Concentration of Non-maximally Entangled States via Entanglement Swapping in Cavity QED

Using the highly detuned interaction between Λ-type three-level atoms and coherent optical fields in cavity QED, we can create a maximally entangled state between an atom and a cavity mode from a non-maximally entangled atomic state and a non-maximally entangled coherent state via entanglement swapping. The averaged output entanglement of the scheme is the product of the initial two non-maximal entanglements rather than the sum of them. The impact made by the spontaneous emission from the atomic excited levels has been canceled here, which makes the current protocol more feasible.     

Generation of Entangled Bloch States for Two Atomic Samples Trapped in Separated Cavities

A scheme is presented for the cavities. In the scheme, each a coherent state with a small generation of entangled states for two atomic ensembles trapped in two distant atomic sample is initially in a Bloch state and the cavity mode is initially in amplitude. The dispersive dependent phase shift on the atomic system. The detection atomic samples collapse to an entangled Bloch state. atom-cavity interaction leads to a photon-number of a photon leaking from the cavities makes the two     

通过Raman相互作用制备三个腔场的W型纠缠相干态

通过对比分立变量量子信息过程和连续变量量子信息过程的差别,利用相干态比较容易获得的这个特点,提出一种方案制备三个腔场的W型纠缠相干态.方案基于Λ型三能级原子与单模腔场的简并Raman 相互作用.三个相同的腔初始分别处于相干态,三个相同的原子初始处于W型纠缠态,通过三个原子分别与三个腔的Raman相互作用、选择适当的相互作用时间并探测作用后的三个原子,三个腔场坍缩为W型纠缠相干态.在原子与腔的相互作用过程中原子不处于高能级,可以忽略原子的自发辐射,系统的相干性能够得到较好的维持.基于当前的腔量子电动力学技术,相信方案能在实验上实现.该方案制备的三个腔场W型纠缠相干态有望在连续变量量子信息过程中有重要的应用价值.文中将方案推广到制备n(n〉3)个腔场的W型纠缠相干态.     

通过Raman相互作用隐形传送未知多原子纠缠态

基于多粒子纠缠态在证明量子非定域性和量子信息处理方面的重要应用,提出一种方案隐形传送未知原子纠缠态.方案基于Λ型三能级原子与单模腔场的简并Raman相互作用.首先让n个原子相继通过一个相干腔场来制备量子通道.然后发送者让携带未知纠缠态的另n个原子相继通过相干腔场并通过对原子与腔场的探测作联合测量.当｜α｜1时,可以用探测正交态的方法探测腔场.最后接收者根据由经典通道得到的联合测量结果重构初始态.方案的特点是用一个相干态与多个原子的纠缠态作为量子通道,简单易行.该方案有望在证明量子非定域性和量子信息过程中有重要的应用价值.     

Conditional Generation of Multiparticle Entanglement via Cavity QED

We propose a simple scheme to not only generate GHZ states and W states of the multiparticle but also form a new category of multiparticle entangled states by letting the λ-type three-level atoms simultaneously interacting with a coherent cavity field followed by the selective measurements on the cavity mode. We investigate the influence of the cavity dissipation on the generated entangled state and discuss the experimental feasibility of our scheme. It is shown that the intensity of the coherent cavity field plays an instructive role in contribution to state preparation process while the cavity decay and the detuning between the atoms and cavity mode result in the deterioration of the generated entangled state.     

Robust Scheme for Entangling Two Distant Atoms

A robust scheme is presented for realizing entangled states for two atoms trapped in separate cavities connected by an optical fiber. The first atom is initially in a superposition of the excited state and an auxiliary ground state not coupled to the first cavity, while the second one is initially in the ground state coupled to the second cavity. The scheme involves two atom-cavity-fiber interactions accompanied by the monitoring of the cavity decay and atomic spontaneous emission. The two atoms evolve to an entangled state through exchanging an excitation after the first interaction. The states with the excitation failing to be transferred are eliminated when a photon is detected during the second interaction. Therefore, the scheme is insensitive to the decoherence effect and detection inefficiency.     

