The influences of dipole-dipole interaction and detuning on the entanglement between two atoms with different initial tripartite entangled W-like states in the Tavis Cummings model have been investigated by means of W...The influences of dipole-dipole interaction and detuning on the entanglement between two atoms with different initial tripartite entangled W-like states in the Tavis Cummings model have been investigated by means of Wootters＇ concurrence, respectively. The results show that the entanglement between the two atoms can be enhanced via appropriately tuning the strength of dipole-dipole interaction of two atoms or the detunings between atom and cavity, and the so-called sudden death effect can he weakened simultaneously.展开更多
We investigate the entanglement dynamics via the concurrence of two distant atoms interacting off-resonantly with two cavity fields in Fock states, respectively. We find that the evolution of entanglement has sudden d...We investigate the entanglement dynamics via the concurrence of two distant atoms interacting off-resonantly with two cavity fields in Fock states, respectively. We find that the evolution of entanglement has sudden death and sudden birth phenomena, that with the increase of photon numbers in the two cavities, the alternate frequency of sudden death and sudden birth turns fast, and that the amplitude of concurrence oscillates regularly with oscillation frequency becoming slow when the cavity fields have the same photon numbers. While, the maximum of concurrence declines and the amplitude of concurrence oscillates irregularly when the two cavity fields have different photon numbers. In addition, we find the length of death time is dependent on the initial entanglement.展开更多
Pairwise thermal entanglement in a three-qubit Heisenberg XX model is investigated when a nonuniform mag- netic field and the Dzyaloshinski-Moriya interaction are included. We find that the nonuniform magnetic field a...Pairwise thermal entanglement in a three-qubit Heisenberg XX model is investigated when a nonuniform mag- netic field and the Dzyaloshinski-Moriya interaction are included. We find that the nonuniform magnetic field and Dzyaloshinski-Moriya interaction are the more efficient control parameters for the increase of entanglement and critical temperature. For both the nearest neighbour sites and the next nearest neighbour sites, the magnetic field can induce entanglement to a certain extent and the Dzyaloshinski-Moriya interaction can enhance the entanglement to a stable value. The steady value of the nearest neighbour site entanglement C12 is larger than the next nearest neighbour site entanglement C13. An interesting phenomenon is that the entanglement curve of C12 appears a peak value when the Dzyaloshinski-Moriya interaction is considered in a nonuniform magnetic field.展开更多
This paper shows that a proposal for implementing all possible two-operator positive-operator-value measurements of single spin qubit can be obtained via introducing another spin qubit as ancilla. The realization proc...This paper shows that a proposal for implementing all possible two-operator positive-operator-value measurements of single spin qubit can be obtained via introducing another spin qubit as ancilla. The realization process is accomplished from the free evolution of the Heisenberg XX model by considering nearest-neighbour spin interaction. A controlled- NOT gate, which is a significant operator for this scheme is also constructed and the generalisation to multiple-operator is considered finally.展开更多
We examine RCoO3 （R=La, Ce, Pr, Nd, Sin, Eu, Gd, and Dy） perovskites prepared with the solid-state reaction method by Raman spectroscopy, and report the Raman active phonons in the RCoO3 perovskites crystallized in ...We examine RCoO3 （R=La, Ce, Pr, Nd, Sin, Eu, Gd, and Dy） perovskites prepared with the solid-state reaction method by Raman spectroscopy, and report the Raman active phonons in the RCoO3 perovskites crystallized in cubic symmetry for RCoO3 （R=La, Ce, Pr and Nd） and orthorhombic symmetry for RCoO3 （R=Sm, Eu, Gd, and Dy）. It is found that the Raman spectra of RCoO3 perovskites are strongly dependent on the ionic radius of the rare earth elements, and the frequency shift of the most intense modes of the orthorhombic samples are correlated with some structural parameters such as Co-O bond distances, ionic radius of the rare earth elements and Jahn-Teller distortion. It is clear that Raman spectroscopy has the advantage of sensitivity to structure distortion and oxygen motion.展开更多
This paper proposes a scheme to generate a new x-type four-atom entangled state for the first time by using linear optics elements, four one-sided cavities （one three-level atom） and a conventional photon detector. ...This paper proposes a scheme to generate a new x-type four-atom entangled state for the first time by using linear optics elements, four one-sided cavities （one three-level atom） and a conventional photon detector. The linear optical elements and conventional photon detector are simple and accessible in experiments, which makes the scheme more feasible with current technology. In addition, the state ｜X^00）3214 with probability 1 can be generated as long as there is no photon loss.展开更多
