Gao Yun-Feng

Entanglement properties in a system of a pairwise entangled state

Based on the quantum information theory, this paper has investigated the entanglement properties of a system which is composed of the two entangled two-level atoms interacting with the two-mode entangled coherent fields. The influences of the strength of light field and the two parameters of entanglement between the two-mode fields on the field entropy and on the negative eigenvalues of partial transposition of density matrix are discussed by using numerical calculations. The result shows that the entanglement properties in a system of a pairwise entangled states can be controlled by appropriately choosing the two parameters of entanglement between the two-mode entangled coherent fields and the strength of two light fields respectively.

Evolution of field entropy and entanglement in the intensity-dependent two-mode Jaynes–Cummings model

The evolution of the entanglement degree of two-mode fields and atom with the intensity-dependent coupling is investigated using von Neumann entropy. The results for the initial fields in both coherent states and two-mode squeezed vacuum state are calculated. The influence of the field intensity on the entropy is discussed. It is found that the field and atom are generally in maximum entanglement but subject to periodic pulsed disentanglement completely under the condition of strong initial field.

Simplified Scheme for Teleportation of a Multipartite Quantum State Using a Single Entangled Pair

A simple scheme for teleporting an unknown M-qubit cat-like state is proposed. The steps of this scheme can be summarized simply: disentangle-teleport-reconstruct entanglement. If proper unitary operations and measurements from senders are given, the teleportation of an unknown M-qubit cat-like state can be converted into single qubit teleportation. In the meantime, the receiver should also carry out right unitary operations with the introduction of appropriate ancillary qubits to confirm the successful teleportation of the demanded entangled state. The present scheme can be generalized to teleport an unknown M-quNit state, i.e., an M-quNit state can be teleported by a single quNit entangled pair.

Emission Spectrum Property of Modulated Atom-Field Coupling System

The emission spectrum of a two-level atom interacting with a single mode radiation field in the case of periodic oscillation coupling coefficient is investigated. A general expression for the emission spectrum is derived. The numerical results for the initial field in pure number stare are calculated. It is found that the effect of the coupling coefficient modulation on the spectral structure is very obvious in the case of a low modulation frequency and larger amplitude when the initial field is vacuum, which is potentially useful for exploring a modulated light source.

Effect of cavity dissipation on the emission spectrum of an atom interacting with a field in the dispersive approximation

The emission spectrum of a two-level atom interacting dispersively with a single mode radiation field in the dissipative cavity is investigated. A general expression for the emission spectrum is derived. The numerical results for the initial field in coherent state are calculated. It is found that the spectrum structure is influenced significantly by the cavity damping constant κ, and the spectrum structure is dependent on the interaction time T when the cavity dissipation is present. Only one peak located at ωa appears in the atomic spectra for larger T.

Establishing path integral in the entangled state representation for Hamiltonians in quantum optics

Based on two mutually conjugate entangled state representations, we establish the path integral formalism for some Hamiltonians of quantum optics in entangled state representations. The Wigner operator in the entangled state representation is presented. Its advantages are explained.

The Normal- and Antinormal-Ordered Decomposition Formulas of Multimode Exponential Operators

We obtain the normally ordered form of the general multimode exponential operator by means of parameter differentiation method and its antinormally ordered form by virtue of the technique of integration within an ordered product of operators. As an application, we obtain a new completeness relation in -mode Fock space.

The Unitary Operator Corresponding to the General Two-Mode Coordinate-Momentum Mixed Transformation*

We discuss the unitary operator corresponding to the general two-mode coordinate-momentum mixed transformation , where and are arbitrary real numbers. Suitably selecting the parameters and , we obtain a new two-mode bosonic realization of the Lie algebra. We also study the squeezing effects of the squeezed vacuum associated with the new two-mode bosonic realization of the Lie algebra. The results show that the new squeezed vacuum does not possess second-order squeezing, but exhibits higher-order squeezing.