ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sat, 18 May 2024 01:38:25 GMT2024-05-18T01:38:25Z50511- Test of einstein-podolsky-rosen steering based on the all-versus-nothing proofhttps://scholarbank.nus.edu.sg/handle/10635/112528Title: Test of einstein-podolsky-rosen steering based on the all-versus-nothing proof
Authors: Wu, C.; Chen, J.-L.; Ye, X.-J.; Su, H.-Y.; Deng, D.-L.; Wang, Z.; Oh, C.H.
Abstract: In comparison with entanglement and Bell nonlocality, Einstein-Podolsky- Rosen steering is a newly emerged research topic and in its incipient stage. Although Einstein-Podolsky-Rosen steering has been explored via violations of steering inequalities both theoretically and experimentally, the known inequalities in the literatures are far from well-developed. As a result, it is not yet possible to observe Einstein-Podolsky-Rosen steering for some steerable mixed states. Recently, a simple approach was presented to identify Einstein-Podolsky-Rosen steering based on all-versus-nothing argument, offering a strong condition to witness the steerability of a family of two-qubit (pure or mixed) entangled states. In this work, we show that the all-versus-nothing proof of Einstein-Podolsky-Rosen steering can be tested by measuring the projective probabilities. Through the bound of probabilities imposed by local-hidden-state model, the proposed test shows that steering can be detected by the all-versus-nothing argument experimentally even in the presence of imprecision and errors. Our test can be implemented in many physical systems and we discuss the possible realizations of our scheme with non-Abelian anyons and trapped ions.
Thu, 06 Mar 2014 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1125282014-03-06T00:00:00Z
- Detecting Einstein-Podolsky-Rosen steering for continuous variable wavefunctionshttps://scholarbank.nus.edu.sg/handle/10635/112413Title: Detecting Einstein-Podolsky-Rosen steering for continuous variable wavefunctions
Authors: Su, H.-Y.; Chen, J.-L.; Wu, C.; Deng, D.-L.; Oh, C.H.
Abstract: By use of Reid's criterion and the entropic criterion, we investigate the Einstein-Podolsky-Rosen (EPR) steering for some entangled continuous variable wavefunctions. We find that some entangled states that violate Bell's inequality will not violate Reid's EPR inequality nor the entropic inequality. This implies that neither criterion gives a necessary and sufficient condition to detect the EPR steering. © 2013 World Scientific Publishing Company.
Fri, 01 Mar 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124132013-03-01T00:00:00Z
- Quantum nonlocality of massive qubits in a moving framehttps://scholarbank.nus.edu.sg/handle/10635/112501Title: Quantum nonlocality of massive qubits in a moving frame
Authors: Su, H.-Y.; Wu, Y.-C.; Chen, J.-L.; Wu, C.; Kwek, L.C.
Abstract: We perform numerical tests on the quantum nonlocality of two-level quantum systems (qubits) observed by a uniformly moving observer. Under a suitable momentum setting, the quantum nonlocality of two-qubit nonmaximally entangled states could be weakened drastically by the Lorentz transformation, allowing for the existence of local-hidden-variable models, whereas three-qubit genuinely entangled states are robust. In particular, the generalized Greenberger-Horne- Zeilinger state remains nonlocal under arbitrary Wigner rotation and the generalized W state could admit local-hidden-variable models within a rather narrow range of parameters. © 2013 American Physical Society.
Wed, 28 Aug 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1125012013-08-28T00:00:00Z
- Bell nonlocality in conventional and topological quantum phase transitionshttps://scholarbank.nus.edu.sg/handle/10635/52808Title: Bell nonlocality in conventional and topological quantum phase transitions
Authors: Deng, D.-L.; Wu, C.; Chen, J.-L.; Gu, S.-J.; Yu, S.; Oh, C.H.
Abstract: We investigate the critical behaviors of the Bell nonlocality, which are measured by the Bell-function values, in conventional and topological quantum-phase transitions. First, by using the quantum-renormalization-group method, we show that the Bell function value of a three-qubit Bell inequality in the anisotropic spin-1/2 XY model exhibits singular behaviors at the critical point. Moreover, for topological quantum-phase transitions, we find that the first-order derivative of the Bell-function value of the well-known Clauser-Horne-Shimony-Holt inequality in the Kitaev-Castelnovo-Chamon model behaves singularly at the topological-phase-transition point. Our results have established a link between quantum nonlocality and phase transitions. © 2012 American Physical Society.
Mon, 10 Sep 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/528082012-09-10T00:00:00Z
- Beyond Gisin's theorem and its applications: Violation of local realism by two-party Einstein-Podolsky-Rosen steeringhttps://scholarbank.nus.edu.sg/handle/10635/175992Title: Beyond Gisin's theorem and its applications: Violation of local realism by two-party Einstein-Podolsky-Rosen steering
Authors: Chen, J.-L; Su, H.-Y; Xu, Z.-P; Wu, Y.-C; Wu, C; Ye, X.-J; Zukowski, M; Kwek, L.C
Abstract: We demonstrate here that for a given mixed multi-qubit state if there are at least two observers for whom mutual Einstein-Podolsky-Rosen steering is possible, i.e. each observer is able to steer the other qubits into two different pure states by spontaneous collapses due to von Neumann type measurements on his/her qubit, then nonexistence of local realistic models is fully equivalent to quantum entanglement (this is not so without this condition). This result leads to an enhanced version of Gisin's theorem (originally: all pure entangled states violate local realism). Local realism is violated by all mixed states with the above steering property. The new class of states allows one e.g. to perform three party secret sharing with just pairs of entangled qubits, instead of three qubit entanglements (which are currently available with low fidelity). This significantly increases the feasibility of having high performance versions of such protocols. Finally, we discuss some possible applications.
