We define an N-order squeezing of the radiation field and study it in the M-photo interactions of a single-mode field with one atom and with two atoms. We present the general relation betwwn N and M for which squeezing of the field is possible.

We have studied squeezing of the field in the N-photon interaction of two two-Level atoms with the radiation field initially in a squeezed state.

A quantization scheme for an RLC circuit with a source is proposed and the fluctuations of the charge and the magnetic flux of the circtit in several quantum states are studied. The equation o motion for the density operator of the circuit is established and solved. The solutions are disussed.

We present the general quantum theory for the micromaser with ultra-cold A-type three-level atoms. We first derive the dressed states for the interaction of a A-type three-level atom with a quantum cavity field. Then treat the interaction between the injection atom with the cavity field as a scattering process, find the reflection and tranmission coefficients in this process, and calculate the atomis emission probability.

We present an operational definition of the Wigner function. Our method relies on the Fresnel transform of measured Rabi oscillations and applies to motional states of trapped atoms as well as to field states in cavities. We illustrate this technique using data from recent experiments in iontraps [D. M. Meekhof et al., Phys. Rev. Lett. 76, 1796 (1996)] and in cavity QED [B. Varcoe et al., Nature 403, 743 (2000)]. The values of the Wigner functions of the underlying states at the origin of phase space are W1) (0)=+1.75 for the vibrational ground state and W1) (0)= -1.4 for the one-photon number state. We generalize this method to wave packets in arbitrary potentials.

提出了重构腔场Wigner函数的一种新方案。该方案可以用微脉塞来实现。发现在腔场的Wigner函数与原子的布居数之间存在一个简单的关系。在实验上测得原子的布居数后，进行一个简单的数值积分，就可得到腔场的Wigner函数。以单光子Fock态和SchrÊdinger猫态为例进行了数值模拟，发现与用精确公式计算的结果很好地相符。

We propose a scheme for measuring the Wigner function of a two-mode cavity field. The scheme bases on the interaction between the two-mode cavity field and three level atoms. We find a simple relation between the Wigner function and the atomic population. One can obtain the Wigner function by measuring the atomic population with a micromaser-like experiment and doing a numerical integral. By using the two-mode Wigner function one can obtain the Clauser-Horne combination and test the Bell's inequalities. We test our equations with a two-mode entanglement state and the results are rather good.

We present an experimental scheme to prepare the three-cavity W-type entangled coherent state in the context or dispersive cavity quantum electrodynamics. The discussion of our scheme indicates that it can be realized by current technology.

We present a scheme to prepare an optical "quantum switch", a superposition of "open" and "closed" states. The scheme is based on the interaction of an K-type three-level atom with a single-mode of quantized cavity field and an external classical driving field, in the regime where the atom and fields are highly detuned. We show how this interaction can be used to generate coherent states of the cavity field in contrast to the usual method used in microwave cavity QED of injecting a coherent state into a cavity. A combination of switches could be used to prepare a quantum superposition of coherent field states located simultaneously in two cavities. Compared with previous proposals, our scheme is simplified due to economizes the Ramsey zone and the time equired for the state generation is short. 2006 Elsevier B.V. All rights reserved.

We analyse a process of remote information concentration achieved by the W state. The result turns out to be neither as good as good as performed by the GHZ state nor sa by the Smolin bound entangled state. Based on this particular phenomenon, the porperties of the three entangled states are realized.