We propose a simple experimental scheme in which an unknown two-qubit state is faithfully and deterministically teleported from Alice to Bob. The scheme is constructed with four photons from parametric down conversion...We propose a simple experimental scheme in which an unknown two-qubit state is faithfully and deterministically teleported from Alice to Bob. The scheme is constructed with four photons from parametric down conversion, linear optical elements, and conventional photon detectors, all of which are available in current technology. It is shown that the probability of successful teleportation ideally reaches 100% based on single-photon two-qubit-assisted Bell-state measurement, which can distinguish all four Bell-states simultaneously via conventional photon detectors. By generalizing the scheme, the teleportation of an unknown multi-qubit system can also be realized.展开更多
A potential acceleration of a quantum open system is of fundamental interest in quantum computation, quantum communication, and quantum metrology. In this paper, we investigate the ＂quantum speed-up capacity＂ which ...A potential acceleration of a quantum open system is of fundamental interest in quantum computation, quantum communication, and quantum metrology. In this paper, we investigate the ＂quantum speed-up capacity＂ which reveals the potential ability of a quantum system to be accelerated. We explore the evolutions of the speed-up capacity in different quantum channels for two-qubit states. We find that although the dynamics of the capacity is varying in different kinds of channels, it is positive in most situations which are considered in the context except one case in the amplitude-damping channel. We give the reasons for the different features of the dynamics. Anyway, the speed-up capacity can be improved by the memory effect. We find two ways which may be used to control the capacity in an experiment： selecting an appropriate coefficient of an initial state or changing the memory degree of environments.展开更多
We present a scheme for probabilistic remote preparation of an entangled two-qubit state with three parties from a sender to either of two receivers. The quantum channel is composed of a paxtially entangled two-qubit ...We present a scheme for probabilistic remote preparation of an entangled two-qubit state with three parties from a sender to either of two receivers. The quantum channel is composed of a paxtially entangled two-qubit state and a partially entangled three-qubit state. We calculate the successful total probabilities of the scheme in general and particular cases, respectively. We also calculate total classical communication cost in a general case and two particular cases, respectively.展开更多
Based on A.K. Pati＇s original idea [Phys. Rev. A 61 （2000） 022308] on single-qubit-state-assisted clone, very recently Zhan has proposed two assisted quantum cloning protocols of a special class of unknown two-qubi...Based on A.K. Pati＇s original idea [Phys. Rev. A 61 （2000） 022308] on single-qubit-state-assisted clone, very recently Zhan has proposed two assisted quantum cloning protocols of a special class of unknown two-qubit entangled states [Phys. Lett. A 336 （2005） 317]. In this paper we further generalize Zhan＇s protocols such that an arbitrary unknown two-qubit entangled state can be treated.展开更多
In this paper, two novel schemes for deterministic joint remote state preparation（JRSP） of arbitrary single- and twoqubit states are proposed. A set of ingenious four-particle partially entangled states are construc...In this paper, two novel schemes for deterministic joint remote state preparation（JRSP） of arbitrary single- and twoqubit states are proposed. A set of ingenious four-particle partially entangled states are constructed to serve as the quantum channels. In our schemes, two senders and one receiver are involved. Participants collaborate with each other and perform projective measurements on their own particles under an elaborate measurement basis. Based on their measurement results,the receiver can reestablish the target state by means of appropriate local unitary operations deterministically. Unit success probability can be achieved independent of the channel＇s entanglement degree.展开更多
We propose a scheme for generating Bell states involving two SQUID-based charge qubits by coupling themto a nanomechanical resonator.We also show that it is possible to implement a two-qubit logic gate between the two...We propose a scheme for generating Bell states involving two SQUID-based charge qubits by coupling themto a nanomechanical resonator.We also show that it is possible to implement a two-qubit logic gate between the twocharge qubits by choosing carefully the interaction time.展开更多
