Interaction of pair coherent state with a three-level Λ-type atom and generation of a modified Bessel-Gaussian state with a vortex structure

The evolution of a system state is derived based on the nonresonant interaction of a three-level "Λ" type atom with two cavity modes at a pair coherent state and two classic fields, and a cavity field state is analysed in detail under conditional detecting. It is found that the quantized modified Bessel-Gaussian states as well as the superposition states consisting of the quantized vortex states with different weighted coefficients may be prepared through carefully preparing an initial atomic state and appropriately adjusting the interaction time. The scheme provides an additional choice to realize the two-mode quantized vortex state within the context of cavity quantum electrodynamics (QED).     

Teleportation of an unknown two-atom state using simultaneous interaction of two two-level atoms with cavity field

Proposal for the teleportation of two-atom state is presented. It is based on the simultaneous interaction of two two-level atoms with a single-mode cavity with a filed of n photons. In the proposed scheme, two pairs of EPR state are used as quantum channel to teleport an unknown two-atom state. The completed time is greatly reduced and cavity field is not required to be detected are shown to be the distinct features of the presented scheme.     

Wigner function and the entanglement of a quantized Bessel-Gaussian vortex state of a quantized radiation field

A new kind of quantum non-Gaussian state with a vortex structure,termed a Bessel-Gaussian vortex state,is constructed,which is an eigenstate of the sum of squared annihilation operators a2+b2.The Wigner function of the quantum vortex state is derived and exhibits negativity which is an indication of nonclassicality.It is also found that a quantized vortex state is always in entanglement.And a scheme for generating such quantized vortex states is proposed.     

Generation of SU（2） Coherent States for a Cavity Mode and a Collective Atomic Mode

We propose a scheme for generation of SU（2） coherent states for an atomic ensemble and a cavity mode. In the scheme a collection of two-level atoms resonantly interact with a single-mode quantized field. Under certain conditions, the system can evolve from a Fock state to a highly entangled SU（2） coherent state. The operation speed increases as the number of atoms increases, which is important in view of deeoherence.     

Generation of any superposition of coherent states along a straight line via resonant atom-cavity interaction

This paper proposes a scheme for generating arbitrary superpositions of several coherent states along a straight line for a cavity mode. In the scheme, several atoms are sent through a cavity initially in a strong coherent state. The superposition of several coherent states with desired coefficients may be generated if each atom is detected in the excited state after it exits the cavity. The scheme is based on resonant atom--cavity interaction and no classical field is required during and after the atom--cavity interaction. Thus, the scheme is very simple and the interaction time is very short, which is important in view of decoherence.     

Teleportation of a Superposition of Three Orthogonal States of an Atom without Bell-State Measurement

A scheme to teleport a superposition of three orthogonal states of an atom without Bell-state measurement in cavity QED is proposed. The scheme based on the resonant interaction of two A-type three-level atoms with a bimodal cavity. The detection of atom ct collapses atom b to the initial state of atom a with cavity mode left in two-mode vacuum state. The probability of success and the fidelity of this scheme are 0.112 and 0.999, respectively.     

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.     

Spontaneous emission of “polarized” V-type three-level atoms strongly coupled with an optical cavity

Polarization, an intrinsic ingredient of photon, plays a critical role in its interaction with matter. A general polarization state can be an appropriate superposition of two basic polarization states, say, the vertical and horizontal linear polarized state. Here we study spontaneous emission of a V-type three-level atom(with two upper states close in energy level)strongly coupled with a single-mode damped optical cavity. By defining a general polarization state of atom as a specific superposition of the two upper quantum states, we can prepare atoms with linear polarization at arbitrary direction, left and right circular polarization, and left and right elliptical polarization, similar to photons. We find that the spontaneous emission of light from these "polarized" three-level atoms shows very different profiles of side and axis spectra. This means that the polarization state of three-level atoms can become an active ingredient to manipulate its interaction with light and control the quantum interference effect. Exploitation of the coherent superposition and interference of quantum states in"polarized" atoms would allow one to deeply explore new frontiers of light–matter interaction.     

Quantum nondemolition measurement of photon—number distribution for a weak cavity field with resonant atoms

We propose a quantum nondemolition measurement of the photon-number distribution for a weak cavity field with no more than two photons. The scheme is based on the resonant interaction of atoms with the cavity field, and thus the required interaction time is much shorter than that using dispersive interaction. This is important in view of decoherence. Our scheme can also be used to generate even and odd coherent states for a weak cavity field with resonant atoms.     

Preparation of Multi—Atom Entangled States with a Single Cavity in a Thermal State

A scheme is suggested for the generation of multi-atom maximally entangled states with a cavity in a thermal state,In this scheme several appropriately prepared two-level atoms are simultaneously sent through the nonresonant cavity.We divide the whole atom-cavity interaction time into two equal parts.At the end of the first part a π pulse is applied to the atome using a classical field.Then the photon-number-dependent shifts on the atomic states are cancelled and the atomic system finally evoloves to a maximally entangled state.     

Preparation and Decoherence of Two-Atom Entangled States in a Dissipative Cavity

We present a scheme for generating four pairs of two-atom Einstein Podolsky-Rosen （EPR） states using the simultaneous interaction of the two atoms with a single-mode cavity field under a large detuning condition. The influence of cavity dissipation on the prepared EPR states is investigated by means of the superoperator method and the state fidelity. It is shown that some kinds of the prepared EPR states are robust against cavity dissipation and the intensity of the field, and maintain their entanglement invariance, and the others are fragile and completely destroyed by the action of cavity dissipation and the intensity of the field in the long-time limit. Decoherence time of the fragile entangled states is extremely small for a typical cavity-QED experimental data.     

