Chen Chang-Yong

Approximate and Conditional Teleportation of an Unknown Atomic-Entangled State Without Bell-State Measurement ⁄

A scheme for approximately and conditionally teleporting an unknown atomic-entangled state in cavity. QED is proposed. It is the novel extension of the scheme of [Phys. Rev. A 69 (2004) 064302], where the state to be teleported is an unknown atomic state and where only a time point of system evolution and the corresponding fidelity implementing the teleportation are given. In fact, there exists multi-time points and the corresponding fidelities, which are shown in this paper and then are used to realize the approximate and conditional teleportation of the unknown atomic-entangled state. Naturally, our scheme does not involve the Bell-state measurement or an additional atom, which is required in the Bell-state measurement, only requiring one single-mode cavity. The scheme may be generalized to not only the teleportation of the cavity-mode-entangled-state by means of a single atom but also the teleportation of the unknown trapped-ion-entangled-state in a linear ion trap and the teleportation of the multi-atomic entangled states included in generalized GHZ states.

Polarizabilities and Hyperpolarizabilities for Lithium Atoms in Debye Plasmas

The effects of plasma environments on energies, oscillator strengths, polarizabilities and hyperpolarizabilities for lithium atom have been calculated by combining the 1-dependent model potential of free lithium atom and linear variation method based on B-spline basis functions. The influence of plasma on lithium atom is represented by the Debye screened potential, which describes effectively the averaged effect of the plasma environment on atomic spectra. The results are in agreement with other reported ones.

Construction of Controlled-NOT Gate with Thermal Ions

A scheme is proposed to construct the controlled-NOT gate in an ion-trap computer, based on the interaction of trapped-thermal ions with bi-chromatic laser fields. In this scheme, a specific laser pulse sequence for the implementation of this gate is given. Furthermore, it is pointed out that this laser pulse sequence is different from that of Ref. [3] [Phys. Rev. Lett. 82 (1999) 1971), which cannot result in a real controlled-NOT gate.

Scheme for Quantum Entanglement Swapping on Cavity QED System

We propose a scheme for realizing quantum entanglement swapping between the atoms in cavity QED. With only virtual excitation of the cavity during the interaction between the atoms and cavity, the scheme is insensitive to the cavity mode states and the cavity decay. The ideas can also be utilized for realizing entanglement swapping between the atomic levels in a single atom and the atomic levels in the Bell states and between the atomic levels in the Bell states and the atomic levels in the W states.

Scheme for N-Qubit Toffoli Gate by Transport of Trapped Ultracold Ions

We propose a potentially practical scheme for implementing an n-qubit Toffoli gate by elaborately controlling the transport of ultracold ions through stationary laser beams. Conditioned on the uniform ionic transport velocity, the n-qubit Toffoli gate can be realized with high fidelity and high successful probability under current experimental conditions,which depends on a single resonant interaction with n trapped ions and has constant implementation time with the increase of qubits. We show that the increase of the ion number can improve the fidelity and the successful probability of the Toffoli gate.

Approximate and Conditional Teleportation of an Unknown Atomic State with Dissipative Jaynes?Cummings Model

A scheme for approximately and conditionally teleporting an unknown atomic state in dissipative cavity QED is proposed. It is the extension of the scheme of [Phys. Rev. A 69 (2004) 064302], where the cavity mode decay has not been considered and only a time point of system evolution and the corresponding fidelity implementing the teleportation are given. In fact, the cavity mode decay exists really and must be delt with. In this paper, we investigate the influence from the cavity mode decay on the implementation of the approximate and conditional teleportation by means of the dissipative Jaynes–Cummings model and then show the analytical expression of the fidelity of realization of the teleportation. Alternatively, our scheme does not involve an additional atom, only requiring two atoms and one single-mode cavity.

High-Order Dispersion Coefficients for Alkali-metal Atoms

High-order dispersion coefficients C9, C11, C12, and C13 for the ground-state alkali-metals were calculated by combining the l-dependent model potential of alkali-metal atoms and linear variation method based on B-spline basis functions. The results were compared.

Effect of Multiphoton Processes on Geometric Quantum Computation in Superconducting Circuit QED

We study the influence of multi-photon processes on the geometric quantum computation in the systems of superconducting qubits based on the displacement-like and the general squeezed operator methods. As an example, we focus on the question about how to implement a two-qubit geometric phase gate using superconducting circuit quantum electrodynamics with both single- and two-photon interaction between the qubits and the cavity modes. We find that the multiphoton processes are not only controllable but also improve the gating speed. The comparison with other physical systems and experimental feasibility are discussed in detail.

Geometric Phase Gate Based on Both Displacement Operator and Squeezed Operators with a Superconducting Circuit Quantum Electrodynamics

We give the brief review on the related definition of the geometric phase independent of specific physical system based on the displacement opreator and the sqeezed operator, then show how the displacement operator and the squeezed operator can induce the general geometric phase. By means of the displacement operator and the squeezed operator concerning the circuit cavity mode state along a closed path in the phase space, we discuss specifically how to implement a two-qubit geometric phase gate in circuit quantum electrodynamics with both single photon interaction and two-photon interaction between the superconducting qubits and the circuit cavity modes. The experimental feasibility is discussed in detail.

High-Speed Geometric Quantum Computation with Trapped Thermal Ions via Vibrational Mode Decay

We utilize the general displacement operator proposed recently [C.Y. Chen, et al., Phys. Rev. A 74 (2006) 032328] to investigate a high-speed geometric quantum computation via vibrational mode decay of two trapped thermal ions. We find that, under some special conditions, the geometric phase gating is somewhat faster in the heating case than in the ideal case. We also investigate analytically the influence from the vibrational mode heating on the fidelity and the success probability of the implementation.