Implementation of quantum controlled phase gate and preparation of multiparticle entanglement in cavity QED

Schemes are presented for realizing quantum controlled phase gate and preparing an N-qubit W-like state, which are based on the large-detuned interaction among three-state atoms, dual-mode cavity and a classical pulse. In particular, a class of W states that can be used for perfect teleportation and superdense coding is generated by only one step. Compared with the previous schemes, cavity decay is largely suppressed because the cavity is only virtually excited and always in the vacuum state and the atomic spontaneous emission is strongly restrained due to a large atom-field detuning.

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.

Efficient Atomic One-Qubit Phase Gate Realized by a Cavity QED and Identical Atoms System

我们在场与穿过一些相同原子在被套住的一个光洞的一个二水平的原子实现一扇 one-qubit 阶段门的一个计划。一个人能方便地由适当地选择在洞和穿过洞的原子的速度套住的原子的数字获得门的任意的阶段移动。现在的计划为实现 one-qubit 阶段门提供一个很简单、有效的方法。

Efficient generation of two-dimensional cluster states in a cavity QED

We propose a scheme to achieve a kind of nontrivial multipartite pair-wise controlled phase operation in a cavity QED setup. The operation implemented is of geometrical nature and is not sensitive to the thermal state of the cavity. In particular, we have managed to avoid the conventional dispersive coupling so that high speed gate operation is achieved which is very important in view of decoherence. We show that this multipartite pair-wise controlled phase operation makes the generation of two-dimensional cluster states very efficient.

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.

Realization of Perfect Teleportation with W-States in Cavity QED

<Abstract>We put forward an experimentally feasible protocol for realizing a perfect teleportation by using a class of W-state in QED.The simple way of generating the entangled channel and distinguishing the measurement bases is the distinct feature of our scheme.In addition,the probability of teleportation is up to 100%.The scheme can be implemented by the present cavity QED techniques.

Scheme for teleportation of an unknown atomic state via a cluster state in cavity QED

This paper proposes an experimentally feasible scheme for teleportation of an unknown two-atom entangled state, where a cluster state is used as the quantum channel. This scheme does not need any joint measurement. In addition, the successful probability and fidelity of teleportation can both reach 1.0. The current scheme can be realized within the current experimental technology.

Generation of an N -qubit phase gate via atom–cavity nonidentical coupling

A scheme for approximate generation of an N-qubit phase gate is proposed in cavity QED based on nonidentical coupling between the atoms and the cavity. The atoms interact with a highly detuned cavity-field mode, but quantum information does not transfer between the atoms and cavity field, and thus the cavity decay is negligible. The gate time does not rise with an increase in the number of qubits. With the choice of a smaller odd number l （related to atom-cavity coupling constants）, the phase gate can be generated with a higher fidelity and a higher success probability in a shorter time （the gate time is much shorter than the atomic radiative lifetime and photon lifetime）. When the number of qubits N exceeds certain small values, the fidelity and success probability rise slowly with an increase in the number of qubits N. When N→∞, the fidelity and success probability infinitely approach 1, but never exceed 1.

Scheme for implementing quantum dense coding with W-class state in cavity QED

An experimentally feasible protocol for realizing dense coding by using a class of W-state in cavity quantum electrodynamics （QED） is proposed in this paper. The prominent advantage of our scheme is that the successful probability of the dense coding with a W-class state can reach 1. In addition, the scheme can be implemented by the present cavity QED techniques.

Scheme for implementing perfect remote state preparation with W-class state in cavity QED

In this paper we present a remote state preparation scheme with a three-qubit W-class state in cavity QED. It has been shown that a special single-qubit state and a special two-qubit entangled state can be remotely prepared perfectly. Furthermore, the classical information cost in this scheme is less than that in the corresponding teleportation scheme and only a single-qubit projective measurement is made by the sender. We also generalize this idea to the multiqubit W-class state.