In this paper, we focus on two-qubit pure state tomography. For an arbitrary unknown two-qubit pure state, separable or entangled, it has been found that the measurement probabilities of 16 projections onto the tensor...In this paper, we focus on two-qubit pure state tomography. For an arbitrary unknown two-qubit pure state, separable or entangled, it has been found that the measurement probabilities of 16 projections onto the tensor products of Pauli eigenstates are enough to uniquely determine the state. Moreover, these corresponding product states are arranged into five orthonormal bases. We design five quantum circuits, which are decomposed into the common gates in universal quantum computation, to simulate the five projective measurements onto these bases. At the end of each circuit, we measure each qubit with the projective measurement {｜0〉〈0 ｜,｜1〉,〈1｜ }. Then, we consider the open problem whether three orthonormal bases are enough to distinguish all two-qubit pure states. A necessary condition is given. Suppose that there are three orthonormal bases {B1,B2,B3}. Denote the unitary transition matrices from B1 to {B2,B3 } as U1 and U2. All 32 elements of matrices U1 and U2 should not be zero. If not, these three bases cannot distinguish all two-qubit pure states.展开更多
We reinvestigate the one-way quantum deficit,which is a measure of quantum correlation emerging from a thermodynamical approach.We give a tight upper bound of the one-way quantum deficit for general mixed states,and g...We reinvestigate the one-way quantum deficit,which is a measure of quantum correlation emerging from a thermodynamical approach.We give a tight upper bound of the one-way quantum deficit for general mixed states,and give a sufficient condition for this bound.Finally,we discuss a universal way to evaluate the one-way quantum deficit for general two-qubit states.展开更多
Maximal and total skew information is studied. For symmetric pure states of two-qubit, they are closely related to the linear entropy, the concurrence, and the spin squeezing parameter. For a two-qubit system implemen...Maximal and total skew information is studied. For symmetric pure states of two-qubit, they are closely related to the linear entropy, the concurrence, and the spin squeezing parameter. For a two-qubit system implemented in three nonlinear interaction models with an external field, we give the exact state vectors and the expectation value （Sz） at any time t. Based on （Sz）2, we give the maximal and the total skew information and a condition in which the maximal and the total skew information can reach 1 and 2, respectively.展开更多
We consider a two-qubit Heisenberg XXZ chain as a resource for quantum teleportation via the standard teleportation protocol To. The effects of anisotropic on teleportation fidelity and entanglement are studied in det...We consider a two-qubit Heisenberg XXZ chain as a resource for quantum teleportation via the standard teleportation protocol To. The effects of anisotropic on teleportation fidelity and entanglement are studied in detail. We find anisotropic not only improves the criticM temperature Tc and criticM magnetic field Bc, beyond which quantum teleportation is inferior to classicM communication protocol, but also enhances the fidelity for fixed magnetic field B and temperature T. For entanglement teleportation, the effects of magnetic field on average fidelity and output entanglement are studied.展开更多
As a widely used reconstruction algorithm in quantum state tomography, maximum likelihood estimation tends to assign a rank-deficient matrix, which decreases estimation accuracy for certain quantum states. Fortunately...As a widely used reconstruction algorithm in quantum state tomography, maximum likelihood estimation tends to assign a rank-deficient matrix, which decreases estimation accuracy for certain quantum states. Fortunately, hedged maximum likelihood estimation （HMLE） [Phys. Rev. Lett. 105 （2010）200504] was proposed to avoid this problem. Here we study more details about this proposal in the two-qubit case and further improve its performance. We ameliorate the HMLE method by updating the hedging function based on the purity of the estimated state. Both performances of HMLE and ameliorated HMLE are demonstrated by numerical simulation and experimental implementation on the Werner states of polarization-entangled photons.展开更多
Two closest single-qubit states could be diagonalised by the same unitary matrix, which helps to find the relative entropy of entanglement of a two-qubit ＇X＇ state. We formulate two binary equations for the relative...Two closest single-qubit states could be diagonalised by the same unitary matrix, which helps to find the relative entropy of entanglement of a two-qubit ＇X＇ state. We formulate two binary equations for the relative entropy of entanglement and the corresponding closest separable state of a given two-qubit ＇X＇ state. This approach can be applied to get the relative entropy of entanglement of many widely-discussed two-qubit states, such as pure states, Werner states, and so on.展开更多
We consider the geometric global quantum discord （GGQD） of two-qubit systems. By analyzing the symmetry of geometric global quantum discord we give an approach for deriving analytical formulae of the extremum proble...We consider the geometric global quantum discord （GGQD） of two-qubit systems. By analyzing the symmetry of geometric global quantum discord we give an approach for deriving analytical formulae of the extremum problem which lies at the core of computing the GGQD for arbitrary two-qubit states. Furthermore, formulae of GGQD of arbitrary two-qubit states and some concrete examples are presented.展开更多
