Probabilistic teleportation of an unknown N-atom state using a two-atom nonmaximally entangled state in cavity QED

We present a scheme for realizing probabilistic teleportation of an unknown N-atom state via cavity QED. This scheme requires only a nonmaximally entangled pair to be used as a quantum channel, so the requirement of entanglement is reduced. In addition, our scheme does not involve the Bell-state measurement and is insensitive to the cavity decay, which is important from the experimental point of view. If the quantum channel is a two-atom maximally entangled state, teleportation of an unknown N-atom state can be realized by a simpler scheme via cavity QED.     

Scheme for splitting quantum information via W states in cavity QED systems

Assisted by multipartite entanglement, Quantum information may be split so that the original qubit can be reconstructed if and only if the recipients cooperate. This paper proposes an experimentally feasible scheme for splitting quantum information via W-type entangled states in cavity QED systems, where three-level Rydberg atoms interact with nonresonant cavities. Since W-type states are used as the quantum channel and the cavities are only virtually excited, the scheme is easy to implement and robust against decoherence, and the dependence on the quality factor of the cavities is greatly reduced.     

A Scheme for Implementing the Deutsch-Jozsa algorithm via Josephson Charge Qubits Coupled through Microwaves

Based on the Josephson charge qubits coupled through microwaves, a scheme for implementation of the Deuutsch-Jozsa algorithm is proposed under the present scalable and feasible microfabrication technique. It would be a valuable step toward complex quantum computation.     

Entanglement between two atoms in the system of SchrSdinger cat state interacting with two entangled atoms

By the negative eigenvalues of partial transposition of density matrix, this paper investigates the time evolution of entanglement of the two entangled atoms in the system of two atoms interacting with SchrSdinger cat state. The result shows that the two atoms are always in the entanglement state, and the degree of entanglement between the two atoms exhibits ordinary collapses and revivals at 0.2 degree of entanglement, when the light field is large enough. On the other hand, the reinforcement of three different light fields on the degree of entanglement between two atoms is not evident.[第一段]     

Realization of Greenberg-Horne-Zeilinger （GHZ） and W Entangled States with Multiple Superconducting Quantum-Interference Device Qubits in Cavity QED

An alternative scheme is proposed for generating the Greenberg-Horne-Zeilinger （GHZ） and W types of the entangled states with multiple superconducting quantum-interference device （SQUID） qubits in a single-mode microwave cavity field. In this scheme, there is no transfer of quantum information between the SQUIDs and the cavity, the cavity is always in the vacuum and thus the requirement on the quality of cavity is greatly loosened. In addition, during the process of the generation of the W entangled state, the present method does not involve a real excitation of intermediate levels. Thus, decoherence due to energy relaxation of intermediate levels is minimized.     

Superposition of Fock states via adiabatic passage in a coupled four-level atom－cavity system

We have investigated the behaviour of an atom－cavity system via a stimulated Raman adiabatic passage technique in a four-level system, in which two dark states are present. We find, because of the coherent control field, that a superposition of Fock states can be prepared, even when the cavity is initially not in its vacuum state. This method provides a way to generate arbitrary quantum states of a cavity field.     

NMR analogue of the generalized Grover＇s algorithm of multiple marked states and its application

The generalized Grover‘s algorithm for the case in which there are multiple marked states is demonstrated on a nuclear magnetic resonance (NMR) quantum computer. The Walsh-Hadamard transform and the phase inversion are all replaced. NMR analogues of Einstein-Podolsky-Rosen states (pseudo-EPR states) are synthesized using the above algorithm.     

Influence of second sideband excitation on the dynamics of trapped ions in a cavity

We study the dynamics of a trapped ion placed at an antinode of the standing wave inside a high finesse cavity with consideration of the second sideband excitation between the ionic internal levels and the light field. We investigate the entanglement of the three subsystems embodying the ionic internal levels, the vibrational mode of the ion and the cavity field.     

Preparation of the W State of Atoms in a Single Cavity or N Distant Cavities by Photon Interference

We suggest two schemes to generate the W state of N A-type three-level atoms. In the schemes, identical N three-level atoms are trapped in a cavity or N distant cavities. The success or failure of the generation of the W state can be determined by detecting the polarization of photon leaking out of the cavity. The result demonstrates that the W state is free from both the cavity loss and the spontaneous emission due to the fact that the two ground states (left and right) of the three-level atoms are stable states (or metastable states).     