Schemes for two-qubit and three-qubit controlled gates based on cross-Kerr nonlinearity are proposed in this paper.The probability of the success of these gates can be increased by quantum nondemolition detectors,whic...Schemes for two-qubit and three-qubit controlled gates based on cross-Kerr nonlinearity are proposed in this paper.The probability of the success of these gates can be increased by quantum nondemolition detectors,which are used to judge which paths the signal photons pass through.These schemes are almost deterministic and require no ancilla photon.The advantages of these gates over the existing ones include less resource consumption and a higher probability of success,which make our schemes more feasible with current technology.展开更多
A robust and scalable scheme to generate a steady three-dimensional entangled state for a V-type atom and a A- type atom trapped in a strongly dissipative bimodal cavity is proposed by direct feedback control based on...A robust and scalable scheme to generate a steady three-dimensional entangled state for a V-type atom and a A- type atom trapped in a strongly dissipative bimodal cavity is proposed by direct feedback control based on quantum-jump detection. The robustness of this scheme reflects in the insensitivity to detection inefficiencies and the strong ability against the parameter fluctuations in the feedback, driving, and coupling strengths. The influence of atomic spontaneous emission can be suppressed by using the local feedback control. The scalability is ensured that N-dimensional entangled states of two atoms can be deterministically generated.展开更多
This paper studies the average fidelity of teleportation and thermal entanglement for a two-qubit Heisenberg XYZ chain in the presence of both an inhomogeneous magnetic field and a Dzyaloshinski-Moriya interaction. It...This paper studies the average fidelity of teleportation and thermal entanglement for a two-qubit Heisenberg XYZ chain in the presence of both an inhomogeneous magnetic field and a Dzyaloshinski-Moriya interaction. It shows that for a fixed Dz, the increase of bz will broaden the critical temperature at the cost of decreasing the thermal entanglement. And it can modulate the inhomogeneous magnetic field and the Dzyaloshinski-Moriya interaction for the average fidelity of teleportation to be optimal.展开更多
We propose an entanglement concentration protocol to concentrate an arbitrary partially-entangled four-photon cluster state.As a pioneering three-step entanglement concentration scheme,our protocol only needs a single...We propose an entanglement concentration protocol to concentrate an arbitrary partially-entangled four-photon cluster state.As a pioneering three-step entanglement concentration scheme,our protocol only needs a single-photon resource to assist the concentration in each step,which makes this protocol more economical.With the help of the linear optical elements and weak cross-Kerr nonlinearity,one can obtain a maximally-entangled cluster state via local operations and classical communication.Moreover,the protocol can be iterated to obtain a higher success probability and is feasible under current experimental conditions.展开更多
A scheme for implementing a two-qubit phase gate with atoms sent through a high-Q optical cavity is proposed by choosing nonidentical coupling constants between the atoms and cavity. The atomic spontaneous emission ca...A scheme for implementing a two-qubit phase gate with atoms sent through a high-Q optical cavity is proposed by choosing nonidentical coupling constants between the atoms and cavity. The atomic spontaneous emission can be suppressed due to the large atom-field detuning. Moreover, the scheme can be generalized to implement an N-qubit phase gate and the gating time does not change with an increase of the number of qubits.展开更多
A scheme for implementing a Fredkin gate with an atom sent through a microwave cavity is proposed. The scheme is based on the resonant atom-cavity interaction so that the gating time is sharply short, which is importa...A scheme for implementing a Fredkin gate with an atom sent through a microwave cavity is proposed. The scheme is based on the resonant atom-cavity interaction so that the gating time is sharply short, which is important in view of decoherence.展开更多
