ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Wed, 22 Jan 2020 13:45:02 GMT2020-01-22T13:45:02Z50481- Entanglement and the berry phase in a new yang-baxter systemhttps://scholarbank.nus.edu.sg/handle/10635/96482Title: Entanglement and the berry phase in a new yang-baxter system
Authors: Wang, G.; Xue, K.; Wu, C.; Liang, H.; Oh, C.H.
Abstract: We present a new S-matrix, a solution of the braid relation and obtain a unitary solution of the Yang-Baxter equation (YBE) via Yang-Baxterization acting on the solution. We show that arbitrary two-qubit entangled states can be achieved by relating the unitary matrix to entanglement. An oscillator Hamiltonian can be constructed from the matrix. The Berry phase of the Yang-Baxter system is investigated. © 2009 IOP Publishing Ltd.
Thu, 01 Jan 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/964822009-01-01T00:00:00Z
- A study on the relations between the topological parameter and entanglementhttps://scholarbank.nus.edu.sg/handle/10635/116912Title: A study on the relations between the topological parameter and entanglement
Authors: Sun, C.; Xue, K.; Wang, G.; Wu, C.
Abstract: In this Letter, some relations between the topological parameter d and concurrences of the projective entangled states have been presented. It is shown that for the case with d=n, all the projective entangled states of two n-dimensional quantum systems are the maximally entangled states (i.e. C=1). And for another case with d≠n, C both approach 0 when d→+∞ for n=2 and 3. Then we study the thermal entanglement and the entanglement sudden death (ESD) for a kind of Yang-Baxter Hamiltonian. It is found that the parameter d influences not only the critical temperature T c but also the maximum entanglement value that the system can arrive at. And we also find that the parameter d has a great influence on the ESD. © 2012 Elsevier B.V.
Mon, 01 Oct 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1169122012-10-01T00:00:00Z
- Geometric phase induced by quantum nonlocalityhttps://scholarbank.nus.edu.sg/handle/10635/115124Title: Geometric phase induced by quantum nonlocality
Authors: Wang, Z.S.; Wu, C.; Feng, X.-L.; Kwek, L.C.; Lai, C.H.; Oh, C.H.; Vedral, V.
Abstract: By analyzing an instructive example, for testing many concepts and approaches in quantum mechanics, of a one-dimensional quantum problem with moving infinite square-well, we define geometric phase of the physical system. We find that there exist three dynamical phases from the energy, the momentum and local change in spatial boundary condition respectively, which is different from the conventional computation of geometric phase. The results show that the geometric phase can fully describe the nonlocal character of quantum behavior. © 2007 Elsevier B.V. All rights reserved.
Mon, 04 Feb 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1151242008-02-04T00:00:00Z
- Optical rotation of heavy hole spins by non-Abelian geometrical meanshttps://scholarbank.nus.edu.sg/handle/10635/97453Title: Optical rotation of heavy hole spins by non-Abelian geometrical means
Authors: Sun, H.; Feng, X.-L.; Wu, C.; Liu, J.-M.; Gong, S.; Oh, C.H.
Abstract: A non-Abelian geometric method is proposed for rotating of heavy hole spins in a singly positive charged quantum dot in Voigt geometry. The key ingredient is the delay-dependent non-Abelian geometric phase, which is produced by the nonadiabatic transition between the two degenerate dark states. We demonstrate, by controlling the pump, the Stokes and the driving fields, that the rotations about y and z axes with arbitrary angles can be realized with high fidelity. Fast initialization and heavy hole-spin-state readout are also possible. © 2009 The American Physical Society.
Thu, 03 Dec 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/974532009-12-03T00:00:00Z
- Nonadiabatic geometric quantum computationhttps://scholarbank.nus.edu.sg/handle/10635/97328Title: Nonadiabatic geometric quantum computation
Authors: Wang, Z.S.; Wu, C.; Feng, X.-L.; Kwek, L.C.; Lai, C.H.; Oh, C.H.; Vedral, V.
