the Ising anyon or Fibonacci quasiparticle statistics, including the quasiparticle quantum dimensions and the fusion rules for such systems. These findings unambiguously demonstrate the topological nature of the quantum states for these flatband models without using the knowledge of model wave functions.
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.
Multimode entanglement in reconfigurable graph states using optical frequency combs
NASA Astrophysics Data System (ADS)
Cai, Y.; Roslund, J.; Ferrini, G.; Arzani, F.; Xu, X.; Fabre, C.; Treps, N.
2017-06-01
Multimode entanglement is an essential resource for quantum information processing and quantum metrology. However, multimode entangled states are generally constructed by targeting a specific graph configuration. This yields to a fixed experimental setup that therefore exhibits reduced versatility and scalability. Here we demonstrate an optical on-demand, reconfigurable multimode entangled state, using an intrinsically multimode quantum resource and a homodyne detection apparatus. Without altering either the initial squeezing source or experimental architecture, we realize the construction of thirteen cluster states of various sizes and connectivities as well as the implementation of a secret sharing protocol. In particular, this system enables the interrogation of quantum correlations and fluctuations for any multimode Gaussian state. This initiates an avenue for implementing on-demand quantum information processing by only adapting the measurement process and not the experimental layout.
Entanglement and nonlocality in diagonal symmetric states of N qubits
NASA Astrophysics Data System (ADS)
Quesada, Ruben; Rana, Swapan; Sanpera, Anna
2017-04-01
We analyze entanglement and nonlocal properties of the convex set of symmetric N -qubit states which are diagonal in the Dicke basis. First, we demonstrate that within this set, semidefinite positivity of partial transposition (PPT) is necessary and sufficient for separability—which has also been reported recently by Yu [Phys. Rev. A 94, 060101(R) (2016), 10.1103/PhysRevA.94.060101]. Furthermore, we show which states among the entangled diagonal symmetric are nonlocal under two-body Bell inequalities. The diagonal symmetric convex set contains a simple and extended family of states that violate the weak Peres conjecture, being PPT with respect to one partition but violating a Bell inequality in such partition. Our method opens directions to address entanglement and nonlocality on higher dimensional symmetric states, where presently very few results are available.
Multimode entanglement in reconfigurable graph states using optical frequency combs
Cai, Y.; Roslund, J.; Ferrini, G.; Arzani, F.; Xu, X.; Fabre, C.; Treps, N.
2017-01-01
Multimode entanglement is an essential resource for quantum information processing and quantum metrology. However, multimode entangled states are generally constructed by targeting a specific graph configuration. This yields to a fixed experimental setup that therefore exhibits reduced versatility and scalability. Here we demonstrate an optical on-demand, reconfigurable multimode entangled state, using an intrinsically multimode quantum resource and a homodyne detection apparatus. Without altering either the initial squeezing source or experimental architecture, we realize the construction of thirteen cluster states of various sizes and connectivities as well as the implementation of a secret sharing protocol. In particular, this system enables the interrogation of quantum correlations and fluctuations for any multimode Gaussian state. This initiates an avenue for implementing on-demand quantum information processing by only adapting the measurement process and not the experimental layout. PMID:28585530
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)
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
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.
Rapid Adiabatic Preparation of Injective Projected Entangled Pair States and Gibbs States
NASA Astrophysics Data System (ADS)
Ge, Yimin; Molnár, András; Cirac, J. Ignacio
2016-02-01
We propose a quantum algorithm for many-body state preparation. It is especially suited for injective projected entangled pair states and thermal states of local commuting Hamiltonians on a lattice. We show that for a uniform gap and sufficiently smooth paths, an adiabatic runtime and circuit depth of O (polylog N ) can be achieved for O (N ) spins. This is an almost exponential improvement over previous bounds. The total number of elementary gates scales as O (N p o l y l o g N ) . This is also faster than the best known upper bound of O (N2) on the mixing times of Monte Carlo Markov chain algorithms for sampling classical systems in thermal equilibrium.
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.
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.
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.
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.
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.
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.
Preparation of a class of multiatom entangled states
Xia Yan; Song Jie; Song Heshan; Zhu Aidong; Jin Zhe; Zhang Shou
2009-08-15
We propose a protocol to generate a class of entangled states of N{sup '} {Lambda}-type three-level atoms trapped in distant cavities by using interference of polarized photons. The proposed setup involves simple linear optical elements, cavities, and the conventional photon detectors that only distinguish the vacuum and the nonvacuum Fock number states.
NASA Astrophysics Data System (ADS)
Wang, Meiyu; Yan, Fengli; Gao, Ting
2017-08-01
We present a new scheme to provide an arbitrary four-photon polarization-entangled state, which enables the encoding of single logical qubit information into a four-qubit decoherence-free subspace robustly against collective decoherence. With the assistance of the cross-Kerr nonlinearities, a spatial entanglement gate and a polarization entanglement gate are inserted into the circuit, where the X-quadrature homodyne measurement is properly performed. According to the outcomes of homodyne measurement in the spatial entanglement process, some swap gates are inserted into the corresponding paths of the photons to swap their spatial modes. Apart from Kerr media, some basic linear optical elements are necessary, which make it feasible with current experimental techniques.
Generation of higher dimensional entangled states in quantum Rabi systems
NASA Astrophysics Data System (ADS)
Albarrán-Arriagada, F.; Alvarado Barrios, G.; Cárdenas-López, F. A.; Romero, G.; Retamal, J. C.
2017-05-01
We present protocols for the generation of high-dimensional entangled states of anharmonic oscillators by means of coherent manipulation of light-matter systems in the ultrastrong coupling regime. Our protocols consider a pair of ultrastrong coupled qubit-cavity systems, each coupled to an ancilla qubit, and combine classical pulses plus the selection rules imposed by the parity symmetry. We study the robustness of the entangling protocols under dissipative effects. This proposal may have applications within state-of-art circuit quantum electrodynamics.
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.
Quantum communication network utilizing quadripartite entangled states of optical field
Shen Heng; Su Xiaolong; Jia Xiaojun; Xie Changde
2009-10-15
We propose two types of quantum dense coding communication networks with optical continuous variables, in which a quadripartite entangled state of the optical field with totally three-party correlations of quadrature amplitudes is utilized. In the networks, the exchange of information between any two participants can be manipulated by one or two of the remaining participants. The channel capacities for a variety of communication protocols are numerically calculated. Due to the fact that the quadripartite entangled states applied in the communication systems have been successfully prepared already in the laboratory, the proposed schemes are experimentally accessible at present.
Generation of Vibrational Entangled Coherent States of Two Trapped Ions
NASA Astrophysics Data System (ADS)
Lin, Li-Hua; Jiang, Yun-Kun; Yang, Zhen-Biao; Ye, Sai-Yun
2005-10-01
We propose a scheme for the generation of entangled coherent states for the center-of-mass and relative vibrational modes of two trapped ions. In the scheme the ions are simultaneously illuminated by a single standing-wave laser tuned to the carrier. The scheme allows the production of an entangled coherent states with a considerably high speed as long as a laser field of sufficiently high intensity is available. The project supported by National Natural Science Foundation of China under Grant No. 10225421 and the Funds from Fuzhou University
Tripartite Controlled Teleportation via a Seven-Qubit Entangled State
NASA Astrophysics Data System (ADS)
Nie, Yi-you; Sang, Ming-huang; Li, Song-song
2017-07-01
We demonstrate that a seven-qubit entangled state can be used to realize the deterministic tripartite controlled teleportation by performing Bell-state measurements, where Alice wants to teleport an arbitrary single-qubit state of qubit a to Bob, Charlie wants to teleport an arbitrary single-qubit state of qubit b to David and at the same time Edison wants to teleport an arbitrary single-qubit state of qubit c to Ford via the control of the supervisor Tom.
Tripartite Controlled Teleportation via a Seven-Qubit Entangled State
NASA Astrophysics Data System (ADS)
Nie, Yi-you; Sang, Ming-huang; Li, Song-song
2017-09-01
We demonstrate that a seven-qubit entangled state can be used to realize the deterministic tripartite controlled teleportation by performing Bell-state measurements, where Alice wants to teleport an arbitrary single-qubit state of qubit a to Bob, Charlie wants to teleport an arbitrary single-qubit state of qubit b to David and at the same time Edison wants to teleport an arbitrary single-qubit state of qubit c to Ford via the control of the supervisor Tom.
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.
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.
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.
Interference and complementarity for two-photon hybrid entangled states
Nogueira, W. A. T.; Santibanez, M.; Delgado, A.; Saavedra, C.; Neves, L.; Lima, G.; Padua, S.
2010-10-15
In this work we generate two-photon hybrid entangled states (HESs), where the polarization of one photon is entangled with the transverse spatial degree of freedom of the second photon. The photon pair is created by parametric down-conversion in a polarization-entangled state. A birefringent double-slit couples the polarization and spatial degrees of freedom of these photons, and finally, suitable spatial and polarization projections generate the HES. We investigate some interesting aspects of the two-photon hybrid interference and present this study in the context of the complementarity relation that exists between the visibility of the one-photon and that of the two-photon interference patterns.
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.
Entanglement-Assisted Transformations of W-Type States
NASA Astrophysics Data System (ADS)
Xiao, Jiayang; Chitambar, Eric
2015-03-01
In multipartite systems, it is usually impossible to transform one entangled state into another via local operations and classical communication (LOCC). However, the transformation may become possible with the help of some extra entanglement. This kind of transformation is called entanglement-assisted LOCC (eLOCC). Beyond the bipartite setting, very little is known about eLOCC. We prove the optimal eLOCC probability for transforming a tripartite W-type state (√{x1} { 100 } +√{x2} { 010 } +√{x3} { 001 }) into a GHZ state √{ 1 / 2 } ({ 000 } + { 111 }) when any two of the parties share a resource EPR state. Interestingly, this is the same optimal probability of converting the given state into an EPR pair with no entanglement resource. Finally, we consider the eLOCC transformation of a more general W-type state (√{x0} { 000 } +√{x1} { 100 } +√{x2} { 010 } +√{x3} { 001 }) into GHZ and compare this with EPR distillation rates for a variety of different protocols.
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.
Coherent control of multipartite entanglement
NASA Astrophysics Data System (ADS)
Hashemi Rafsanjani, Seyed Mohammad; Eberly, Joseph H.
2015-01-01
Quantum entanglement between an arbitrary number of remote qubits is examined analytically. We show that there is a nonprobabilistic way to address in one context the management of entanglement of an arbitrary number of mixed-state qubits by engaging quantitative measures of entanglement and a specific external control mechanism. Both all-party entanglement and weak inseparability are considered. We show that for N ≥4 , the death of all-party entanglement is permanent after an initial collapse. In contrast, weak inseparability can be deterministically managed for an arbitrarily large number of qubits almost indefinitely. Our result suggests a picture of the path that the system traverses in the Hilbert space.
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.
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
2016-04-18
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.
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
Quantum Private Comparison Based on χ-Type Entangled States
NASA Astrophysics Data System (ADS)
Hong-Ming, Pan
2017-08-01
A two-party quantum private comparison (QPC) protocol is constructed with χ-type entangled states in this paper. The proposed protocol employs a semi-honest third party (TP) that is allowed to misbehave on his own but cannot conspire with the adversary. The proposed protocol need perform Bell basis measurements and single-particle measurements but neither unitary operations nor quantum entanglement swapping technology. The proposed protocol possesses good security toward both the outside attack and the participant attack. TP only knows the comparison result of the private information from two parties in the proposed protocol.
Quantum Private Comparison Based on χ-Type Entangled States
NASA Astrophysics Data System (ADS)
Hong-Ming, Pan
2017-10-01
A two-party quantum private comparison (QPC) protocol is constructed with χ-type entangled states in this paper. The proposed protocol employs a semi-honest third party (TP) that is allowed to misbehave on his own but cannot conspire with the adversary. The proposed protocol need perform Bell basis measurements and single-particle measurements but neither unitary operations nor quantum entanglement swapping technology. The proposed protocol possesses good security toward both the outside attack and the participant attack. TP only knows the comparison result of the private information from two parties in the proposed protocol.
Generating and probing entangled states for optical atomic clocks
NASA Astrophysics Data System (ADS)
Braverman, Boris; Kawasaki, Akio; Vuletic, Vladan
2016-05-01
The precision of quantum measurements is inherently limited by projection noise caused by the measurement process itself. Spin squeezing and more complex forms of entanglement have been proposed as ways of surpassing this limitation. In our system, a high-finesse asymmetric micromirror-based optical cavity can mediate the atom-atom interaction necessary for generating entanglement in an 171 Yb optical lattice clock. I will discuss approaches for creating, characterizing, and optimally utilizing these nonclassical states for precision measurement, as well as recent progress toward their realization. This research is supported by DARPA QuASAR, NSF, and NSERC.