We examine the entanglement dynamics between two strongly driven atoms off-resonantly coupled with a singlemode cavity via the two-photon process with the help of negativity in two different types of initial states. T...We examine the entanglement dynamics between two strongly driven atoms off-resonantly coupled with a singlemode cavity via the two-photon process with the help of negativity in two different types of initial states. The results show that entanglement sudden death may occur under both the above conditions and the sudden death effect can be monitored by modulating the atom-cavity detunings. Furthermore, we also find an atomic decoherence-free subspace so that the initial entanglement between two atoms remains invariable in application.展开更多
We propose a method to construct an optical cluster-state analyzer based on cross-Kerr nonlinearity combined with linear optics elements. In the scheme, we employ two four-qubit parity gates and the controlled phase g...We propose a method to construct an optical cluster-state analyzer based on cross-Kerr nonlinearity combined with linear optics elements. In the scheme, we employ two four-qubit parity gates and the controlled phase gate （CPG） from only the cross-Kerr nonlinearity and show that all the orthogonal four-qubit cluster states can be completely identified. The scheme is significant for the large-scale quantum communication and quantum information processing networks. In addition, the scheme is feasible and deterministic under current experimental conditions.展开更多
We study the effect of Kerr medium on the intrinsic decoherence of a system which consists of two two-level atoms and a optical cavity. The entanglement of the system is calculated by making use of concurrence. Our re...We study the effect of Kerr medium on the intrinsic decoherence of a system which consists of two two-level atoms and a optical cavity. The entanglement of the system is calculated by making use of concurrence. Our results show that the intrinsic decoherence is very sensitive to the nonlinear coupling constant of Kerr medium. Both the oscillation period and the amplitude of the concurrence increase with the increasing nonlinear coupling constant.展开更多
We propose a scheme to implement the n-qubit Deutsch-Jozsa algorithm based on resonant interaction between the atoms and a single-mode cavity. In the scheme, the resonant transitions between two ground states and one ...We propose a scheme to implement the n-qubit Deutsch-Jozsa algorithm based on resonant interaction between the atoms and a single-mode cavity. In the scheme, the resonant transitions between two ground states and one excited state of an atom are changed alternately by adjusting the cavity frequency appropriately, and the operations required to complete the algorithm can be significantly simplified following the increment of the number of qubits. The implementation of the scheme in experiment would show the full power of quantum algorithm and would be significative and important for more complicated quantum algorithm in cavity quantum electrodynamics.展开更多
This paper proposes a scheme to generate arbitrary four-atom entangled decoherence-free states by using simple linear optical elements, four one-sided cavities in which four atoms are confined respectively. By conveni...This paper proposes a scheme to generate arbitrary four-atom entangled decoherence-free states by using simple linear optical elements, four one-sided cavities in which four atoms are confined respectively. By conveniently tuning the titled angle of one half-wave plate, it can obtain arbitrary four-atom entangled decoherence-free states with a successful probability of 1 as long as there is no photon loss.展开更多
Based on squeezed operators this paper has implemented an ideal unconventional geometric quantum gate （GQG） in ion trap-optical cavity system by radiating the trapped ions with the cavity field of frequency ωc and ...Based on squeezed operators this paper has implemented an ideal unconventional geometric quantum gate （GQG） in ion trap-optical cavity system by radiating the trapped ions with the cavity field of frequency ωc and an external laser field of frequency ωL. It can ensure that the gate time is shorter than the coherence time for qubits and the decay time of the optical cavity by appropriately tuning the ionic transition frequency ω0, the frequencies of the cavity mode ωc and the vibrational mode v. It has also realized the unconventional GQG under the influence of the cavity decay based on the squeezed-like operators and found that the present scheme works well for the smaller cavity decay by investigating the corresponding fidelity and success probability.展开更多
This paper proposes a method to measure directly the concurrence of an arbitrary two-qubit pure state based on a generalized Grover quantum iteration algorithm and a phase estimation algorithm. The concurrence can be ...This paper proposes a method to measure directly the concurrence of an arbitrary two-qubit pure state based on a generalized Grover quantum iteration algorithm and a phase estimation algorithm. The concurrence can be calculated by applying quantum algorithms to two available copies of the bipartite system, and a final measurement on the auxiliary working qubits gives a better estimation of the concurrence. This method opens new prospects of entanglement measure by the application of quantum algorithms. The implementation of the protocol would be an important step toward quantum information processing and more complex entanglement measure of the finite-dimensional quantum system with an arbitrary number of qubits.展开更多