Abstract: A different way to realize nonadiabatic geometric quantum computation is proposed by varying parameters in the Hamiltonian for nuclear-magnetic resonance, where the dynamical and geometric phases are implemented separately without the usual operational process. Therefore the phase accumulated in the geometric gate is a pure geometric phase for any input state. In comparison with the conventional geometric gates by rotating operations, our approach simplifies experimental implementations making them robust to certain experimental errors. In contrast to the unconventional geometric gates, our approach distinguishes the total and geometric phases and offers a wide choice of the relations between the dynamical and geometric phases. © 2007 The American Physical Society.
Fri, 05 Oct 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/973282007-10-05T00:00:00Z
- Fault-tolerant Greenberger-Horne-Zeilinger paradox based on non-Abelian anyonshttps://scholarbank.nus.edu.sg/handle/10635/52936Title: Fault-tolerant Greenberger-Horne-Zeilinger paradox based on non-Abelian anyons
Authors: Deng, D.-L.; Wu, C.; Chen, J.-L.; Oh, C.H.
Abstract: We propose a scheme to test the Greenberger-Horne-Zeilinger paradox based on braidings of non-Abelian anyons, which are exotic quasiparticle excitations of topological states of matter. Because topological ordered states are robust against local perturbations, this scheme is in some sense "fault- tolerant" and might close the detection inefficiency loophole problem in previous experimental tests of the Greenberger-Horne-Zeilinger paradox. In turn, the construction of the Greenberger-Horne-Zeilinger paradox reveals the nonlocal property of non-Abelian anyons. Our results indicate that the non-Abelian fractional statistics is a pure quantum effect and cannot be described by local realistic theories. Finally, we present a possible experimental implementation of the scheme based on the anyonic interferometry technologies. © 2010 The American Physical Society.
Wed, 04 Aug 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/529362010-08-04T00:00:00Z
- 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
- Dynamics of quantum-classical hybrid systems: Effect of matter-wave pressurehttps://scholarbank.nus.edu.sg/handle/10635/112423Title: Dynamics of quantum-classical hybrid systems: Effect of matter-wave pressure
Authors: Shen, J.; Huang, X.L.; Yi, X.X.; Wu, C.; Oh, C.H.
Abstract: Radiation pressure affects the kinetics of a system exposed to radiation and it constitutes the basis of laser cooling. In this article, we study matter-wave pressure through examining the dynamics of a quantum-classical hybrid system. The quantum and classical subsystems are affected mutually via a changing boundary condition. Two systems, that is, an atom and a Bose-Einstein condensate (BEC), are considered as the quantum subsystems, while an oscillating wall is taken as the classical subsystem. We show that the classical subsystem would experience a force proportional to Q-3 from the quantum atom, where Q denotes the distance between the two walls, whereas it acquires an additional force proportional to Q-2 from the BEC due to the atom-atom interaction in the BEC. These forces can be understood as the matter-wave pressure. © 2010 The American Physical Society.
Tue, 07 Dec 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124232010-12-07T00:00:00Z
- Quantum nonlocality of N -qubit W stateshttps://scholarbank.nus.edu.sg/handle/10635/97698Title: Quantum nonlocality of N -qubit W states
Authors: Wu, C.; Chen, J.-L.; Kwek, L.C.; Oh, C.H.
Abstract: An experimental setup for testing quantum nonlocality of N qubits is proposed. This method is a generalization of the optical setup proposed by Banaszek and Wódkiewicz [Phys. Rev. Lett. 82, 2009 (1999)]. The quantum nonlocality of N qubits can be obtained through its violation of N -qubit Bell inequalities. The correlation function measured in the experiment is described by the Wigner function. The effect of inefficient detector is also considered. © 2006 The American Physical Society.
Sun, 01 Jan 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/976982006-01-01T00:00:00Z
- Geometric entangling gates in decoherence-free subspaces with minimal requirementshttps://scholarbank.nus.edu.sg/handle/10635/96714Title: Geometric entangling gates in decoherence-free subspaces with minimal requirements
Authors: Feng, X.-L.; Wu, C.; Sun, H.; Oh, C.H.
Abstract: We introduce a new strongly driven dispersive atom-cavity interaction and develop a new scheme for implementing the nontrivial entangling gates for two logical qubits in decoherence-free subspaces (DFSs). Our scheme combines the robust advantages of DFS and the geometric phase. Moreover, only two neighboring physical qubits, which encode a logical qubit, are required to undergo the collective dephasing in our scheme. © 2009 The American Physical Society.
