ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Tue, 17 Sep 2019 14:31:51 GMT2019-09-17T14:31:51Z50401- Entanglement dynamics of non-interacting two-qubit system under a squeezed vacuum environmenthttps://scholarbank.nus.edu.sg/handle/10635/96484Title: Entanglement dynamics of non-interacting two-qubit system under a squeezed vacuum environment
Authors: Qian, J.; Feng, X.; Gong, S.
Abstract: Entanglement dynamics of two non-interacting atoms in a squeezed vacuum reservoir is studied. Several examples with different initial entangled states are investigated, and it is found that entangled atoms become disentangled faster in squeezed vacuum than in ordinary vacuum, and larger squeezing results in faster entanglement decay. The time evolution of the concurrence and the separability 'distance' A can be used to explain this novel entanglement sudden death phenomenon.
Wed, 01 Aug 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/964842007-08-01T00:00:00Z
- Universal quantum cloning machine in circuit quantum electrodynamicshttps://scholarbank.nus.edu.sg/handle/10635/98528Title: Universal quantum cloning machine in circuit quantum electrodynamics
Authors: Lv, D.-D.; Lu, H.; Yu, Y.-F.; Feng, X.-L.; Zhang, Z.-M.
Abstract: We propose a scheme for realizing the 1 → 2 universal quantum cloning machine (UQCM) with superconducting quantum interference device (SQUID) qubits in circuit quantum electrodynamics (circuit QED). In this scheme, in order to implement UQCM, we only need phase shift gate operation on SQUID qubits and the Raman transitions. The cavity number we need is only one. Thus our scheme is simple and has advantages in the experimental realization. Furthermore, both the cavity and the SQUID qubits are virtually excited, so the decoherence can be neglected. © 2010 Chinese Physical Society and IOP Publishing Ltd.
Fri, 01 Jan 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/985282010-01-01T00:00:00Z
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- Long-range adiabatic quantum state transfer through a tight-binding chain as a quantum data bushttps://scholarbank.nus.edu.sg/handle/10635/115173Title: Long-range adiabatic quantum state transfer through a tight-binding chain as a quantum data bus
Authors: Chen, B.; Fan, W.; Xu, Y.; Chen, Z.-Y.; Feng, X.-L.; Oh, C.H.
Abstract: We introduce a scheme based on adiabatic passage that allows for long-range quantum communication through tight-binding chain with always-on interaction. By adiabatically varying the external gate voltage applied on the system, the electron can be transported from the sender's dot to the aim one. We numerically solve the Schrödinger equation for a system with a given number of quantum dots. It is shown that this scheme is a simple and efficient protocol to coherently manipulate the population transfer under suitable gate pulses. The dependence of the energy gap and the transfer time on system parameters is analyzed and shown numerically. Our method provides a guidance for future realization of adiabatic quantum state transfer in experiments. © 2012 American Physical Society.
Thu, 05 Jul 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1151732012-07-05T00:00:00Z
- 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
- 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
- Optical quantum computation with cavities in the intermediate coupling regionhttps://scholarbank.nus.edu.sg/handle/10635/97452Title: Optical quantum computation with cavities in the intermediate coupling region
Authors: Mei, F.; Yu, Y.F.; Feng, X.L.; Zhu, S.L.; Zhang, Z.M.
Abstract: Large-scale quantum computation is currently a hot area of research. The scalable quantum computation scheme with cavities originally proposed by Duan and Kimble (Phys. Rev. Lett., 92 (2004) 127902) is further developed here to operate in the intermediate coupling region, which not only greatly relaxes experimental demands on the Purcell factor, but also eliminates the need to consider internal trade-off between cavity quality and efficiency. In our scheme, by controlling the reflectivity of the input single-photon pulse in the cavity, we can realize local atomphoton and nonlocal atom-atom controlled phase-flip (CPF) gates. We also introduce a theoretical model to analyze the performance of our scheme under practical noise. Furthermore, we show that the nonlocal CPF gate can be used to realize a quantum repeater. © EPLA, 2010.