Maximally entangled states in a Bose-Hubbard trimer
NASA Astrophysics Data System (ADS)
Reyes, Sebastian; Morales-Molina, Luis; Orszag, Miguel
2014-03-01
We study the generation of entanglement for interacting cold atoms in a three-site Bose-Hubbard ring. We propose a scheme by which maximally entangled states (MES) between two distinct atomic species can be prepared. Depending on the choice of experimental parameters, we demonstrate that it is possible to obtain different types of MES. Furthermore, we show that these MES are highly protected against experimental noise, making them good candidates for potential applications. S. R. acknowledges the support of FONDECYT grant 11110537.
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.
Optimal dense coding with arbitrary pure entangled states
Feng, Yuan; Duan, Runyao; Ji, Zhengfeng
2006-07-15
We examine dense coding with an arbitrary pure entangled state sharing between the sender and the receiver. Upper bounds on the average success probability in approximate dense coding and on the probability of conclusive results in unambiguous dense coding are derived. We also construct the optimal protocol which saturates the upper bound in each case.
Entanglement of Spin States in 15N@C60
NASA Astrophysics Data System (ADS)
Scherer, W.; Weidinger, A.; Mehring, M.
2004-09-01
The endohedral fullerene 15N@C60 comprises an electron spin S = 3/2 coupled to a nuclear spin I = 1/2 and is therefore ideally suited for experimental testing of basic properties of quantum mechanics. We will show that the 15N@C60 molecule represents a multi qubit system where different kinds of entangled states can be generated.
Absolutely Maximally Entangled States of Seven Qubits Do Not Exist.
Huber, Felix; Gühne, Otfried; Siewert, Jens
2017-05-19
Pure multiparticle quantum states are called absolutely maximally entangled if all reduced states obtained by tracing out at least half of the particles are maximally mixed. We provide a method to characterize these states for a general multiparticle system. With that, we prove that a seven-qubit state whose three-body marginals are all maximally mixed, or equivalently, a pure ((7,1,4))_{2} quantum error correcting code, does not exist. Furthermore, we obtain an upper limit on the possible number of maximally mixed three-body marginals and identify the state saturating the bound. This solves the seven-particle problem as the last open case concerning maximally entangled states of qubits.
Absolutely Maximally Entangled States of Seven Qubits Do Not Exist
NASA Astrophysics Data System (ADS)
Huber, Felix; Gühne, Otfried; Siewert, Jens
2017-05-01
Pure multiparticle quantum states are called absolutely maximally entangled if all reduced states obtained by tracing out at least half of the particles are maximally mixed. We provide a method to characterize these states for a general multiparticle system. With that, we prove that a seven-qubit state whose three-body marginals are all maximally mixed, or equivalently, a pure (7,1,4)2 quantum error correcting code, does not exist. Furthermore, we obtain an upper limit on the possible number of maximally mixed three-body marginals and identify the state saturating the bound. This solves the seven-particle problem as the last open case concerning maximally entangled states of qubits.
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.
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.
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.
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.
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.
All pure bipartite entangled states can be self-tested
NASA Astrophysics Data System (ADS)
Coladangelo, Andrea; Goh, Koon Tong; Scarani, Valerio
2017-05-01
Quantum technologies promise advantages over their classical counterparts in the fields of computation, security and sensing. It is thus desirable that classical users are able to obtain guarantees on quantum devices, even without any knowledge of their inner workings. That such classical certification is possible at all is remarkable: it is a consequence of the violation of Bell inequalities by entangled quantum systems. Device-independent self-testing refers to the most complete such certification: it enables a classical user to uniquely identify the quantum state shared by uncharacterized devices by simply inspecting the correlations of measurement outcomes. Self-testing was first demonstrated for the singlet state and a few other examples of self-testable states were reported in recent years. Here, we address the long-standing open question of whether every pure bipartite entangled state is self-testable. We answer it affirmatively by providing explicit self-testing correlations for all such states.
Speedup of quantum evolution of multiqubit entanglement states.
Zhang, Ying-Jie; Han, Wei; Xia, Yun-Jie; Tian, Jian-Xiang; Fan, Heng
2016-06-10
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.
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.
Generic preparation and entanglement detection of equal superposition states
NASA Astrophysics Data System (ADS)
Yu, Qi; Zhang, YanBao; Li, Jun; Wang, HengYan; Peng, XinHua; Du, JiangFeng
2017-07-01
Quantum superposition is a fundamental principle of quantum mechanics, so it is not surprising that equal superposition states (ESS) serve as powerful resources for quantum information processing. In this work, we propose a quantum circuit that creates an arbitrary dimensional ESS. The circuit construction is efficient as the number of required elementary gates scales polynomially with the number of required qubits. For experimental realization of the method, we use techniques of nuclear magnetic resonance (NMR).We have succeeded in preparing a 9-dimensional ESS on a 4-qubit NMR quantum register. The full tomography indicates that the fidelity of our prepared state with respect to the ideal 9-dimensional ESS is over 96%. We also prove the prepared state is pseudo-entangled by directly measuring an entanglement witness operator. Our result can be useful for the implementation of those quantum algorithms that require an ESS as an input state.
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
The maximally entangled set of 4-qubit states
Spee, C.; Kraus, B.; Vicente, J. I. de
2016-05-15
Entanglement is a resource to overcome the natural restriction of operations used for state manipulation to Local Operations assisted by Classical Communication (LOCC). Hence, a bipartite maximally entangled state is a state which can be transformed deterministically into any other state via LOCC. In the multipartite setting no such state exists. There, rather a whole set, the Maximally Entangled Set of states (MES), which we recently introduced, is required. This set has on the one hand the property that any state outside of this set can be obtained via LOCC from one of the states within the set and on the other hand, no state in the set can be obtained from any other state via LOCC. Recently, we studied LOCC transformations among pure multipartite states and derived the MES for three and generic four qubit states. Here, we consider the non-generic four qubit states and analyze their properties regarding local transformations. As already the most coarse grained classification, due to Stochastic LOCC (SLOCC), of four qubit states is much richer than in case of three qubits, the investigation of possible LOCC transformations is correspondingly more difficult. We prove that most SLOCC classes show a similar behavior as the generic states, however we also identify here three classes with very distinct properties. The first consists of the GHZ and W class, where any state can be transformed into some other state non-trivially. In particular, there exists no isolation. On the other hand, there also exist classes where all states are isolated. Last but not least we identify an additional class of states, whose transformation properties differ drastically from all the other classes. Although the possibility of transforming states into local-unitary inequivalent states by LOCC turns out to be very rare, we identify those states (with exception of the latter class) which are in the MES and those, which can be obtained (transformed) non-trivially from (into) other states
The maximally entangled set of 4-qubit states
NASA Astrophysics Data System (ADS)
Spee, C.; de Vicente, J. I.; Kraus, B.
2016-05-01
Entanglement is a resource to overcome the natural restriction of operations used for state manipulation to Local Operations assisted by Classical Communication (LOCC). Hence, a bipartite maximally entangled state is a state which can be transformed deterministically into any other state via LOCC. In the multipartite setting no such state exists. There, rather a whole set, the Maximally Entangled Set of states (MES), which we recently introduced, is required. This set has on the one hand the property that any state outside of this set can be obtained via LOCC from one of the states within the set and on the other hand, no state in the set can be obtained from any other state via LOCC. Recently, we studied LOCC transformations among pure multipartite states and derived the MES for three and generic four qubit states. Here, we consider the non-generic four qubit states and analyze their properties regarding local transformations. As already the most coarse grained classification, due to Stochastic LOCC (SLOCC), of four qubit states is much richer than in case of three qubits, the investigation of possible LOCC transformations is correspondingly more difficult. We prove that most SLOCC classes show a similar behavior as the generic states, however we also identify here three classes with very distinct properties. The first consists of the GHZ and W class, where any state can be transformed into some other state non-trivially. In particular, there exists no isolation. On the other hand, there also exist classes where all states are isolated. Last but not least we identify an additional class of states, whose transformation properties differ drastically from all the other classes. Although the possibility of transforming states into local-unitary inequivalent states by LOCC turns out to be very rare, we identify those states (with exception of the latter class) which are in the MES and those, which can be obtained (transformed) non-trivially from (into) other 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.
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.
Teleportation of the three-level three-particle entangled state and classical communication cost
NASA Astrophysics Data System (ADS)
Dai, Hong-Yi; Zhang, Ming; Kuang, Le-Man
2008-06-01
We propose a scheme to probabilistically teleport an unknown three-level three-particle entangled state. The quantum channel is composed of a partial entangled three-level two-particle state and a partial entangled three-level three-particle state. We calculate the successful total probability and the classical communication cost required in the ideal probabilistic teleportation process, respectively. It is shown that an unknown three-level three-particle entangled state can be teleported using fewer entangled particles and lesser classical communication cost than Bennett et al.’s original protocol.
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.
Duality and the geometric measure of entanglement of general multiqubit W states
NASA Astrophysics Data System (ADS)
Tamaryan, Sayatnova; Sudbery, Anthony; Tamaryan, Levon
2010-05-01
We find the nearest product states for arbitrary generalized W states of n qubits, and show that the nearest product state is essentially unique if the W state is highly entangled. It is specified by a unit vector in Euclidean n-dimensional space. We use this duality between unit vectors and highly entangled W states to find the geometric measure of entanglement of such states.
NASA Astrophysics Data System (ADS)
Liu, Zhi-Hao; Chen, Han-Wu
2017-09-01
The novel quantum dialogue (QD) protocol by using the three-dimensional Bell states and entanglement swapping (Wang et al. in Quantum Inf Process 15(6):2593-2603, 2016) is analyzed. It is shown that there is the information leakage problem in this QD protocol. To be specific, one quarter information of the secret messages exchanged is leaked out unconsciously. Afterward, it is improved to a truly secure one without information leakage. Besides, the security of the improved QD protocol is analyzed in detail. It is shown that the improved QD protocol has some obvious features compared with the original one.
Direct measurement of nonlocal entanglement of two-qubit spin quantum states.
Cheng, Liu-Yong; Yang, Guo-Hui; Guo, Qi; Wang, Hong-Fu; Zhang, Shou
2016-01-18
We propose efficient schemes of direct concurrence measurement for two-qubit spin and photon-polarization entangled states via the interaction between single-photon pulses and nitrogen-vacancy (NV) centers in diamond embedded in optical microcavities. For different entangled-state types, diversified quantum devices and operations are designed accordingly. The initial unknown entangled states are possessed by two spatially separated participants, and nonlocal spin (polarization) entanglement can be measured with the aid of detection probabilities of photon (NV center) states. This non-demolition entanglement measurement manner makes initial entangled particle-pair avoid complete annihilation but evolve into corresponding maximally entangled states. Moreover, joint inter-qubit operation or global qubit readout is not required for the presented schemes and the final analyses inform favorable performance under the current parameters conditions in laboratory. The unique advantages of spin qubits assure our schemes wide potential applications in spin-based solid quantum information and computation.
Direct measurement of nonlocal entanglement of two-qubit spin quantum states
NASA Astrophysics Data System (ADS)
Cheng, Liu-Yong; Yang, Guo-Hui; Guo, Qi; Wang, Hong-Fu; Zhang, Shou
2016-01-01
We propose efficient schemes of direct concurrence measurement for two-qubit spin and photon-polarization entangled states via the interaction between single-photon pulses and nitrogen-vacancy (NV) centers in diamond embedded in optical microcavities. For different entangled-state types, diversified quantum devices and operations are designed accordingly. The initial unknown entangled states are possessed by two spatially separated participants, and nonlocal spin (polarization) entanglement can be measured with the aid of detection probabilities of photon (NV center) states. This non-demolition entanglement measurement manner makes initial entangled particle-pair avoid complete annihilation but evolve into corresponding maximally entangled states. Moreover, joint inter-qubit operation or global qubit readout is not required for the presented schemes and the final analyses inform favorable performance under the current parameters conditions in laboratory. The unique advantages of spin qubits assure our schemes wide potential applications in spin-based solid quantum information and computation.
