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.     

好腔中的Bell态原子与纠缠相干态光场相互作用系统的保真度

考虑原子间偶极相互作用,求出好腔中的Bell态原子与纠缠相干态光场相互作用系统的保真度.结果表明,对于理想腔,若原子初始时刻处于相干保持态,系统保真度始终等于1;若原子初始时刻处于其余Bell态之一.腔场初态的平均光子数很小,系统保真度在0～1之间作周期性振荡,随着腔场初态的平均光子数的增加,系统保真度的振荡频率增大,振幅减小.对于好腔,若原子初始时刻处于相干保持态,系统保真度呈指数单调衰减;若原子初始时刻处于其余Bell态之一,系统保真度呈指数振荡衰减,且随着腔场初态的平均光子数的增加,系统保真度的振荡频率增大,振幅减小.     

好腔中的Bell态原子与纠缠相干态光场相互作用系统的保真度

考虑原子间偶极相互作用,求出好腔中的Bell态原子与纠缠相干态光场相互作用系统的保真度。结果表明,对于理想腔,若原子初始时刻处于相干保持态,系统保真度始终等于1;若原子初始时刻处于其余Bell态之一,腔场初态的平均光子数很小,系统保真度在0～1之间作周期性振荡,随着腔场初态的平均光子数的增加,系统保真度的振荡频率增大,振幅减小。对于好腔,若原子初始时刻处于相干保持态,系统保真度呈指数单调衰减;若原子初始时刻处于其余Bell态之一,系统保真度呈指数振荡衰减,且随着腔场初态的平均光子数的增加,系统保真度的振荡频率增大,振幅减小。     

边界振动的微腔中薛定谔猫态的产生

采用全量子理论,考虑了边界振动的微腔(振动边界视作频率为ωm的量子谐振子)与单模辐射场构成的系统,在薛定谔绘景中,给出了系统的时间演化算符,得到了系统的态函数随时间的演化关系.结果表明,当振动边界回到初态时的腔场态能给出许多与已有文献不同的薛定谔猫态,且通过调整单模辐射场的频率可以选择想要的薛定谔猫态.     

利用原子-腔场的拉曼相互作用制备双模SU(2)薛定谔猫态

利用一个参量频率转换过程,在腔中制备双模ＳＵ（２）相干态,然后注入一个与腔场的一个个模发生拉曼相互作用的Ａ型三能级原子,通过原子－腔场相互作用生成腔场－原子纠缠,通过对原子进行选择性测量,腔场－原子纠缠态将塌缩到纯态,即双模ＳＵ（２）薛定谔猫态。     

制备奇偶SU(2)相干态腔场纠缠态

利用一个参量频率转换过程，在腔中制备双模SU(2)相干态，然后在一系列全同的SU(2)相干态腔场注入一个A型三能级原子，使之与腔场的一个模发生拉曼相互作用，通过系列原子一腔场相互作用生成腔场一原子纠缠态，通过对原子进行选择性测量，可获得奇偶SU(2)相干态腔场纠缠态。     

利用原子与SU(2)相干态腔场的Raman相互作用制备原子纠缠态

利用一个参量频率转换过程,在腔中制备双模SU(2)相干态,然后注入一系列全同的Λ型三能级原子,这些原子与腔场的一个模发生拉曼相互作用,通过系列原子-腔场相互作用生成腔场-原子纠缠态,通过对腔场进行选择性测量,可获得多种形式多原子纠缠态.     

利用V-型三能级原子与双模腔场双光子大失谐相互作用制备W纠缠态

本文提出利用V-型三能级原子与双模腔场的双光子大失谐相互作用制备W纠缠态,该方案要求三个三能级原子和一个双模腔场,第一个与腔场作用的原子最初处于激发态,第二个和第三个原子均处于基态,腔场最初处于真空态,合适地选择原子与腔场之间的相互作用时间即可获得三原子W纠缠态.并且此方案可以推广至多原子W纠缠态和多腔场W纠缠态的制备;通过计算共生纠缠度研究系统中态的纠缠演化以及热纠缠现象.     