Thu, 01 Jul 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/974522010-07-01T00:00:00Z
- Mixed entanglement distillation by means of parity measurementshttps://scholarbank.nus.edu.sg/handle/10635/97225Title: Mixed entanglement distillation by means of parity measurements
Authors: Feng, X.-L.; Song, X.-G.; Kwek, L.C.; Oh, C.H.
Abstract: We present a mixed entanglement distillation protocol by means of the parity measurement of qubits. Without the use of controlled-NOT (CNOT) operations, the efficiency of our protocol can approach that of the CNOT protocol. In comparison, the total successful probability of our protocol can reach a quantity twice as large as that of the linear optics-based protocol. © 2007 MAIK "Nauka/Interperiodica".
Wed, 01 Aug 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/972252007-08-01T00:00:00Z
- Quantum computation based on a quantum switch in cavity QEDhttps://scholarbank.nus.edu.sg/handle/10635/97667Title: Quantum computation based on a quantum switch in cavity QED
Authors: Feng, X.-L.; Kwek, L.C.; Lai, C.H.; Oh, C.H.
Abstract: A feasible scheme for constructing quantum logic gates is proposed on the basis of quantum switches in cavity QED. It is shown that the light field which is fed into the cavity due to the passage of an atom in a certain state can be used to manipulate the conditioned quantum logical gate. In our scheme, the quantum information is encoded in the states of Rydberg atoms and the cavity mode is not used as logical qubits or as a communicating "bus"; thus, the effect of atomic spontaneous emission can be neglected and the strict requirements for the cavity can be relaxed. © Nauka/Interperiodica 2006.
Wed, 01 Nov 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/976672006-11-01T00:00:00Z
- Electronic entanglement purification scheme enhanced by charge detectionshttps://scholarbank.nus.edu.sg/handle/10635/96424Title: Electronic entanglement purification scheme enhanced by charge detections
Authors: Feng, X.-L.; Kwek, L.C.; Oh, C.H.
Abstract: We present an entanglement purification scheme for the mixed entangled states of electrons with the aid of charge detections. Our scheme adopts the electronic polarizing beam splitters rather than the controlled-NOT (CNOT) operations, but the total successful probability of our scheme can reach the quantity as large as that of the the CNOT-operation-based protocol and twice as large as that of linear-optics-based protocol for the purification of photonic entangled states. Thus our scheme can achieve a high successful prabability without the usage of CNOT operations. © 2005 The American Physical Society.
Wed, 01 Jun 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/964242005-06-01T00:00:00Z
- Remote preparation of arbitrary two- and three-qubit stateshttps://scholarbank.nus.edu.sg/handle/10635/97802Title: Remote preparation of arbitrary two- and three-qubit states
Authors: Liu, J.-M.; Feng, X.-L.; Oh, C.H.
Abstract: We present a scheme for remotely preparing an arbitrary two-qubit pure state by using two bipartite partially entangled states as the quantum channel, the scheme is then generalized to the arbitrary three-qubit case. For the two cases of remote state preparation, we construct two different efficient projective measurement bases at sender's side and calculate the corresponding success probabilities. It is shown that remote preparation of the two-qubit or three-qubit state can be probabilistically achieved with unity fidelity. Moreover, for some special ensembles of the initial states, we find that the success probability of preparation can be increased to four times for two-qubit states and eight times for three-qubit states, and is equal to one in the case of the maximal entanglement resources. © 2009 Europhysics Letters Association.
Sat, 01 Aug 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/978022009-08-01T00:00:00Z
- Entanglement purification based on photonic polarization parity measurementshttps://scholarbank.nus.edu.sg/handle/10635/96494Title: Entanglement purification based on photonic polarization parity measurements
Authors: Song, X.-G.; Feng, X.-L.; Kwek, L.C.; Oh, C.H.