The entangled triplet pair state in acene and heteroacene materials
Yong, Chaw Keong; Musser, Andrew J.; Bayliss, Sam L.; Lukman, Steven; Tamura, Hiroyuki; Bubnova, Olga; Hallani, Rawad K.; Meneau, Aurélie; Resel, Roland; Maruyama, Munetaka; Hotta, Shu; Herz, Laura M.; Beljonne, David; Anthony, John E.; Clark, Jenny; Sirringhaus, Henning
2017-01-01
Entanglement of states is one of the most surprising and counter-intuitive consequences of quantum mechanics, with potent applications in cryptography and computing. In organic materials, one particularly significant manifestation is the spin-entangled triplet-pair state, which mediates the spin-conserving fission of one spin-0 singlet exciton into two spin-1 triplet excitons. Despite long theoretical and experimental exploration, the nature of the triplet-pair state and inter-triplet interactions have proved elusive. Here we use a range of organic semiconductors that undergo singlet exciton fission to reveal the photophysical properties of entangled triplet-pair states. We find that the triplet pair is bound with respect to free triplets with an energy that is largely material independent (∼30 meV). During its lifetime, the component triplets behave cooperatively as a singlet and emit light through a Herzberg–Teller-type mechanism, resulting in vibronically structured photoluminescence. In photovoltaic blends, charge transfer can occur from the bound triplet pairs with >100% photon-to-charge conversion efficiency. PMID:28699637
The entangled triplet pair state in acene and heteroacene materials
NASA Astrophysics Data System (ADS)
Yong, Chaw Keong; Musser, Andrew J.; Bayliss, Sam L.; Lukman, Steven; Tamura, Hiroyuki; Bubnova, Olga; Hallani, Rawad K.; Meneau, Aurélie; Resel, Roland; Maruyama, Munetaka; Hotta, Shu; Herz, Laura M.; Beljonne, David; Anthony, John E.; Clark, Jenny; Sirringhaus, Henning
2017-07-01
Entanglement of states is one of the most surprising and counter-intuitive consequences of quantum mechanics, with potent applications in cryptography and computing. In organic materials, one particularly significant manifestation is the spin-entangled triplet-pair state, which mediates the spin-conserving fission of one spin-0 singlet exciton into two spin-1 triplet excitons. Despite long theoretical and experimental exploration, the nature of the triplet-pair state and inter-triplet interactions have proved elusive. Here we use a range of organic semiconductors that undergo singlet exciton fission to reveal the photophysical properties of entangled triplet-pair states. We find that the triplet pair is bound with respect to free triplets with an energy that is largely material independent (~30 meV). During its lifetime, the component triplets behave cooperatively as a singlet and emit light through a Herzberg-Teller-type mechanism, resulting in vibronically structured photoluminescence. In photovoltaic blends, charge transfer can occur from the bound triplet pairs with >100% photon-to-charge conversion efficiency.
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.
Tripartite entangled plaquette state in a cluster magnet
NASA Astrophysics Data System (ADS)
Carrasquilla, Juan; Chen, Gang; Melko, Roger G.
2017-08-01
Using large-scale quantum Monte Carlo simulations we show that a spin-1/2 X X Z model on a two-dimensional anisotropic kagome lattice exhibits a tripartite entangled plaquette state that preserves all of the Hamiltonian symmetries. It is connected via phase boundaries to a ferromagnet and a valence-bond solid that break U (1 ) and lattice translation symmetries, respectively. We study the phase diagram of the model in detail, in particular the transitions to the tripartite entangled plaquette state, which are consistent with conventional order-disorder transitions. Our results can be interpreted as a description of the charge sector dynamics of a Hubbard model applied to the spin liquid candidate LiZn2Mo3O8 , as well as a model of strongly correlated bosonic atoms loaded onto highly tunable trimerized optical kagome lattices.
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.
Chiral projected entangled-pair state with topological order.
Yang, Shuo; Wahl, Thorsten B; Tu, Hong-Hao; Schuch, Norbert; Cirac, J Ignacio
2015-03-13
We show that projected entangled-pair states (PEPS) can describe chiral topologically ordered phases. For that, we construct a simple PEPS for spin-1/2 particles in a two-dimensional lattice. We reveal a symmetry in the local projector of the PEPS that gives rise to the global topological character. We also extract characteristic quantities of the edge conformal field theory using the bulk-boundary correspondence.
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.
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
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.
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.
Hofmann, Holger F.; Ono, Takafumi
2007-09-15
We show that the quantum interference between down-converted photon pairs and photons from coherent laser light can produce a maximally path entangled N-photon output component with a fidelity greater than 90% for arbitrarily high photon numbers. A simple beam splitter operation can thus transform the two-photon coherence of down-converted light into an almost optimal N-photon coherence.
NASA Astrophysics Data System (ADS)
Zhan, You-Bang; Zhang, Qun-Yong; Wang, Yu-Wu; Ma, Peng-Cheng
2010-01-01
We propose a scheme to teleport an unknown single-qubit state by using a high-dimensional entangled state as the quantum channel. As a special case, a scheme for teleportation of an unknown single-qubit state via three-dimensional entangled state is investigated in detail. Also, this scheme can be directly generalized to an unknown f-dimensional state by using a d-dimensional entangled state (d > f) as the quantum channel.
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.
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
NASA Astrophysics Data System (ADS)
Mičuda, M.; Koutný, D.; Miková, M.; Straka, I.; Ježek, M.; Mišta, L.
2017-03-01
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.
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.
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.
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.
A Powerful Source of Entangled States of Light
Gorbachev, V.N.; Kazakov, A.Ya.; Trubilko, A.I.
2005-08-15
The simultaneous interaction of N two-level atoms with a quasi-resonant classical field and two quantized modes is considered under the assumption that the Rabi parameter of the classical mode substantially exceeds the effective Rabi parameters of the quantized modes. It is shown that, in a certain domain of the parameters, the population of the quantized modes exponentially depends on time and the number N. At certain instants of time, the states of the quantized modes prove to be close to the totally entangled state.
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.
Family of Bell inequalities violated by higher-dimensional bound entangled states
NASA Astrophysics Data System (ADS)
Pál, Károly F.; Vértesi, Tamás
2017-08-01
We construct (d ×d )-dimensional bound entangled states, which violate, for any d >2 , a bipartite Bell inequality introduced in this paper. We conjecture that the proposed class of Bell inequalities acts as a dimension witness for bound entangled states: For any d >2 there exists a Bell inequality from this class that can be violated with bound entangled states only if their Hilbert space dimension is at least d ×d . Numerics supports this conjecture up to d =8 .
Construction of the Superposition of Displaced Fock States and Entangled Displaced Fock States
NASA Astrophysics Data System (ADS)
Karimi, Amir
2017-09-01
In this paper, at first we will construct the superposition of two displaced Fock states and two-mode entangled displaced Fock states mathematically by presenting theoretical methods. In these methods, we will introduce new operators using the parity and displacement operators. It will be observed that the superposition of two displaced Fock states and two-mode entangled displaced Fock states are constructed via the action of the introduced operators on one-mode and two-mode Fock states, respectively. Next, we will show that the presented methods have the potential ability to produce the superposition consist of more than two displaced Fock states and multi-mode entangled displaced Fock states, too.
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
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.
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.
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.
Channel kets, entangled states, and the location of quantum information
Griffiths, Robert B.
2005-04-01
The well-known duality relating entangled states and noisy quantum channels is expressed in terms of a channel ket, a pure state on a suitable tripartite system, which functions as a pre-probability allowing the calculation of statistical correlations between, for example, the entrance and exit of a channel, once a framework has been chosen so as to allow a consistent set of probabilities. In each framework the standard notions of ordinary (classical) information theory apply, and it makes sense to ask whether information of a particular sort about one system is or is not present in another system. Quantum effects arise when a single pre-probability is used to compute statistical correlations in different incompatible frameworks, and various constraints on the presence and absence of different kinds of information are expressed in a set of all-or-nothing theorems which generalize or give a precise meaning to the concept of 'no-cloning'. These theorems are used to discuss the location of information in quantum channels modeled using a mixed-state environment, the classical-quantum channels introduced by Holevo, and the location of information in the physical carriers of a quantum code. It is proposed that both channel and entanglement problems be classified in terms of pure states (functioning as pre-probabilities) on systems of p{>=}2 parts, with mixed bipartite entanglement and simple noisy channels belonging to the category p=3, a five-qubit code to the category p=6, etc., then by the dimensions of the Hilbert spaces of the component parts, along with other criteria yet to be determined.
Channel kets, entangled states, and the location of quantum information
NASA Astrophysics Data System (ADS)
Griffiths, Robert B.
2005-04-01
The well-known duality relating entangled states and noisy quantum channels is expressed in terms of a channel ket, a pure state on a suitable tripartite system, which functions as a pre-probability allowing the calculation of statistical correlations between, for example, the entrance and exit of a channel, once a framework has been chosen so as to allow a consistent set of probabilities. In each framework the standard notions of ordinary (classical) information theory apply, and it makes sense to ask whether information of a particular sort about one system is or is not present in another system. Quantum effects arise when a single pre-probability is used to compute statistical correlations in different incompatible frameworks, and various constraints on the presence and absence of different kinds of information are expressed in a set of all-or-nothing theorems which generalize or give a precise meaning to the concept of “no-cloning.” These theorems are used to discuss the location of information in quantum channels modeled using a mixed-state environment, the classical-quantum channels introduced by Holevo, and the location of information in the physical carriers of a quantum code. It is proposed that both channel and entanglement problems be classified in terms of pure states (functioning as pre-probabilities) on systems of p⩾2 parts, with mixed bipartite entanglement and simple noisy channels belonging to the category p=3 , a five-qubit code to the category p=6 , etc., then by the dimensions of the Hilbert spaces of the component parts, along with other criteria yet to be determined.
Experimental generation of tripartite polarization entangled states of bright optical beams
Wu, Liang; Liu, Yanhong; Deng, Ruijie; Yan, Zhihui; Jia, Xiaojun Xie, Changde; Peng, Kunchi
2016-04-18
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.
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.
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.
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.
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.
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.
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.
Chiral projected entangled-pair state with topological order
NASA Astrophysics Data System (ADS)
Yang, Shuo; Wahl, Thorsten; Tu, Hong-Hao; Schuch, Norbert; Cirac, J. Ignacio
We show that projected entangled-pair states (PEPS) can describe chiral topologically ordered phases. For that, we construct a simple PEPS for spin-1/2 particles in a two-dimensional lattice. We reveal a symmetry in the local projector of the PEPS that gives rise to the global topological character. We also extract characteristic quantities of the edge conformal field theory using the bulk-boundary correspondence. EU projects SIQS and QALGO, the Alexander von Humboldt foundation, the Government of Canada through Industry Canada, and the Province of Ontario through the Ministry of Economic Development & Innovation.
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.
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.
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.
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.
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.
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.
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
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.
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.
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).
Entanglement of two movable mirrors with a single photon superposition state
NASA Astrophysics Data System (ADS)
Ge, Wenchao; Zubairy, M. Suhail
2015-06-01
We propose a simple scheme to generate deterministic entanglement between two movable end mirrors in a Fabry-Perot cavity using a single photon superposition state. We derive analytically the expressions of the generated entangled states and the degree of entanglement for each state. We show that strong entanglement can be obtained either in the single-photon strong coupling regime deterministically or in the single-photon weak coupling regime conditionally. We extend our heartiest congratulations to Margarita and Vladimir Man'ko of a magnificent 150 years and dedicate this article to them.
Teleportation of entangled states without Bell-state measurement via a two-photon process
NASA Astrophysics Data System (ADS)
dSouza, A. D.; Cardoso, W. B.; Avelar, A. T.; Baseia, B.
2011-02-01
In this letter we propose a scheme using a two-photon process to teleport an entangled field state of a bimodal cavity to another one without Bell-state measurement. The quantum information is stored in a zero- and two-photon entangled state. This scheme requires two three-level atoms in a ladder configuration, two bimodal cavities, and selective atomic detectors. The fidelity and success probability do not depend on the coefficients of the state to be teleported. For convenient choices of interaction times, the teleportation occurs with fidelity close to the unity.
Quantum entanglement between an optical photon and a solid-state spin qubit.
Togan, E; Chu, Y; Trifonov, A S; Jiang, L; Maze, J; Childress, L; Dutt, M V G; Sørensen, A S; Hemmer, P R; Zibrov, A S; Lukin, M D
2010-08-05
Quantum entanglement is among the most fascinating aspects of quantum theory. Entangled optical photons are now widely used for fundamental tests of quantum mechanics and applications such as quantum cryptography. Several recent experiments demonstrated entanglement of optical photons with trapped ions, atoms and atomic ensembles, which are then used to connect remote long-term memory nodes in distributed quantum networks. Here we realize quantum entanglement between the polarization of a single optical photon and a solid-state qubit associated with the single electronic spin of a nitrogen vacancy centre in diamond. Our experimental entanglement verification uses the quantum eraser technique, and demonstrates that a high degree of control over interactions between a solid-state qubit and the quantum light field can be achieved. The reported entanglement source can be used in studies of fundamental quantum phenomena and provides a key building block for the solid-state realization of quantum optical networks.
Gradient optimization of finite projected entangled pair states
NASA Astrophysics Data System (ADS)
Liu, Wen-Yuan; Dong, Shao-Jun; Han, Yong-Jian; Guo, Guang-Can; He, Lixin
2017-05-01
Projected entangled pair states (PEPS) methods have been proven to be powerful tools to solve strongly correlated quantum many-body problems in two dimensions. However, due to the high computational scaling with the virtual bond dimension D , in a practical application, PEPS are often limited to rather small bond dimensions, which may not be large enough for some highly entangled systems, for instance, frustrated systems. Optimization of the ground state using the imaginary time evolution method with a simple update scheme may go to a larger bond dimension. However, the accuracy of the rough approximation to the environment of the local tensors is questionable. Here, we demonstrate that by combining the imaginary time evolution method with a simple update, Monte Carlo sampling techniques and gradient optimization will offer an efficient method to calculate the PEPS ground state. By taking advantage of massive parallel computing, we can study quantum systems with larger bond dimensions up to D =10 without resorting to any symmetry. Benchmark tests of the method on the J1-J2 model give impressive accuracy compared with exact results.
