This paper proposes a scheme for the implementation of 1→ 3 optimal phase-covariant quantum cloning with trapped ions. In the present protocol, the required time for the whole procedure is short due to the resonant i...This paper proposes a scheme for the implementation of 1→ 3 optimal phase-covariant quantum cloning with trapped ions. In the present protocol, the required time for the whole procedure is short due to the resonant interaction, which is important in view of decoherence. Furthermore, the scheme is feasible based on current technologies.展开更多
We review the basic theory of approximate quantum cloning for discrete variables and some schemes for implementing quantum cloning machines. Several types of approximate quantum clones and their expansive quantum clon...We review the basic theory of approximate quantum cloning for discrete variables and some schemes for implementing quantum cloning machines. Several types of approximate quantum clones and their expansive quantum clones are intro- duced. As for the implementation of quantum cloning machines, we review some design methods and recent experimental results.展开更多
This paper presents a quantum network to implement the optimal 1→2 quantum cloning in 2 dimensions, including the optimal asymmetric universal, the optimal symmetric phase-covariant, and the asymmetric real state clo...This paper presents a quantum network to implement the optimal 1→2 quantum cloning in 2 dimensions, including the optimal asymmetric universal, the optimal symmetric phase-covariant, and the asymmetric real state cloning. By only choosing different angles of the single-qubit rotations, the quantum network can implement three optimal quantum cloning.展开更多
Quantum steering in a global state allows an observer to remotely steer a subsystem into different ensembles by performing different local measurements on the other part. We show that, in general, this property cannot...Quantum steering in a global state allows an observer to remotely steer a subsystem into different ensembles by performing different local measurements on the other part. We show that, in general, this property cannot be perfectly cloned by any joint operation between a steered subsystem and a third system. Perfect cloning is viable if and only if the initial state is of zero discord. We also investigate the process of cloning the steered qubit of a Bell state using a universal cloning machine. Einstein–Podolsky–Rosen(EPR) steering, which is a type of quantum correlation existing in the states without a local-hidden-state model, is observed in the two copy subsystems. This contradicts the conclusion of no-cloning of quantum steering(EPR steering) [C. Y. Chiu et al.,npj Quantum Inf. 2, 16020(2016)] based on a mutual information criterion for EPR steering.展开更多
Probabilistic quantum cloning(PQC) cannot copy a set of linearly dependent quantum states.In this paper,we show that if incorrect copies are allowed to be produced,linearly dependent quantum states may also be clone...Probabilistic quantum cloning(PQC) cannot copy a set of linearly dependent quantum states.In this paper,we show that if incorrect copies are allowed to be produced,linearly dependent quantum states may also be cloned by the PQC.By exploiting this kind of PQC to clone a special set of three linearly dependent quantum states,we derive the upper bound of the maximum confidence measure of a set.An explicit transformation of the maximum confidence measure is presented.展开更多
By means of cavity-assisted photon interference, a simple scheme is proposed to implement a symmetric economical phase-covariant quantum cloning machine of two remote qubits, with each in a separate cavity. With our p...By means of cavity-assisted photon interference, a simple scheme is proposed to implement a symmetric economical phase-covariant quantum cloning machine of two remote qubits, with each in a separate cavity. With our present scheme, a high-fidelity cloning machine is realized. Our scheme may be quite useful in terms of distributed quantum information processing.展开更多
A scheme for implementing nonlocal quantum cloning via quantum dots trapped in cavities is proposed.By modulating the parameters of the system,the optimal 1 → 2 universal quantum cloning machine,1 → 2 phase-covarian...A scheme for implementing nonlocal quantum cloning via quantum dots trapped in cavities is proposed.By modulating the parameters of the system,the optimal 1 → 2 universal quantum cloning machine,1 → 2 phase-covariant cloning machine,and 1 → 3 economical phase-covariant cloning machine are constructed.The present scheme,which is attainable with current technology,saves two qubits compared with previous cloning machines.展开更多
Two quantum logic networks are proposed to simulate a cloning machine that copies the states near a given one. Probabilistie cloning based on the first network is realized and the cloning probability of success based ...Two quantum logic networks are proposed to simulate a cloning machine that copies the states near a given one. Probabilistie cloning based on the first network is realized and the cloning probability of success based on the second network is lOOe/0. Therefore, the second network is more motivative than the first one.展开更多
We show that the secret key generation rate can be balanced with the maximum secure distance of four-state continuous-variable quantum key distribution(CV-QKD) by using the linear optics cloning machine(LOCM). Ben...We show that the secret key generation rate can be balanced with the maximum secure distance of four-state continuous-variable quantum key distribution(CV-QKD) by using the linear optics cloning machine(LOCM). Benefiting from the LOCM operation, the LOCM-tuned noise can be employed by the reference partner of reconciliation to achieve higher secret key generation rates over a long distance. Simulation results show that the LOCM operation can flexibly regulate the secret key generation rate and the maximum secure distance and improve the performance of four-state CV-QKD protocol by dynamically tuning parameters in an appropriate range.展开更多