Thu, 01 Jan 2015 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1759922015-01-01T00:00:00Z
- Geometric phases for nondegenerate and degenerate mixed stateshttps://scholarbank.nus.edu.sg/handle/10635/52963Title: Geometric phases for nondegenerate and degenerate mixed states
Authors: Singh, K.; Tong, D.M.; Basu, K.; Chen, J.L.; Du, J.F.
Abstract: The issue of phase holonomy of both nondegenerate and degenerate mixed state undergoing unitary evolution was considered. Starting with the nondegenerate case, it was shown that the usual procedure of subtracting the dynamical phase from the total phase to yield the geometric phase, does not hold for mixed states. To this end, an expression for the geometric phase that was gauge invariant was furnished.
Sat, 01 Mar 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/529632003-03-01T00:00:00Z
- Geometric phase for mixed stateshttps://scholarbank.nus.edu.sg/handle/10635/114336Title: Geometric phase for mixed states
Authors: Kwek, L.C.; Tong, D.M.; Chen, J.L.; Du, J.F.; Choo, K.W.; Ravishankar, R.; Kaszlikowski, D.; Oh, C.H.
Abstract: We present a kinematic approach for obtaining the geometric phase of a mixed state under nonunitary evolution. This phase is gauge-invariant and measurable and leads to well-known results for unitary evolution. © Nauka/Interperiodica 2006.
Wed, 01 Feb 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1143362006-02-01T00:00:00Z
- Geometric phase for mixed stateshttps://scholarbank.nus.edu.sg/handle/10635/114335Title: Geometric phase for mixed states
Authors: Tong, D.-M.; Chen, J.-L.; Du, J.-F.
Abstract: The geometric phase of mixed states with non-degenerate eigenvalues is investigated. A general formula of geometric phase for mixed state under unitary evolution is given. In particular, we also furnish an expression of Hamiltonians for equivalent evolutions, by which one can understand what kind of evolutional operator U(t) (or Hamiltonian) is related to zero instantaneous dynamic phase. Moreover, the geometric phase and related Hamiltonians in the spin-half case are provided as an explicit example.
Sun, 01 Jun 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1143352003-06-01T00:00:00Z
- Quantum contextuality for a relativistic spin-1/2 particlehttps://scholarbank.nus.edu.sg/handle/10635/116545Title: Quantum contextuality for a relativistic spin-1/2 particle
Authors: Chen, J.-L.; Su, H.-Y.; Wu, C.; Deng, D.-L.; Cabello, A.; Kwek, L.C.; Oh, C.H.
Abstract: The quantum predictions for a single nonrelativistic spin-1/2 particle can be reproduced by noncontextual hidden variables. Here we show that quantum contextuality for a relativistic electron moving in a Coulomb potential naturally emerges if relativistic effects are taken into account. The contextuality can be identified through the violation of noncontextuality inequalities. We also discuss quantum contextuality for the free Dirac electron as well as the relativistic Dirac oscillator. © 2013 American Physical Society.
Wed, 13 Feb 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1165452013-02-13T00:00:00Z
- Quantum contextuality in a one-dimensional quantum harmonic oscillatorhttps://scholarbank.nus.edu.sg/handle/10635/116546Title: Quantum contextuality in a one-dimensional quantum harmonic oscillator
Authors: Su, H.-Y.; Chen, J.-L.; Wu, C.; Yu, S.; Oh, C.H.
Abstract: We investigate quantum contextuality of one-dimensional quantum harmonic oscillator. Through the violation of a noncontextuality inequality, any eigenstate of quantum harmonic oscillator and some typical continuous-variable states, such as the coherent state and the squeezed state, exhibit quantum contextuality. The state-independent demonstration of quantum contextuality in continuous-variable states is also demonstrated. © 2012 American Physical Society.
Tue, 29 May 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1165462012-05-29T00:00:00Z
- Hardy's paradox for high-dimensional systemshttps://scholarbank.nus.edu.sg/handle/10635/116380Title: Hardy's paradox for high-dimensional systems
Authors: Chen, J.-L.; Cabello, A.; Xu, Z.-P.; Su, H.-Y.; Wu, C.; Kwek, L.C.
Abstract: Hardy's proof is considered the simplest proof of nonlocality. Here we introduce an equally simple proof that (i) has Hardy's as a particular case, (ii) shows that the probability of nonlocal events grows with the dimension of the local systems, and (iii) is always equivalent to the violation of a tight Bell inequality. Our proof has all the features of Hardy's and adds the only ingredient of the Einstein-Podolsky-Rosen scenario missing in Hardy's proof: It applies to measurements with an arbitrarily large number of outcomes. © 2013 American Physical Society.
Mon, 30 Dec 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1163802013-12-30T00:00:00Z
- A bell inequality based on correlation functions for three qubitshttps://scholarbank.nus.edu.sg/handle/10635/95599Title: A bell inequality based on correlation functions for three qubits
Authors: Wu, C.; Chen, J.-L.; Kwek, L.C.; Oh, C.H.