Tue, 10 Nov 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/967142009-11-10T00:00:00Z
- Entanglement of three qubitshttps://scholarbank.nus.edu.sg/handle/10635/96490Title: Entanglement of three qubits
Authors: Wu, C.; Chen, J.-L.; Kwek, L.C.; Yeo, Y.; Oh, C.H.
Abstract: For the formulation of Bell inequalities, it is important to include not just N-site correlation functions, but also (N-n)-site correlation functions. In this article, we focus on a three-qubit Bell inequality, which has been shown to be a good candidate for generalizing Gisin's theorem to three qubits. The three-qubit Bell inequality can be used to detect the W-type entanglement in a proposed experiment. © 2007 MAIK "Nauka/Interperiodica".
Wed, 01 Aug 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/964902007-08-01T00:00:00Z
- Modified heisenbeg model and the structure of its energy spectrumhttps://scholarbank.nus.edu.sg/handle/10635/97240Title: Modified heisenbeg model and the structure of its energy spectrum
Authors: Wang, X.-H.; Wu, C.
Abstract: In this paper, we show the interesting structure of energy spectrum for a modified Heisenberg XX model, explicit examples for low dimensions N=2,3,6 are also provided. © 2007 Springer Science+Business Media, LLC.
Thu, 01 Nov 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/972402007-11-01T00:00:00Z
- 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
- Scheme for unconventional geometric quantum computation in cavity QEDhttps://scholarbank.nus.edu.sg/handle/10635/97867Title: Scheme for unconventional geometric quantum computation in cavity QED
Authors: Feng, X.-L.; Wang, Z.; Wu, C.; Kwek, L.C.; Lai, C.H.; Oh, C.H.
Abstract: In this paper, we present a scheme for implementing the unconventional geometric two-qubit phase gate with nonzero dynamical phase based on two-channel Raman interaction of two atoms in a cavity. We show that the dynamical phase and the total phase for a cyclic evolution are proportional to the geometric phase in the same cyclic evolution; hence they possess the same geometric features as does the geometric phase. In our scheme, the atomic excited state is adiabatically eliminated, and the operation of the proposed logic gate involves only the metastable states of the atoms; thus the effect of the atomic spontaneous emission can be neglected. The influence of the cavity decay on our scheme is examined. It is found that the relations regarding the dynamical phase, the total phase, and the geometric phase in the ideal situation are still valid in the case of weak cavity decay. Feasibility and the effect of the phase fluctuations of the driving laser fields are also discussed. © 2007 The American Physical Society.
Wed, 09 May 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/978672007-05-09T00:00:00Z
- 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
- 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
- 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
- Geometric phase gate with trapped ions in thermal motion by adiabatic passagehttps://scholarbank.nus.edu.sg/handle/10635/112445Title: Geometric phase gate with trapped ions in thermal motion by adiabatic passage
Authors: Zhang, X.L.; Feng, X.L.; Wu, C.F.; Oh, C.H.
Abstract: We propose a scheme for implementing two-qubit geometric phase gate via the adiabatic evolution for trapped ions in thermal motion, leveraging on the stimulated Raman adiabatic passage with the geometric phase mechanism. Evolution along a dark state makes our scheme not only immune from decoherence due to spontaneous emission from excited states, but also rid off the dynamical phase. Furthermore, due to the opposite detuning of the driving lasers, the vibrational states of the trapped ions are only virtually excited during the operations, so our scheme is also insensitive to the occupation number of the vibrational mode. © 2010 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.
Mon, 01 Nov 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124452010-11-01T00:00:00Z
- Quantum gate operations in the decoherence-free subspace of superconducting quantum-interference deviceshttps://scholarbank.nus.edu.sg/handle/10635/97682Title: Quantum gate operations in the decoherence-free subspace of superconducting quantum-interference devices
Authors: Wu, C.; Feng, X.-L.; Yi, X.X.; Chen, I.M.; Oh, C.H.