The quantum correlation dynamics in an anisotropic Heisenberg XY Z model under decoherence are investigated with the use of concurrence C and quantum discord （QD）. There is a remarkable difference between the time e...The quantum correlation dynamics in an anisotropic Heisenberg XY Z model under decoherence are investigated with the use of concurrence C and quantum discord （QD）. There is a remarkable difference between the time evolution behaviors of these two correlation measures： there is a entanglement-sudden-death phenomenon in the concurrence while there is none in QD, which is valid for all of the initial states of this system, and the interval time of the entanglement death is found to be strongly dependent on the initial states and the parameters B and △. With the long-time limit the steady entanglement （SC） and steady quantum discord （SO, D） can be obtained. The magnitudes of SC and SQD are closely related to the parameters B and △, while the strength of the Dzyaloshinskii-Moriya interaction, D, has no influence. In addition, the effects of the parameters B and △ on SC and SQD display such different and complicated features that one cannot obtain a uniform law about them, thus we give an analytical explanation of this phenomenon. Lastly, it can be noted that the value of SC is not always larger than SQD, which is strongly dependent on the parameters B and △.展开更多
We investigate the dynamics of coherence for a central two-qubit system coupled to an XY spin chain with the Dzyaloshinsky–Moriya interaction. It is found that a sudden transition of coherence exists near the critica...We investigate the dynamics of coherence for a central two-qubit system coupled to an XY spin chain with the Dzyaloshinsky–Moriya interaction. It is found that a sudden transition of coherence exists near the critical point in the weak-coupling case, and an oscillatory envelope appears in the strong-coupling case. In both cases the freezing phenomenon of coherence can be found.展开更多
Using Lindblad approach to study decoherence of quantum systems, we study the decoherence and decay of entangled states, formed by two basic states of a chain of thee qubits. We look on these states for a possible reg...Using Lindblad approach to study decoherence of quantum systems, we study the decoherence and decay of entangled states, formed by two basic states of a chain of thee qubits. We look on these states for a possible regular dependence on their decay as a function of their energy separation between the basic states under different types of environments. We didn’t find regular or significant dependence on this energy separation for the type of environment considered.展开更多
High-quality entangling gates are crucial for scalable quantum information processing.Implementing all-microwave two-qubit gates on fixed-frequency transmons offers advantages in reducing wiring complexity,but the gat...High-quality entangling gates are crucial for scalable quantum information processing.Implementing all-microwave two-qubit gates on fixed-frequency transmons offers advantages in reducing wiring complexity,but the gate performance is often limited due to the residual ZZ interaction and the frequency crowding problem.Here,we introduce a novel scheme that enables a microwave drive-activated CZ gate compatible with the coupler structure to suppress the residual ZZ interaction.The microwave drive is applied to the coupler and the microwave drive frequency remains far detuned from the system’s transition frequency to alleviate the frequency crowding problem.We model the gate process analytically and demonstrate a theoretical gate fidelity up to 99.9%numerically.Our scheme is compatible with current coupler-structure-based circuits,and insensitive to microwave crosstalk,showing a possible path for all-microwave quantum operations at scale.展开更多
We revisit the quantum features of an anti-ferromagnetic (AF) spin environment at finite temperature with gap in its frequency spectrum, on the dynamics quantum correlations of a coupled central two qubits system with...We revisit the quantum features of an anti-ferromagnetic (AF) spin environment at finite temperature with gap in its frequency spectrum, on the dynamics quantum correlations of a coupled central two qubits system with Dzyaloshinskii-Moriya (DM) interaction, prepared in two entangled Bell states. Using entanglement and quantum discord as quantum meters of decoherence, the prepared entangled states are classified as robust or fragile relative to the degree of information leakage to the AF environment. By tailoring the size of the frequency gap, anisotropy field strength and induced field, due to system AF spin environment coupling, size of the AF environment and DM interaction parameter, a decoherence-free sub-space can be accessed for efficient execution of quantum protocols encoded in the entangled states.展开更多
文摘We propose a simple experimental scheme in which an unknown two-qubit state is faithfully and deterministically teleported from Alice to Bob. The scheme is constructed with four photons from parametric down conversion, linear optical elements, and conventional photon detectors, all of which are available in current technology. It is shown that the probability of successful teleportation ideally reaches 100% based on single-photon two-qubit-assisted Bell-state measurement, which can distinguish all four Bell-states simultaneously via conventional photon detectors. By generalizing the scheme, the teleportation of an unknown multi-qubit system can also be realized.