Abstract: We discuss a Bell inequality based on correlation function for three qubits. The inequality is violated by any pure entangled state for 3 qubits. The strength of the violation is the same as the result in Ref. © World Scientific Publishing Company.
Tue, 01 Nov 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/955992005-11-01T00:00:00Z
- Solving the anharmonic oscillator problem with the SU(2) grouphttps://scholarbank.nus.edu.sg/handle/10635/97968Title: Solving the anharmonic oscillator problem with the SU(2) group
Authors: Chen, J.-L.; Kwek, L.C.; Oh, C.H.; Liu, Y.
Abstract: A new perspective for the anharmonic oscillator problem based on the SU(2) group method (SGM) is provided. One finds that the SGM is a possible unified approach to treat both the harmonic oscillator and the anharmonic oscillator, although for the latter only part of the energy spectrum can be obtained. Coordinate translation x → x + λ for the anharmonic potential is also discussed, as one expects that the energy spectrum of an anharmonic oscillator is not affected by the translation.
Fri, 26 Oct 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/979682001-10-26T00:00:00Z
- Zitterbewegung in Bogoliubov's systemhttps://scholarbank.nus.edu.sg/handle/10635/123359Title: Zitterbewegung in Bogoliubov's system
Authors: Li Yan; Su Hong-Yi; Zhang Fu-Lin; Chen Jingling; Wu, Chun-Feng; Kwek, Leong-Chuan
Thu, 01 Jan 2015 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1233592015-01-01T00:00:00Z
- Violating Bell inequalities maximally for two d -dimensional systemshttps://scholarbank.nus.edu.sg/handle/10635/98560Title: Violating Bell inequalities maximally for two d -dimensional systems
Authors: Chen, J.-L.; Wu, C.; Kwek, L.C.; Oh, C.H.; Ge, M.-L.
Abstract: We show the maximal violation of Bell inequalities for two d -dimensional systems by using the method of the Bell operator. The maximal violation corresponds to the maximal eigenvalue of the Bell operator matrix. The eigenvectors corresponding to these eigenvalues are described by asymmetric entangled states. We estimate the maximum value of the eigenvalue for large dimension. A family of elegant entangled states app that violate Bell inequality more strongly than the maximally entangled state but are somewhat close to these eigenvectors is presented. These approximate states can potentially be useful for quantum cryptography as well as many other important fields of quantum information. © 2006 The American Physical Society.
Sun, 01 Jan 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/985602006-01-01T00:00:00Z
- Entangled three-state systems violate local realism more strongly than qubits: An analytical proofhttps://scholarbank.nus.edu.sg/handle/10635/96479Title: Entangled three-state systems violate local realism more strongly than qubits: An analytical proof
Authors: Chen, J.-L.; Kaszlikowski, D.; Kwek, L.C.; Oh, C.H.; Zukowski, M.
Abstract: An analysis for the violation of local realism for two maximally entangled N-dimensional quantum objects was presented. The analysis was performed using two unbiased three input and three output beam splitters. It was proved that the violation of local realism for two maximally entangled N-dimensional quantum object was stronger than for two maximally entangled qubits. The explicit expression for the minimal noise admixture was also proved analytically.
Thu, 01 Nov 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/964792001-11-01T00:00:00Z
- Coincidence Bell inequality for three three-dimensional systemshttps://scholarbank.nus.edu.sg/handle/10635/96012Title: Coincidence Bell inequality for three three-dimensional systems
Authors: Acín, A.; Chen, J.L.; Gisin, N.; Kaszlikowski, D.; Kwek, L.C.; Oh, C.H.; Zukowski, M.
Abstract: A Bell inequality for coincidence probabilities on a three-dimensional (qutrit) system was constructed. The inequality was shown to be violated when each observer measures two noncommuting observables, defined by the six-port beam splitter on a maximally entangled states of two qutrits. For two particles of dimension greater than two, it was observed that the CHSH inequality can be violated in higher dimension system. It was also proven that the inequality defines facets of the polytope of local variable models.
Fri, 25 Jun 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/960122004-06-25T00:00:00Z
- Clauser-Horne inequality for three-state systemshttps://scholarbank.nus.edu.sg/handle/10635/95996Title: Clauser-Horne inequality for three-state systems
Authors: Kaszlikowski, D.; Kwek, L.C.; Chen, J.-L.; Zukowski, M.; Oh, C.H.
Abstract: 36 (of which 32 are independent) inequalities were derived as a necessary condition for the probabilities of correlations observed in two three-dimensional physical systems to be describable in terms of local realism. It was shown that these inequalities are violated by maximally entangled state of two qutrits and the strength of violation defined as the minimal noise admixture Fthr hiding nonclassical nature of quantum correlations agrees with the numerical results in previous studies. Using the inequalities, the critical quantum efficiency of detectors ηcr below which there exists a local realistic description of the investigated quantum system was calculated. The results are consistent with the hypothesis that the inequalities are also sufficient conditions for local realistic description.
Fri, 01 Mar 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/959962002-03-01T00:00:00Z
- Continuous multipartite entangled state in Wigner representation and violation of the Żukowski-Brukner inequalityhttps://scholarbank.nus.edu.sg/handle/10635/96073Title: Continuous multipartite entangled state in Wigner representation and violation of the Żukowski-Brukner inequality
Authors: Wu, C.; Chen, J.-L.; Kwek, L.C.; Oh, C.H.; Xue, K.