Entropy evolvement properties in a system of Schrodinger cat state light field interacting with two entangled atoms

The field entropy can be regarded as a measurement of the degree of entanglement between the light field and the atoms of a system which is composed of two-level atoms initially in an entangled state interacting with the Schr\"{o}dinger cat state. The influences of the strength of light field and the phase angle between the two coherent states on the field entropy are discussed by using numerical calculations. The result shows that when the strength of light field is large enough the field entropy is not zero and the degrees of entanglement between the atoms and the three different states of the light fields are equal. When the strength of the light field is small, the degree of entanglement is maximum in a system of the two entangled atoms interacting with an odd coherent state; it is intermediate for a system of the two entangled atoms interacting with the Yurke--Stoler coherent state, and it is minimum in a system of the two entangled atoms interacting with an even coherent state.     

Implementation of n-qubit Deutsch--Jozsa algorithm using resonant interaction in cavity QED

We propose a scheme to implement the n-qubit Deutsch--Jozsa algorithm based on resonant interaction between the atoms and a single-mode cavity. In the scheme, the resonant transitions between two ground states and one excited state of an atom are changed alternately by adjusting the cavity frequency appropriately, and the operations required to complete the algorithm can be significantly simplified following the increment of the number of qubits. The implementation of the scheme in experiment would show the full power of quantum algorithm and would be significative and important for more complicated quantum algorithm in cavity quantum electrodynamics.     

利用介观LC电路制备薛定谔猫态

提出了一种制备相干态的叠加态，即薛定谔猫态的方案. 该方案是基于将外加冲激信号作用于介观LC电路系统而设计的. 在该薛定谔猫态下，介观电路系统有非经典的量子压缩效应. 关键词： 介观LC电路 冲激信号 薛定谔猫态     

原子薛定谔猫态中角动量的压缩及其时间演化

在低Q值腔内，原子相干态在一些特定时刻可以演化为原子薛定谔猫态.讨论了在这种原子薛定谔猫态中原子角动量的涨落和高阶涨落.根据不确定性原理，进一步研究了原子角动量的压缩和高阶压缩性质及其演化.研究表明，原子薛定谔猫态可以被压缩到二阶和六阶，但不能被压缩到四阶.当原子薛定谔猫态中被叠加的原子相干态数为无限多项时，其压缩特性与原子相干态相同. 关键词： 原子相干态 薛定谔猫态 角动量压缩 Bloch态     

Generation of nonclassical states in a large detuning cavity

By using the theory of cavity QED, we study the system in which a two-level atom interacts with a cavity in the case of large detuning. Through the selective detecting of atomic state, Schrodinger cat states and entangled coherent states are easily generated. When the atom is driven by a weak classical field and the cavity field is in the Schrodinger cat state, we study the conditions of generating the Fock states and the maximal success probability. The maximal success probability in our scheme is larger than the previous one.     

多腔场猫态制备新方案研究

我们提出了一个制备多腔场薛定谔猫态的新方案.在这个方案里,我们需要一个两能级原子和几个铜的单模腔.其中,原子跃迁频率与各腔场频率是大失谐的.将原子同时注入几个腔中,原子与各腔同时发生相互作用.系统按大失谐情况下J-C模型演化.着重讨论了三腔场薛定谔猫态的制备,我们的方案可以很容易被推广到多腔场薛定谔猫态的制备.     

Generation of motional cat states for a trapped ion in a cavity

Beyond the Lamb－Dicke limit, we propose a simple scheme for generating Schr?dinger cat states of the motion of a trapped two-level ion interacting with a quantized light field in a single-mode cavity.     

Generation of four-particle GHZ states in bimodal cavity QED

We propose a scheme for preparing four-particle Greenberger--Horne--Zeilinger states using two identical bimodal cavities, each supports two modes with different frequencies. This scheme is an alternative to another published work [Christopher C Gerry 1996 {\it Phys. Rev.} A {\bf 53} 4591]. Comparisons between them are discussed. The fidelity and the probability of success influenced by cavity decay for the generated states are also considered.     

The quantum sling and the Schrödinger cat

The quantum sling is defined as a quantum harmonic oscillator with an abruptly vanishing frequency. It is shown in this article that a particle released by such a mechanism remains in acorrelated coherent state, i.e., a quantum state with the minimum dispersion in position and momentum allowed by the Schrödinger-Robertson uncertainty principle. This simple model permits to describe a Schrödinger-cat state (a quantum superposition of macroscopically distinguishable states) released by the sling. The result is a superposition of two correlated coherent states propagating in two opposite directions and with an interference term.