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.
Smallest state spaces for which bipartite entangled quantum states are separable
NASA Astrophysics Data System (ADS)
Anwar, Hussain; Jevtic, Sania; Rudolph, Oliver; Virmani, Shashank
2015-09-01
According to usual definitions, entangled states cannot be given a separable decomposition in terms of products of local density operators. If we relax the requirement that the local operators be positive, then an entangled quantum state may admit a separable decomposition in terms of more general sets of single-system operators. This form of separability can be used to construct classical models and simulation methods when only a restricted set of measurements is available. With these motivations in mind, we ask what are the smallest sets of local operators such that a pure bipartite entangled quantum state becomes separable? We find that in the case of maximally entangled states there are many inequivalent solutions, including for example the sets of phase point operators that arise in the study of discrete Wigner functions. We therefore provide a new way of interpreting these operators, and more generally, provide an alternative method for constructing local hidden variable models for entangled quantum states under subsets of quantum measurements.
Quantifying entanglement properties of qudit mixed states with incomplete permutation symmetry
NASA Astrophysics Data System (ADS)
Barasiński, Artur; Nowotarski, Mateusz
2017-04-01
The characterization of entanglement properties in mixed states is important from both a theoretical and a practical point of view. While the estimation of entanglement of bipartite pure states is well established, for mixed states it is a considerably much harder task. The key elements of the mixed-state entanglement theory are given by the exact solutions which sometimes are possible for special states of high symmetry problems. In this paper, we present the exact investigation on the entanglement properties for a five-parameter family of highly symmetric two-qudit mixed states with equal but arbitrary finite local Hilbert space dimension. We achieve this by extensive analysis of various conditions of separability and the entanglement classification with respect to stochastic local operations and classical communication. Furthermore, our results can be used for an arbitrary state by proper application of the proposed twirling operator.
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.
Entangled entanglement: A construction procedure
NASA Astrophysics Data System (ADS)
Uchida, Gabriele; Bertlmann, Reinhold A.; Hiesmayr, Beatrix C.
2015-10-01
The familiar Greenberger-Horne-Zeilinger (GHZ) states can be rewritten by entangling the Bell states for two qubits with a third qubit state, which is dubbed entangled entanglement. We show that in a constructive way we obtain all eight independent GHZ states that form the simplex of entangled entanglement, the magic simplex. The construction procedure allows a generalization to higher dimensions both, in the degrees of freedom (considering qudits) as well as in the number of particles (considering n-partite states). Such bases of GHZ-type states exhibit a cyclic geometry, a Merry Go Round, that is relevant for experimental and quantum information theoretic applications.
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.
Simultaneous entanglement swapping of multiple orbital angular momentum states of light.
Zhang, Yingwen; Agnew, Megan; Roger, Thomas; Roux, Filippus S; Konrad, Thomas; Faccio, Daniele; Leach, Jonathan; Forbes, Andrew
2017-09-21
High-bit-rate long-distance quantum communication is a proposed technology for future communication networks and relies on high-dimensional quantum entanglement as a core resource. While it is known that spatial modes of light provide an avenue for high-dimensional entanglement, the ability to transport such quantum states robustly over long distances remains challenging. To overcome this, entanglement swapping may be used to generate remote quantum correlations between particles that have not interacted; this is the core ingredient of a quantum repeater, akin to repeaters in optical fibre networks. Here we demonstrate entanglement swapping of multiple orbital angular momentum states of light. Our approach does not distinguish between different anti-symmetric states, and thus entanglement swapping occurs for several thousand pairs of spatial light modes simultaneously. This work represents the first step towards a quantum network for high-dimensional entangled states and provides a test bed for fundamental tests of quantum science.Entanglement swapping in high dimensions requires large numbers of entangled photons and consequently suffers from low photon flux. Here the authors demonstrate entanglement swapping of multiple spatial modes of light simultaneously, without the need for increasing the photon numbers with dimension.
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.
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.
Entangled states with positive partial transposes arising from indecomposable positive linear maps
NASA Astrophysics Data System (ADS)
Ha, Kil-Chan; Kye, Seung-Hyeok; Park, Young Sung
2003-06-01
We construct entangled states with positive partial transposes using indecomposable positive linear maps between matrix algebras. We also exhibit concrete examples of entangled states with positive partial transposes arising in this way, and show that they generate extreme rays in the cone of all positive semi-definite matrices with positive partial transposes. They also have Schmidt numbers two.
NASA Astrophysics Data System (ADS)
Kunkri, Samir; Choudhary, Sujit K.; Ahanj, Ali; Joag, Pramod
2006-02-01
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.
Generating multi-mode entangled coherent W and GHZ states via optical system based fusion mechanism
NASA Astrophysics Data System (ADS)
Zang, Xue-Ping; Yang, Ming; Wu, Wei-Feng; Fan, Hong-Yi
2017-05-01
Fusion technology has been demonstrated to be a good method for generating a large-scale entangled coherent W or GHZ state from two small ones in QED system. It is of importance to study how to fuse small-scale entangled coherent W or GHZ states via optical system. In this paper, we present a scheme for generating larger entangled coherent W or GHZ state in an optical system by virtue of fusion technology. The key fusion mechanism is realized by photon detectors and a Mach-Zehnder interferometer with its two arms immersed in Kerr media, by which an n-mode entangled coherent W state and an m-mode entangled coherent W state can be probabilistically fused into an (n+m-2)-mode entangled coherent W state. This fusion scheme applies to entangled coherent GHZ state too but with a unit probability of success. Feasibility analysis indicates that our fusion scheme may be realized with current experimental technology. Large-scale entangled coherent W and GHZ states may find new applications in quantum communication.
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.
Steady-state entanglement for distant atoms by dissipation in coupled cavities
Shen Lituo; Chen Xinyu; Wu Huaizhi; Zheng Shibiao; Yang Zhenbiao
2011-12-15
We propose a scheme for the generation of entangled states for two atoms trapped in separate cavities coupled to each other. The scheme is based on the competition between the unitary dynamics induced by the classical fields and the collective decays induced by the dissipation of two delocalized field modes. Under certain conditions, the symmetric or asymmetric entangled state is produced in the steady state. The analytical result shows that the distributed steady entanglement can be achieved with high fidelity independent of the initial state and is robust against parameter fluctuations. We also find out that the linear scaling of entanglement fidelity has a quadratic improvement compared to distributed entangled state preparation protocols based on unitary dynamics.
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.
NASA Astrophysics Data System (ADS)
Xia, Yan; Song, Jie; Song, He-Shan
2008-06-01
We present an explicit protocol for probabilistic teleport an arbitrary and unknown two-qubit entangled state via a one-dimensional four-particle non-maximally entangled cluster state. By construction, our four-partite state is not reducible to a pair of Bell states. We show that teleportation can be successfully realized with a certain probability. This protocol indicate that the four-qubit state is a likely candidate for the genuine four-particle analogue to a Bell state.
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
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)
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)
Gómez, Angela Viviana; Rodríguez, Ferney Javier; Quiroga, Luis; García-Ripoll, Juan José
2016-06-01
Quantum correlations present in a broadband two-line squeezed microwave state can induce entanglement in a spatially separated bipartite system consisting of either two single qubits or two-qubit ensembles. By using an appropriate master equation for a bipartite quantum system in contact with two separate but entangled baths, the generating entanglement process in spatially separated quantum systems is thoroughly characterized. Decoherence thermal effects on the entanglement transfer are also discussed. Our results provide evidence that this entanglement transfer by dissipation is feasible, yielding to a steady-state amount of entanglement in the bipartite quantum system which can be optimized for a wide range of realistic physical systems that include state-of-the-art experiments with nitrogen-vacancy centers in diamond, superconducting qubits, or even magnetic molecules embedded in a crystalline matrix.
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.
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.
NASA Astrophysics Data System (ADS)
Lin, Jason; Hwang, Tzonelih
2013-02-01
This work presents two robust entanglement swappings against two types of collective noises, respectively. The entanglement swapping can be achieved by performing two Bell state measurements on two logical qubits that come from two original logical Bell states, respectively. Two fault tolerant quantum secret sharing (QSS) protocols are further proposed to demonstrate the usefulness of the newly proposed entanglement swappings. The proposed QSS schemes are not only free from Trojan horse attacks but also quite efficient. Moreover, by adopting two Bell state measurements instead of four-qubit joint measurements, the proposed protocols are practical in combating collective noises. The proposed fault tolerant entanglement swapping can also be used to replace the traditional Bell-state entanglement swapping used in various quantum cryptographic protocols to provide robustness in combating collective noises.
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.
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.
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.
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.
NASA Astrophysics Data System (ADS)
Tang, Jing-Wu; Zhao, Guan-Xiang; He, Xiong-Hui
2011-05-01
Recently, Peng et al. [2010 Eur. Phys. J. D 58 403] proposed to teleport an arbitrary two-qubit state with a family of four-qubit entangled states, which simultaneously include the tensor product of two Bell states, linear cluster state and Dicke-class state. This paper proposes to implement their scheme in cavity quantum electrodynamics and then presents a new family of four-qubit entangled state |Ω4>1234. It simultaneously includes all the well-known four-qubit entangled states which can be used to teleport an arbitrary two-qubit state. The distinct advantage of the scheme is that it only needs a single setup to prepare the whole family of four-qubit entangled states, which will be very convenient for experimental realization. After discussing the experimental condition in detail, we show the scheme may be feasible based on present technology in cavity quantum electrodynamics.
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.
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.
NASA Astrophysics Data System (ADS)
Sang, Zhi-wen
2017-07-01
We demonstrate that a seven-particle entangled state can be used to realize the deterministic asymmetric bidirectional controlled remote state preparation. That is to say Alice can remotely prepare an arbitrary known single-particle state for Bob and at the same time Bob can remotely prepare an arbitrary known two-particle state for Alice with the help of the supervisor Charlie. In our scheme, only single-particle projective measurements and two-particle projective measurement are needed.
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.
Quantum metrology. Fisher information and entanglement of non-Gaussian spin states.
Strobel, Helmut; Muessel, Wolfgang; Linnemann, Daniel; Zibold, Tilman; Hume, David B; Pezzè, Luca; Smerzi, Augusto; Oberthaler, Markus K
2014-07-25
Entanglement is the key quantum resource for improving measurement sensitivity beyond classical limits. However, the production of entanglement in mesoscopic atomic systems has been limited to squeezed states, described by Gaussian statistics. Here, we report on the creation and characterization of non-Gaussian many-body entangled states. We develop a general method to extract the Fisher information, which reveals that the quantum dynamics of a classically unstable system creates quantum states that are not spin squeezed but nevertheless entangled. The extracted Fisher information quantifies metrologically useful entanglement, which we confirm by Bayesian phase estimation with sub-shot-noise sensitivity. These methods are scalable to large particle numbers and applicable directly to other quantum systems. Copyright © 2014, American Association for the Advancement of Science.
Protecting Distribution Entanglement for Two-Qubit State Using Weak Measurement and Reversal
NASA Astrophysics Data System (ADS)
Li, Wenjuan; He, Zhi; Wang, Qiong
2017-09-01
Protection of entanglement from disturbance of the environment is an essential task in quantum information processing. We investigate the effect of the weak measurement and reversal (WMR) on the protection of the entanglement for an arbitrarily entangled two-qubit pure state from these three typical quantum noisy channels, i.e., amplitude damping channel, phase damping channel and depolarizing quantum channel. Given the parameters of the Bell-like initial qubits' state | ψ〉 = a|00〉 + d|11〉, it is found that the WMR operation indeed helps for protecting distributed entanglement from the above three noisy quantum channels. But for the Bell-like initial qubits' state | ϕ〉 = b|01〉 + c|10〉, the WMR operation only protects entanglement in the amplitude damping channel, not for the phase damping and depolarizing quantum channels. In addition, we discuss how the concurrence and the success probability behave with adjusting the weak or the reversal weak measurement strength.
Sheng Yubo; Deng Fuguo
2010-03-15
Entanglement purification is a very important element for long-distance quantum communication. Different from all the existing entanglement purification protocols (EPPs) in which two parties can only obtain some quantum systems in a mixed entangled state with a higher fidelity probabilistically by consuming quantum resources exponentially, here we present a deterministic EPP with hyperentanglement. Using this protocol, the two parties can, in principle, obtain deterministically maximally entangled pure states in polarization without destroying any less-entangled photon pair, which will improve the efficiency of long-distance quantum communication exponentially. Meanwhile, it will be shown that this EPP can be used to complete nonlocal Bell-state analysis perfectly. We also discuss this EPP in a practical transmission.