利用V-型三能级原子与双模腔场 双光子大失谐相互作用制备W纠缠态

本文提出利用 型三能级原子与双模腔场的双光子大失谐相互作用制备W纠缠态,该方案要求三个三能级原子和一个双模腔场,第一个与腔场作用的原子最初处于激发态,第二个和第三个原子均处于基态,腔场最初处于真空态,合适地选择原子与腔场之间的相互作用时间即可获得三原子W纠缠态。并且此方案可以推广至多原子W纠缠态和多腔场W纠缠态的制备;通过计算共生纠缠度研究系统中态的纠缠演化以及热纠缠现象。     

利用原子与光场的非最大纠缠态传送薛定谔猫态

利用二能级原子与腔场的共振相互作用Jaynes-Cummings(J-C)模型，制备出原子与光场的纠缠态，通过改变相互作用时间，可以控制纠缠态的纠缠程度。提出了利用这个原子与光场的非最大纠缠态，通过大失谐的J-C模型传送腔场的薛定谔猫态的方案。     

利用V型原子与单模光场的非共振相互作用制备四光子相干态

提出了一种利用简并V型三能级原子与振幅很大的单模相干光场的远离共振相互作用,制备四光子相干态的有效新方案.同时证明了在相同的条件下,按照相同的方法不能制备出四成分以上的相干态的叠加态, 即当在腔中注入的第三个原子的速度与第二个原子的速度相等时,腔场将保持这种四光子相干态不变.     

Quantum Logic Gates and Cluster States with Four-level Atoms in Cavity QED

We propose a model to implement the two-qubit quantum logic gates, i.e., the quantum phase gate and the Controlled-NOT gate, and generate the atomic qubits cluster states with a large detuned interaction between four-level atoms and a single-mode cavity field. In the presented protocol, the quantum information is encoded on the stable ground states of the atoms, and the effect of decoherence from atomic spontaneous emission is negligible. In addition, the interaction between atoms and the cavity is large detuned, and the cavity is only virtually excited. Therefore, the scheme is insensitive to the cavity decay. The experimental feasibility of our proposal is also discussed.     

Generation of quantum switch and nonlocal fields with an external field in a high quality dispersive cavity

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 Λ-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 required for the state generation is short.     

Efficient scheme of quantum SWAP gate and multi-atom cluster state via cavity QED

In this paper, we propose a physical scheme to realize quantum SWAP gate by using a large-detuned single-mode cavity field and two identical Rydberg atoms. It is shown that the scheme can also be used to create multi-atom cluster state. During the interaction between atom and cavity, the cavity is only virtually excited and thus the scheme is insensitive to the cavity field states and cavity decay. With the help of our scheme it is very simple to prepare the $N$-atom cluster state with perfect fidelity and probability. The practical feasibility of this method is also discussed.     

Efficient scheme of quantum SWAP gate and multi-atom cluster state via cavity QED

In this paper, we propose a physical scheme to realize quantum SWAP gate by using a large-detuned single-mode cavity field and two identical Rydberg atoms. It is shown that the scheme can also be used to create multi-atom cluster state. During the interaction between atom and cavity, the cavity is only virtually excited and thus the scheme is insensitive to the cavity field states and cavity decay. With the help of our scheme it is very simple to prepare the N-atom cluster state with perfect fidelity and probability. The practical feasibility of this method is also discussed.     

利用V型三能级原子与单模光场的非共振相互作用制备压缩相干态的叠加态

介绍了单模压缩相干态及其基本性质,根据简并V型三能级原子与单模光场的改进型有效哈密顿量,通过矩阵方法推导出原子-光场系统的态矢量.提出利用简并V型三能级原子与单模光场的非共振相互作用制备压缩相干态的叠加态的一种新方案,讨论了怎样进行控制单模压缩相干态光场中的压缩方向问题.     

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.     

Preparation of Macroscopic Quantum Superposition States of Cavity Modes Using rf-SQUIDs in a Cavity

We propose a potential scheme of preparing Schrödinger-cat state of the cavity mode by placing an rf-superconducting quantum interference device (rf-SQUID) in a single-mode microwave cavity. By properly adjusting the detuning and the strength regarding the radiation fields, we show how to generate single-mode Schrödinger-cat state. Generalizing this method we discuss the generation of the engtangled coherent states. The experimental feasibility of our scheme is discussed under consideration of the cavity decay.     

Efficient generation of N-photon binomial states and their use in quantum gates in cavity QED

A high-fidelity scheme to generate N-photon generalized binomial states (NGBSs) in a single-mode high-Q cavity is proposed. A method to construct superpositions of exact orthogonal NGBSs is also provided. It is then shown that these states, for any value of N, may be used for a realization of a controlled-NOT gate, based on the dispersive interaction between the cavity field and a control two-level atom. The possible implementation of the schemes is finally discussed.     

Scheme for Robust Storage of Multi-particle Entanglement with a Cavity QED System

We propose a scheme for robustly storing multi-atom entangled states involving Bell states, three-particle W-state, n-particle W-like-states, generalized multi-particle W-states, n-particle GHZ-states, and partially entangled states in cavity QED. Our scheme can preserve the internal structure of the entangled states above, with only generation of a global phase corresponding to each of entangled states during the storage of them. One single-mode cavity and n identical two-level atoms are required. Our scheme may be realized in the present technology. The idea may be also utilized to store multi-trapped-ion entangled states in linear ion trap.