Abstract: We construct an explicit Wigner function for the N -mode squeezed state. Based on a previous observation that the Wigner function describes correlations in the joint measurement of the phase-space displaced parity operator, we investigate the nonlocality of the multipartite entangled state by the violation of the Żukowski-Brukner N -qubit Bell inequality. We find that quantum predictions for such a squeezed state violate these inequalities by an amount that grows with the number N. © 2005 The American Physical Society.
Tue, 01 Feb 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/960732005-02-01T00:00:00Z
- Constructing physical systems with dynamical symmetryhttps://scholarbank.nus.edu.sg/handle/10635/96071Title: Constructing physical systems with dynamical symmetry
Authors: Li, Y.; Zhang, F.-L.; Gu, R.-J.; Chen, J.-L.; Kwek, L.C.
Abstract: An approach to constructing quantum systems with dynamical symmetry is proposed. As examples, we construct generalized systems of the hydrogen atom and harmonic oscillator, which can be regarded as the systems with position-dependent mass. They have symmetries that are similar to the corresponding ones, and can be solved by using the algebraic method. We also exhibit an example of the method applied to the noncentral field. © 2013 Published by NRC Research Press.
Wed, 01 Jan 2014 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/960712014-01-01T00:00:00Z
- Unconventional photon blockade in weakly nonlinear photonic molecules with bilateral drivehttps://scholarbank.nus.edu.sg/handle/10635/140946Title: Unconventional photon blockade in weakly nonlinear photonic molecules with bilateral drive
Authors: Gangcheng Wang; H.Z. Shen; Chunfang Sun; Chunfeng Wu; Jing-Ling Chen; Kang Sue
Tue, 01 Nov 2016 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1409462016-11-01T00:00:00Z
- Demonstrating an additional law of relativistic velocities based on squeezed lighthttps://scholarbank.nus.edu.sg/handle/10635/96161Title: Demonstrating an additional law of relativistic velocities based on squeezed light
Authors: Yang, D.-B.; Li, Y.; Zhang, F.-L.; Chen, J.-L.
Abstract: The special relativity is the foundation for many branches of modern physics, of which the theoretical results are far beyond our daily experience and hard to realized in kinematic experiments. However, its outcomes could be demonstrated by making use of the convenient substitute, i.e., the squeezed light in the present paper. The squeezed light is very important in the field of quantum optics, and the corresponding transformation can be regarded as the coherent state of SU(1,1). In this paper, the connection between the squeezed operator and the Lorentz boost is built under certain conditions. Furthermore, the additional law of relativistic velocities and the angle of the Wigner rotation are deduced as well. © 2012 Chinese Physical Society and IOP Publishing Ltd.
Sun, 01 Jul 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/961612012-07-01T00:00:00Z
- Geometric phases for mixed states during cyclic evolutionshttps://scholarbank.nus.edu.sg/handle/10635/96720Title: Geometric phases for mixed states during cyclic evolutions
Authors: Fu, L.-B.; Chen, J.-L.
Abstract: The geometric phases of cyclic evolutions for mixed states are discussed in the framework of unitary evolution. A canonical 1-form is defined whose line integral gives the geometric phase, which is gauge invariant. It reduces to the Aharonov and Anandan phase in the pure state case. Our definition is consistent with the phase shift in the proposed experiment (Sjöqvist et al 2000 Phys. Rev. Lett. 85 2845) for a cyclic evolution if the unitary transformation satisfies the parallel transport condition. A comprehensive geometric interpretation is also given. It shows that the geometric phases for mixed states share the same geometric sense with the pure states.
Fri, 19 Mar 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/967202004-03-19T00:00:00Z
- General formalism of Hamiltonians for realizing a prescribed evolution of a qubithttps://scholarbank.nus.edu.sg/handle/10635/96700Title: General formalism of Hamiltonians for realizing a prescribed evolution of a qubit
Authors: Tong, D.M.; Chen, J.-L.; Kwek, L.C.; Lai, C.H.; Oh, C.H.
Abstract: The inverse problem for the evolution of a qubit was investigated. A general formalism was proposed to establish the Hamiltonian for a qubit system that is required to evolve along a particular path. Both the unitary and nonunitary evolutions of mixed states of a qubit system were detailed.
Mon, 01 Dec 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/967002003-12-01T00:00:00Z
- Non-adiabatic holonomic quantum computation in linear system-bath couplinghttps://scholarbank.nus.edu.sg/handle/10635/180283Title: Non-adiabatic holonomic quantum computation in linear system-bath coupling
Authors: Sun, C; Wang, G; Wu, C; Liu, H; Feng, X.-L; Chen, J.-L; Xue, K
Abstract: Non-adiabatic holonomic quantum computation in decoherence-free subspaces protects quantum information from control imprecisions and decoherence. For the non-collective decoherence that each qubit has its own bath, we show the implementations of two non-commutable holonomic single-qubit gates and one holonomic nontrivial two-qubit gate that compose a universal set of non-adiabatic holonomic quantum gates in decoherence-free-subspaces of the decoupling group, with an encoding rate of N-2/N . The proposed scheme is robust against control imprecisions and the non-collective decoherence, and its non-adiabatic property ensures less operation time. We demonstrate that our proposed scheme can be realized by utilizing only two-qubit interactions rather than many-qubit interactions. Our results reduce the complexity of practical implementation of holonomic quantum computation in experiments. We also discuss the physical implementation of our scheme in coupled microcavities.