基金supported by the EU FP7 Marie–Curie Career Integration Fund(Grant No.631883)the Royal Society Research Fund(Grant No.RG150036)the Fundamental Research Fund for the Central Universities,China(Grant No.2018IB010)
文摘A potential acceleration of a quantum open system is of fundamental interest in quantum computation, quantum communication, and quantum metrology. In this paper, we investigate the ＂quantum speed-up capacity＂ which reveals the potential ability of a quantum system to be accelerated. We explore the evolutions of the speed-up capacity in different quantum channels for two-qubit states. We find that although the dynamics of the capacity is varying in different kinds of channels, it is positive in most situations which are considered in the context except one case in the amplitude-damping channel. We give the reasons for the different features of the dynamics. Anyway, the speed-up capacity can be improved by the memory effect. We find two ways which may be used to control the capacity in an experiment： selecting an appropriate coefficient of an initial state or changing the memory degree of environments.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 10404039 and 60674040)
文摘We present a scheme for probabilistic remote preparation of an entangled two-qubit state with three parties from a sender to either of two receivers. The quantum channel is composed of a paxtially entangled two-qubit state and a partially entangled three-qubit state. We calculate the successful total probabilities of the scheme in general and particular cases, respectively. We also calculate total classical communication cost in a general case and two particular cases, respectively.
基金The project supported by National Natural Science Foundation of China under Grant No. 10304022, the Science-Technology Fund of Anhui Province for 0utstanding Youth under Grant No. 06042087, the Key Fund of the Ministry of Education of China under Grant No. 206063, Natural Science Foundation of Hubei Province of China under Grant No, 2006ABA354
文摘Based on A.K. Pati＇s original idea [Phys. Rev. A 61 （2000） 022308] on single-qubit-state-assisted clone, very recently Zhan has proposed two assisted quantum cloning protocols of a special class of unknown two-qubit entangled states [Phys. Lett. A 336 （2005） 317]. In this paper we further generalize Zhan＇s protocols such that an arbitrary unknown two-qubit entangled state can be treated.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61372076 and 61301171)the 111 Project(Grant No.B08038)the Fundamental Research Funds for the Central Universities,China(Grant No.K5051201021)
文摘In this paper, two novel schemes for deterministic joint remote state preparation（JRSP） of arbitrary single- and twoqubit states are proposed. A set of ingenious four-particle partially entangled states are constructed to serve as the quantum channels. In our schemes, two senders and one receiver are involved. Participants collaborate with each other and perform projective measurements on their own particles under an elaborate measurement basis. Based on their measurement results,the receiver can reestablish the target state by means of appropriate local unitary operations deterministically. Unit success probability can be achieved independent of the channel＇s entanglement degree.
基金The project supported by National Natural Science Foundation of China under Grant No. 10325523the National Fundamental Research Program of China under Grant No. 2001CB309310the Scientific Research Fund of the Education Department of Hunan Province under Grant No. 06C354
文摘We propose a scheme for generating Bell states involving two SQUID-based charge qubits by coupling themto a nanomechanical resonator.We also show that it is possible to implement a two-qubit logic gate between the twocharge qubits by choosing carefully the interaction time.