Abstract: We present an entanglement purification protocol for photonic mixed entangled states based on the two-mode polarization nondemolition parity detectors. Without the use of the controlled-NOT (CNOT) operations, the efficiency of our protocol can nearly approach that of the CNOT protocol. The total successful probability of our protocol can be nearly enhanced to the quantity twice as large as that of the linear-optics-based protocol. Besides, our protocol adopts common photon detectors rather than the sophisticated single-photon detectors required in the linear-optics-based protocol. © 2005 IOP Publishing Ltd.
Sun, 14 Aug 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/964942005-08-14T00:00:00Z
- Beam splitter entangler for light fieldshttps://scholarbank.nus.edu.sg/handle/10635/95859Title: Beam splitter entangler for light fields
Authors: Feng, X.-L.; Li, R.-X.; Xu, Z.-Z.
Abstract: We propose an experimentally feasible scheme to generate various types of entangled states of light fields by using beam splitters and single-photon detectors. Two beams of light fields are incident on two beam splitters respectively with each beam being asymmetrically split into two parts in which one part is supposed to be so weak that it contains at most one photon. We let the two weak output modes interfere at a third beam splitter. A conditional joint measurement on both weak output modes may result in an entanglement between the other two output modes. The conditions for the maximal entanglement are discussed based on the concurrence. Several specific examples are also examined. © 2005 The American Physical Society.
Tue, 01 Mar 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/958592005-03-01T00:00:00Z
- Giant cross-Kerr nonlinearity in carbon nanotube quantum dots with spin-orbit couplinghttps://scholarbank.nus.edu.sg/handle/10635/96725Title: Giant cross-Kerr nonlinearity in carbon nanotube quantum dots with spin-orbit coupling
Authors: Sun, H.; Feng, X.-L.; Gong, S.; Oh, C.H.
Abstract: We investigate the nonlinear interaction between two weak optical fields in carbon nanotube quantum dots based on electromagnetically induced transparency and spin-orbit coupling. Our results show, owing to the energy differences produced by strong spin-orbit coupling, that a giant cross-Kerr nonlinearity can be achieved with group-velocity matching, while the probe- and signal-fields absorptions are suppressed simultaneously. We demonstrate that such enhanced nonlinear optical effects can be employed to implement controlled-phase gate between pairs of single-photon pulses with high fidelity and to generate entanglement of coherent Schrödinger-cat states. © 2009 The American Physical Society.
Fri, 01 May 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/967252009-05-01T00:00:00Z
- 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
- Universal Greenberger-Horne-Zeilinger-state analyzer based on two-photon polarization parity detectionhttps://scholarbank.nus.edu.sg/handle/10635/98526Title: Universal Greenberger-Horne-Zeilinger-state analyzer based on two-photon polarization parity detection
Authors: Qian, J.; Feng, X.-L.; Gong, S.-Q.
Abstract: We present a universal analyzer for the three-particle Greenberger-Horne- Zeilinger (GHZ) states with quantum nondemolition parity detectors and linear-optics elements. In our scheme, all of the three-photon GHZ states can be discriminated with nearly unity probability in the regime of weak nonlinearity feasible at the present state of the art experimentally. We also show that our scheme can be easily extended to the analysis of the multi-particle GHZ states. © 2005 The American Physical Society.
Tue, 01 Nov 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/985262005-11-01T00:00:00Z
- Transmission spectrum of a double quantum-dot-nanocavity system in photonic crystalshttps://scholarbank.nus.edu.sg/handle/10635/98441Title: Transmission spectrum of a double quantum-dot-nanocavity system in photonic crystals
Authors: Qian, J.; Qian, Y.; Feng, X.-L.; Jin, S.-Q.; Gong, S.-Q.
Abstract: We investigate the optical transmission properties of a combined system which consists of two quantum-dot-nanocavity subsystems indirectly coupled to a waveguide in a planar photonic crystal. A Mollow-like triplet and the growth of sidebands are found, reflecting intrinsic optical responses in the complex microstructure. © 2008 The American Physical Society.