In this paper, we derive the explicit transformations of the optimal 1→3, 4, 5 phase-covariant cloning in three dimensions, and then generalize them to the cases of 1 → M = 3n, 3n + 1, 3n + 2 (n ≥ 1 integer) cl...In this paper, we derive the explicit transformations of the optimal 1→3, 4, 5 phase-covariant cloning in three dimensions, and then generalize them to the cases of 1 → M = 3n, 3n + 1, 3n + 2 (n ≥ 1 integer) cloning. The clone fidelities are coincident with the theoretical bounds found.展开更多
This paper proposes a scheme where one can realize quantum cloning of an unknown two-atom entangled state with assistance of a state preparer in cavity QED. The first stage of the scheme requires usual teleportation. ...This paper proposes a scheme where one can realize quantum cloning of an unknown two-atom entangled state with assistance of a state preparer in cavity QED. The first stage of the scheme requires usual teleportation. In the second stage of the scheme, with the assistance of the preparer, the perfect copies of an unknown atomic entangled state can be produced.展开更多
This paper presents a very simple method to derive the explicit transformations of the optimal economical 1 to M phase-covariant cloning. The fidelity of clones reaches the theoretic bound [D'Ar]ano G M and Macchiave...This paper presents a very simple method to derive the explicit transformations of the optimal economical 1 to M phase-covariant cloning. The fidelity of clones reaches the theoretic bound [D'Ar]ano G M and Macchiavello C 2003 Phys. Rev. A 67 042306]. The derived transformations cover the previous contributions [Delgado Y, Lamata Let al, 2007 Phys. Rev. Lett. 98 150502] in which M must be odd.展开更多
In this paper, from the original definition of fidelity in a pure state, we first give a well-defined expansion fidelity between two Gaussian mixed states. It is related to the variances of output and input states in ...In this paper, from the original definition of fidelity in a pure state, we first give a well-defined expansion fidelity between two Gaussian mixed states. It is related to the variances of output and input states in quantum information pro- cessing. It is convenient to quantify the quantum teleportation (quantum clone) experiment since the variances of the input (output) state are measurable. Furthermore, we also give a conclusion that the fidelity of a pure input state is smaller than the fidelity of a mixed input state in the same quantum information processing.展开更多
In conventional quantum mechanics,quantum no-deleting and no-cloning theorems indicate that two different and nonorthogonal states cannot be perfectly and deterministically deleted and cloned,respectively.Here,we inve...In conventional quantum mechanics,quantum no-deleting and no-cloning theorems indicate that two different and nonorthogonal states cannot be perfectly and deterministically deleted and cloned,respectively.Here,we investigate the quantum deleting and cloning in a pseudo-unitary system.We first present a pseudo-Hermitian Hamiltonian with real eigenvalues in a two-qubit system.By using the pseudo-unitary operators generated from this pseudo-Hermitian Hamiltonian,we show that it is possible to delete and clone a class of two different and nonorthogonal states,and it can be generalized to arbitrary two different and nonorthogonal pure qubit states.Furthermore,state discrimination,which is strongly related to quantum no-cloning theorem,is also discussed.Last but not least,we simulate the pseudo-unitary operators in conventional quantum mechanics with post-selection,and obtain the success probability of simulations.Pseudo-unitary operators are implemented with a limited efficiency due to the post-selections.Thus,the success probabilities of deleting and cloning in the simulation by conventional quantum mechanics are less than unity,which maintain the quantum no-deleting and no-cloning theorems.展开更多
Although the no-cloning theorem forbids perfect replication of quantum information, it is sometimes possible to produce large numbers of replicas with vanishingly small error. This phenomenon, known as quantum superre...Although the no-cloning theorem forbids perfect replication of quantum information, it is sometimes possible to produce large numbers of replicas with vanishingly small error. This phenomenon, known as quantum superreplication, can occur for both quantum states and quantum gates. The aim of this paper is to review the central features of quantum superreplication and provide a unified view of existing results. The paper also includes new results. In particular, we show that when quantum superreplication can be achieved, it can be achieved through estimation up to an error of size O(M/N2), where N and M are the number of input and output copies, respectively. Quantum strategies still offer an advantage for superreplication in that they allow for exponentially faster reduction of the error. Using the relation with estimation, we provide i) an alternative proof of the optimality of Heisenberg scaling in quantum metrology, ii) a strategy for estimating arbitrary unitary gates with a mean square error scaling as log N/N2, and iii) a protocol that generates O(N2) nearly perfect copies of a generic pure state U|0) while using the corresponding gate U only N times. Finally, we point out that superreplication can be achieved using interactions among k systems, provided that k is large compared to M2/N2.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos10574022 and 10575022)the Funds of the Natural Science of Fujian Province,China(Grant Nos Z0512006 and A0210014)
文摘This paper proposes a scheme for the implementation of 1→ 3 optimal phase-covariant quantum cloning with trapped ions. In the present protocol, the required time for the whole procedure is short due to the resonant interaction, which is important in view of decoherence. Furthermore, the scheme is feasible based on current technologies.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11074002,61275119,and 11247009)the Doctoral Foundation of the Ministry of Education of China(Grant No.20103401110003)
文摘We review the basic theory of approximate quantum cloning for discrete variables and some schemes for implementing quantum cloning machines. Several types of approximate quantum clones and their expansive quantum clones are intro- duced. As for the implementation of quantum cloning machines, we review some design methods and recent experimental results.
