Alternative Scheme for Generation of Atomic Schrdinger Cat States and Entangled Coherent States in an Optical Cavity

We propose an alternative scheme for generation of atomic Schrodinger cat states in an optical cavity. In the scheme the atoms are always populated in the two ground states and the cavity remains in the vacuum state. Therefore, the scheme is insensitive to the atomic spontaneous emission and cavity decay. The scheme may be generalized to the deterministic generation of entangled coherent states for two atomic samples. In contrast with the previously proposed schemes of [Commun. Theor. Phys. 40 （2003） 103 and Chin. our scheme is greatly shortened and thus the deeoherence can Phys. B 18 （2009） 1045], the required interaction time in be effectively suppressed.

Preparation of Entanglement and Schrdinger Cat States of Superconducting Quantum Interference Devices Qubits via Coupling to a Microwave Cavity

An alternative scheme is proposed for the generation of n-qubit W states of superconducting quantum interference devices （SQUID） in cavity QED. In this scheme, Raman coupling of two lower flux states of SQUID system is achieved via a microwave pulse and the cavity mode. Conditioned on no photon leakage from the cavity, the n-qubit W state can be generated whether the effective coupling parameters of the SQUID to cavity mode and classical microwave fields are the same or different. Our strictly numerical simulations of the time evolution of the system including decay show that the success probability of our scheme is almost unity and the interaction time is on the order of 10-9 s. The scheme can also be used to generate the Schrodinger cat states of multi-SQUID.

Coherent-Entangled State in Three-Mode and Its Applications

We introduce the new concept of coherent-entangled state （CES）. By virtue of the technique of integration within an ordered product of operators we introduce a new kind of three-mode CES [β,γ,x）, which exhibits both properties of the coherent state and the entangled state. [β,γ,x） makes up a new quantum mechancial representation. Its applications in quantum optics are also presented.

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 -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.

A Scheme for Teleportation of an Unknown Entangled Coherent State via Raman Interaction

A scheme is reported for the teleportation of entangled coherent states through the degenerate Raman interaction. The scheme uses an entangled state of an atom and two coherent states as a quantum channel. It makes lull use of coherent cavity fields. Furthermore, it does not need any classical field to transform the atom states.

Generation of Four-Mode Cluster-Type Entangled Coherent States in Free-Traveling Optical Fields

In this paper, we propose an optical scheme to generate four-mode cluster-type entangled coherent states （ECSs） in free traveling optical fields by using two single-photon sources, coherent state sources, beam splitters, pho- todetectors, cross-Kerr media, and phase shifters. And the success probability of the states preparation is calculated. At last we discuss the experimental feasibility of such proposal.

Teleportation of a Bipartite Entangled Coherent State via a Four-Partite Cluster-Type Entangled State

We present an optical scheme to almost completely teleport a bipartite entangled coherent state using afour-partite cluster-type entangled coherent state as quantum channel.The scheme is based on optical elements suchas beam splitters,phase shifters,and photon detectors.We also obtain the average fidelity of the teleportation process.It is shown that the average fidelity is quite close to unity if the mean photon number of the coherent state is not toosmall.

Creation and Destruction of Entanglement via Fourier Multiport Devices

We study entangling and disentangling functions of optical Fourier multiport devices in which input-output relation for the creation and annihilation operators is given by a finite Fourier transform. It is shown that these Fourier multiport devices can act as entanglement converters which can not only create entanglement from an unentangled state at the input but also destroy entanglement in an entangled state at the input. Creation and destruction of two-mode and three-mode entangled coherent states （ECSs） are investigated in detail. The creation and destruction of Bell-type two-mode ECS, GHZ-type and W-type three-mode ECSs are indicated explicitly through using Fourier four-port and six-port devices, respectively.

Conditional Synthesis of Entangled Coherent States with Continuous ExternalPumping in a Dispersive Cavity QED

The interaction of N two-level atoms with both a two-mode cavity field and an external classical pumpingfield, and with the fields being degenerate in frequency, is studied in the regime where the atoms and fields are highlydetuned. This dispersive interaction can be used to generate a large number of important entangled coherent statesconditional on the initial atomic states and state-selective measurements. A dynamical relation is established betweenthe results for the case with continuous pumping and the case without external driving where the coherent field is putin as the initial condition.