We present a scheme to prepare cluster-type entangled squeezed vacuum states （CTESVS） by considering the two-photon interaction between a two-level atom and a high-quality cavity, driven by a strong classical field....We present a scheme to prepare cluster-type entangled squeezed vacuum states （CTESVS） by considering the two-photon interaction between a two-level atom and a high-quality cavity, driven by a strong classical field. After the realization of simple atomic measurements, the generation of CTESVS in four separate cavities is accomplished within the cavity decay time. In the case of large atom=cavity detuning, the scheme is immune to the effect of atomic spontaneous emission.展开更多
基金supported by the National Natural Science Foundation of China (Grant No 60667001)
文摘The influences of dipole-dipole interaction and detuning on the entanglement between two atoms with different initial tripartite entangled W-like states in the Tavis Cummings model have been investigated by means of Wootters＇ concurrence, respectively. The results show that the entanglement between the two atoms can be enhanced via appropriately tuning the strength of dipole-dipole interaction of two atoms or the detunings between atom and cavity, and the so-called sudden death effect can he weakened simultaneously.
基金Project supported by the National Natural Science Foundation of China (Grant No. 60667001)
文摘We investigate the entanglement dynamics via the concurrence of two distant atoms interacting off-resonantly with two cavity fields in Fock states, respectively. We find that the evolution of entanglement has sudden death and sudden birth phenomena, that with the increase of photon numbers in the two cavities, the alternate frequency of sudden death and sudden birth turns fast, and that the amplitude of concurrence oscillates regularly with oscillation frequency becoming slow when the cavity fields have the same photon numbers. While, the maximum of concurrence declines and the amplitude of concurrence oscillates irregularly when the two cavity fields have different photon numbers. In addition, we find the length of death time is dependent on the initial entanglement.
文摘Pairwise thermal entanglement in a three-qubit Heisenberg XX model is investigated when a nonuniform mag- netic field and the Dzyaloshinski-Moriya interaction are included. We find that the nonuniform magnetic field and Dzyaloshinski-Moriya interaction are the more efficient control parameters for the increase of entanglement and critical temperature. For both the nearest neighbour sites and the next nearest neighbour sites, the magnetic field can induce entanglement to a certain extent and the Dzyaloshinski-Moriya interaction can enhance the entanglement to a stable value. The steady value of the nearest neighbour site entanglement C12 is larger than the next nearest neighbour site entanglement C13. An interesting phenomenon is that the entanglement curve of C12 appears a peak value when the Dzyaloshinski-Moriya interaction is considered in a nonuniform magnetic field.
基金supported by the National Natural Science Foundation of China (Grant No.60667001)
文摘This paper shows that a proposal for implementing all possible two-operator positive-operator-value measurements of single spin qubit can be obtained via introducing another spin qubit as ancilla. The realization process is accomplished from the free evolution of the Heisenberg XX model by considering nearest-neighbour spin interaction. A controlled- NOT gate, which is a significant operator for this scheme is also constructed and the generalisation to multiple-operator is considered finally.
基金Supported by the National Natural Science Foundation of China under Grant No 30370406.
文摘We examine RCoO3 （R=La, Ce, Pr, Nd, Sin, Eu, Gd, and Dy） perovskites prepared with the solid-state reaction method by Raman spectroscopy, and report the Raman active phonons in the RCoO3 perovskites crystallized in cubic symmetry for RCoO3 （R=La, Ce, Pr and Nd） and orthorhombic symmetry for RCoO3 （R=Sm, Eu, Gd, and Dy）. It is found that the Raman spectra of RCoO3 perovskites are strongly dependent on the ionic radius of the rare earth elements, and the frequency shift of the most intense modes of the orthorhombic samples are correlated with some structural parameters such as Co-O bond distances, ionic radius of the rare earth elements and Jahn-Teller distortion. It is clear that Raman spectroscopy has the advantage of sensitivity to structure distortion and oxygen motion.