Fri, 01 Jan 2016 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1802832016-01-01T00:00:00Z
- Compact Bell inequalities for multipartite experimentshttps://scholarbank.nus.edu.sg/handle/10635/96025Title: Compact Bell inequalities for multipartite experiments
Authors: Wu, Y.-C.; Zukowski, M.; Chen, J.-L.; Guo, G.-C.
Abstract: A method for construction of multipartite Clauser-Horne-Shimony-Holt- (CHSH-) type Bell inequalities, for the case of local binary observables, is presented. The standard CHSH-type Bell inequalities can be obtained as special cases. An iterative method for deriving (N+1)-partite CHSH-type Bell inequalities from N-partite ones is derived. As an application, compact Bell inequalities for eight observers involving just four correlation functions are proposed. They require much less experimental effort than standard methods and thus are experimentally friendly in multiphoton experiments. © 2013 American Physical Society.
Thu, 29 Aug 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/960252013-08-29T00:00:00Z
- Higgs algebraic symmetry of screened system in a spherical geometryhttps://scholarbank.nus.edu.sg/handle/10635/96777Title: Higgs algebraic symmetry of screened system in a spherical geometry
Authors: Li, Y.; Zhang, F.-L.; Gu, R.-J.; Chen, J.-L.
Abstract: The orbits and the dynamical symmetries for the screened Coulomb potentials and isotropic harmonic oscillators have been studied by Wu and Zeng [Z.B. Wu and J.Y. Zeng, Phys. Rev. A 62 (2000) 032509]. We find similar properties in the corresponding systems in a spherical space, whose dynamical symmetries are described by Higgs algebra. There exist extended Runge - Lenz vector for screened Coulomb potentials and extended quadruple tensor for screened harmonic oscillators. They, together with angular momentum, constitute the generators of the geometrical symmetry group. Moreover, there exist an infinite number of closed orbits for suitable angular momentum values, and we give the equations of the classical orbits. The eigenenergy spectrum and corresponding eigenstates in these systems are derived. © 2013 Chinese Physical Society and IOP Publishing Ltd.
Sun, 01 Sep 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/967772013-09-01T00:00:00Z
- Multicomponent Bell inequality and its violation for continuous-variable systemshttps://scholarbank.nus.edu.sg/handle/10635/97267Title: Multicomponent Bell inequality and its violation for continuous-variable systems
Authors: Chen, J.-L.; Wu, C.; Kwek, L.C.; Kaszlikowski, D.; Zukowski, M.; Oh, C.H.
Abstract: Multicomponent correlation functions are developed by utilizing d-outcome measurements. Based on multicomponent correlation functions, we propose a Bell inequality for bipartite d-dimensional systems. Violation of the Bell inequality for continuous-variable (CV) systems is investigated. The violation of maximally entangled states can exceed the Cirel'son bound; the maximal violation is 2.96981. For finite values of the squeezing parameter, the violation strength of CV states increases with dimension d. Numerical results show that the violation strength of CV states with finite squeezing parameters is stronger than that of maximally entangled states. ©2005 The American Physical Society.
Tue, 01 Mar 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/972672005-03-01T00:00:00Z
- Multipartite bound entanglement and three-setting Bell inequalitieshttps://scholarbank.nus.edu.sg/handle/10635/97276Title: Multipartite bound entanglement and three-setting Bell inequalities
Authors: Kaszlikowski, D.; Kwek, L.C.; Chen, J.; Oh, C.H.
Abstract: The three-setting Bell inequalities are shown to be better for the detection of multipartite bound entanglement for the family ℱ. Application of the three-setting Bell inequalities allows to detect bound entanglement for seven qubits whereas such a detection is possible for two-setting Bell inequalities only for eight qubits and only for a certain choice of the parameter αN. Thus, a family of entanglement witnesses which detect bound entanglement for all members of the family ℱ is derived.
Fri, 01 Nov 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/972762002-11-01T00:00:00Z
- Operator-sum representation of time-dependent density operators and its applicationshttps://scholarbank.nus.edu.sg/handle/10635/97435Title: Operator-sum representation of time-dependent density operators and its applications
Authors: Tong, D.M.; Kwek, L.C.; Oh, C.H.; Chen, J.-L.; Ma, L.
Abstract: An arbitrary time-dependent density operator of an open system was described in terms of an operator-sum representation. Its initial condition and the path of its evolution in the state space were ignored. A general expression of Kraus operators for arbitrary time-dependent density operator was obtained. The significance of the results was proved through several examples.
Sat, 01 May 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/974352004-05-01T00:00:00Z
- Bell inequalities for three particleshttps://scholarbank.nus.edu.sg/handle/10635/115609Title: Bell inequalities for three particles
Authors: Chen, J.-L.; Wu, C.; Kwek, L.C.; Oh, C.H.
Abstract: We present tight Bell inequalities expressed by probabilities for three four- and five-dimensional systems. A tight structure of Bell inequalities for three d -dimensional systems (qudits) is proposed. Some interesting Bell inequalities of three qubits reduced from those of three qudits are also studied. © 2008 The American Physical Society.
Mon, 08 Sep 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1156092008-09-08T00:00:00Z
- All-versus-nothing proof of Einstein-Podolsky-Rosen steeringhttps://scholarbank.nus.edu.sg/handle/10635/115577Title: All-versus-nothing proof of Einstein-Podolsky-Rosen steering
Authors: Chen, J.-L.; Ye, X.-J.; Wu, C.; Su, H.-Y.; Cabello, A.; Kwek, L.C.; Oh, C.H.