Abstract: We propose a scheme for implementing single-qubit and nontrivial two-qubit gate operations in a system with superconducting quantum interference devices (SQUIDs) via Raman transitions in circuit QED. The gate operations only involve the two lower flux states of the SQUID, and hence the effect of the excited state can be neglected. By encoding quantum information into the decoherence free subspace of the SQUID system, the evolution of the system results in fault-tolerant quantum gates. The effect of decoherence caused by the decay of the transmission line resonator is investigated. © 2008 The American Physical Society.
Thu, 11 Dec 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/976822008-12-11T00:00:00Z
- Nongeometric multiqubit conditional phase gates by adiabatic evolution for trapped ionshttps://scholarbank.nus.edu.sg/handle/10635/97339Title: Nongeometric multiqubit conditional phase gates by adiabatic evolution for trapped ions
Authors: Zhang, X.L.; Feng, X.-L.; Wu, C.; Oh, C.H.
Abstract: We propose a scheme for realizing controlled multiqubit quantum phase gates via the adiabatic evolution for trapped ions. Leveraging on the adiabatic operation, the scheme is tolerant to ambient noise and insensitive to the randomness of moderate fluctuations in experimental parameters. In our scheme, the ions are illuminated by lasers tuned to the first lower vibrational sideband or quasiresonant transition, the vibrational mode is not utilized as a data bus, and dark state evolution is required. The required gate operation time does not increase with the increasing number of qubits. This leads to a more efficient implementation of multiqubit gates than that of a series of one-qubit and two-qubit operations for quantum circuits and quantum algorithms. © 2009 The American Physical Society.
Tue, 03 Mar 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/973392009-03-03T00:00:00Z
- Proposed entanglement swapping in continuous variable systems via braidinghttps://scholarbank.nus.edu.sg/handle/10635/97630Title: Proposed entanglement swapping in continuous variable systems via braiding
Authors: Su, H.-Y.; Chen, J.-L.; Deng, D.-L.; Wu, C.-F.
Abstract: We study entanglement swapping in continuous variable systems by using braiding transformations. It is found that entanglement swapping in two-mode squeezed vacuum states and squeezed coherent states can be realized based on the braiding operators. © Chinese Physical Society and IOP Publishing Ltd.
Wed, 01 Dec 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/976302010-12-01T00:00:00Z
- 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
- The Berry phase subject to q-deformed magnetic fieldhttps://scholarbank.nus.edu.sg/handle/10635/112530Title: The Berry phase subject to q-deformed magnetic field
Authors: Du, G.; Xue, K.; Wang, G.; Wu, C.; Zhou, C.; Sun, C.
Abstract: We investigate the Berry phase of a spin system in a q-deformed magnetic field. The Berry phase depends on parameter q and which causes the deformation of the Berry phase. When q ≠ 1, the parameter space for the spin-half particles in magnetic field is deformed and immovable at the point of φ = 0, π/2, π. The same Hamiltonian can also be constructed by q-deformed Lie-algebra and magnetic field. © 2012 Springer Science+Business Media, LLC.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1125302013-01-01T00:00:00Z
- Thermal entanglement in the two-qubit systems constructed from the Yang-Baxter Ř-matrixhttps://scholarbank.nus.edu.sg/handle/10635/98356Title: Thermal entanglement in the two-qubit systems constructed from the Yang-Baxter Ř-matrix
Authors: Sun, C.; Hu, T.; Wang, G.; Wu, C.; Xue, K.
Abstract: Some new Hamiltonians are constructed via the unitary Yang-Baxter matrices Ři,i+1 (θ, φ) acting on a Hamiltonian H0 which describes nearest spin-spin interaction. By the concept of concurrence, we explore the thermal entanglement of these systems. We find that the interaction of z-component of two neighboring spins g has great influences on the thermal entanglement. It not only influences the critical temperature Tc, but can also influence the critical magnetic field Bc. © 2009 World Scientific Publishing Company.
Thu, 01 Jan 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/983562009-01-01T00:00:00Z
- Berry phase and entanglement of three qubits in a new Yang-Baxter systemhttps://scholarbank.nus.edu.sg/handle/10635/95863Title: Berry phase and entanglement of three qubits in a new Yang-Baxter system
Authors: Hu, T.; Xue, K.; Wu, C.
