制备n原子GHZ类态

我们提出一个方案通过极化光子的干涉来制备囚禁在相距很远的腔中的n原子GHZ类态。在该方案中,原子腔耦合强度小于腔衰减率。因此对腔的品质因子的要求大大降低了,而且,该方案的保真度不受探测器效率和原子自发衰变的影响。 中文关键词：纠缠制备;GHZ类态;腔QED     

Scheme for implementing quantum logic gates for two atomstrapped in different cavities

A scheme is presented for realizing quantum logic gates for two atoms localized in two distant optical cavities. Our scheme works in a regime in which the atom--cavity coupling strength is smaller than the cavity decay rate. Thus the requirement on the quality factor of the cavities is greatly relaxed. Furthermore, the fidelity of our scheme is not affected by detection inefficiency and atomic decay. These advantages are important in view of experiment.     

Tripartite entanglement of atoms trapped in coupled cavities via quantum Zeno dynamics

A scheme is proposed for the generation of a W state for three atoms trapped in spatially separated cavities connected by optical fibers via quantum Zeno dynamics. Our scheme is based on the resulting effective dynamics induced by continuous coupling between the atoms and cavities. The effects of decoherence such as atomic spontaneous emission and the fiber and cavity losses are considered. Numerical results show that the scheme is very robust against the cavity decay due to a tiny excitation probability of the cavity fields during the operation.     

Purification of entangled states for two atoms via cavity decay

In this paper a scheme is proposed for the purification of entangled states for two atoms trapped in two distant cavities via cavity decay. In the scheme, the atoms have no probability of being populated in the excited state and thus the atomic spontaneous emission is suppressed. This scheme is valid no matter when the cavity decay rate is larger or smaller than the effective atom-cavity coupling strength. The fidelity of the final state is not affected by the imperfection of the photodetectors.     

Universal quantum gates between distant quantum dot spins

We propose a scheme to engineer a nonlocal two-qubit phase gate between two remote quantum-dot spins in cavities. As the effect of cavity decay is considered and strong coupling condition is not used, the scheme has good adaptability. Along with single qubit operations, one can perform in principle various types of distributed quantum information processing.     

Establishment of Entanglement for Two Atoms Trapped in Two Distant Bad Cavities

A scheme is presented for generation of entangled states for two atoms trapped in two distant bad cavities. The scheme can work with bad cavities with the coupling strength smaller than the cavity decay rate, which is important from the viewpoint of experiment. In the scheme the atoms have no probability of being populated in the excited state and thus the atomic spontaneous emission is suppressed, which increases the probability of success. The fidelity of the entangled state is not affected by the detection eflciency. Furthermore, the scheme does not require the detection of the left-polarized photon and right-polarized photon at the same time.     

Deterministic Generation of Quantum State Transfer Between Spatially Separated Single Molecule Magnets

We propose a new scheme for realizing deterministic quantum statetransfer (QST) between two spatially separated single moleculemagnets (SMMs) with the framework of cavity quantum electrodynamics(QED). In the present scheme, two SMMs are trapped in two spatiallyseparated optical cavities coupled by an optical fiber. Through strictly numerically simulating, we demonstrate that our scheme is robust with respect to the SMMs' spontaneous decay and fiber loss under the conditions of dispersive SMMs-field interaction and strong coupling of cavity fiber. In addition, we also discuss the influence of photon leakage out of cavities and show that our proposal is good enough to demonstrate the generation of QST with high fidelity utilizing the current experimental technology. Thepresent investigation provides research opportunities for realizingQST between solid-state qubits and may result in a substantial impact on the progress of solid-state-based quantum communications network.     

Possible Realization of Cluster States and Quantum Information Transfer in Cavity QED via Raman Transition

We present a scheme to generate cluster states with many scheme, no transfer of quantum information between the atoms in cavity QED via Raman transition. In this atoms and cavities is required, the cavity fields are only virtually excited and thus the cavity decay is suppressed during the generation of cluster states. The atoms are always populated in the two ground states. Therefore, the scheme is insensitive to the atomic spontaneous emission and cavity decay. We also show how to transfer quantum information from one atom to another.     

Accelerated and Robust Generation of W State by Parametric Amplification and Inverse Hamiltonian Engineering

A scheme to realize the accelerated and robust generation of W state in a cavity quantum electrodynamics (QED) system by combining parametric amplification (PA) with inverse Hamiltonian engineering (IHE) is proposed. The atom-cavity coupling strength can be exponentially enhanced via parametrically squeezing the cavity mode, which facilitates the generation of W state. Moreover, the evolution of the system can be optimized with suppressing the populations of the intermediate states. Numerical simulations show that the scheme is fast and high-fidelity, immune to systematic parameter deviations, robust against spontaneous emission of atoms, and decay of cavities. Therefore, this scheme may provide some useful applications in entanglement generation.     