New Two-Mode Coherent-Intermediate-Entangled State and Its Squeezing Operator

The coherent-intermediate-entangled state ｜α, x）λ,v is proposed in the two-mode Fock Space, which exhibits both the properties of the coherent and entangled states. The ｜α, x）λ,v makes up a new quantum mechanical representation, and the completeness relation of ｜α, x）λ,v is proved by virtue of the technique of integral within an ordered product of operators. The corresponding squeezing operators are derived. Furthermore, Generalized P-representation is constructed in the coherent-intermediate-entangled state ｜α, x）λ,v and the Schmidt decomposition of ｜α, x）λ,v is investigated.

Entanglement and Teleportation of Pair Cat States in Amplitude Decoherence Channel

The dynamic behavior of the entanglement for the pair cat states in the amplitude decoherence channel isstudied by adopting the entanglement of formation determined by the concurrence.Then,we consider the teleportationby using joint measurements of the photon-number sum and phase difference with the pair cat states as an entangleresource and discuss the influence of amplitude decoherence on the mean fidelity of the teleportation.

Generation of Entangled States of Multiple Superconducting Quantum Interference Devices in Cavity

We propose a scheme for generating the maximally entangled states of many superconducting quantum interference devices （SQUIDs） by using a quantized cavity field and classical microwave pulses in cavity. In the scheme, the maximally entangled states can be generated without requiring the measurement and individual addressing of the SQUIDs.

Entanglement Evolution of Three-Qubit States under Local Decoherence

By using negativity as entanglement measure,we have investigated the effect of local decoherence from anon-Markovian environment on the time evolution of entanglement of three-qubit states including the GHZ state,the Wstate,and the Werner state.From the results,we find that the entanglement dynamics depends not only on the couplingstrengths but also on the specific states of concern.Specifically,the entanglement takes different behaviors under weakor strong coupling and it varies with the quantum states under study.The entanglement of the GHZ state and theWerner state can be destroyed completely by the local decoherence,while the entanglement of the W state can survivethrough the local decoherence partially.

Entropy and Entanglement in Master Equation of Effective Hamiltonian for Jaynes-Cummings Model

In this paper, we analytically solve the master equation for Jaynes-Cummings model in the dispersive regime including phase damping and the field is assumed to be initially in a superposition of coherent states. Using an established entanglement measure based on the negativity of the eigenvalues of the partially transposed density matrix we find a very strong sensitivity of the maximally generated entanglement to the amount of phase damping. Qualitatively this behavior is also reflected in alternative entanglement measures, but the quantitative agreement between different measures depends on the chosen noise model The phase decoherence for this model results in monotonic increase in the total entropy while the atomic sub-entropy keeps its periodic behaviour without any effect.

Controllable Amplification of Entanglement for Two Qutrits under Decoherence

Entanglement dynamics of a two-qutrit Heisenberg spin chain with the external magnetic fields and DM interaction under the intrinsic deeoherence is investigated. Depending on whether there is inhomogeneous magnetic field, the entanglement amplification, i.e. the phenomenon that the finally stable entanglement is bigger than that of the initial one, is found for one kind of initial states. The reasons for the controllable entanglement amplification are discussed.

Efficient Scheme for Entanglement and Quantum Information Processing with Two Superconducting Quantum-Interference Devices in Cavity QED

In this paper, a scheme is proposed to create the entanglement of two superconducting quantum-interference devices （SQUIDs） and implement a two-quhit quantum phase gate between two SQUIDs in cavity. The scheme only requires resonant interactions. Thus the scheme is very simple and the quantum dynamics operation can he realized at a high speed, which is important in view of decoherence.

Multipartite Entanglement Transfer from Multi-Mode Coherent State to Spin Qubits

The multipartite entanglement transfer from continuous variable system to spin qubits is investigated. We select multi-mode coherent field as continuous variable field. It is found that the qubits can not gain tripartite entanglement for states of close to GHZ state from the multi-mode coherent field. Moreover, the ability of the qubits gain the tripartite entanglement for states close to W state and bipartite entanglement from the continuous variable system is depended on the phase of multi-mode coherent field.

Entanglement Involved in Pair Coherent State Studied via Wigner Function Formalism

We calculate Wigner function, tomogram of the pair coherent state by using its Sehmidt decomposition in the coherent state representation. It turns out that the Wigner function can be seen as the quantum entanglement （QE） between two two-variable Hermite polynomials （TVHP） and the tomogram is further simplified as QE of two single-variable Hermite polynomials. The Husimi function of pair coherent state is also calculated.