Abstract: In this paper we construct a new 8×8 M matrix from the 4×4 M matrix, where M/M is the image of the braid group representation. The 8×8 M matrix and the 4×4 M matrix both satisfy extraspecial 2-group algebra relations. By Yang-Baxteration approach, we derive a unitary R (θ,) matrix from the M matrix with parameters and θ. Three-qubit entangled states can be generated by using the R (θ,) matrix. A Hamiltonian for three qubits is constructed from the unitary R (θ,) matrix. We then study the entanglement and Berry phase of the Yang-Baxter system. © 2009 The American Physical Society.
Thu, 01 Jan 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/958632009-01-01T00:00:00Z
- Driving quantum systems into decoherence-free subspaces by Lyapunov controlhttps://scholarbank.nus.edu.sg/handle/10635/52879Title: Driving quantum systems into decoherence-free subspaces by Lyapunov control
Authors: Yi, X.X.; Huang, X.L.; Wu, C.; Oh, C.H.
Abstract: We present a scheme to drive a finite-dimensional quantum system into the decoherence-free subspaces (DFS) by Lyapunov control. Control fields are established by Lyapunov function. This proposal works well for both closed and open quantum systems, with replacing the DFS by desired subspaces for closed systems. An example which consists of a four-level system with three degenerate states driven by three lasers is presented to gain further insight on the scheme. Numerical simulations for the dynamics of the system are performed and the results are good. © 2009 The American Physical Society.
Thu, 12 Nov 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/528792009-11-12T00:00:00Z
- Effective Hamiltonian approach to open systems and its applicationshttps://scholarbank.nus.edu.sg/handle/10635/96352Title: Effective Hamiltonian approach to open systems and its applications
Authors: Huang, X.L.; Yi, X.X.; Wu, C.; Feng, X.L.; Yu, S.X.; Oh, C.H.
Abstract: By using the effective Hamiltonian approach, we present a self-consistent framework for the analysis of geometric phases and dynamically stable decoherence-free subspaces in open systems. Comparisons to the earlier works are made. This effective Hamiltonian approach is then extended to a non-Markovian case with the generalized Lindblad master equation. Based on this extended effective Hamiltonian approach, the non-Markovian master equation describing a dissipative two-level system is solved, an adiabatic evolution is defined, and the corresponding adiabatic condition is given. © 2008 The American Physical Society.
Tue, 30 Dec 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/963522008-12-30T00:00:00Z
- Effects of a squeezed-vacuum reservoir on geometric phasehttps://scholarbank.nus.edu.sg/handle/10635/52894Title: Effects of a squeezed-vacuum reservoir on geometric phase
Authors: Wang, Z.S.; Wu, C.; Feng, X.-L.; Kwek, L.C.; Lai, C.H.; Oh, C.H.
Abstract: Geometric phase, for a two-level atom in an electromagnetic field interacting with a squeezed-vacuum reservoir, is calculated by establishing connecting density matrices, describing an evolution of a quantum open system, with a nonunit vector ray in a complex projective Hilbert space. Because the geometric phase depends only on the smooth curve on this space, it is formulated entirely in terms of geometric structures. The results show that the geometric phase for the squeezed-vacuum reservoir has fully different behavior in comparison with one for the normal vacuum reservoir. © 2007 The American Physical Society.
Thu, 15 Feb 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/528942007-02-15T00:00:00Z
- The hybrid quantum computerhttps://scholarbank.nus.edu.sg/handle/10635/98280Title: The hybrid quantum computer
Authors: Kwek, L.C.; Lim, Y.L.; Wu, C.; Chen, J.-L.; Liu, X.; Feng, X.; Tong, D.M.; Choo, K.W.; Oh, C.H.
Abstract: In this paper, we look at the possibility of realizing one-way quantum computing through a hybrid quantum computing architecture based on stationary qubits inside an optical cavity and flying qubits (photons). It has been shown that direct qubit-qubit interactions for two-qubit gate implementations can be replaced by the experimentally less demanding generation of single photons on demand and linear optics photon pair measurements. The outcomes of these measurements indicate either the completion of the gate or the presence of the original qubits, such that the operation can be repeated until success. © 2007 MAIK "Nauka/Interperiodica".