Efficient concentration protocols for the single-photon entanglement state with polarization feature
NASA Astrophysics Data System (ADS)
Zhou, Lan; Wang, Dan-Dan; Wang, Xing-Fu; Gu, Shi-Pu; Sheng, Yu-Bo
2017-05-01
We propose two efficient entanglement concentration protocols (ECPs) for arbitrary less-entangled single-photon entanglement state, in which the photon qubit has the polarization feature. The first ECP is in linear optics, and the second ECP is in nonlinear optics. The two ECPs have some attractive advantages. First, they can preserve the polarization feature of the photon qubit, while all the other existing ECPs for single photon state cannot achieve this goal. Second, they only require one pair of less-entangled single-photon entanglement state and some auxiliary single photons. Third, they only require local operations. Especially, the second ECP can be used repeatedly, which can increase its success probability largely. Based on above properties, our two ECPs, especially the second one may be useful in current and future quantum communication.
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.
Accurate calculation of the geometric measure of entanglement for multipartite quantum states
NASA Astrophysics Data System (ADS)
Teng, Peiyuan
2017-07-01
This article proposes an efficient way of calculating the geometric measure of entanglement using tensor decomposition methods. The connection between these two concepts is explored using the tensor representation of the wavefunction. Numerical examples are benchmarked and compared. Furthermore, we search for highly entangled qubit states to show the applicability of this method.
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.
Efficient Polarization Entanglement Purification Using Spatial Entanglement
NASA Astrophysics Data System (ADS)
Gu, Bin; Chen, Yu-Lin; Zhang, Cheng-Yi; Huang, Yu-Gai
2010-10-01
The protocol using spatial entanglement to purify polarization entanglement by entanglement transformation between different degrees of freedom in a realistic environment is elaborated. Our analyses show that the bit-flip error can be completely purified, but the pure maximally entangled state can not be obtained ultimately if the spatial entanglement is impure. The fidelity of the purified state is decided by the spatial entanglement. Furthermore, this protocol can also be extended to purify the multi-particle Greenberg—Horne—Zeilinger (GHZ) state. It is presented that the spatial entanglement can be served as another source to improve the quality of entanglement.
Bidirectional Quantum Controlled Teleportation by Using a Genuine Six-qubit Entangled State
NASA Astrophysics Data System (ADS)
Chen, Yan
2015-01-01
A bidirectional quantum controlled teleportation scheme by using a genuine six-qubit entangled state is proposed. In our scheme, such a six-qubit entangled state is employed as the quantum channel linking three legitimate participants. And Alice may transmit an arbitrary single qubit state of qubit A to Bob and Bob may transmit an arbitrary single qubit state of qubit B to Alice via the control of the supervisor Charlie. This bidirectional quantum controlled teleportation is deterministic.
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.
NASA Astrophysics Data System (ADS)
Wang, Dong; Hoehn, Ross D.; Ye, Liu; Kais, Sabre
2016-07-01
We present a strategy for realizing multiparty-controlled remote state preparation (MCRSP) for a family of four-qubit cluster-type states by taking a pair of partial entanglements as the quantum channels. In this scenario, the encoded information is transmitted from the sender to a spatially separated receiver with control of the transmission by multiple parties. Predicated on the collaboration of all participants, the desired state can be faithfully restored at the receiver's location with high success probability by application of additional appropriate local operations and necessary classical communication. Moreover, this proposal for MCRSP can be faithfully achieved with unit total success probability when the quantum channels are distilled to maximally entangled ones.
Entanglement dynamics of quantum states generated by a Kerr medium and a beam splitter
NASA Astrophysics Data System (ADS)
Rohith, M.; Sudheesh, C.; Rajeev, R.
2016-01-01
We study theoretically the dynamics of entangled states created in a beam splitter with a nonlinear Kerr medium placed into one input arm. Entanglement dynamics of initial classical and nonclassical states are studied and compared. Signatures of revival and fractional revival phenomena exhibited during the time evolution of states in the Kerr medium are captured in the entangled states produced by the beam splitter. Dynamics of entanglement shows local minima at the instants of fractional revivals. These minima correspond to the generation of two-component Schrödinger cat states or multi-component Schrödinger cat-like states if the initial state considered is a coherent state. Maximum entanglement is obtained at the instants of collapses of wave packets in the medium. Our analysis shows increase in entanglement with increase in the degree of nonclassicality of the initial states considered. We show that the states generated at the output of the beam splitter using initial nonclassical states are more robust against decoherence due to photon absorption by an environment than those formed by an initial classical state.
Deterministic generation of a three-dimensional entangled state via quantum Zeno dynamics
Li Wenan; Huang Guangyao
2011-02-15
A scheme is proposed for the generation of a three-dimensional entangled state for two atoms trapped in a cavity via quantum Zeno dynamics. Because the scheme is based on the resonant interaction, the time required to produce entanglement is very short compared with the dispersive protocols. We show that the resulting effective dynamics allows for the creation of robust qutrit-qutrit entanglement. The influence of various decoherence processes such as spontaneous emission and photon loss on the fidelity of the entangled state is investigated. Numerical results show that the scheme is robust against the cavity decay since the evolution of the system is restricted to a subspace with null-excitation cavity fields. Furthermore, the present scheme has been generalized to realize N-dimensional entanglement for two atoms.
How a single photon can mediate entanglement between two others
Lima Bernardo, Bertúlio de
2016-10-15
We describe a novel quantum information protocol, which probabilistically entangles two distant photons that have never interacted. Different from the entanglement swapping protocol, which requires two pairs of maximally entangled photons as the input states, as well as a Bell-state measurement (BSM), the present scheme only requires three photons: two to be entangled and another to mediate the correlation, and no BSM, in a process that we call “entanglement mediation”. Furthermore, in analyzing the paths of the photons in our arrangement, we conclude that one of them, the mediator, exchanges information with the two others simultaneously, which seems to be a new quantum-mechanical feature.
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.
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.
Teleportation of an arbitrary unknown N-qubit entangled state under the controlling of M controllers
NASA Astrophysics Data System (ADS)
Liu, Yu-Ling; Man, Zhong-Xiao; Xia, Yun-Jie
2008-07-01
A new quantum protocol to teleport an arbitrary unknown N-qubit entangled state from a sender to a fixed receiver under M controllers( M < N) is proposed. The quantum resources required are M non-maximally entangled Greenberger-Horne-Zeilinger (GHZ) state and N-M non-maximally entangled Einstein-Podolsky-Rosen (EPR) pairs. The sender performs N generalized Bell-state measurements on the 2 N particles. Controllers take M single-particle measurement along x-axis, and the receiver needs to introduce one auxiliary two-level particle to extract quantum information probabilistically with the fidelity unit if controllers cooperate with it.
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.
Not all pure entangled states are useful for sub-shot-noise interferometry
Hyllus, Philipp; Smerzi, Augusto; Guehne, Otfried
2010-07-15
We investigate the connection between the shot-noise limit in linear interferometers and particle entanglement. In particular, we ask whether sub-shot-noise sensitivity can be reached with all pure entangled input states of N particles if they can be optimized with local operations. Results on the optimal local transformations allow us to show that for N=2 all pure entangled states can be made useful for sub-shot-noise interferometry while for N>2 this is not the case. We completely classify the useful entangled states available in a bosonic two-mode interferometer. We apply our results to several states, in particular to multiparticle singlet states and to cluster states. The latter turn out to be practically useless for sub-shot-noise interferometry. Our results are based on the Cramer-Rao bound and the Fisher information.
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.
Detection efficiency for loophole-free Bell tests with entangled states affected by colored noise
NASA Astrophysics Data System (ADS)
Cañas, Gustavo; Barra, Johanna F.; Gómez, Esteban S.; Lima, Gustavo; Sciarrino, Fabio; Cabello, Adán
2013-01-01
Loophole-free Bell tests for quantum nonlocality and long-distance secure communication require photodetection efficiencies beyond a threshold ηcrit that depends on the Bell inequality and the noise affecting the entangled state received by the distant parties. Most calculations of ηcrit assume that the noise is random and can be modeled as white noise. However, most sources suffer from colored noise. Indeed, since entangled states are usually created as a superposition of two possible deexcitation paths, a partial distinguishability between the two processes leads to the appearance of colored noise in the generated state. Recently, there was a proposal for a loophole-free Bell test [A. Cabello and F. Sciarrino, Phys. Rev. X 2, 021010 (2012)], where a specific colored noise appears as a consequence of the precertification of the photon's presence through single-photon spontaneous parametric down-conversion. Here we obtain ηcrit, the optimal quantum states, and the local settings for a loophole-free Bell test as a function of the amount of colored noise. We consider three bipartite Bell inequalities with n dichotomic settings: Clauser-Horne-Shimony-Holt (n=2), I3322 (n=3), and A5 (n=4), both for the case of symmetric efficiencies, corresponding to photon-photon Bell tests, and for the totally asymmetric case, corresponding to atom-photon Bell tests. Remarkably, in all these cases, ηcrit is robust against the colored noise. The present analysis can find application in any test of Bell inequalities in which the dominant noise is of the colored type.
Quantum Splitting a Two-qubit State with a Genuinely Entangled Five-qubit State
NASA Astrophysics Data System (ADS)
Sang, Ming-Huang; Dai, Hai-Lang
2014-08-01
A new application of the genuinely entangled five-qubit state is investigated for quantum information splitting of a particular type of two-qubit state. In this scheme, a genuinely entangled five-qubit state is shared by Alice (a sender), Charlie (a controller) and Bob (a receiver), and Alice only needs to perform two Bell-state measurements and Charlie performs a single-qubit measurement, Bob can reconstruct the two-qubit state by performing some appropriately unitary transformations on his qubits after he knows the measured results of both Alice and Charlie. This quantum information splitting scheme is deterministic, i.e. the probability of success is 100 %. The presented protocol is showed to be secure against certain eavesdropping attacks.
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.
Dissipative production of a maximally entangled steady state of two quantum bits.
Lin, Y; Gaebler, J P; Reiter, F; Tan, T R; Bowler, R; Sørensen, A S; Leibfried, D; Wineland, D J
2013-12-19
Entangled states are a key resource in fundamental quantum physics, quantum cryptography and quantum computation. Introduction of controlled unitary processes--quantum gates--to a quantum system has so far been the most widely used method to create entanglement deterministically. These processes require high-fidelity state preparation and minimization of the decoherence that inevitably arises from coupling between the system and the environment, and imperfect control of the system parameters. Here we combine unitary processes with engineered dissipation to deterministically produce and stabilize an approximate Bell state of two trapped-ion quantum bits (qubits), independent of their initial states. Compared with previous studies that involved dissipative entanglement of atomic ensembles or the application of sequences of multiple time-dependent gates to trapped ions, we implement our combined process using trapped-ion qubits in a continuous time-independent fashion (analogous to optical pumping of atomic states). By continuously driving the system towards the steady state, entanglement is stabilized even in the presence of experimental noise and decoherence. Our demonstration of an entangled steady state of two qubits represents a step towards dissipative state engineering, dissipative quantum computation and dissipative phase transitions. Following this approach, engineered coupling to the environment may be applied to a broad range of experimental systems to achieve desired quantum dynamics or steady states. Indeed, concurrently with this work, an entangled steady state of two superconducting qubits was demonstrated using dissipation.
A proposal to generate entangled compass states with sub-Planck structure
Choudhury, Sayan; Panigrahi, Prasanta K.
2011-09-23
We illustrate a procedure to generate a bipartite, entangled compass state, which shows sub-Planck structure. The proposed method uses the interaction of a standing wave laser field, with two, two-level atoms and relies on the ability of this system to choose certain mesoscopic bipartite states to couple with the internal degrees of freedom. An appropriate measurement on the internal degrees of freedom then leads to the entangled state, which shows sub-Planck structures, desired for quantum metrology.
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.
Bidirectional Quantum Controlled Teleportation via a Six-Qubit Entangled State
NASA Astrophysics Data System (ADS)
Duan, Ya-Jun; Zha, Xin-Wei
2014-11-01
A new application of six-qubit entangled state introduced by Chen et al. (Phys. Rev. A 74, 032324, 2006) is studied for the bidirectional quantum controlled teleportation. In our scheme, a six-qubit entangled state is shared by Alice, Bob and Charlie, Alice and Bob can transmit simultaneously an arbitrary single-qubit state to each other under the control of the supervisor Charlie.
Barium Qubit State Detection and Ba Ion-Photon Entanglement
NASA Astrophysics Data System (ADS)
Sosnova, Ksenia; Inlek, Ismail Volkan; Crocker, Clayton; Lichtman, Martin; Monroe, Christopher
2016-05-01
A modular ion-trap network is a promising framework for scalable quantum-computational devices. In this architecture, different ion-trap modules are connected via photonic buses while within one module ions interact locally via phonons. To eliminate cross-talk between photonic-link qubits and memory qubits, we use different atomic species for quantum information storage (171 Yb+) and intermodular communication (138 Ba+). Conventional deterministic Zeeman-qubit state detection schemes require additional stabilized narrow-linewidth lasers. Instead, we perform fast probabilistic state detection utilizing efficient detectors and high-NA lenses to detect emitted photons from circularly polarized 493 nm laser excitation. Our method is not susceptible to intensity and frequency noise, and we show single-shot detection efficiency of ~ 2%, meaning that we can discriminate between the two qubits states with 99% confidence after as little as 50 ms of averaging. Using this measurement technique, we report entanglement between a single 138 Ba+ ion and its emitted photon with 86% fidelity. This work is supported by the ARO with funding from the IARPA MQCO program, the DARPA Quiness program, the AFOSR MURI on Quantum Transduction, and the ARL Center for Distributed Quantum Information.