Abstract: Einstein-Podolsky-Rosen steering is a form of quantum nonlocality intermediate between entanglement and Bell nonlocality. Although Schrödinger already mooted the idea in 1935, steering still defies a complete understanding. In analogy to "all-versus-nothing" proofs of Bell nonlocality, here we present a proof of steering without inequalities rendering the detection of correlations leading to a violation of steering inequalities unnecessary. We show that, given any two-qubit entangled state, the existence of certain projective measurement by Alice so that Bob's normalized conditional states can be regarded as two different pure states provides a criterion for Alice-to-Bob steerability. A steering inequality equivalent to the all-versus-nothing proof is also obtained. Our result clearly demonstrates that there exist many quantum states which do not violate any previously known steering inequality but are indeed steerable. Our method offers advantages over the existing methods for experimentally testing steerability, and sheds new light on the asymmetric steering problem.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1155772013-01-01T00:00:00Z
- Testing leggett's inequality using aharonov-casher effecthttps://scholarbank.nus.edu.sg/handle/10635/117177Title: Testing leggett's inequality using aharonov-casher effect
Authors: Su, H.-Y.; Chen, J.-L.; Wu, C.; Deng, D.-L.; Oh, C.H.
Abstract: Bell's inequality is established based on local realism. The violation of Bell's inequality by quantum mechanics implies either locality or realism or both are untenable. Leggett's inequality is derived based on nonlocal realism. The violation of Leggett's inequality implies that quantum mechanics is neither local realistic nor nonlocal realistic. The incompatibility of nonlocal realism and quantum mechanics has been currently confirmed by photon experiments. In our work, we propose to test Leggett's inequality using the Aharonov-Casher effect. In our scheme, four entangled particles emitted from two sources manifest a two-qubit-typed correlation that may result in the violation of the Leggett inequality, while satisfying the no-signaling condition for spacelike separation. Our scheme is tolerant to some local inaccuracies due to the topological nature of the Aharonov-Casher phase. The experimental implementation of our scheme can be possibly realized by a calcium atomic polarization interferometer experiment.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1171772013-01-01T00:00:00Z
- Maximal violation of Clauser-Horne-Shimony-Holt inequality for four-level systemshttps://scholarbank.nus.edu.sg/handle/10635/97153Title: Maximal violation of Clauser-Horne-Shimony-Holt inequality for four-level systems
Authors: Fu, L.-B.; Chen, J.-L.; Chen, S.-G.
Abstract: The unbiased eight-port beam splitters measurements were used to investigate Clauser-Horne-Shimony-Holt (CHSH) inequality for bipartite systems of four dimensions. The optimal angles and the optimal states were also measured. The uniform formulas for the minimum and maximum values of the inequality for such measurement were derived. By compairing the two states, it was found that an optimal nonmaximally entangled state was about 6 percent more resistant to noise than the maximally entangled state.
Mon, 01 Mar 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/971532004-03-01T00:00:00Z
- Maximal violation of the Clauser-Horne-Shimony-Holt inequality for two qutritshttps://scholarbank.nus.edu.sg/handle/10635/97154Title: Maximal violation of the Clauser-Horne-Shimony-Holt inequality for two qutrits
Authors: Fu, L.-B.; Chen, J.-L.; Zhao, X.-G.
Abstract: The application of tritter measurements for investigating maximal violation of the Bell-Clauser-Horne-Shimoy-Holt (BCHSH) inequality for two qutrits was discussed. The BCHSH inequality was violated by the nonmaximally entangled states more strongly. The optimal nonmaximally entangled state of two qutrits was found 3% more resistant to noise than the maximally entangled one.
Fri, 01 Aug 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/971542003-08-01T00:00:00Z
- Most robust and fragile two-qubit entangled states under depolarizing channelshttps://scholarbank.nus.edu.sg/handle/10635/97262Title: Most robust and fragile two-qubit entangled states under depolarizing channels
Authors: Pang, C.-Q.; Zhang, F.-L.; Jiang, Y.; Liang, M.-L.; Chen, J.-L.
Abstract: For a two-qubit system under local depolarizing channels, the most robust and most fragile states are derived for a given concurrence or negativity. For the one-sided channel, the pure states are proved to be the most robust ones, with the aid of the evolution equation for entanglement given by Konrad et al. [Nat. Phys. 4, 99 (2008)]. Based on a generalization of the evolution equation for entanglement, we classify the ansatz states in our investigation by the amount of robustness, and consequently derive the most fragile states. For the two-sided channel, the pure states are the most robust for a fixed concurrence. Under the uniform channel, the most fragile states have the minimal negativity when the concurrence is given in the region [1/2, 1]. For a given negativity, the most robust states are the ones with the maximal concurrence, and the most fragile ones are the pure states with minimum of concurrence. When the entanglement approaches zero, the most fragile states under general nonuniform channels tend to the ones in the uniform channel. Influences on robustness by entanglement, degree of mixture, and asymmetry between the two qubits are discussed through numerical calculations. It turns out that the concurrence and negativity are major factors for the robustness. When they are fixed, the impact of the mixedness becomes obvious. In the nonuniform channels, the most fragile states are closely correlated with the asymmetry, while the most robust ones with the degree of mixture. © Rinton Press.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/972622013-01-01T00:00:00Z
- Reply to 'comment on geometric phases for mixed states during cyclic evolutions'https://scholarbank.nus.edu.sg/handle/10635/99019Title: Reply to 'comment on geometric phases for mixed states during cyclic evolutions'
Authors: Fu, L.-B.; Chen, J.-L.