Fri, 22 Feb 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/984412008-02-22T00:00:00Z
- Generation and discrimination of Greenberger-Horne-Zeilinger states using dipole-induced transparency in a cavity-waveguide systemhttps://scholarbank.nus.edu.sg/handle/10635/96708Title: Generation and discrimination of Greenberger-Horne-Zeilinger states using dipole-induced transparency in a cavity-waveguide system
Authors: Qian, J.; Qian, Y.; Feng, X.-L.; Yang, T.; Gong, S.-Q.
Abstract: We propose an efficient scheme to build an arbitrary multipartite Greenberger-Horne-Zeilinger state and discriminate all the universal Greenberger-Horne-Zeilinger states using parity measurement based on dipole-induced transparency in a cavity-waveguide system. A prominent advantage is that initial entangled states remain after nondetective identification and they can be used for successive tasks. We analyze the performance and possible errors of the required single-qubit rotations and emphasize that the scheme is reliable and can satisfy the current experimental technology. © 2007 The American Physical Society.
Thu, 08 Mar 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/967082007-03-08T00:00:00Z
- Quantum entanglement distribution with hybrid parity gatehttps://scholarbank.nus.edu.sg/handle/10635/97674Title: Quantum entanglement distribution with hybrid parity gate
Authors: Mei, F.; Yu, Y.-F.; Feng, X.-L.; Zhang, Z.-M.; Oh, C.H.
Abstract: We propose a scheme for entanglement distribution among different single atoms trapped in separated cavities. In our scheme, by reflecting an input coherent optical pulse from a cavity with a single trapped atom, a controlled phase-shift gate between the atom and the coherent optical pulse is achieved. Based on this gate and homodyne detection, we construct an n-qubit parity gate and show its use for the distribution of a large class of entangled states in one shot, including the GHZ state {box drawings light vertical}GHZ n〉, W state {box drawings light vertical}W n〉, Dicke state {box drawings light vertical}D n,k〉, and certain sums of Dicke states {box drawings light vertical}G n,k〉. We also show that such a distribution could be performed with high success probability and high fidelity even in the presence of channel loss. ©2010 The American Physical Society.
Fri, 01 Jan 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/976742010-01-01T00:00:00Z
- Remote preparation of a three-particle state via positive operator-valued measurementhttps://scholarbank.nus.edu.sg/handle/10635/97801Title: Remote preparation of a three-particle state via positive operator-valued measurement
Authors: Liu, J.-M.; Feng, X.-L.; Oh, C.H.
Abstract: We present a scheme to remotely prepare an arbitrary three-particle pure state in real Hilbert space by using three bipartite partially entangled pairs as a quantum channel, and then generalize it to the tripartite equatorial-like case. Our results show that remote preparation of the three-particle state both in real space and in imaginary space can be probabilistically achieved with unity fidelity by performing an appropriate three-particle projective measurement at the sender's side and an optimal positive operator-valued measurement at the receiver's side. Moreover, the probability of success of our scheme is determined by the smaller parameters of the three initial entangled pairs. © 2009 IOP Publishing Ltd.
Thu, 01 Jan 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/978012009-01-01T00:00:00Z
- Repeat-until-success distributed quantum computation by using single-photon interference at a beam splitterhttps://scholarbank.nus.edu.sg/handle/10635/115264Title: Repeat-until-success distributed quantum computation by using single-photon interference at a beam splitter
Authors: Feng, X.-L.; Qian, J.; Kwek, L.C.; Oh, C.H.
Abstract: A repeat-until-success (RUS) measurement-based scheme for the implementation of the distributed quantum computation by using single-photon interference at a 50:50 beam splitter is proposed. It is shown that the 50:50 beam splitter can naturally project a suitably encoded matter-photon state to either a desired entangling gate-operated state of the matter qubits or to their initial state when the photon is detected. The recurrence of the initial state permits us to implement the desired entangling gate in a RUS way. To implement a distributed quantum computation we suggest an encoding method by means of the effect of dipole-induced transparency proposed recently. The effects of the unfavorable factors on our scheme are also discussed. © 2008 The American Physical Society.