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.
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
2015-11-27
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.
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.
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.
Asymmetric Controlled Bidirectional Remote State Preparation by Using a Ten-qubit Entangled State
NASA Astrophysics Data System (ADS)
Ma, Peng-Cheng; Chen, Gui-Bin; Li, Xiao-Wei; Zhang, Jian; Zhan, You-Bang
2017-09-01
We present a novel scheme for asymmetric controlled bidirectional remote state preparation (ACBRSP) with complex coefficients via a ten-qubit entangled state as the quantum channel. In this scheme, two distant parties, Alice and Bob are not only senders but also receivers, and Alice wants to remotely prepare a single-qubit state at Bob's site, at the same time, Bob wishes to help Alice remotely prepares an arbitrary two-qubit entangled state. It is shown that, only if the two senders and the controller collaborate with each other, the ACBRSP can be completed successfully. We demonstrate that the total success probability of the ACBRSP in this scheme can reach 1, that is, the scheme is deterministic.
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.
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.
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 ...).
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.
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.
NASA Astrophysics Data System (ADS)
Zhang, Da; Zha, Xin-Wei; Duan, Ya-Jun; Wei, Zhao Hui
2016-01-01
It is presented that a bidirectional remote state preparation scheme uses six-qubit maximally entangled state. In this paper we propose a new protocol which allows two distant parties to simultaneously and deterministically exchange their states under controling of a third remote party. In such a way, it cannot be successful without permission of the controller. Based on the von Neumann measurement and Bell state measurement, Alice can transmit an arbitrary single qubit state to Bob, while Bob can transmit an arbitrary single qubit state to Alice via the control of the supervisor Charlie.
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.
Carving complex many-atom entangled states by single-photon detection
NASA Astrophysics Data System (ADS)
Hu, Jiazhong; Chen, Wenlan; Duan, Yiheng; Braverman, Boris; Zhang, Hao; Vuletic, Vladan
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 multi-frequency 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 trials, and can generate complex entangled states such as multicomponent Schrödinger cat states with high fidelity.
Proposed optical realisation of a two photon, four-qubit entangled χ state
NASA Astrophysics Data System (ADS)
Ritboon, Atirach; Croke, Sarah; Barnett, Stephen M.
2017-07-01
The four-qubit states | {χ }{ij}> , exhibiting genuine multi-partite entanglement have been shown to have many interesting properties and have been suggested for novel applications in quantum information processing. In this work we propose a simple quantum circuit and its corresponding optical embodiment with which to prepare photon pairs in the | {χ }{ij}> states. Our approach uses hyper-entangled photon pairs, produced by the type-I spontaneous parametric down-conversion process in two contiguous nonlinear crystals, together with a set of simple linear-optical transformations. Our photon pairs are maximally hyper-entangled in both their polarisation and orbital angular momentum. After one of these daughter photons passes through our optical setup, we obtain photon pairs in the hyper-entangled state | {χ }00> , and the | {χ }{ij}> states can be achieved by further simple transformations.
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.
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.
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.
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.
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).
Einstein-Podolsky-Rosen-steering swapping between two Gaussian multipartite entangled states
NASA Astrophysics Data System (ADS)
Wang, Meihong; Qin, Zhongzhong; Wang, Yu; Su, Xiaolong
2017-08-01
Multipartite Einstein-Podolsky-Rosen (EPR) steering is a useful quantum resource for quantum communication in quantum networks. It has potential applications in secure quantum communication, such as one-sided device-independent quantum key distribution and quantum secret sharing. By distributing optical modes of a multipartite entangled state to space-separated quantum nodes, a local quantum network can be established. Based on the existing multipartite EPR steering in a local quantum network, secure quantum communication protocol can be accomplished. In this manuscript, we present swapping schemes for EPR steering between two space-separated Gaussian multipartite entangled states, which can be used to connect two space-separated quantum networks. Two swapping schemes, including the swapping between a tripartite Greenberger-Horne-Zeilinger (GHZ) entangled state and an EPR entangled state and that between two tripartite GHZ entangled states, are analyzed. Various types of EPR steering are presented after the swapping of two space-separated independent multipartite entanglement states without direct interaction, which can be used to implement quantum communication between two quantum networks. The presented schemes provide technical reference for more complicated quantum networks with EPR steering.
Approximate transformations of bipartite pure-state entanglement from the majorization lattice
NASA Astrophysics Data System (ADS)
Bosyk, G. M.; Sergioli, G.; Freytes, H.; Holik, F.; Bellomo, G.
2017-05-01
We study the problem of deterministic transformations of an initial pure entangled quantum state, | ψ > , into a target pure entangled quantum state, | ϕ > , by using local operations and classical communication (LOCC). A celebrated result of Nielsen (1999) gives the necessary and sufficient condition that makes this entanglement transformation process possible. Indeed, this process can be achieved if and only if the majorization relation ψ ≺ ϕ holds, where ψ and ϕ are probability vectors obtained by taking the squares of the Schmidt coefficients of the initial and target states, respectively. In general, this condition is not fulfilled. However, one can look for an approximate entanglement transformation. Vidal et al. (2000) have proposed a deterministic transformation using LOCC in order to obtain a target state |χopt > most approximate to | ϕ > in terms of maximal fidelity between them. Here, we show a strategy to deal with approximate entanglement transformations based on the properties of the majorization lattice. More precisely, we propose as approximate target state one whose Schmidt coefficients are given by the supremum between ψ and ϕ. Our proposal is inspired on the observation that fidelity does not respect the majorization relation in general. Remarkably enough, we find that for some particular interesting cases, like two-qubit pure states or the entanglement concentration protocol, both proposals are coincident.
Dong Yunxia; Zhang Xiangdong
2010-03-15
A rigorous quantum theory for the generation of multiphoton entangled states based on two consecutive three-frequency interactions of waves in a one-dimensional nonlinear photonic crystal is developed using the field expansion and differentiation methods. The three-photon correlation coefficient and the average photon numbers generated in the structure are calculated. All order expansion terms are included in the calculation. The generation conditions for multiphoton entangled states in such a structure are also analyzed. It is shown that the created photons in the present structures obey the super-Poisson statistics at the interacting frequencies and are in a multiparticle entangled state. This means the nonlinear photonic crystal can be applied as a highly efficient source of an entangled multiphoton for highly integrated all-optical circuits.
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)
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.
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)
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.
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
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.
Deterministic controlled bidirectional remote state preparation via a six-qubit entangled state
NASA Astrophysics Data System (ADS)
Zhang, Da; Zha, Xin-wei; Duan, Ya-jun; Yang, Yu-quan
2016-05-01
In this paper, we presented a controlled bidirectional remote state preparation scheme which used the six-qubit entangled state as quantum channel. In our scheme, Alice and Bob can prepare simultaneously an arbitrary single-qubit state in each other's place with the control of the supervisor Charlie. The success probability for our scheme reaches unit. Furthermore, we analyze the expression of quantum channel for controlled bidirectional remote state preparation. Finally, we discuss the security of our scheme, the detailed security analysis shows that the supervisor Charlie's control can greatly improve the security of our scheme.
Breakdown of the Coherent State Path Integral: Two Simple Examples
Wilson, Justin H.; Galitski, Victor
2011-03-18
We show how the time-continuous coherent state path integral breaks down for both the single-site Bose-Hubbard model and the spin-path integral. Specifically, when the Hamiltonian is quadratic in a generator of the algebra used to construct coherent states, the path integral fails to produce correct results following from an operator approach. As suggested by previous authors, we note that the problems do not arise in the time-discretized version of the path integral.
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.
Quantum critical phase with infinite projected entangled paired states
NASA Astrophysics Data System (ADS)
Poilblanc, Didier; Mambrini, Matthieu
2017-07-01
A classification of SU(2)-invariant projected entangled paired states (PEPS) on the square lattice, based on a unique site tensor, has been recently introduced by Mambrini et al. [M. Mambrini, R. Orús, and D. Poilblanc, Phys. Rev. B 94, 205124 (2016), 10.1103/PhysRevB.94.205124]. It is not clear whether such SU(2)-invariant PEPS can either (i) exhibit long-range magnetic order (such as in the Néel phase) or (ii) describe a genuine quantum critical point (QCP) or quantum critical phase (QCPh) separating two ordered phases. Here, we identify a specific family of SU(2)-invariant PEPS of the classification which provides excellent variational energies for the J1-J2 frustrated Heisenberg model, especially at J2=0.5 , corresponding to the approximate location of the QCP or QCPh separating the Néel phase from a dimerized phase. The PEPS are built from virtual states belonging to the 1/2⊗N⊕0 SU(2) representation, i.e., with N "colors" of virtual spin-1/2 . Using a full-update infinite-PEPS approach directly in the thermodynamic limit, based on the corner transfer matrix renormalization algorithm supplemented by a conjugate gradient optimization scheme, we provide evidence of (i) the absence of magnetic order and of (ii) diverging correlation lengths (i.e., showing no sign of saturation with increasing environment dimension) in both the singlet and triplet channels, when the number of colors N ≥3 . We argue that such a PEPS gives a qualitative description of the QCP or QCPh of the J1-J2 model.
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.
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
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.
NASA Astrophysics Data System (ADS)
Liang, Bian-Bian; Hu, Shi; Cui, Wen-Xue; An, Cheng-Shou; Xing, Yan; Hu, Jing-Si; Sun, Guo-Qing; Jiang, Xin-Xin; Wang, Hong-Fu
2014-11-01
Assisted by a quantum dot-microcavity coupled system, we propose an entanglement concentration scheme for concentrating two unknown partially entangled three-photon W states into a maximally entangled three-photon W state based on spin selective photon reflection from the cavity and the interference of polarized photons. In the scheme, three parties, say Alice, Bob, and Charlie in different distant locations can successfully share the maximally entangled three-photon W state with a high probability of success by local operations performed by Alice and classical communication. We calculate the probability of success of the scheme and the fidelity of the obtained three-photon W state under practical conditions, whose results show that the scheme can work in both weak coupling and strong coupling regimes.
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. PMID:28397793
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)
Wu, Jin-Lei; Ji, Xin; Zhang, Shou
2017-04-01
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.
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.
Deterministic Clone of an Unknown N-Qubit Entangled State with Assistance
NASA Astrophysics Data System (ADS)
Ma, Song-Ya; Chen, Xiu-Bo; Guan, Xiao-Wei; Niu, Xin-Xin; Yang, Yi-Xian
2010-11-01
We propose a deterministic scheme to realize assisted-clone of an unknown N(≥3)-qubit entangled state. The first stage of the protocol requires teleportation via maximal entanglement as the quantum channel. In the second stage of the protocol, a novel set of mutually orthogonal basis vectors are constructed. With the assistance of the preparer through an N-particle projective measurement under this basis, the perfect copy of an original state can be produced. Comparing with the previous protocols which produce the unknown state and its orthogonal complement state at the site of the sender, our scheme generates the unknown state deterministically.
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.
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.
Steady-state entanglement between distant quantum dots in photonic crystal dimers
NASA Astrophysics Data System (ADS)
Vasco, J. P.; Gerace, D.; Guimarães, P. S. S.; Santos, M. F.
2016-10-01
We show that two spatially separated semiconductor quantum dots under resonant and continuous-wave excitation can be strongly entangled in the steady state, thanks to their radiative coupling by mutual interaction through the normal modes of a photonic crystal dimer. We employ a quantum master equation formalism to quantify the steady-state entanglement by calculating the system negativity. Calculations are specified to consider realistic semiconductor nanostructure parameters for the photonic crystal dimer-quantum dots coupled system, determined by a guided-mode expansion solution of Maxwell equations. Negativity values of the order of 0.1 (20 % of the maximum value) are shown for interdot distances that are larger than the resonant wavelength of the system. It is shown that the amount of entanglement is almost independent of the interdot distance, as long as the normal mode splitting of the photonic dimer is larger than their linewidths, which becomes the only requirement to achieve a local and individual qubit addressing. Considering inhomogeneously broadened quantum dots, we find that the steady-state entanglement is preserved as long as the detuning between the two quantum dot resonances is small when compared to their decay rates. The steady-state entanglement is shown to be robust against the effects of pure dephasing of the quantum dot transitions. We finally study the entanglement dynamics for a configuration in which one of the two quantum dots is initially excited and find that the transient negativity can be enhanced by more than a factor of two with respect to the steady-state value. These results are promising for practical applications of entangled states at short time scales.
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.
