Scheme for the implementation of 1 → 3 optimal phase-covariant quantum cloning in ion-trap systems

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.

Scheme for Implementation of Ancillary-Free 1→3 Optimal Phase-Covariant Quantum Cloning with Trapped Ions

We propose a simple scheme for the implementation of the ancillary-free 1→3 optimal phase-covariant quantum cloning for x-y equatorial qubits in ion-trap system. In the scheme, the vibrational mode is only virtually excited, which is very important in view of decoherence. The present proposal can be realized based on current available technologies.

Scheme for implementing an economical phase-covariant quantum cloning machine of distant atomic qubits with single-photon interference

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.

Scheme to Implement Optimal Asymmetric Economical Phase-Covariant Quantum Cloning in Cavity QED

We propose an experimentally feasible scheme to implement the optimal asymmetric economical 1→2 phase-covariant quantum cloning in two dimensions based on the cavity QED technique. The protocol is very simple and only two atoms are required. Our scheme is insensitive to the cavity field states and cavity decay. During the processes, the cavity is only virtually excited and it thus greatly prolongs the efficient decoherent time. Therefore, it may be realized in experiment.

Economical phase-covariant cloning with multiclones

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.

Optimal 1 → M phase-covariant cloning in three dimensions

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.

Quantum cloning machines and their implementation in physical systems

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.

Quantum logic networks for cloning a quantum state near a given state

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.

A quantum network for implementation of the optimal quantum cloning

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.

Quantum Cloning of Steering

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.

Nonlocal quantum cloning via quantum dots trapped in distant cavities

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.

Maximum confidence measurements via probabilistic quantum cloning

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.

Finite-size analysis of eight-state continuous-variable quantum key distribution with the linear optics cloning machine

We propose a method to improve the secret key rate of an eight-state continuous-variable quantum key distribution（CVQKD） by using a linear optics cloning machine（LOCM）. In the proposed scheme, an LOCM is exploited to compensate for the imperfections of Bob＇s apparatus, so that the generated secret key rate of the eight-state protocol could be well enhanced. We investigate the security of our proposed protocol in a finite-size scenario so as to further approach the practical value of a secret key rate. Numeric simulation shows that the LOCM with reasonable tuning gain λ and transmittance τcan effectively improve the secret key rate of eight-state CVQKD in both an asymptotic limit and a finite-size regime.Furthermore, we obtain the tightest bound of the secure distance by taking the finite-size effect into account, which is more practical than that obtained in the asymptotic limit.

Quantum Logic Network for Probabilistic Cloning Quantum States

We construct efficient quantum logic network for probabilistic cloning the quantum states used in imple mented tasks for which cloning provides some enhancement in performance.

Scheme for Implementing Assisted Cloning of an Unknown d-Dimension Equatorial Quantum State by Remote State Preparation

In this paper, we propose a protocol that can produce perfect copy of an unknown d-dimensional equatorial quantum state with assistance from a state preparer. In this protocol, the maximally and non-maximally entangled bipartite d-dimensional of states are used as the quantum channels, respectively. The first stage of the protocol requires usual teleportation. In the second stage of the protocol, with the assistance of the preparer, the perfect copy of an original unknown state can be produced.

Scheme for Implementing Quantum Cloning Restoring Machine in Cavity QED

We propose an experimentally feasible scheme for implementing quantum restoring machine of the optimal universal 1→ 2 quantum cloning machine in the context of cavity QED. In our scheme, two atoms （the clones） simultaneously interact with a cavity field, and meanwhile they are driven by a classical field. Then an arbitrary unknown input state can be restored in the ancilla by applying appropriate unitary local operation.

Implementing a Universal Quantum Cloning Machine via Adiabatic Evolution in Ion-Trap System

A scheme for the realization of a universal quantum cloning machine is proposed in this paper. The present protocol does not need the vibrational mode to act as the memory and it is robust against small changes of experimental parameters due to adiabatic passages. Furthermore, the scheme may be realized based on current technology.

Balancing four-state continuous-variable quantum key distribution with linear optics cloning machine

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.

PROBABILISTIC CLONE-RESEND ATTACK STRATEGY IN QUANTUM KEY DISTRIBUTION

A kind of attack strategy based on a probabilistic cloning machine is proposed in this letter. The security of BB84 and the six-state quantum key distribution protocols under this attack is studied by theoretic analyses and corroborated by simulations. It is concluded that the quantum key distribution protocols still have an asymptotic perfect security even if the eavesdropper adopts the proposed attack strategy.

Scheme for realizing assisted cloning of an unknown two-atom entangled state via cavity QED

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.