Teleportation of a two-atom entangled state via cavity decay

This paper proposes a scheme for teleporting a two-atom entangled state using leaky cavities. It uses resonant atom--cavity interaction to map the atomic state onto the cavity field. Then it utilizes the interference of polarized photons to establish the correlation between the distant sender and receiver. The advantage of the scheme is that the fidelity is independent of the cavity decay rate, atomic decay and detection efficiency.     

Quantum teleportation of an arbitrary superposition of atomic states

This paper proposes a scheme to teleport an arbitrary multi-particle two-level atomic state between two parties or an arbitrary zero- and one-photon entangled state of multi-mode between two high-Q cavities in cavity QED. This scheme is based on the resonant interaction between atom and cavity and does not involve Bell-state measurement. It investigates the fidelity of this scheme and find out the case of this unity fidelity of this teleportation. Considering the practical case of the cavity decay, this paper finds that the condition of the unity fidelity is also valid and obtains the effect of the decay of the cavity on the successful probability of the teleportation.     

Non-Markovian effects on entanglement dynamics in lossy cavities

We consider the non-markovian entanglement dynamics of two independent atoms, each off-resonantly coupling with a zero temperature reservoir. For two types of initial entanglement, corresponding to spin correlated and anti-correlated Bell-like states |φ〉 and |ψ〉, we study the dependence of the two-qubit entanglement transfer on both the off-resonant interactions and the cavity pseudomode decay. The speed of the entanglement transfer is related to the choice of the atom detuning from the cavity pseudomode, the cavity pseudomode decay and the relative coupling. Furthermore, compared to the ideal cavities, entanglement transfer and sudden death can not be prevented using off-resonant interactions in the lossy cavities, and the conservation rules are always satisfied in the off-resonant and lossy system.     

Scheme for Teleportation of Four-Level Atomic States in Thermal Cavities

We propose a scheme for teleportation of four-level atomic states in thermal cavities. The scheme does not involve the generalized Bell-state or generalized GHZ-state measurement, which is difficult in practice. Another feature of the scheme is that it does not require individual addressing of atoms in cavity and is insensitive to both cavity decay and thermal field, which is of importance in point of experiment.     

Effective Scheme for Generating Cluster States in Cavity QED

We propose a scheme to prepare many two-mode cavities into one-dimensional cluster states in the context of cavity QED. The left-circularly polarized state and right-circularly polarized state of the cavity are encoded as the logic zero and one of the qubits. In the scheme, the atomic spontaneous emission is suppressed, and the fidelity is unaffected by the cavity decay on the assumption that the detection efficiencies of all the photondetectors are 1.     

Teleportation of an Arbitrary Two-Atom Entangled State via Thermal Cavity

We present an experimentally feasible scheme for teleportation of an arbitrary unknown two-atom entangled state by using two-atom Bell states in driven thermal cavities. In this scheme, the effects of thermal field and cavity decay can be all eliminated. Moreover, the present scheme is feasible according to current technologies.     

Engineering Multi-atom Entangled States via Cavity Decay

A scheme is proposed for the generation of entangled states for multiple atoms trapped in a cavity by detecting photon decay. The scheme is valid no matter when the effective atom-cavity coupling strength is larger than the cavity decay rate or not, which is of importance in view of experiment. The fidelity of entanglement is insensitive to the inefticiency of the photo-detector. The scheme does not require a photon to be initially injected into the cavity.     

Scheme for generating a cluster-type entangled squeezed vacuum state via cavity QED

A scheme is proposed to generate an N-qubit cluster-type entangled squeezed vacuum state （CTESVS） based on the two-photon interaction between a two-level atomand the cavity fields with the cavity QED system. The CTESVS in N separate cavities can be effectively obtained after performing a simple one-qubit measurement on the atom. The influence of cavity decay on the CTESVS is also discussed.     

Generation of cluster-type entangled squeezed vacuum states

We present a scheme to prepare cluster-type entangled squeezed vacuum states （CTESVS） by considering the two-photon interaction between a two-level atom and a high-quality cavity, driven by a strong classical field. After the realization of simple atomic measurements, the generation of CTESVS in four separate cavities is accomplished within the cavity decay time. In the case of large atom=cavity detuning, the scheme is immune to the effect of atomic spontaneous emission.     

Teleportation via decay

We present a rare example of a decay mechanism playing a constructive role in quantum information processing. We show how the state of an atom trapped in a cavity can be teleported to a second atom trapped in a distant cavity by the joint detection of photon leakage from the cavities. The scheme, which is probabilistic, requires only a single three level atom in a cavity. We also show how this scheme can be modified to a teleportation with insurance.     

Schemes of Implementing a Two-Atom Iswap Gate via Cavity QED

We propose two schemes for implementing a two-atom quantum iswap gate via cavity QED. In the first scheme, only one cavity and two classical fields are used to realizing iswap gate and thus reducing the operating time. The second scheme needs three cavities for atom-cavity interaction and single-qubit rotations without the assistant of the auxiliary level. Our schemes can effectively reduce the cavity decay owing to the reason that the cavity is only virtually excited during the interaction process between atoms and the cavity. Operator fidelity is applied to analyzing the influence when two atoms enter a cavity without accurate simultaneity.