Simplified Scheme for Teleportation of a Multipartite Quantum State Using a Single Entangled Pair
NASA Astrophysics Data System (ADS)
Yan, Li-Hua; Gao, Yun-Feng
2009-02-01
A simple scheme for teleporting an unknown M-qubit cat-like state is proposed. The steps of this scheme can be summarized simply: disentangle-teleport-reconstruct entanglement. If proper unitary operations and measurements from senders are given, the teleportation of an unknown M-qubit cat-like state can be converted into single qubit teleportation. In the meantime, the receiver should also carry out right unitary operations with the introduction of appropriate ancillary qubits to confirm the successful teleportation of the demanded entangled state. The present scheme can be generalized to teleport an unknown M-quNit state, i.e., an M-quNit state can be teleported by a single quNit entangled pair.
Rotating entangled states of an exchange-coupled dimer of single-molecule magnets
Owerre, S. A.
2014-04-21
An antiferromagnetically exchange-coupled dimer of single molecule magnets which possesses a large spin tunneling has been investigated. For this system, the ground and first excited states are entangled states, and the Hamiltonian is effectively similar to that of a two-state system at 2sth order in perturbation theory; thus this system can be mapped to an entangled pseudospin 1/2 particles. We study the effects of interaction and rotation of this system about its staggered easy-axis direction. The corresponding Hamiltonian of a rotated two-state entangled spin system is derived with its exact low-energy eigenstates and eigenvalues. We briefly discuss the effect of a dissipative environment on this rotated two-state system.
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.
A Multipli-entangled Photon Source for Cluster State Generation
2012-04-01
AFRL), Timothy Genda (AFRL), A. Matthew Smith (NRC), Reinhard Erdmann (AAC) and Enrique Galvez ( Colgate University) 5d. PROJECT NUMBER T2QC 5e...Corporation, Rome, NY (USA) Enrique J. Galvez Colgate University, Hamilton, NY (USA) 1. ABSTRACT This paper expands upon prior work on an entangled
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.
Bidirectional Quantum Controlled Teleportation by using a Seven-qubit Entangled State
NASA Astrophysics Data System (ADS)
Sang, Ming-huang
2016-01-01
We propose a new protocol of bidirectional quantum controlled teleportation by using a seven-qubit entangled state as the quantum channel. That is to say Alice may transmit an arbitrary single-qubit state to Bob and Bob may transmit an arbitrary two-qubit state to Alice via the control of the supervisor Charlie.
Bidirectional Controlled Quantum Teleportation by Using Five-Qubit Entangled State
NASA Astrophysics Data System (ADS)
Chen, Yan
2014-05-01
We propose a scheme for bidirectional controlled quantum teleportation by using a genuine five-qubit entangled state. In our scheme, Alice may transmit an arbitrary single qubit state of qubit A to Bob and at the same time, Bob may transmit an arbitrary single qubit state of qubit B to Alice via the control of the supervisor Charlie.
Bidirectional Quantum Controlled Teleportation via a Maximally Seven-qubit Entangled State
NASA Astrophysics Data System (ADS)
Duan, Ya-Jun; Zha, Xin-Wei; Sun, Xin-Mei; Xia, Jia-Fan
2014-08-01
A bidirectional quantum controlled teleportation scheme using a seven-qubit maximally entangled state as quantum channel is proposed. This means that Alice can transmit an arbitrary single qubit state of qubit a to Bob and Bob can transmit an arbitrary single qubit state of qubit b to Alice via the control of the supervisor Charlie.
Experimentally testing Hardy’s theorem on nonlocality with entangled mixed states
NASA Astrophysics Data System (ADS)
Fan, Dai-He; Dai, Mao-Chun; Guo, Wei-Jie; Wei, Lian-Fu
2017-04-01
Hardy’s theorem on nonlocality has been verified by a series of experiments with two-qubit entangled pure states. However, in this paper we demonstrate the experimental test of the theorem by using the two-photon entangled mixed states. We first investigate the generic logic in Hardy’s proof of nonlocality, which can be applied for arbitrary two-qubit mixed polarization entangled states and can be reduced naturally to the well-known logic tested successfully by the previous pure state experiments. Then, the optimized violations of locality for various experimental parameters are delivered by the numerical method. Finally, the logic argued above for testing Hardy’s theorem on nonlocality is demonstrated experimentally by using the mixed entangled-photon pairs generated via pumping two type-I BBO crystals. Our experimental results shows that Hardy’s proof of nonlocality can also be verified with two-qubit polarization entangled mixed states, with a violation of about 3.4 standard deviations. Project supported by the National Natural Science Foundation of China (Grant Nos. 61308008 and U1330201).
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.
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.
Electronic Entanglement Concentration for the Concatenated Greenberger-Horne-Zeilinger State
NASA Astrophysics Data System (ADS)
Ding, Shang-Ping; Zhou, Lan; Gu, Shi-Pu; Wang, Xing-Fu; Sheng, Yu-Bo
2017-06-01
Concatenated Greenberger-Horne-Zeilinger (C-GHZ) state, which encodes many physical qubits in a logic qubit will have important applications in both quantum communication and computation. In this paper, we will describe an entanglement concentration protocol (ECP) for electronic C-GHZ state, by exploiting the electronic polarization beam splitters (PBSs) and charge detection. This protocol has several advantages. First, the parties do not need to know the exact coefficients of the initial less-entangled C-GHZ state, which makes this protocol feasible. Second, with the help of charge detection, the distilled maximally entangled C-GHZ state can be remained for future application. Third, this protocol can be repeated to obtain a higher success probability. We hope that this protocol can be useful in future quantum computation based on electrons.
Controllable preparation of two-mode entangled coherent states in circuit QED
NASA Astrophysics Data System (ADS)
Ji, Ying-Hua; Liu, Yong-Mei
2014-11-01
Although the multi-level structure of superconducting qubits may result in calculation errors, it can be rationally used to effectively improve the speed of gate operations. Utilizing a current-biased Josephson junction (λ-type rf-SQUID) as a tunable coupler for superconducting transmission line resonators (TLRs), under the large detuning condition, we demonstrate the controllable generation of entangled coherent states in circuit quantum electrodynamics (circuit QED). The coupling between the TLRs and the qubit can be effectively regulated by an external bias current or coupling capacitor. Further investigations indicate that the maximum entangled state can be obtained through measuring the excited state of the superconducting qubits. Then, the influence of the TLR decay on the prepared entangled states is analyzed.
Three-photon frequency down-conversion as an event-ready source of entangled states
Hnilo, Alejandro A.
2005-03-01
An event-ready (or deterministic) source of entangled states is of interest in the practical implementation of schemes of quantum computation and cryptography as well as in the experiments aimed to elucidate the foundations of quantum mechanics. I study the phase matching geometry and detection conditions for the process of three-photon frequency down-conversion, which is a possible source of that kind. It is apparently free of some limitations of the schemes based on two-photon frequency down-conversion. The goal of the proposed setup is not the generation of an entangled state of three photons (in a GHZ-state sense), but of an entangled state of two photons with a 'trigger' signal. As an example, I estimate the values of the trios' flux and trigger's reliability for the particular case of crystal calcite illuminated by the fourth harmonic of a Nd:YAG mode-locked laser.
Sub-Rayleigh lithography using high flux loss-resistant entangled states of light.
Rosen, Shamir; Afek, Itai; Israel, Yonatan; Ambar, Oron; Silberberg, Yaron
2012-09-07
Quantum lithography achieves phase superresolution using fragile, experimentally challenging entangled states of light. We propose a scalable scheme for creating features narrower than classically achievable with reduced use of quantum resources and, consequently, enhanced resistance to loss. The scheme is an implementation of interferometric lithography using a mixture of a spontaneous parametric down-converted entangled state with intense classical coherent light. We measure coincidences of up to four photons mimicking multiphoton absorption. The results show a narrowing of the interference fringes of up to 30% with respect to the best analogous classical scheme using only 10% of the nonclassical light required for creating NOON states.
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.
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.
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.
Discrete-time reservoir engineering with entangled bath and stabilising squeezed states
NASA Astrophysics Data System (ADS)
Miao, Zibo; Sarlette, Alain
2017-09-01
This theoretical proposal investigates how resonant interactions occurring when a harmonic oscillator is fed with a stream of entangled qubits allow us to stabilise squeezed states of the harmonic oscillator. We show that the properties of the squeezed state stabilised by this engineered reservoir, including the squeezing strength, can be tuned at will through the parameters of the ‘input’ qubits, albeit in tradeoff with the convergence rate. We also discuss the influence of the type of entanglement in the input from a pairwise case to a more widely distributed case. This paper can be read either as a proposal to stabilise squeezed states or as a step toward treating quantum systems with time-entangled reservoir inputs.
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.
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.
Quantum Information Splitting of Arbitrary Three-Qubit State by Using Seven-Qubit Entangled State
NASA Astrophysics Data System (ADS)
Li, Dong-fen; Wang, Rui-jin; Zhang, Feng-li; Deng, Fu-hu
2015-06-01
In this paper, we propose a scheme of quantum information splitting arbitrary three-qubit state by using seven-qubit entangled as quantum channel. The sender Alice first performs Bell-state measurements (BSMs) on her qubits pairs respectively and tells her measurement outcome to authorizers Bob to reconstruct the original state, then Charlie should carries out single-qubit measurement (SQM) on his qubits. According to the results from Alice and Charlie, Bob can reconstruct the original state by applying an appropriate unitary operation. After analyzing, the method achieved the desired effect of quantum information splitting (QIS). We also realize the QIS of arbitrary three-qubit state in cavity quantum electrodynamics (QED).
Remote preparation of an arbitrary multi-qubit state via two-qubit entangled states
NASA Astrophysics Data System (ADS)
Wei, Jiahua; Shi, Lei; Ma, Lihua; Xue, Yang; Zhuang, Xuchun; Kang, Qiaoyan; Li, Xuesong
2017-10-01
We propose a novel scheme for remote preparation of an arbitrary n-qubit state with the aid of an appropriate local 2^n× 2^n unitary operation and n maximally entangled two-qubit states. The analytical expression of local unitary operation, which is constructed in the form of iterative process, is presented for the preparation of n-qubit state in detail. We obtain the total successful probabilities of the scheme in the general and special cases, respectively. The feasibility of our scheme in preparing remotely multi-qubit states is explicitly demonstrated by theoretical studies and concrete examples, and our results show that the novel proposal could enlarge the applied range of remote state preparation.
Scheme for Implementing Teleporting an Arbitrary Tripartite Entangled State in Cavity QED
NASA Astrophysics Data System (ADS)
Wang, Xue-Wen; Peng, Zhao-Hui
2009-10-01
We propose to teleport an arbitrary tripartite entangled state in cavity QED. In this scheme, the five-qubit Brown state is chosen as the quantum channel. It has been shown that the teleportation protocol can be completed perfectly with two different measurement methods. In the future, our scheme might be realizable based on present experimental technology.
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.
Quantum Coherent Feedback Control for Generation System of Optical Entangled State
Zhou, Yaoyao; Jia, Xiaojun; Li, Fang; Yu, Juan; Xie, Changde; Peng, Kunchi
2015-01-01
The non-measurement based coherent feedback control (CFC) is a control method without introducing any backaction noise into the controlled system, thus is specially suitable to manipulate various quantum optical systems for preparing nonclassical states of light. By simply tuning the transmissivity of an optical controller in a CFC loop attached to a non-degenerate optical parametric amplifier (NOPA), the quantum entanglement degree of the output optical entangled state of the system is improved. At the same time, the threshold pump power of the NOPA is reduced also. The experimental results are in reasonable agreement with the theoretical expectation. PMID:26047357
NASA Astrophysics Data System (ADS)
Liu, Tang-Kun; Tao, Yu; Shan, Chuan-Jia; Liu, Ji-bing
2017-10-01
Using the three criterions of the concurrence, the negative eigenvalue and the geometric quantum discord, we investigate the quantum entanglement and quantum correlation dynamics of two two-level atoms interacting with the coherent state optical field. We discuss the influence of different photon number of the mean square fluctuations on the temporal evolution of the concurrence, the negative eigenvalue and the geometric quantum discord between two atoms when the two atoms are initially in specific three states. The results show that different photon number of the mean square fluctuations can lead to different effects of quantum entanglement and quantum correlation dynamics.
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.
NASA Astrophysics Data System (ADS)
Osorio Iregui, Juan; Troyer, Matthias; Corboz, Philippe
2017-09-01
In spite of their intrinsic one-dimensional nature, matrix product states have been systematically used to obtain remarkably accurate results for two-dimensional systems. Motivated by basic entropic arguments favoring projected entangled-pair states as the method of choice, we assess the relative performance of infinite matrix product states and infinite projected entangled-pair states on cylindrical geometries. By considering the Heisenberg and half-filled Hubbard models on the square lattice as our benchmark cases, we evaluate their variational energies as a function of both bond dimension and cylinder width. In both examples, we find crossovers at moderate cylinder widths, i.e., for the largest bond dimensions considered, we find an improvement on the variational energies for the Heisenberg model by using projected entangled-pair states at a width of about eleven sites, whereas for the half-filled Hubbard model, this crossover occurs at about seven sites.
