Quantum communication and entanglement between two distant atoms via vacuum fields

This paper proposes an efficient scheme for quantum communication between two atoms trapped in distant cavities which are connected by an optical fibre. During the operation, all the atomic system, the cavity modes and the fibre are not excited. The quantum state is mediated by the vacuum fields. The idea can be used to realize quantum entanglement between two distant atoms via vacuum.     

Scheme for direct measurement of Wigner function in two-mode cavity QED driven by classical fields

We propose a scheme for the direct measurement of Wigner function in two-mode cavity QED.The atoms are sent to resonantly interact with two orthogonally polarized cavity modes in the presence of strong classical field.The probability of measuring the atom in the ground state directly gives the useful information of the cavity field.This method can be used for quantum non-demolition measurement of the photon number.     

Scheme for Direct Measurement of the Wigner Function via Resonant Interaction

We propose a scheme for direct measurement of the Wigner function for a cavity mode. In the scheme the cavity field resonantly interacts with an atomic ensemble. Under certain conditions, the state of the cavity mode is transferred to the atomic system. After a displacement the measurement of the parity of the atomic excitation number directly yields the Wigner function of the initial state of the cavity mode.     

Observation of geometric phase in a dispersively coupled resonator-qutrit system

We present an experiment of observing the geometric phase in a superconducting circuit where the resonator and the qutrit energy levels are dispersively coupled. The drive applied to the resonator displaces its state components associated with the qutrit's ground state and first-excited state along different circular trajectories in phase space. We identify the resonator's phase-space trajectories by Wigner tomography using an ancilla qubit, following which we observe the difference between the geometric phases associated with these trajectories using Ramsey interferometry. This geometric phase is further used to construct the single-qubit π-phase gate with a process fidelity of 0.851 ± 0.001.     

Simplified Scheme for Cloning and Telecloning Quantum States near a Given State

We describe a simple protocol to produce two approximate copiers of an input state in the neighbourhood of a particular state.We show that the scheme can be realized within the framework of cavity quantum electrodynamics,We also present a scheme for telecloning this kind of states.     

利用原子干涉方法来制备压缩相干迭加态

在文中我们提出了一种基于原子干涉的方法产生压缩相干迭加态，由此方法产生的迭加态的位相及权重因子均可控制。     

GENERATION OF ENTANGLED FOCK STATES OF TWO NONLOCAL CAVITY MODES WITH DIFFERENT FREQUENCIES

We present a method to generate entangled Fock states of two nonlocal cavity modes with different frequencies. We send an atom with three levels g,e, and f across two cavities. The atomic transition frequency between level g and e is resonant with the first cavity frequency, while the atomic transition frequency between level g and f is resonant with the second cavity frequency. The detection of the atomic state leaves the pure field in an entangled Fock state.     

Scheme for Realizing Kerr Nonlinearity in Cavity QED

We propose a scheme for realizing the Kerr-type nonlinearity for a cavity mode. In the scheme the cavity mode interacts with a single three-level atom dispersively. Under certain conditions, the evolution of the cavity field, decoupled from the atomic degree of freedom, corresponds to the Kerr effect. The scheme can be generalized to implement cross-Kerr effect and two-qubit phase gates for two cavity modes.     

Quantum state swap for two trapped Rydberg atoms

The quantum swap gate is one of the most useful gates for quantum computation. Two-qubit entanglement and a controlled-NOT quantum gate in a neutral Rydberg atom system have been achieved in recent experiments. It is therefore very interesting to propose a scheme here for swapping a quantum state between two trapped neutral atoms via the Rydberg blockade mechanism. The atoms interact with a sequence of laser pulses without individual addressing. The errors of the swap gate due to imprecision of pulse length, finite Rydberg interaction, and atomic spontaneous emission are discussed.