Mon, 28 Jul 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1152642008-07-28T00:00:00Z
- Probing a half-odd topological number sequence with cold atoms in a non-Abelian optical latticehttps://scholarbank.nus.edu.sg/handle/10635/97612Title: Probing a half-odd topological number sequence with cold atoms in a non-Abelian optical lattice
Authors: Mei, F.; Zhu, S.-L.; Feng, X.-L.; Zhang, Z.-M.; Oh, C.H.
Abstract: We propose an experimental scheme to probe the contribution of a single Dirac cone to the Hall conductivity as a half-odd topological number sequence. In the scheme, the quantum anomalous Hall effect in graphene is simulated with cold atoms trapped in an optical lattice and subjected to a laser-induced non-Abelian gauge field. By tuning the laser intensity to change the gauge flux, the energies of the four Dirac points in the first Brillouin zone are shifted from each other and the contribution of the single Dirac cone to the total atomic Hall conductivity is manifested. We also show that the atomic Hall numbers can be experimentally probed with atomic density profile measurements. © 2011 American Physical Society.
Tue, 16 Aug 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/976122011-08-16T00:00:00Z
- Geometric entangling gates for coupled cavity system in decoherence-free subspaceshttps://scholarbank.nus.edu.sg/handle/10635/115123Title: Geometric entangling gates for coupled cavity system in decoherence-free subspaces
Authors: Chen, Y.-Y.; Feng, X.-L.; Oh, C.H.
Abstract: We propose a scheme to implement geometric entangling gates for two logical qubits in a coupled cavity system in decoherence-free subspaces. Each logical qubit is encoded with two atoms trapped in a single cavity and the geometric entangling gates are achieved by cavity coupling and controlling the external classical laser fields. Based on the coupled cavity system, the scheme allows the scalability for quantum computing and relaxes the requirement for individually addressing atoms. © 2012 Elsevier B.V. All rights reserved.
Thu, 01 Nov 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1151232012-11-01T00:00:00Z
- Quantum phase transition of two-mode Bose-Einstein condensates with an entanglement order parameterhttps://scholarbank.nus.edu.sg/handle/10635/112503Title: Quantum phase transition of two-mode Bose-Einstein condensates with an entanglement order parameter
Authors: Fan, W.; Xu, Y.; Chen, B.; Chen, Z.; Feng, X.; Oh, C.H.
Abstract: The ground-state entanglement of the two-mode Bose-Einstein condensate is investigated through a quantum-phase-transition approach. The entanglement measure is taken as the order parameter and this is a nonlocal order parameter, which is different from the conventional order parameter of the Mott-insulator-superfluid-phase transitions. For this nonlocal order parameter, the scaling behavior corresponding to a continuous phase transition is obtained and a power-law divergence near the critical region follows it. This scaling behavior of quantum entanglement is analyzed by the finite-size scaling and the critical exponents are obtained as ν=1.01 and γ=0.86. A close connection between quantum fluctuations and the phase transition of entanglement is also obtained. © 2012 American Physical Society.
Tue, 31 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1125032012-01-31T00:00:00Z
- Improvement on controlled-controlled-NOT operation-based entanglement purification protocolhttps://scholarbank.nus.edu.sg/handle/10635/112452Title: Improvement on controlled-controlled-NOT operation-based entanglement purification protocol
Authors: Xu, Y.; Feng, X.; Zhang, Z.
Abstract: We show that controlled-controlled-NOT (CCN) operation-based entanglement purification protocol can be further improved. CCN protocol requires Bell state measurements after performing the CCN operations. In the original CCN protocol, the measured states are assumed to be destroyed. However, if controlled-NOT gates are used to perform such Bell state measurements, in some unsuccessful situations of the CCN protocol, one can further purify the two mixed entangled states which are to be measured. In this way, the total efficiency of the CCN protocol is further increased. © 2012 Chinese Optics Letters.