Continuous Pump Assisted Conditional Synthesis of Nonclassical States in a Dispersive Cavity QED

The interaction of N identical atoms with both a quantized cavity field and an external classical pumping field with the fields being degenerate in frequency, is studied in the regime where the atoms and fields are highly detuned. This dispersive interaction can be used to generate coherent states for the cavity field. By preparing the injected atoms in a superposition of the bare atomic states, various types of Schroedinger-cat-like states may be generated.     

Teleportation of arbitrary unknown two-atom statewith cluster state via thermal cavity

This paper proposes a scheme for implementing the teleportation of an arbitrary unknown two-atom state by using a cluster state of four identical 2-level atoms as quantum channel in a thermal cavity. The two distinct advantages of the present scheme are： （i） The discrimination of 16 orthonormal cluster states in the standard teleportation protocol is transformed into the discrimination of single-atom states. Consequently, the discrimination difficulty of states is degraded. （ii） The scheme is insensitive to the cavity field state and the cavity decay for the thermal cavity is only virtually excited when atoms interact with it. Thus, the scheme is more feasible.     

Efficient Scheme for Entangling Two Distant Atoms

A scheme is presented for the generation of entangled states for two atoms trapped in two distant cavities. In the scheme each atom is resonantly coupled with the respective cavity mode and driven by a strong classical field. The detection of a photon decaying from the cavities and passing through a beam-splitter collapses the atoms to an entangled state. The required atom-field interaction time is very short and thus the decoherence effect is suppressed. Our scheme is within the reach of presently available cavity QED techniques.     

Generation of Maximally Entangled States for Many Two-Level Atoms in a Thermal Cavity

We propose a scheme for generating maximally entangled states for two or more two-level atoms in a thermal cavity. The cavity frequency is large-detuned from the atomic transition frequency, so the Hamiltonian can be expressed as an effective form. The photon-number-dependent parts in the effective Hamiltonian are cancelled with the assistance of a strong classical field, thus the scheme is insensitive to both the cavity decay and the thermal field. The scheme can be used to generate multi-atom Bell-state and Greenberger-Horne-Zeiliner （GHZ） state.     

A Test of Two-photon Entanglement in Spatial Modes

Two schemes for unconditionally generating two-mode motional entanglement for two ions trapped in a cavity have been proposed. The first scheme is： the vibrational mode of the first ion is coupled to the cavity field via a linear-mixing interaction and the vibrational mode of the second ion is coupled to the cavity field via an effective parametric interaction respectively. The two ions can evolve into a steady-state two-mode entangled Gaussian state, which is a mixed state. The second scheme is. the two ions are trapped in a bimodal cavity, through choosing the frequency and intensity of the driven lasers, the two ions can evolve into a two-mode entangled state, which is a pure state.     

Nonclassical Properties in the Resonant Interaction of a Three Level A-type Atom with Two-mode Coherent state

A potential scheme is proposed to deterministically generate complete sets of entangled photons in the context of cavity quantum electrodynamics （QED）. The scheme includes twice interactions of atoms with cavities, in which the first interaction is made in two-mode optical cavities and the second one exists in a microwave cavity. In the optical cavities the atoms are resonant with the cavity modes, while the detuned interaction of the atoms with a singlemode of the microwave cavity is driven by a classical field. The favorable features of our scheme include ： （ 1 ） it is very straightforward in implementation because we carry out the scheme by only sending atoms through the cavities. The requirement for the implementation is very close to the reach of current cavity QED techniques. （2） The com- plete set of the entangled two- or more-photon states can be generated deterministically by our scheme, and the implementation time remains constant with the size of the entangled photon states. （3） Our scheme is more efficient than previous proposals with cavities, and the generated photons may be collected much more efficiently, due to cavities, than previous proposals by spontaneous emission.     

Concentration of Unknown Atomic Entangled States via Entanglement Swapping through Raman Interaction

We show that entanglement concentration of unknown atomic entangled states is achieved via the implementation of entanglement swapping based on Raman interaction in cavity QED. A maximally entangled state is obtained from a pair of partially entangled states probabilistically. Due to Raman interaction of two atoms with a cavity mode and an external driving field, the influence of atomic spontaneous emission has been eliminated. Because of the virtual excitation of the cavity mode, the decoherence of cavity decay and thermal field is neglected.     

Preparation of entangled states of atomic qubits via atom-cavity-laser interaction

<正>We propose a scheme to prepare the Bell states for atomic qubits trapped in separate optical cavities via atom-cavity-laser interaction.The quantum information of each qubit is encoded on the degenerate ground states of the atom,so the entanglement between them is relatively stable against spontaneous emission.The proposed scheme consists of a Mach-Zehnder interferometer(MZI) with two arms,and each arm contains a cavity with an N-type atom in it.It requires two classical fields and a single-photon source. By controlling the sequence and time of atom-cavity-laser interaction,the deterministic production of the atomic Bell states is shown.We also introduce the generalization of the present scheme to generate the 2N-atom Greenberger-Horne-Zeilinger state.     

Fast Generation of Einstein–Podolsky–Rosen States for Two Cavity Modes with a Collection of Driven Atoms

We propose an efficient scheme for realizing two-mode squeezing for two cavity modes with an atomic ensemble trapped in the cavity and driven by two classical fields. Through a suitable choice of the driving classical fields, the evolution dynamics of the two cavity modes is decoupled with the atomic system and described by a two-mode squeezing operator. We show that a highly squeezed state can be obtained at the output even with a bad cavity. The required experimental techniques are within the scope of what can be obtained in the BEG-cavity setup.