Wed, 01 Aug 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/982802007-08-01T00:00:00Z
- 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
- 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
- Quantum nonlocality of four-qubit entangled stateshttps://scholarbank.nus.edu.sg/handle/10635/97696Title: Quantum nonlocality of four-qubit entangled states
Authors: Wu, C.; Yeo, Y.; Kwek, L.C.; Oh, C.H.
Abstract: 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 | χ that has recently been proposed in. The Bell inequality is optimally violated by | χ but not violated by the GHZ state. The linear cluster state also violates the Bell inequality though not optimally. The state | χ 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. © 2007 The American Physical Society.
Mon, 26 Mar 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/976962007-03-26T00:00:00Z
- 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
- Strongly interacting photons in asymmetric quantum well via resonant tunnelinghttps://scholarbank.nus.edu.sg/handle/10635/112523Title: Strongly interacting photons in asymmetric quantum well via resonant tunneling
Authors: Sun, H.; Fan, S.L.; Feng, X.L.; Wu, C.F.; Gong, S.Q.; Huang, G.X.; Oh, C.H.
Abstract: We propose an asymmetric quantum well structure to realize strong interaction between two slow optical pulses. The essential idea is the combination of the advantages of inverted-Y type scheme and resonant tunneling. We analytically demonstrate that giant cross-Kerr nonlinearity can be achieved with vanishing absorptions. Owing to resonant tunneling, the contributions of the probe and signal cross-Kerr nonlinearities to total nonlinear phase shift vary from destructive to constrictive, leading to nonlinear phase shift on order of π at low light level. In this structure, the scheme is inherent symmetric for the probe and signal pulses. Consequently, the condition of group velocity matching can be fulfilled with appropriate initial electron distribution. © 2012 Optical Society of America.
Mon, 09 Apr 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1125232012-04-09T00:00:00Z
- Effects of uncertainties and errors on a Lyapunov controlhttps://scholarbank.nus.edu.sg/handle/10635/116997Title: Effects of uncertainties and errors on a Lyapunov control
Authors: Yi, X.X.; Cui, B.; Wu, C.; Oh, C.H.
Abstract: A Lyapunov (open-loop) control is often confronted with uncertainties and errors in practical applications. In this paper, we analyse the robustness of the Lyapunov control against the uncertainties and errors in quantum control systems. The analysis is carried out by examining the uncertainties and errors and calculating the control fidelity under the influence of the certainties and errors. Two examples, a closed control system and an open control system, are presented to illustrate the general formalism, discussions on the effect caused by the uncertainties and errors are given. © 2011 IOP Publishing Ltd.
Sun, 28 Aug 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1169972011-08-28T00:00:00Z
- 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
- Time-delay effects and simplified control fields in quantum Lyapunov controlhttps://scholarbank.nus.edu.sg/handle/10635/115335Title: Time-delay effects and simplified control fields in quantum Lyapunov control
Authors: Yi, X.X.; Wu, S.L.; Wu, C.; Feng, X.L.; Oh, C.H.
Abstract: Lyapunov-based quantum control has the advantage that it is free from the measurement-induced decoherence and it includes the instantaneous information of the system in the control. The Lyapunov control is often confronted with time delay in the control fields and difficulty in practical implementations of the control. In this paper, we study the effect of time delay on the Lyapunov control and explore the possibility of replacing the control field with a pulse train or a bang-bang signal. The efficiency of the Lyapunov control is also presented through examining the convergence time of the system. These results suggest that the Lyapunov control is robust against time delay, easy to realize and effective for high-dimensional quantum systems. © 2011 IOP Publishing Ltd.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1153352011-01-01T00:00:00Z
- Unconventional geometric quantum computation in a two-mode cavityhttps://scholarbank.nus.edu.sg/handle/10635/53248Title: Unconventional geometric quantum computation in a two-mode cavity
Authors: Wu, C.; Wang, Z.; Feng, X.-L.; Goan, H.-S.; Kwek, L.C.; Lai, C.H.; Oh, C.H.