基金Project supported partially by the National Key Research and Development Program of China(Grant No.2016YFB1000902)the National Natural Science Foundation of China(Grant No.61472412)the Program for Creative Research Group of the National Natural Science Foundation of China(Grant No.61621003)
文摘In this paper, we focus on two-qubit pure state tomography. For an arbitrary unknown two-qubit pure state, separable or entangled, it has been found that the measurement probabilities of 16 projections onto the tensor products of Pauli eigenstates are enough to uniquely determine the state. Moreover, these corresponding product states are arranged into five orthonormal bases. We design five quantum circuits, which are decomposed into the common gates in universal quantum computation, to simulate the five projective measurements onto these bases. At the end of each circuit, we measure each qubit with the projective measurement {｜0〉〈0 ｜,｜1〉,〈1｜ }. Then, we consider the open problem whether three orthonormal bases are enough to distinguish all two-qubit pure states. A necessary condition is given. Suppose that there are three orthonormal bases {B1,B2,B3}. Denote the unitary transition matrices from B1 to {B2,B3 } as U1 and U2. All 32 elements of matrices U1 and U2 should not be zero. If not, these three bases cannot distinguish all two-qubit pure states.
基金Supported by National Natural Science Foundation of China under Grant Nos. 11271237 and 61228305
文摘We reinvestigate the one-way quantum deficit,which is a measure of quantum correlation emerging from a thermodynamical approach.We give a tight upper bound of the one-way quantum deficit for general mixed states,and give a sufficient condition for this bound.Finally,we discuss a universal way to evaluate the one-way quantum deficit for general two-qubit states.
基金Project supported by the College Young Talents Foundation of Anhui Province,China (Grant No.2010SQRL107)
文摘Maximal and total skew information is studied. For symmetric pure states of two-qubit, they are closely related to the linear entropy, the concurrence, and the spin squeezing parameter. For a two-qubit system implemented in three nonlinear interaction models with an external field, we give the exact state vectors and the expectation value （Sz） at any time t. Based on （Sz）2, we give the maximal and the total skew information and a condition in which the maximal and the total skew information can reach 1 and 2, respectively.
基金National Natural Science Foundation of China under Grant Nos.10575017
文摘We consider a two-qubit Heisenberg XXZ chain as a resource for quantum teleportation via the standard teleportation protocol To. The effects of anisotropic on teleportation fidelity and entanglement are studied in detail. We find anisotropic not only improves the criticM temperature Tc and criticM magnetic field Bc, beyond which quantum teleportation is inferior to classicM communication protocol, but also enhances the fidelity for fixed magnetic field B and temperature T. For entanglement teleportation, the effects of magnetic field on average fidelity and output entanglement are studied.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11574291,61108009 and 61222504
文摘As a widely used reconstruction algorithm in quantum state tomography, maximum likelihood estimation tends to assign a rank-deficient matrix, which decreases estimation accuracy for certain quantum states. Fortunately, hedged maximum likelihood estimation （HMLE） [Phys. Rev. Lett. 105 （2010）200504] was proposed to avoid this problem. Here we study more details about this proposal in the two-qubit case and further improve its performance. We ameliorate the HMLE method by updating the hedging function based on the purity of the estimated state. Both performances of HMLE and ameliorated HMLE are demonstrated by numerical simulation and experimental implementation on the Werner states of polarization-entangled photons.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10804042)supported by the Scientific Research Foundation of the Education Department of Jiangxi Province,China (Project No. GJJ09440)
文摘Two closest single-qubit states could be diagonalised by the same unitary matrix, which helps to find the relative entropy of entanglement of a two-qubit ＇X＇ state. We formulate two binary equations for the relative entropy of entanglement and the corresponding closest separable state of a given two-qubit ＇X＇ state. This approach can be applied to get the relative entropy of entanglement of many widely-discussed two-qubit states, such as pure states, Werner states, and so on.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11275131,11305105,and 11271138)Simons Foundation(Grant No.198129)
文摘We consider the geometric global quantum discord （GGQD） of two-qubit systems. By analyzing the symmetry of geometric global quantum discord we give an approach for deriving analytical formulae of the extremum problem which lies at the core of computing the GGQD for arbitrary two-qubit states. Furthermore, formulae of GGQD of arbitrary two-qubit states and some concrete examples are presented.