Distillation of bi-partite entanglement from W state with cavity QED

Following the theoretical protocol described by Fortescue and Lo [Fortescue B and Lo H K 2007 Phys. Rev. Lett. 98 2605011, we present a scheme in which one can distill maximally entangled bi-partite states from a tri-partite W state with cavity QED. Our scheme enables the concrete physical system to realize its protocol. In our scheme, the rate distillation also asymptotically approaches one. Based on the present cavity QED techniques, we discuss the experimental feasibility.

Entangled W State Generation via Adiabatic Passage in Cavity QED

A scheme is proposed to generate W state of N atoms trapped in a cavity,based on adiabatic passage alongdark state.Taking advantage of adiabatic passage,the atoms have no probability of being excited and thus the atomicspontaneous emission is suppressed.The scheme is simple.It does not need to adjust the interaction time accurately,anddoes not need to prepare the cavity field in one-photon state.Numerical simulation shows that the successful probabilityof the scheme increases with the increasing of the atom number.

Scheme for Implementing Perfect Quantum Teleportation with Non-maximally Entangled W-Class State in Cavity QED

We propose an experimentally feasible teleportation scheme with three-atom W-class state,which was first proposed by Agrawal and Pati [P.Agrawal and A.Pati,Phys.Rev.A 74 (2006) 062320 ],in cavity QED.In this scheme atoms interact simultaneously with a nonresonant cavity and there is no energy exchange between the atoms and the cavity.Thus it is insensitive to the cavity decay,which is of importance in view of experiment.

Preparation of the W state via cavity QED

A scheme for preparation of the tripartite W state via cavity quantum electrodynamics is presented in this paper. And the scheme can be generalized to prepare the n-atom W states. The second part of this paper shows how to prepare n-cavity W states. All cavities involved are initially in the vacuum states, thus the requirement on the quality factor of the cavities is greatly loosened.

A scheme of quantum phase gate for trapped ion

We propose a scheme to implement two-qubit controlled quantum phase gate（CQPG） via a single trapped two-level ion located in the standing wave field of a quantum cavlty, in which the trap works beyond the Lamb--Dicke limit. When the light field is resonant with the atomic transition ｜g） →← ｜e） of the ion located at the antinode of the standing wave, we can perform CQPG between the internal and external states of the trapped ion; while the frequency of the light field is chosen to be resonant with the first red sideband of the collective vibrational mode of the ion located at the node of the standing wave, we can perform CQPG between the cavity mode and the collective vibrational mode of the trapped ion. Neither the Lamb--Dicke approximation nor the assistant classical laser is needed. Also we can generate a GHZ state if assisted with a classical laser.

Implementation of a many-qubit Grover search by cavity QED

We explore the possibility of an N-qubit （N 〉 3） Grover search in cavity QED, based on a fast operation of an N-qubit controlled phase-flip with atoms in resonance with the cavity mode. We demonstrate both analytically and numerically that our scheme can be achieved efficiently to find a marked state with high fidelity and high success probability. As an example, a ten-qubit Grover search is simulated specifically under the discussion of experimental feasibility and challenge. We argue that our scheme is applicable to the case involving an arbitrary number of qubits. As cavity decay is involved in our quantum trajectory treatment, we can analytically understand the implementation of a Grover search subject to dissipation, which will be very helpful for relevant experiments.

Efficient generation of Bell and W-type states in cavity QED

Two generation schemes for Bell and W-type states of single-photon in cavity QED are proposed. The proposed schemes are simple and efficient in the sense that it requires no measurements on the particles.

Faithful Controlled Teleportation of an Arbitrary Unknown Two-Atom State via Special W-States and QED Cavity

一个计划被建议因为经由特殊 W 类型的一个任意的二原子的状态的控制远距传物纠缠了状态和证完洞。计划不包含直接联合的 Bell-state-measurement (BSM ) 。我们证明量信息被分成二部分，没有另外的代理人的合作和古典通讯，因此，原来的原子状态不能被接收装置完美地恢复。另外，这个计划的物理实现不是困难的。

腔QED制备三原子W态的一般方案(英文)

本文提出了一个基于腔QED技术的制备三原子最大W态的一般方案。通过讨论表明三个原子不论是被同时注入腔中还是在不同的时刻被注入腔中我们都能得到三原子最大W态。