Engineering multipartite steady entanglement of distant atoms via dissipation

We propose a scheme for generating an entangled state for three atoms trapped in separate optical cavities that are coupled to each other through two optical fibers based on coherent driving and dissipation, which are induced by the classical fields and the decay of non-local bosonic modes, respectively. In our scheme, the interaction time need not be controlled strictly in the overall dynamics process, and the cavity field decay can be changed into a vital resource. The numerical simulation shows that the fidelity of the target state is insensitive to atomic spontaneous emission, and our scheme is good enough to generate the W state of distant atoms with a high fidelity and purity. In addition, the present scheme can also be generalized to prepare the N-partite W state of distant atoms.     

Scheme for Teleportation of Unknown Entangled Atomic States via Cavity Decay

We present a physical scheme to teleport an unknown atomic entangled state via cavity decay. In the teleportation process, four-particle Greenberger-Horne-Zeilinger (GHZ) state is used as quantum channel, and two unknown entangled atoms and two of four atoms in the four-particle GHZ state are trapped in four leaky cavities,respectively. Based on the joint detection of the photons leak out from the four cavities, we can teleport an unknown entangled state to two other remote atoms with certain probability and high fidelity.     

Preparation of Multi—Atom Entangled States with a Single Cavity in a Thermal State

A scheme is suggested for the generation of multi-atom maximally entangled states with a cavity in a thermal state,In this scheme several appropriately prepared two-level atoms are simultaneously sent through the nonresonant cavity.We divide the whole atom-cavity interaction time into two equal parts.At the end of the first part a π pulse is applied to the atome using a classical field.Then the photon-number-dependent shifts on the atomic states are cancelled and the atomic system finally evoloves to a maximally entangled state.     

Scheme for Teleportation of Unknown Entangled Atomic States via Cavity Decay

We present a physical scheme to teleport an unknown atomic entangled state via cavity decay. In the teleportation process, four-particle Greenberger-Horne-Zeilinger （GHZ） state is used as quantum channel, and two unknown entangled atoms and two of four atoms in the four-particle GHZ state are trapped in four leaky cavities, respectively. Based on the joint detection of the photons leak out from the four cavities, we can teleport an unknown entangled state to two other remote atoms with certain probability and high fidelity.     

A Cavity-QED Scheme for Generating Long-Lived Maximally Entangled States

We propose a potentially practical scheme to generate two-atom maximally entangled states by the large-detuning interaction between two three-level ∧-type atoms and coherent optical fields. Conditioned on the results of detecting cavity field, four pairs of atomic maximally entangled states with unity fidelity and high successful probability can be prepared. We also investigate the influence of the cavity dissipation on the generated entangledstates and discuss the experimental feasibility of our scheme.     

Scheme for Preparation of Macroscopic Multi-component Entanglement in Cavity QED

We propose a scheme of generating multi-component entangled coherent states of cavity fields. In this scheme, the atoms pass through cavities one by one, simultaneously driven by a strong classical field in each cavity. Then the detection of the atomic states collapses the cavity fields onto multi-component entangled coherent states. It is shown that, with a judicious choice of the parameters of the classical field, we can conditionally produce macroscopic multi-dimensional maximal entanglement for the cavity modes.     

利用大失谐Jaynes-Cummings模型实现原子的隐形传态

提出了一个未知原子的隐形传态方案,它是通过原子与腔场大失谐相互作用实现的.方案中,两原子缠结的EPR态作为联系发送者与接收者之间的量子信息通道,将欲传送的未知原子和EPR态中的一个原子依次注入到初始制备于相干态 |α>的腔场,然后分别对两原子和腔场进行联合测量,通过经典信息通道将测量结果传递给接收者.这样,接收者只要对EPR的另一个原子执行相应的幺正操作就能重构未知原子态.     