Sun, 01 Apr 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124522012-04-01T00:00:00Z
- 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
- 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
- Scheme for the generation of entangled atomic state in cavity QEDhttps://scholarbank.nus.edu.sg/handle/10635/97866Title: Scheme for the generation of entangled atomic state in cavity QED
Authors: Duan, Z.-L.; Chen, Z.-Y.; Zhang, J.-T.; Feng, X.-L.; Xu, Z.-Z.
Abstract: We propose a scheme to generate the entangled state of two Λ-type three-level atoms trapped in a cavity. The atoms are initially prepared in their excited state and the cavity in vacuum state. Each atom has two possibilities to deexcite to one of the ground states. If two different polarized photons are detected subsequently, it is sure that both atoms are in different ground states. But which atom is in which ground state cannot be determined, the atoms are thus prepared in a superposition of two ground states, i.e., an entangled state. In comparison with the proposal of Hong and Lee [Phys. Rev. Lett. 89, 237901 (2002)], the requirement of a single polarized photon source can be avoided in our scheme.
Sun, 01 Aug 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/978662004-08-01T00:00:00Z
- 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
- 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
- Hybrid quantum computation based on repeat-until-success schemehttps://scholarbank.nus.edu.sg/handle/10635/96842Title: Hybrid quantum computation based on repeat-until-success scheme
Authors: Kwek, L.C.; Feng, X.L.
Abstract: In this paper, we focus on a hybrid quantum computing architecture using 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 IOP Publishing Ltd.
Fri, 13 Jul 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/968422007-07-13T00:00:00Z
- Breakdown of the dipole blockade with a zero-area phase-jump pulsehttps://scholarbank.nus.edu.sg/handle/10635/95889Title: Breakdown of the dipole blockade with a zero-area phase-jump pulse
Authors: Qian, J.; Qian, Y.; Ke, M.; Feng, X.-L.; Oh, C.H.; Wang, Y.
Abstract: We theoretically investigate the effect of a zero-area pulse on the excitations of interacting Rydberg atoms. The unexpected breakdown of dipole blockade occurs in the strong Rydberg blockade regime, which results from the nonadiabatic character of a phase-jump pulse interacting with the atoms. We also check the effect of the modulation on the final probability of double excitations and find that the switching time should be short enough to observe the breakdown of dipole blockade. © 2009 The American Physical Society.
Wed, 11 Nov 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/958892009-11-11T00:00:00Z
- 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
- Cavity quantum electrodynamics with rapidly vibrating atomhttps://scholarbank.nus.edu.sg/handle/10635/112392Title: Cavity quantum electrodynamics with rapidly vibrating atom
Authors: Feng, X.-L.; Xu, Y.; Oh, C.H.
Abstract: In cavity quantum electrodynamics (QED) the Jaynes-Cummings (JC) model deals with the interaction between a two-level atom and a single quantized mode of a cavity under the rotating-wave approximation in which the counter-rotating terms (CRTs) with large oscillating frequencies are neglected. In this work we investigate the cavity QED with a single rapidly vibrating two-level atom (ion) in a cavity and find novel interesting results due to atom vibration: (1) the single mode approximation is no longer applicable, (2) the usual CRTs in the JC model cannot be neglected any more if the atom vibration frequency is comparable to or larger than the cavity resonance frequency and the atomic transition frequency; in some specific situations they even play a major role, for example, (3) atom vibration can give rise to the excitation of the atom from its ground state and photon creation from the vacuum. Our model can be realized experimentally in the microwave domain of cavity QED with an ion strongly confined in a Paul trap. © 2014 Astro Ltd.
Sat, 01 Feb 2014 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123922014-02-01T00:00:00Z