Xie Li-Jun

Realization of Three-Qubit Controlled-Phase Gate Operation with Atoms in Cavity QED System

We propose a scheme for realization of three-qubit controlled-phase gate via passing two three-level atoms through a high-Q optical cavity in a cavity QED system. In the presented protocol, the two stable ground states of the atoms act as the two controlling qubits and the zero- and one-photon Fock states of the cavity-field form the target qubit, and no auxiliary state or any measurement is required. The numerical simulation shows that the gate fidelities remain at a high level under the influence of the atomic spontaneous emission, the decay of the cavity mode and deviation of the coupling strength. The experimental feasibility of our proposal is also discussed.

Thermal entanglement and teleportation in a three-qubit Heisenberg XXZ model with Dzyaloshinski–Moriya anisotropic antisymmetric interaction

This paper investigates the thermal pairwise entanglement of a three-qubit Heisenberg XXZ chain in the presence of the Dzyaloshinski–Moriya (DM) anisotropic antisymmetric interaction and quantum teleportation when using the Heisenberg chain as a channel. The entanglement dependences on the DM interaction and temperature are given in detail. It obtains the relation between the concurrence and average fidelity, and shows that the same concurrence can lead different average fidelities. Moreover, it finds the thermally entangled states which do not violate the Bell inequalities, and can still be used for quantum teleportation.

Tripartite States Bell-Nonlocality Sudden Death under Stochastic Dephasing

We demonstrate that the multipartite Bell-inequality violations can be fully destroyed in a unite time in three-qubit systems under decoherence induced by stochastic dephasing. It is significant that the study of tripartite systems can show fundamental characteristics which do not exist in bipartite systems.

Realization of Toffoli gate operation using four-level atoms in cavity QED system

This paper proposes a scheme for realization of a three-qubit Toffoli gate operation using three four-level atoms by a selective atom-field interaction in a cavity quantum electrodynamics system. In the proposed protocol, the quantum information is encoded on the stable ground states of atoms, and atomic spontaneous emission is negligible as the large atom-cavity detuning effectively suppresses the spontaneous decay of the atoms. The influence of the dissipation on fidelity and success probability of the three-qubit Toffoli gate is also discussed. The scheme can also be applied to realize an N-qubit Toffoli gate and the interaction time required does not rise with increasing the number of qubits.

Selective Atom-Cavity Interaction Scheme for Quantum Controlled-NOT Gate Using Four-Level Atoms in Cavity QED System

We propose a scheme for realization a quantum Controlled-NOT gate operation using two four-level atoms through a selective atom–cavity interaction in cavity quantum electrodynamics system. In our protocol, the quantum information is encoded on the stable ground states of the two atoms. During the interaction between atoms and single-mode vacuum cavity-field, the atomic spontaneous emission is negligible as the large atom–cavity detuning effectively suppresses the spontaneous decay of the atoms. The influences of the dissipation and the deviation of interaction time on fidelity and corresponding success probability of the quantum Controlled-NOT gate and the experimental feasibility of our proposal are also discussed.

A Simple Scheme for Realizing a Multiqubit Controlled-Phase Gate Through a Resonant Interaction of Three-Level Atoms with a Single-Mode Cavity

A very simple theoretical scheme is proposed to implement two- and three-qubit controlled-phase gates firstly only using a single resonant interaction between ladder-type three-level atoms and the single-mode cavity. In the presented protocol, the quantum information is encoded on the stable ground states of the atoms (as the controlling qubits) and the zero- and one-photon Fock states of cavity-field (as the target qubit). Under the influence of the atomic spontaneous emission, the decay of the cavity-mode, and deviation of the coupling strength, the three-qubit controlled-phase gate may have a comparatively high fidelity. The experimental feasibility of controlled-phase gate and the case that is extended to realize N-qubit controlled-phase gate are also discussed.

Effects of Anisotropy on Entanglement in a Two-Qubit Heisenberg XYZ Chain with Intrinsic Decoherence

Taking the intrinsic decoherence effect into account, the entanglement of a two-qubit anisotropic Heisenberg XYZ chain in the presence of the Dzyaloshinski–Moriya (DM) anisotropic antisymetric interaction is investigated in this paper. Concurrence, the measurement of entanglement, is calculated. Compared with the anisotropic in XY plane, the DM interaction is another kind of anisotropic antisymmetric exchange interaction. It is shown that the intrinsic decoherence obviously suppresses the time evolution of the entanglement. The DM interaction only acts on the time evolution of the entanglement when the initial state is |ψ(0) = cosα|01 + sinα|10 and weakens the degree of entanglement. The anisotropic in XY plane merely impacts on the time evolution of the entanglement when the system is initially in a state |ψ(0) = cosα|00 +sinα|11. The sufficiently weak anisotropic in XY plane can effectively enhance the degree of entanglement.