Abstract: We propose a scheme for implementing unconventional geometric quantum computation by using the interaction of two atoms with a two-mode cavity field. The evolution of the system results in a nontrivial two-qubit phase gate. The operation of the proposed gate involves only metastable states of the atom and hence is not affected by spontaneous emission. The effect of cavity decay on the gate is investigated. It is shown that the evolution time of the gate in the two-mode case is less than that in the single-mode case proposed by Feng [Phys. Rev. A 75, 052312 (2007)]. Thus the gate can be more decay tolerant than the previous one. The scheme can also be generalized to a system consisting of two atoms interacting with an N -mode cavity field. © 2007 The American Physical Society.
Thu, 09 Aug 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/532482007-08-09T00:00:00Z
- Certain quantum key distribution achieved by using Bell stateshttps://scholarbank.nus.edu.sg/handle/10635/95941Title: Certain quantum key distribution achieved by using Bell states
Authors: Li, C.; Wang, Z.; Wu, C.; Song, H.-S.; Zhou, L.
Abstract: A new protocol for quantum key distribution based on entanglement swapping is proposed. In this protocol, both certain key and random key can be generated without any loss of security. © 2006 World Scientific Publishing Company.
Fri, 01 Dec 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/959412006-12-01T00:00:00Z
- 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
- Detecting full N-particle entanglement in arbitrarily-high-dimensional systems with Bell-type inequalitieshttps://scholarbank.nus.edu.sg/handle/10635/96185Title: Detecting full N-particle entanglement in arbitrarily-high-dimensional systems with Bell-type inequalities
Authors: Chen, J.-L.; Deng, D.-L.; Su, H.-Y.; Wu, C.; Oh, C.H.
Abstract: We derive a set of Bell-type inequalities for arbitrarily-high-dimensional systems based on the assumption of partial separability in the hybrid local-nonlocal hidden-variable model. Partially entangled states would not violate the inequalities, and thus, upon violation, these Bell-type inequalities are sufficient conditions to detect the full N-particle entanglement and invalidity of the hybrid local-nonlocal hidden-variable description. © 2011 American Physical Society.
Fri, 18 Feb 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/961852011-02-18T00:00:00Z
- 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
- 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
- Correlation-function Bell inequality with improved visibility for three qubitshttps://scholarbank.nus.edu.sg/handle/10635/115658Title: Correlation-function Bell inequality with improved visibility for three qubits
Authors: Wu, C.; Chen, J.-L.; Kwek, L.C.; Oh, C.H.
Abstract: We construct a Bell inequality in terms of correlation functions for three qubits. The inequality is violated by quantum mechanics for all pure entangled states of three qubits. The strength of the violation for the GHZ state is stronger than the result given by Chen, indicating that our three-qubit Bell inequality is more resistant to noise than those presented in the literature and hence is more useful in its practical applications. © 2008 The American Physical Society.
Thu, 05 Jun 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1156582008-06-05T00:00:00Z
- Yangian realization for Dirac oscillatorhttps://scholarbank.nus.edu.sg/handle/10635/99036Title: Yangian realization for Dirac oscillator
Authors: Wu, C.; Xue, K.
Abstract: We investigate the realizations of Yangian algebra for a Dirac oscillator. Applying the representation theory of Y(sl(2)) to Dirac oscillator, shift operators for different energy levels for this system are obtained. © 2005 Springer Science + Business Media, Inc.
Mon, 01 Aug 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/990362005-08-01T00:00:00Z
- 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
- 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
- Universal quantum computation with trapped ions in thermal motion by adiabatic passagehttps://scholarbank.nus.edu.sg/handle/10635/98529Title: Universal quantum computation with trapped ions in thermal motion by adiabatic passage
Authors: Feng, X.-L.; Wu, C.; Lai, C.H.; Oh, C.H.
Abstract: We propose a universal quantum computation scheme for trapped ions in thermal motion via the technique of adiabatic passage, which incorporates the advantages of both the adiabatic passage and the model of trapped ions in thermal motion. Our scheme is immune from the decoherence due to spontaneous emission from excited states as the system in our scheme evolves along a dark state. In our scheme the vibrational degrees of freedom are not required to be cooled to their ground states because they are only virtually excited. It is shown that the fidelity of the resultant gate operation is still high even when the magnitude of the effective Rabi frequency moderately deviates from the desired value. © 2008 The American Physical Society.
Thu, 26 Jun 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/985292008-06-26T00:00:00Z