基金supported by the National Natural Science Foundation of China (Grant No 60667001)the Science Foundation of Yanbian University,China (Grant No 2007-35)
文摘This paper proposes a scheme to generate a new x-type four-atom entangled state for the first time by using linear optics elements, four one-sided cavities （one three-level atom） and a conventional photon detector. The linear optical elements and conventional photon detector are simple and accessible in experiments, which makes the scheme more feasible with current technology. In addition, the state ｜X^00）3214 with probability 1 can be generated as long as there is no photon loss.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61068001 and 11264042)the Program for Chun Miao Excellent Talents of Department of Education of Jilin Province,China (Grant No. 201316)
文摘Schemes for two-qubit and three-qubit controlled gates based on cross-Kerr nonlinearity are proposed in this paper.The probability of the success of these gates can be increased by quantum nondemolition detectors,which are used to judge which paths the signal photons pass through.These schemes are almost deterministic and require no ancilla photon.The advantages of these gates over the existing ones include less resource consumption and a higher probability of success,which make our schemes more feasible with current technology.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61068001 and 11264042)the Postdoctoral Science Foundation of China(Grant No.2012M520612)the Talent Program of Yanbian University of China(Grant No.950010001)
文摘A robust and scalable scheme to generate a steady three-dimensional entangled state for a V-type atom and a A- type atom trapped in a strongly dissipative bimodal cavity is proposed by direct feedback control based on quantum-jump detection. The robustness of this scheme reflects in the insensitivity to detection inefficiencies and the strong ability against the parameter fluctuations in the feedback, driving, and coupling strengths. The influence of atomic spontaneous emission can be suppressed by using the local feedback control. The scalability is ensured that N-dimensional entangled states of two atoms can be deterministically generated.
基金supported by the National Natural Science Foundation of China (Grant No.60667001)
文摘This paper studies the average fidelity of teleportation and thermal entanglement for a two-qubit Heisenberg XYZ chain in the presence of both an inhomogeneous magnetic field and a Dzyaloshinski-Moriya interaction. It shows that for a fixed Dz, the increase of bz will broaden the critical temperature at the cost of decreasing the thermal entanglement. And it can modulate the inhomogeneous magnetic field and the Dzyaloshinski-Moriya interaction for the average fidelity of teleportation to be optimal.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61068001 and 11264042)the Talent Program of Yanbian University,China (Grant No. 950010001)+1 种基金the National Science Foundation for Post-doctoral Scientists of China (Grant No. 2012M520612)the Program for Chun Miao Excellent Talents of Department of Education of Jilin Province,China (Grant No. 201316)
文摘We propose an entanglement concentration protocol to concentrate an arbitrary partially-entangled four-photon cluster state.As a pioneering three-step entanglement concentration scheme,our protocol only needs a single-photon resource to assist the concentration in each step,which makes this protocol more economical.With the help of the linear optical elements and weak cross-Kerr nonlinearity,one can obtain a maximally-entangled cluster state via local operations and classical communication.Moreover,the protocol can be iterated to obtain a higher success probability and is feasible under current experimental conditions.
基金Supported by the National Natural Science Foundation of China under Grant No 60667001, and the Education Foundation of Yanbian University.
文摘A scheme for implementing a two-qubit phase gate with atoms sent through a high-Q optical cavity is proposed by choosing nonidentical coupling constants between the atoms and cavity. The atomic spontaneous emission can be suppressed due to the large atom-field detuning. Moreover, the scheme can be generalized to implement an N-qubit phase gate and the gating time does not change with an increase of the number of qubits.
基金Supported by the National Natural Science Foundation of China under Grant No 60667001, and the Education Foundation of Yanbian University.
文摘A scheme for implementing a Fredkin gate with an atom sent through a microwave cavity is proposed. The scheme is based on the resonant atom-cavity interaction so that the gating time is sharply short, which is important in view of decoherence.
基金Project supported by the National Natural Science Foundation of China (Grant No 60667001)the Education Foundation of Yanbian University of China
文摘We examine the entanglement dynamics between two strongly driven atoms off-resonantly coupled with a singlemode cavity via the two-photon process with the help of negativity in two different types of initial states. The results show that entanglement sudden death may occur under both the above conditions and the sudden death effect can be monitored by modulating the atom-cavity detunings. Furthermore, we also find an atomic decoherence-free subspace so that the initial entanglement between two atoms remains invariable in application.