Abstract: We show that the geometric phase for mixed state during a cyclic evolution suggested in 2004 J. Phys. A: Math. Gen. 37 3699 is U(1) gauge invariant and can be observed by modern techniques.
Fri, 23 Jul 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/990192004-07-23T00:00:00Z
- Wringing out new bell inequalities for three-dimensional systems (Qutrits)https://scholarbank.nus.edu.sg/handle/10635/98994Title: Wringing out new bell inequalities for three-dimensional systems (Qutrits)
Authors: Chen, J.-L.; Kaszlikowski, D.; Kwek, L.C.; Oh, C.H.
Abstract: We briefly trace the progress in study of Bell-CH inequalities from two-level systems to its higher dimensional versions. We also present a Bell-CH and CHSH-like inequality for three-dimensional systems.
Sun, 10 Nov 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/989942002-11-10T00:00:00Z
- Improved lower bounds on genuine-multipartite-entanglement concurrencehttps://scholarbank.nus.edu.sg/handle/10635/96882Title: Improved lower bounds on genuine-multipartite-entanglement concurrence
Authors: Chen, Z.-H.; Ma, Z.-H.; Chen, J.-L.; Severini, S.
Abstract: Genuine-multipartite-entanglement (GME) concurrence is a measure of genuine multipartite entanglement that generalizes the well-known notion of concurrence. We define an observable for GME concurrence. The observable permits us to avoid full state tomography and leads to different analytic lower bounds. By means of explicit examples we show that entanglement criteria based on the bounds have a better performance with respect to the known methods. © 2012 American Physical Society.
Fri, 22 Jun 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/968822012-06-22T00:00:00Z
- Gisin's theorem for three qubitshttps://scholarbank.nus.edu.sg/handle/10635/96729Title: Gisin's theorem for three qubits
Authors: Chen, J.-L.; Wu, C.; Kwek, L.C.; Oh, C.H.
Abstract: The gisin's theorem for three quibits are discussed. A theorem was presented initially that all generalized GHZ states of a three quibit system violates a bell inequality in terms of probabilities. The theorem shows that it was possible for a bell inequality in terms of probability to be violated by all pure entangled generalized GHZ state. The results show that bell inequality can be used to measure the degree of entanglement of the state by knowing that a pure state is a 2-entangled state of three quibit system or not.
Fri, 01 Oct 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/967292004-10-01T00:00:00Z
- Irreducible multiqutrit correlations in Greenberger-Horne-Zeilinger-type stateshttps://scholarbank.nus.edu.sg/handle/10635/97007Title: Irreducible multiqutrit correlations in Greenberger-Horne-Zeilinger-type states
Authors: Zhang, F.-L.; Chen, J.-L.
Abstract: Following the idea of the continuity approach by D. L. Zhou, we obtain the degrees of irreducible multiparty correlations in two families of n-qutrit Greenberger-Horne-Zeilinger-type states. For the pure states in one of the families, the irreducible 2-party, n-party, and (n-m)-party (0
Wed, 28 Dec 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/970072011-12-28T00:00:00Z
- Kraus representation for the density operator of a qubithttps://scholarbank.nus.edu.sg/handle/10635/97027Title: Kraus representation for the density operator of a qubit
Authors: Tong, D.M.; Chen, J.L.; Huang, J.Y.; Kwek, L.C.; Oh, C.H.
Abstract: We show that the time evolution of the density operator of a qubit can always be described in terms of the Kraus representation. A general scheme on how to construct the Kraus operators for an open qubit system is proposed, which can be generalized to open higher dimensional quantum systems. © Nauka/Interperiodica 2006.
Wed, 01 Nov 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/970272006-11-01T00:00:00Z
- Quantum nonlocality of Heisenberg XX model with site-dependent coupling strengthhttps://scholarbank.nus.edu.sg/handle/10635/97697Title: Quantum nonlocality of Heisenberg XX model with site-dependent coupling strength
Authors: Wu, C.; Chen, J.-L.; Tong, D.M.; Kwek, L.C.; Oh, C.H.
Abstract: We show that the generalized Bell inequality is violated in the extended Heisenberg model when the temperature is below a threshold value. The threshold temperature values are obtained by constructing exact solutions of the model using the temperature-dependent correlation functions. The effect due to the presence of an external magnetic field is also illustrated.
Fri, 26 Nov 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/976972004-11-26T00:00:00Z
- Nonlocal distillation based on multisetting Bell inequalityhttps://scholarbank.nus.edu.sg/handle/10635/97353Title: Nonlocal distillation based on multisetting Bell inequality
Authors: Ye, X.-J.; Deng, D.-L.; Chen, J.-L.
Abstract: Inspired by the recent works of Foster and Brunner, we present a nonlocality distillation protocol for two three-level (qutrit) systems in the framework of generalized nonsignaling theories. Our protocol is based on a three-setting Bell inequality. It works efficiently for a specific class of three-input-three-output nonlocal boxes. In the asymptotic limit, all these nonlocal boxes can be distilled to the maximally nonlocal box defined by the inequality and nonsignaling constraints. Then we introduce a contracting protocol that reduces these boxes to the so-called "correlated nonlocal boxes." As a result, our three-input-three-output nonlocal boxes also make communication complexity trivial and appear very unlikely to exist in nature. © 2012 American Physical Society.