基金supported by the National Natural Science Foundation of China (Grant No 10674001)also by the Program of the Education Department of Anhui Province (Grant No KJ2007A002)
文摘This paper presents a quantum network to implement the optimal 1→2 quantum cloning in 2 dimensions, including the optimal asymmetric universal, the optimal symmetric phase-covariant, and the asymmetric real state cloning. By only choosing different angles of the single-qubit rotations, the quantum network can implement three optimal quantum cloning.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11675119, 11575125, and 11105097)。
文摘Quantum steering in a global state allows an observer to remotely steer a subsystem into different ensembles by performing different local measurements on the other part. We show that, in general, this property cannot be perfectly cloned by any joint operation between a steered subsystem and a third system. Perfect cloning is viable if and only if the initial state is of zero discord. We also investigate the process of cloning the steered qubit of a Bell state using a universal cloning machine. Einstein–Podolsky–Rosen(EPR) steering, which is a type of quantum correlation existing in the states without a local-hidden-state model, is observed in the two copy subsystems. This contradicts the conclusion of no-cloning of quantum steering(EPR steering) [C. Y. Chiu et al.,npj Quantum Inf. 2, 16020(2016)] based on a mutual information criterion for EPR steering.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11074002,61073048,and 11104057)the Natural Science Foundation of the Education Department of Anhui Province,China (Grant Nos. KJ2010ZD08 and KJ2012A245)the Postgraduate Program of Huainan Normal University of China
文摘Probabilistic quantum cloning(PQC) cannot copy a set of linearly dependent quantum states.In this paper,we show that if incorrect copies are allowed to be produced,linearly dependent quantum states may also be cloned by the PQC.By exploiting this kind of PQC to clone a special set of three linearly dependent quantum states,we derive the upper bound of the maximum confidence measure of a set.An explicit transformation of the maximum confidence measure is presented.
文摘By means of cavity-assisted photon interference, a simple scheme is proposed to implement a symmetric economical phase-covariant quantum cloning machine of two remote qubits, with each in a separate cavity. With our present scheme, a high-fidelity cloning machine is realized. Our scheme may be quite useful in terms of distributed quantum information processing.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61068001 and 11165015)the Nature Science Foundation of Jilin Province,China (Grant No. 201115226)
文摘A scheme for implementing nonlocal quantum cloning via quantum dots trapped in cavities is proposed.By modulating the parameters of the system,the optimal 1 → 2 universal quantum cloning machine,1 → 2 phase-covariant cloning machine,and 1 → 3 economical phase-covariant cloning machine are constructed.The present scheme,which is attainable with current technology,saves two qubits compared with previous cloning machines.
文摘Two quantum logic networks are proposed to simulate a cloning machine that copies the states near a given one. Probabilistie cloning based on the first network is realized and the cloning probability of success based on the second network is lOOe/0. Therefore, the second network is more motivative than the first one.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61379153 and 61572529)
文摘We show that the secret key generation rate can be balanced with the maximum secure distance of four-state continuous-variable quantum key distribution(CV-QKD) by using the linear optics cloning machine(LOCM). Benefiting from the LOCM operation, the LOCM-tuned noise can be employed by the reference partner of reconciliation to achieve higher secret key generation rates over a long distance. Simulation results show that the LOCM operation can flexibly regulate the secret key generation rate and the maximum secure distance and improve the performance of four-state CV-QKD protocol by dynamically tuning parameters in an appropriate range.