基金Supported by the Natural Science Foundation for Young Scientists of Shanxi Province under Grant No 2012021003-3the Special Funds of the National Natural Foundation of China under Grant No 11247247
文摘The quantum correlation dynamics in an anisotropic Heisenberg XY Z model under decoherence are investigated with the use of concurrence C and quantum discord （QD）. There is a remarkable difference between the time evolution behaviors of these two correlation measures： there is a entanglement-sudden-death phenomenon in the concurrence while there is none in QD, which is valid for all of the initial states of this system, and the interval time of the entanglement death is found to be strongly dependent on the initial states and the parameters B and △. With the long-time limit the steady entanglement （SC） and steady quantum discord （SO, D） can be obtained. The magnitudes of SC and SQD are closely related to the parameters B and △, while the strength of the Dzyaloshinskii-Moriya interaction, D, has no influence. In addition, the effects of the parameters B and △ on SC and SQD display such different and complicated features that one cannot obtain a uniform law about them, thus we give an analytical explanation of this phenomenon. Lastly, it can be noted that the value of SC is not always larger than SQD, which is strongly dependent on the parameters B and △.
基金Supported by the National Natural Science Foundation of China under Grant No 11404246the Shandong Provincial Natural Science Foundation under Grant No ZR2017MF040
文摘We investigate the dynamics of coherence for a central two-qubit system coupled to an XY spin chain with the Dzyaloshinsky–Moriya interaction. It is found that a sudden transition of coherence exists near the critical point in the weak-coupling case, and an oscillatory envelope appears in the strong-coupling case. In both cases the freezing phenomenon of coherence can be found.
文摘Using Lindblad approach to study decoherence of quantum systems, we study the decoherence and decay of entangled states, formed by two basic states of a chain of thee qubits. We look on these states for a possible regular dependence on their decay as a function of their energy separation between the basic states under different types of environments. We didn’t find regular or significant dependence on this energy separation for the type of environment considered.
基金Project supported by the Key-Area Research and Development Program of Guangdong Province,China(Grant No.2020B0303030002)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB0670000)the National Key Research and Development Program of China(Grant No.2023YFB4404904).
文摘High-quality entangling gates are crucial for scalable quantum information processing.Implementing all-microwave two-qubit gates on fixed-frequency transmons offers advantages in reducing wiring complexity,but the gate performance is often limited due to the residual ZZ interaction and the frequency crowding problem.Here,we introduce a novel scheme that enables a microwave drive-activated CZ gate compatible with the coupler structure to suppress the residual ZZ interaction.The microwave drive is applied to the coupler and the microwave drive frequency remains far detuned from the system’s transition frequency to alleviate the frequency crowding problem.We model the gate process analytically and demonstrate a theoretical gate fidelity up to 99.9%numerically.Our scheme is compatible with current coupler-structure-based circuits,and insensitive to microwave crosstalk,showing a possible path for all-microwave quantum operations at scale.
文摘We revisit the quantum features of an anti-ferromagnetic (AF) spin environment at finite temperature with gap in its frequency spectrum, on the dynamics quantum correlations of a coupled central two qubits system with Dzyaloshinskii-Moriya (DM) interaction, prepared in two entangled Bell states. Using entanglement and quantum discord as quantum meters of decoherence, the prepared entangled states are classified as robust or fragile relative to the degree of information leakage to the AF environment. By tailoring the size of the frequency gap, anisotropy field strength and induced field, due to system AF spin environment coupling, size of the AF environment and DM interaction parameter, a decoherence-free sub-space can be accessed for efficient execution of quantum protocols encoded in the entangled states.