Mon, 10 Dec 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/973532012-12-10T00:00:00Z
- Quartic anharmonic oscillator and non-hermiticityhttps://scholarbank.nus.edu.sg/handle/10635/97721Title: Quartic anharmonic oscillator and non-hermiticity
Authors: Chen, J.-L.; Kwek, L.C.; Oh, C.H.
Abstract: The nature of the energy spectrum, particularly the wave function, of the quartic anharmonic oscillator was investigated using group-theoretic approach. The approach allowed to explore the relation of the associated wave function to hermiticity of the Hamiltonian.
Wed, 01 Jan 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/977212003-01-01T00:00:00Z
- State-independent contextuality sets for a qutrithttps://scholarbank.nus.edu.sg/handle/10635/123572Title: State-independent contextuality sets for a qutrit
Authors: Xu, Zhenpeng; Chen, Jingling; Su, Hongyi
Thu, 01 Jan 2015 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1235722015-01-01T00:00:00Z
- Searching a database under decoherencehttps://scholarbank.nus.edu.sg/handle/10635/97871Title: Searching a database under decoherence
Authors: Chen, J.; Kaszlikowski, D.; Kwek, L.C.; Oh, C.H.
Abstract: We report the effects of a simple decoherence model on the quantum search algorithm. Despite its simplicity, the decoherence model is an instructive model that can genuinely imitate realistic noisy environment in many situations. As one would expect, as the size of the database gets larger, the effects of decoherence on the efficiency of the quantum search algorithm cannot be ignored. Moreover, with decoherence, it may not be useful to iterate beyond the first maxima in the probability distribution of the search entry. Surprisingly, we also find that the number of iterations for maximum probability of the search entry reduces with decoherence. © 2002 Elsevier Science B.V. All rights reserved.
Mon, 13 Jan 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/978712003-01-13T00:00:00Z
- Security of quantum key distributions with entangled quditshttps://scholarbank.nus.edu.sg/handle/10635/97875Title: Security of quantum key distributions with entangled qudits
Authors: Durt, T.; Kaszlikowski, D.; Chen, J.-L.; Kwek, L.C.
Abstract: The generality of Ekert's entanglement-based cryptographic protocol where qubits were relaced by N or d-dimensional system was presented. The information gained by a potential eavesdropper was derived, to study its robustness against optimal incoherent attacks, during a cloning -based individual attack. It was shown that the accepatable error rate of the N-DEB protocol increases with the dimension N. It was found that the maximal error rate provides a good qualitative measure of the security of the protocol.
Mon, 01 Mar 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/978752004-03-01T00:00:00Z
- Demonstration of Einstein–Podolsky–Rosen steering with enhanced subchannel discriminationhttps://scholarbank.nus.edu.sg/handle/10635/212529Title: Demonstration of Einstein–Podolsky–Rosen steering with enhanced subchannel discrimination
Authors: Sun, K.; Ye, X.-J.; Xiao, Y.; Xu, X.-Y.; Wu, Y.-C.; Xu, J.-S.; Chen, J.-L.; Li, C.-F.; Guo, G.-C.
Abstract: Einstein–Podolsky–Rosen (EPR) steering describes a quantum nonlocal phenomenon in which one party can nonlocally affect the other’s state through local measurements. It reveals an additional concept of quantum non-locality, which stands between quantum entanglement and Bell nonlocality. Recently, a quantum information task named as subchannel discrimination (SD) provides a necessary and sufficient characterization of EPR steering. The success probability of SD using steerable states is higher than using any unsteerable states, even when they are entangled. However, the detailed construction of such subchannels and the experimental realization of the corresponding task are still technologically challenging. In this work, we designed a feasible collection of subchannels for a quantum channel and experimentally demonstrated the corresponding SD task where the probabilities of correct discrimination are clearly enhanced by exploiting steerable states. Our results provide a concrete example to operationally demonstrate EPR steering and shine a new light on the potential application of EPR steering. © 2018, The Author(s).
Mon, 01 Jan 2018 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/2125292018-01-01T00:00:00Z
- Requirement of dissonance in assisted optimal state discriminationhttps://scholarbank.nus.edu.sg/handle/10635/115913Title: Requirement of dissonance in assisted optimal state discrimination
Authors: Zhang, F.-L.; Chen, J.-L.; Kwek, L.C.; Vedral, V.
Abstract: A fundamental problem in quantum information is to explore what kind of quantum correlations is responsible for successful completion of a quantum information procedure. Here we study the roles of entanglement, discord, and dissonance needed for optimal quantum state discrimination when the latter is assisted with an auxiliary system. In such process, we present a more general joint unitary transformation than the existing results. The quantum entanglement between a principal qubit and an ancilla is found to be completely unnecessary, as it can be set to zero in the arbitrary case by adjusting the parameters in the general unitary without affecting the success probability. This result also shows that it is quantum dissonance that plays as a key role in assisted optimal state discrimination and not quantum entanglement. A necessary criterion for the necessity of quantum dissonance based on the linear entropy is also presented. PACS numbers: 03.65.Ta, 03.67.Mn, 42.50.Dv.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1159132013-01-01T00:00:00Z