Relative entropy of entanglement of two-qubit Ux-invariant states
NASA Astrophysics Data System (ADS)
Wang, Zhen; Wang, Zhi-Xi
2015-01-01
It is strictly proved that a two-qubit Ux-invariant state reaches its relative entropy of entanglement (REE) by the separable state having the same matrix structure. We also formulate three quadratic equations for the corresponding closest separable state (CSS) of Ux-invariant states by their symmetric property. Thus, the CSS of Ux-invariant state can be provided. Furthermore, to illustrate our result we consider two concrete examples.
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.
Maximal entanglement concentration for a set of (n+1)-qubit states
NASA Astrophysics Data System (ADS)
Banerjee, Anindita; Shukla, Chitra; Pathak, Anirban
2015-12-01
We propose two schemes for concentration of (n+1)-qubit entangled states that can be written in the form of ( α |\\varphi 0rangle |0rangle +β |\\varphi 1rangle |1rangle ) _{n+1} where |\\varphi 0rangle and |\\varphi 1rangle are mutually orthogonal n-qubit states. The importance of this general form is that the entangled states such as Bell, cat, GHZ, GHZ-like, |\\varOmega rangle , |Q5rangle , 4-qubit cluster states and specific states from the nine SLOCC-nonequivalent families of 4-qubit entangled states can be expressed in this form. The proposed entanglement concentration protocol is based on the local operations and classical communications (LOCC). It is shown that the maximum success probability for ECP using quantum nondemolition technique (QND) is 2β 2 for (n+1)-qubit states of the prescribed form. It is shown that the proposed schemes can be implemented optically. Further, it is also noted that the proposed schemes can be implemented using quantum dot and microcavity systems.
Transferring entangled states through spin chains by boundary-state multiplets
NASA Astrophysics Data System (ADS)
Lorenz, Peter; Stolze, Joachim
2014-10-01
Quantum spin chains may be used to transfer quantum states between elements of a quantum information processing device. A scheme discovered recently [Phys. Rev. A 85, 022312 (2012), 10.1103/PhysRevA.85.022312] was shown to have favorable transfer properties for single-qubit states even in the presence of built-in static disorder caused by manufacturing errors. We extend that scheme in a way suggested already in Bruderer et al. [Phys. Rev. A 85, 022312 (2012), 10.1103/PhysRevA.85.022312] and study the transfer of the four Bell states which form a maximally entangled basis in the two-qubit Hilbert space. We show that perfect transfer of all four Bell states separately and of arbitrary linear combinations may be achieved for chains with hundreds of spins. For simplicity we restrict ourselves to systems without disorder.
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.
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.
Controllable high-fidelity quantum state transfer and entanglement generation in circuit QED
Xu, Peng; Yang, Xu-Chen; Mei, Feng; Xue, Zheng-Yuan
2016-01-01
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. PMID:26804326
NASA Astrophysics Data System (ADS)
Ivanov, Dmitri A.
2017-07-01
Noninteracting bosons were proposed to be used for a demonstration of quantum-computing supremacy in a boson-sampling setup. A similar demonstration with fermions would require that the fermions are initially prepared in an entangled state. I suggest that pairwise entanglement of fermions would be sufficient for this purpose. Namely, it is shown that computing multiparticle scattering amplitudes for fermions entangled pairwise in groups of four single-particle states is #P-hard. In linear algebra, such amplitudes are expressed as exterior products of two-forms of rank 2. In particular, a permanent of a N ×N matrix may be expressed as an exterior product of N2 two forms of rank 2 in dimension 2 N2 , which establishes the #P-hardness of the latter.
Quantum mutual information of an entangled state propagating through slow- and fast-light media
NASA Astrophysics Data System (ADS)
Glasser, Ryan T.; Clark, Jeremy B.; Glorieux, Quentin; Vogl, Ulrich; Lett, Paul D.
2013-03-01
Due to its vital role in many quantum information and communication protocols, much theoretical and experi- mental work has been conducted in order to investigate the fundamental properties of entanglement. In this work we describe an experimental investigation into the behavior of continuous-variable entanglement and quantum mutual information upon propagation through slow- and fast-light media. A four-wave mixing process in warm atomic vapor is used to generate an entangled two-mode squeezed vacuum state of light. One of the two modes of the resulting state is then sent through a second four-wave mixing process that is tuned to exhibit either slow- or fast-light properties. The cross-correlation and quantum mutual information shared between the resulting modes is quanti ed, and di erences in their behavior after propagation through slow- and fast-light media are discussed.
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.
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.
Two-Party Quantum Private Comparison with Five-Qubit Entangled States
NASA Astrophysics Data System (ADS)
Ye, Tian-Yu; Ji, Zhao-Xu
2017-05-01
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.
Atomic homodyne detection of continuous-variable entangled twin-atom states.
Gross, C; Strobel, H; Nicklas, E; Zibold, T; Bar-Gill, N; Kurizki, G; Oberthaler, M K
2011-11-30
Historically, the completeness of quantum theory has been questioned using the concept of bipartite continuous-variable entanglement. The non-classical correlations (entanglement) between the two subsystems imply that the observables of one subsystem are determined by the measurement choice on the other, regardless of the distance between the subsystems. Nowadays, continuous-variable entanglement is regarded as an essential resource, allowing for quantum enhanced measurement resolution, the realization of quantum teleportation and quantum memories, or the demonstration of the Einstein-Podolsky-Rosen paradox. These applications rely on techniques to manipulate and detect coherences of quantum fields, the quadratures. Whereas in optics coherent homodyne detection of quadratures is a standard technique, for massive particles a corresponding method was missing. Here we report the realization of an atomic analogue to homodyne detection for the measurement of matter-wave quadratures. The application of this technique to a quantum state produced by spin-changing collisions in a Bose-Einstein condensate reveals continuous-variable entanglement, as well as the twin-atom character of the state. Our results provide a rare example of continuous-variable entanglement of massive particles. The direct detection of atomic quadratures has applications not only in experimental quantum atom optics, but also for the measurement of fields in many-body systems of massive particles.
Quantum Entanglement and Chemical Reactivity.
Molina-Espíritu, M; Esquivel, R O; López-Rosa, S; Dehesa, J S
2015-11-10
The water molecule and a hydrogenic abstraction reaction are used to explore in detail some quantum entanglement features of chemical interest. We illustrate that the energetic and quantum-information approaches are necessary for a full understanding of both the geometry of the quantum probability density of molecular systems and the evolution of a chemical reaction. The energy and entanglement hypersurfaces and contour maps of these two models show different phenomena. The energy ones reveal the well-known stable geometry of the models, whereas the entanglement ones grasp the chemical capability to transform from one state system to a new one. In the water molecule the chemical reactivity is witnessed through quantum entanglement as a local minimum indicating the bond cleavage in the dissociation process of the molecule. Finally, quantum entanglement is also useful as a chemical reactivity descriptor by detecting the transition state along the intrinsic reaction path in the hypersurface of the hydrogenic abstraction reaction corresponding to a maximally entangled state.
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
Arkhipov, Ievgen I; Peřina, Jan; Haderka, Ondřej; Allevi, Alessia; Bondani, Maria
2016-09-23
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.
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.
Nonexistence of entangled continuous-variable Werner states with positive partial transpose
NASA Astrophysics Data System (ADS)
McNulty, Daniel; Tatham, Richard; Mišta, Ladislav
2014-03-01
We address an open question about the existence of entangled continuous-variable (CV) Werner states with positive partial transpose (PPT). We prove that no such state exists by showing that all PPT CV Werner states are separable. The separability follows by observing that these CV Werner states can be approximated by truncating the states into a finite-dimensional convex mixture of product states. In addition, the constituents of the product states comprise a generalized non-Gaussian measurement which gives, rather surprisingly, a strictly tighter upper bound on quantum discord than photon counting. These results uncover the presence of only negative partial transpose entanglement and illustrate the complexity of more general nonclassical correlations in this paradigmatic class of genuine non-Gaussian quantum states.
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.
Efficient Generation of Large Number-Path Entanglement Using Only Linear Optics and Feed-Forward
Cable, Hugo; Dowling, Jonathan P.
2007-10-19
We show how an idealized measurement procedure can condense photons from two modes into one and how, by feeding forward the results of the measurement, it is possible to generate efficiently superposition states commonly called N00N states. For the basic procedure sources of number states leak onto a beam splitter, and the output ports are monitored by photodetectors. We find that detecting a fixed fraction of the input at one output port suffices to direct the remainder to the same port, with high probability, however large the initial state. When instead photons are detected at both ports, macroscopic quantum superposition states are produced. We describe a linear-optical circuit for making the components of such a state orthogonal, and another to convert the output to a N00N state. Our approach scales exponentially better than existing proposals. Important applications include quantum imaging and metrology.
Asymmetric Bidirectional Controlled Teleportation by using a Seven-qubit Entangled State
NASA Astrophysics Data System (ADS)
Hong, Wen-qin
2016-01-01
We propose a new protocol of asymmetric bidirectional controlled teleportation by using a seven-qubit entangled state as the quantum channel. That is to say Alice wants to transmit an arbitrary single-qubit state to Bob and Bob wants to transmit an arbitrary two-qubit state to Alice via the control of the supervisor Charlie. One only need perform the Bell-state measurements and single-qubit measurement.
NASA Astrophysics Data System (ADS)
Sang, Ming-huang; Nie, Li-ping
2017-09-01
We demonstrate that a seven-particle entangled state can be used to realize the deterministic asymmetric bidirectional controlled quantum information transmission by performing only Bell-state measurement and two-particle projective measurement and single-particle measurement. In our protocol, Alice can teleport an arbitrary unknown single-particle state to Bob and at the same time Bob can remotely prepare an arbitrary known two-particle state for Alice via the control of the supervisor Charlie.
On-chip generation of high-dimensional entangled quantum states and their coherent control
NASA Astrophysics Data System (ADS)
Kues, Michael; Reimer, Christian; Roztocki, Piotr; Cortés, Luis Romero; Sciara, Stefania; Wetzel, Benjamin; Zhang, Yanbing; Cino, Alfonso; Chu, Sai T.; Little, Brent E.; Moss, David J.; Caspani, Lucia; Azaña, José; Morandotti, Roberto
2017-06-01
Optical quantum states based on entangled photons are essential for solving questions in fundamental physics and are at the heart of quantum information science. Specifically, the realization of high-dimensional states (D-level quantum systems, that is, qudits, with D > 2) and their control are necessary for fundamental investigations of quantum mechanics, for increasing the sensitivity of quantum imaging schemes, for improving the robustness and key rate of quantum communication protocols, for enabling a richer variety of quantum simulations, and for achieving more efficient and error-tolerant quantum computation. Integrated photonics has recently become a leading platform for the compact, cost-efficient, and stable generation and processing of non-classical optical states. However, so far, integrated entangled quantum sources have been limited to qubits (D = 2). Here we demonstrate on-chip generation of entangled qudit states, where the photons are created in a coherent superposition of multiple high-purity frequency modes. In particular, we confirm the realization of a quantum system with at least one hundred dimensions, formed by two entangled qudits with D = 10. Furthermore, using state-of-the-art, yet off-the-shelf telecommunications components, we introduce a coherent manipulation platform with which to control frequency-entangled states, capable of performing deterministic high-dimensional gate operations. We validate this platform by measuring Bell inequality violations and performing quantum state tomography. Our work enables the generation and processing of high-dimensional quantum states in a single spatial mode.
On-chip generation of high-dimensional entangled quantum states and their coherent control.
Kues, Michael; Reimer, Christian; Roztocki, Piotr; Cortés, Luis Romero; Sciara, Stefania; Wetzel, Benjamin; Zhang, Yanbing; Cino, Alfonso; Chu, Sai T; Little, Brent E; Moss, David J; Caspani, Lucia; Azaña, José; Morandotti, Roberto
2017-06-28
Optical quantum states based on entangled photons are essential for solving questions in fundamental physics and are at the heart of quantum information science. Specifically, the realization of high-dimensional states (D-level quantum systems, that is, qudits, with D > 2) and their control are necessary for fundamental investigations of quantum mechanics, for increasing the sensitivity of quantum imaging schemes, for improving the robustness and key rate of quantum communication protocols, for enabling a richer variety of quantum simulations, and for achieving more efficient and error-tolerant quantum computation. Integrated photonics has recently become a leading platform for the compact, cost-efficient, and stable generation and processing of non-classical optical states. However, so far, integrated entangled quantum sources have been limited to qubits (D = 2). Here we demonstrate on-chip generation of entangled qudit states, where the photons are created in a coherent superposition of multiple high-purity frequency modes. In particular, we confirm the realization of a quantum system with at least one hundred dimensions, formed by two entangled qudits with D = 10. Furthermore, using state-of-the-art, yet off-the-shelf telecommunications components, we introduce a coherent manipulation platform with which to control frequency-entangled states, capable of performing deterministic high-dimensional gate operations. We validate this platform by measuring Bell inequality violations and performing quantum state tomography. Our work enables the generation and processing of high-dimensional quantum states in a single spatial mode.
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