基金supported by the National Natural Science Foundation of China (Grant Nos. 60667001 and 11165015)
文摘We propose a method to construct an optical cluster-state analyzer based on cross-Kerr nonlinearity combined with linear optics elements. In the scheme, we employ two four-qubit parity gates and the controlled phase gate （CPG） from only the cross-Kerr nonlinearity and show that all the orthogonal four-qubit cluster states can be completely identified. The scheme is significant for the large-scale quantum communication and quantum information processing networks. In addition, the scheme is feasible and deterministic under current experimental conditions.
基金Supported by the National Natural Science Foundation of China under Grant No 60667001.
文摘We study the effect of Kerr medium on the intrinsic decoherence of a system which consists of two two-level atoms and a optical cavity. The entanglement of the system is calculated by making use of concurrence. Our results show that the intrinsic decoherence is very sensitive to the nonlinear coupling constant of Kerr medium. Both the oscillation period and the amplitude of the concurrence increase with the increasing nonlinear coupling constant.
基金Project supported by the National Natural Science Foundation of China (Grant No 60667001)
文摘We propose a scheme to implement the n-qubit Deutsch-Jozsa algorithm based on resonant interaction between the atoms and a single-mode cavity. In the scheme, the resonant transitions between two ground states and one excited state of an atom are changed alternately by adjusting the cavity frequency appropriately, and the operations required to complete the algorithm can be significantly simplified following the increment of the number of qubits. The implementation of the scheme in experiment would show the full power of quantum algorithm and would be significative and important for more complicated quantum algorithm in cavity quantum electrodynamics.
基金Project supported by the National Natural Science Foundation of China (Grant No 60667001)the Science Foundation of Yanbian University,China (Grant No 2007-35)
文摘This paper proposes a scheme to generate arbitrary four-atom entangled decoherence-free states by using simple linear optical elements, four one-sided cavities in which four atoms are confined respectively. By conveniently tuning the titled angle of one half-wave plate, it can obtain arbitrary four-atom entangled decoherence-free states with a successful probability of 1 as long as there is no photon loss.
基金Project supported by the National Natural Science Foundation of China (Grant No 60667001)the Science Foundation of Yanbian University in China (Grant No 2007-31)
文摘Based on squeezed operators this paper has implemented an ideal unconventional geometric quantum gate （GQG） in ion trap-optical cavity system by radiating the trapped ions with the cavity field of frequency ωc and an external laser field of frequency ωL. It can ensure that the gate time is shorter than the coherence time for qubits and the decay time of the optical cavity by appropriately tuning the ionic transition frequency ω0, the frequencies of the cavity mode ωc and the vibrational mode v. It has also realized the unconventional GQG under the influence of the cavity decay based on the squeezed-like operators and found that the present scheme works well for the smaller cavity decay by investigating the corresponding fidelity and success probability.
基金Project supported by the National Natural Science Foundation of China (Grant No 60667001)
文摘This paper proposes a method to measure directly the concurrence of an arbitrary two-qubit pure state based on a generalized Grover quantum iteration algorithm and a phase estimation algorithm. The concurrence can be calculated by applying quantum algorithms to two available copies of the bipartite system, and a final measurement on the auxiliary working qubits gives a better estimation of the concurrence. This method opens new prospects of entanglement measure by the application of quantum algorithms. The implementation of the protocol would be an important step toward quantum information processing and more complex entanglement measure of the finite-dimensional quantum system with an arbitrary number of qubits.
基金supported by the National Natural Science Foundation of China (Grant No 60667001)
文摘We present a scheme to prepare cluster-type entangled squeezed vacuum states （CTESVS） by considering the two-photon interaction between a two-level atom and a high-quality cavity, driven by a strong classical field. After the realization of simple atomic measurements, the generation of CTESVS in four separate cavities is accomplished within the cavity decay time. In the case of large atom=cavity detuning, the scheme is immune to the effect of atomic spontaneous emission.