基金supported by the National Natural Science Foundation of China(Grant Nos.11074002,61073048,and 11104057)the Natural Science Foundationof the Education Department of Anhui Province,China(Grant Nos.KJ2010ZD08 and KJ2012A245)the Postgraduate Program of Huainan NormalUniversity of China
文摘In this paper, we derive the explicit transformations of the optimal 1→3, 4, 5 phase-covariant cloning in three dimensions, and then generalize them to the cases of 1 → M = 3n, 3n + 1, 3n + 2 (n ≥ 1 integer) cloning. The clone fidelities are coincident with the theoretical bounds found.
文摘This paper proposes a scheme where one can realize quantum cloning of an unknown two-atom entangled state with assistance of a state preparer in cavity QED. The first stage of the scheme requires usual teleportation. In the second stage of the scheme, with the assistance of the preparer, the perfect copies of an unknown atomic entangled state can be produced.
基金supported by the National Natural Science Foundation of China (Grant No 10674001)the Program of the Education Department of Anhui Province of China (Grant No KJ2007A002)
文摘This paper presents a very simple method to derive the explicit transformations of the optimal economical 1 to M phase-covariant cloning. The fidelity of clones reaches the theoretic bound [D'Ar]ano G M and Macchiavello C 2003 Phys. Rev. A 67 042306]. The derived transformations cover the previous contributions [Delgado Y, Lamata Let al, 2007 Phys. Rev. Lett. 98 150502] in which M must be odd.
基金supported by the National Basic Research Program of China(Grant No.2013CB338002)the Foundation of Science and Technology on Information Assurance Laboratory(Grant No.KJ-14-001)
文摘In this paper, from the original definition of fidelity in a pure state, we first give a well-defined expansion fidelity between two Gaussian mixed states. It is related to the variances of output and input states in quantum information pro- cessing. It is convenient to quantify the quantum teleportation (quantum clone) experiment since the variances of the input (output) state are measurable. Furthermore, we also give a conclusion that the fidelity of a pure input state is smaller than the fidelity of a mixed input state in the same quantum information processing.
基金This work was funded by the National Natural Science Foundation of China(Grant Nos.11734015,11474049,and 11674056)the K.C.Wong Magna Fund in Ningbo University,the financial support from Research Grants Council of Hong Kong(RGC,Hong Kong)(Grant No.538213)+1 种基金M.G.was supported by the National Youth Thousand Talents Program(Grant No.KJ2030000001)the USTC start-up funding(Grant No.KY2030000053).
文摘In conventional quantum mechanics,quantum no-deleting and no-cloning theorems indicate that two different and nonorthogonal states cannot be perfectly and deterministically deleted and cloned,respectively.Here,we investigate the quantum deleting and cloning in a pseudo-unitary system.We first present a pseudo-Hermitian Hamiltonian with real eigenvalues in a two-qubit system.By using the pseudo-unitary operators generated from this pseudo-Hermitian Hamiltonian,we show that it is possible to delete and clone a class of two different and nonorthogonal states,and it can be generalized to arbitrary two different and nonorthogonal pure qubit states.Furthermore,state discrimination,which is strongly related to quantum no-cloning theorem,is also discussed.Last but not least,we simulate the pseudo-unitary operators in conventional quantum mechanics with post-selection,and obtain the success probability of simulations.Pseudo-unitary operators are implemented with a limited efficiency due to the post-selections.Thus,the success probabilities of deleting and cloning in the simulation by conventional quantum mechanics are less than unity,which maintain the quantum no-deleting and no-cloning theorems.
文摘Although the no-cloning theorem forbids perfect replication of quantum information, it is sometimes possible to produce large numbers of replicas with vanishingly small error. This phenomenon, known as quantum superreplication, can occur for both quantum states and quantum gates. The aim of this paper is to review the central features of quantum superreplication and provide a unified view of existing results. The paper also includes new results. In particular, we show that when quantum superreplication can be achieved, it can be achieved through estimation up to an error of size O(M/N2), where N and M are the number of input and output copies, respectively. Quantum strategies still offer an advantage for superreplication in that they allow for exponentially faster reduction of the error. Using the relation with estimation, we provide i) an alternative proof of the optimality of Heisenberg scaling in quantum metrology, ii) a strategy for estimating arbitrary unitary gates with a mean square error scaling as log N/N2, and iii) a protocol that generates O(N2) nearly perfect copies of a generic pure state U|0) while using the corresponding gate U only N times. Finally, we point out that superreplication can be achieved using interactions among k systems, provided that k is large compared to M2/N2.