Scheme for Controlled Dense Coding via Cavity Decay

A scheme for controlled dense coding via cavity decay is proposed.In the scheme,two degenerate groundstates of six-level atoms are used as the storage qubits and the leaky photons act as flying qubits.The system isrobust against atomic spontaneous emissions and decoherence of cavity field.And the successful probability is nearly1 with quantum nondemolition parity detectors and photon detectors.The scheme may be realized based on currenttechnologies.

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.

Effect of Cavity Decay on Entanglement of Ladder-Type Three-Level Atoms and a Two-Mode Cavity Field

Considering the adiabatical approximation and the large detuning condition, we give the effective Hamiltonian of a ladder-type three levels atom interacting with a bimodal cavity field. If two identical three-level atoms are sent through the cavity one by one, a two-atom entangled state can be generated. With the choice of the appropriate interaction time, a maximally entangled state of two atoms can be obtained if decoherence effect is ignored. Moreover, we discuss the effect of cavity decay on four physical quantities including atomic population probability, residual entanglement of the first atom and the cavity field, concurrence between the two atoms, and fidelity for generating atomic EPR state, all of which decrease with the increase of cavity decay when the other parameters are fixed.

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.

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.

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.

Unconventional geometric logic gate in a strong-driving-assisted multi-mode cavity

We propose a scheme to implement an unconventional geometric logic gate separately in a two-mode cavity and a multi-mode cavity assisted by a strong classical driving field. The effect of the cavity decay is included in the investigation. The numerical calculation is carried out, and the result shows that our scheme is more tolerant to cavity decay than the previous one because the time consumed for finishing the logic gate is doubly reduced.

Influence of cavity loss on regular pumping one-atom micromaser

Based on step-by-step microscopic calculation, the regular pumping one-atom micromaser is studied when the cavity decay in interaction time is considered. By numerical simulation, the steady-state photon distribution and mean photon number are presented, and influence of cavity loss in the interaction time on the micromaser discussed. It has been found that, for different loss in the interaction time, the discrepancy is large.

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.

An Effective Entanglement among Three Fibre-Connected Distant Atoms

Under the enlightenment of the scheme of Mancini and Bose [Phys. Rev. A 70 （2004）022307], we discuss two-atom entanglement in a fibre-connected triple-distant-atom system. Under adiabatic approximation, we obtain an effective Hamiltonian in form of the triple-body Ising-model interaction, The existence of a third atom is found to damage the other two-atom entanglement, The nearest-neighbouring two atoms that share a larger Ising strength are more strongly entangled.

Generation of various multiatom entangled graph states via resonant interactions

In this paper, a scheme for generating various multiatom entangled graph states via resonant interactions is proposed. We investigate the generation of various four-atom graph states first in the ideal case and then in the case in which the cavity decay and atomic spontaneous emission are taken into consideration in the process of interaction. More importantly, we improve the possible distortion of the graph states coming from cavity decay and atomic spontaneous emission by performing appropriate unitary transforms on atoms. The generation of multiatom entangled graph states is very important for constructing quantum one-way computer in a fault-tolerant manner. The resonant interaction time is very short, which is important in the sense of decoherence. Our scheme is easy and feasible within the reach of current experimental technology.

Teleportation of an Unknown Atomic State via Adiabatic Passage

We propose a scheme for teleporting an unknown atomic state via adiabatic passage. Taking advantage of adiabatic passage, the atom has no probability of being excited and thus the atomic spontaneous emission is suppressed. We also show that the fidelity can reach 1 under certain condition.