W态纠缠实现双腔远程控制原子的非经典特性

考虑将双模纠缠相干光场的两模场同时分别注入两个腔中,初态处于W态的三体纠缠二能级原子中的两个分别在这两个腔内,并且都与光场发生共振相互作用,经腔QED演化之后,对纠缠相干光场进行光子探测和对纠缠原子进行选择性测量,通过操纵相互作用的时间和光场的参数可控制W态中处于腔外的第三个原子的非经典效应,如粒子数布居差的崩塌一回复现象和偶极压缩现象,从而实现了更强地远程控制原子的非经典特性.     

Quantum State Transfer for Two Atoms with a Single Resonant Interaction

We present a scheme for transferring an unknown atomic entangled state with a single resonant interaction. This scheme only requires a single resonant interaction of two atoms with a cavity mode and does not use the cavity mode as the memory. Thus the scheme is very simple and the interaction time is very short, which is important, in view of decoherence. Quantum state can be directly transferred from two atoms to another two at, oms with a successful probability of 100 percent.     

Extended entanglement to quantum networks

Connecting individual quantum systems through quantum channels leads to develop quantum networks crucial to perform multipartite communication or quantum cryptography. We present two techniques to generate entanglement among different parties at larger scale. In the first approach cavity QED technique is used to produce extended entanglement in atomic internal and external degrees of freedom. In this scheme we entangle two tagged atoms in their momentum state with cavity fields. Later, interaction of two auxiliary atoms with the two cavity fields in non-dispersive and dispersive fashion transforms the atoms–fields entanglement to atoms–atoms entanglement. Quantum measurement on auxiliary atoms generates extended entangled state in atomic degrees of freedom. In the second approach we take three cavities in which the two cavities have separate entangled state with third cavity in two modes which are distinguishable. Applying quantum measurement process on third cavity, we develop extended entangled state among the three cavities. We provide experimental parameters to realize the work in laboratory experiment.     

Preparation of Highly Squeezed States and Multi—component Entangled Coherent States via the Raman Interaction

A method is presented for generating highly squeezed states of a cavity field via the atom-cavity field interaction of the Raman type.In the scheme a sequence of three-level Λ-type atoms interacts with a cavity field,displaced by a classical source,in a Raman manner.Then the atomic states are measured.By this way the cavity field may collapse onto a superposition of several coherent states,which exhibits strong squeezing.The scheme can also be used to prepare superpositions of many two-mode coherent states for two cavity fields.The coherent states in each mode are on a straight line.This is the first way for preparing multi-component entangled coherent states of this type in cavity QED.     

Preparation of Entanglement of Atoms and of Photons via Cavity Input-Output Process

We propose a method to prepare multipartite entangled states such as cluster states and graph states based on the cavity input-output process and single photon measurement. Two quantum gates, a controlled phase gate and a fusion gate between two atoms trapped in respective cavities, are proposed to prepare atomic cluster states and graph states with one and two dimensions. We also introduce a scheme that can generate an arbitrary multipartite photon duster state which uses two coherent states as a qubit basis.     

基于Tavis-Cummings模型实现非定域三原子系统量子特性的远程控制

运用全量子理论并结合数值计算方法,研究了三个二能级原子系统的量子特性。初始三原子处于W纠缠态,让其中的两原子A、B与相干态光腔场发生共振作用,经腔QED演化以后,对原子进行Bell基测量,通过调节相干态光场的强度和原子间的偶极相互作用,来控制腔外原子C的布居差演化;对相干态光场进行光子探测,通过改变探测到的光子数、相干光场参量和原子间偶极相互作用,来控制腔外原子C的偶极压缩,最终实现了远程操纵腔外原子非经典特性的目的。     

Generation of entangled coherent states for two cavity modes via resonant interaction with a V-type three-level atom

This paper proposes a scheme for the generation of entangled coherent states for two cavity modes. In the scheme a V-type three-level atom is sent through a two-mode cavity filled with a coherent field. After the atom cavity interaction and detection of the atomic state the cavity modes may evolve to a superposition of two-mode coherent states. As the scheme is based on resonant atom-cavity interaction, the required interaction time is short, which is important in view of the decoherence. Moreover, additional classical pulses are unnecessary before and after the atom-cavlty interaction.