Floquet spectrum and universal dynamics of a periodically driven two-atom system

We investigate the Floquet spectrum and excitation properties of a two-ultracold-atom system with periodically driven interaction in a three-dimensional harmonic trap.The interaction between the atoms is changed by varying the s-wave scattering length in two ways,the cosine and the square-wave modulations.It is found that as the driving frequency increases,the Floquet spectrum exhibits two main features for both modulations,the accumulating and the spreading of the quasienergy levels,which further lead to different dynamical behaviors.The accumulation is associated with collective excitations and the persistent growth of the energy,while the spread indicates that the energy is bounded at all times.The initial scattering length,the driving frequency and amplitude can all significantly change the Floquet spectrum as well as the dynamics.However,the corresponding relation between them is valid universally.Finally,we propose a mechanism for selectively exciting the system to one specific state by using the avoided crossing of two quasienergy levels,which could guide preparation of a desired state in experiments.

Recommender System Combining Popularity and Novelty Based on One-Mode Projection of Weighted Bipartite Network

Personalized recommendation algorithms,which are effective means to solve information overload,are popular topics in current research.In this paper,a recommender system combining popularity and novelty(RSCPN)based on one-mode projection of weighted bipartite network is proposed.The edge between a user and item is weighted with the item’s rating,and we consider the difference in the ratings of different users for an item to obtain a reasonable method of measuring the similarity between users.RSCPN can be used in the same model for popularity and novelty recommendation by setting different parameter values and analyzing how a change in parameters affects the popularity and novelty of the recommender system.We verify and compare the accuracy,diversity and novelty of the proposed model with those of other models,and results show that RSCPN is feasible.

Teleportation of two-atom entangled state in resonant cavity quantum electrodynamics

An alternative scheme is presented for teleportation of a two-atom entangled state in cavity quantum electrodynamics （QED）. It is based on the resonant atom-cavity field interaction. In the scheme, only one cavity is involved, and the number of the atoms needed to be detected is decreased compared with the previous scheme. Since the resonant atom-cavity field interaction greatly reduces the interaction time, the decoherence effect can be effectively suppressed during the teleportation process. The experimental feasibility of the scheme is discussed. The scheme can easily be generalized to the teleportation of N-atom Greeninger-Horne-Zeilinger （GHZ） entangled states. The number of atoms needed to be detected does not increase as the number of the atoms in the GHZ state increases.

Probabilistic remote preparation of a two-atom entangled state

A scheme for remotely preparing a two-atom entangled state via entanglement swapping in cavity quantum electronic dynamics （QED） with the help of separate measurements is proposed. And the effect of cavity decay is eliminated in our scheme.

Teleportation of a two-atom entangled state using a single EPR pair in cavity QED

We propose a scheme for teleporting a two-atom entangled state in cavity quantum electrodynamics （QED）, In the scheme, we choose a single Einstein Podolsky Rosen （EPR） pair as the quantmn channel which is shared by the sender and the receiver. By using the atom cavity-field interaction and introducing an additional atom, we can teleport the two-atom entangled state successfully with a probability of 1.0. Moreover, we show that the scheme is insensitive to cavity decay and thermal field.

Scheme for realizing assisted cloning of an unknown two-atom entangled state via cavity QED

This paper proposes a scheme where one can realize quantum cloning of an unknown two-atom entangled state with assistance of a state preparer in cavity QED. The first stage of the scheme requires usual teleportation. In the second stage of the scheme, with the assistance of the preparer, the perfect copies of an unknown atomic entangled state can be produced.

Effects of spatial interference on intensity-intensity correlations in collective two-atom emission

In this paper, we investigate the effects of the spatial variation of driving-laser phase in a collective two-atom system on the intensity intensity correlations of the resonant fluorescence. It is shown that the intensity-intensity correlations exhibit quite different characteristics for the different values of the spatial phase of the laser at the position of the two atoms in both cases of the weak and strong driving lasers. Our results suggest that the intensity intensity correlations can serve as a probe of the spatial interference effect arising from the spatial variation of the laser phase.

Quantum Dynamics of a Charge Qubit in a Squeezed Field

The quantum dynamics of a charge qubit, which makes up of a single-Cooper-pair box, are explored. The Cooper-pair box is irradiated by a squeezed field in an ideal one-mode cavity. By the result of the Schrodinger equation, the Cooper pairs number 〈N〉 is conveniently obtained. Then it is proved that the oscillations of the Cooper-pair number 〈N〉 are decreasing with the increasing squeezing parameter of the squeezed field.

Robust scheme for implemention of quantum phase gates for two atoms

We propose a scheme for implementing conditional quantum phase gates for two four-state atoms trapped in a cavity. The two ground states of the atoms are coupled through two Raman processes induced by the cavity mode and two classical fields. Under certain conditions nonresonant Raman processes lead to two-atom coupling and can be used to produce conditional phase gates. The scheme is insensitive to cavity decay, thermal photons, and atomic spontaneous emission. The scheme does not require individual addressing of the atoms.

Entanglement of two atoms in two-mode Raman coupled model with intrinsic decoherence

Considering intrinsic decoherence, the two-atom two-mode Raman coupled model is investigated in this paper. Utilizing the constants of motion in this model, we obtain the analytic expressions of the density operator of the system for investigating the entanglement of two atoms. The speed of entanglement decay increases with the increasing of the coupling coefficient of one atom. The difference between the oscillation periods when the initial state parameter of atomic subsystem belongs to two intervals becomes smaller with the increasing of the coupling coefficient of one atom. The increasing of the initial photon number of the second field can hasten the vanishing of entanglement of atomic subsystem. The robustness of atomic entanglement against decoherence depends on the interval of the initial state parameter of atomic subsystem.

Preparation of genuine Yeo-Chua entangled state and teleportation of two-atom state via cavity QED

We first propose a scheme for preparing the genuine Yeo-Chua 4-qubit entangled state via cavity QED. Using the genuine Yeo-Chua atomic state, we further propose a cavity QED scheme for teleporting an arbitrary two-atom state. In two schemes the large-detuning is chosen and the necessary time is designed to be much shorter than Rydberg-atom’s lifespan. Both schemes share the distinct advantage that cavity decay and atom decay can be neglected. As for the interaction manipulation, our preparation scheme is more feasible than a recent similar one. Compared with the Yeo and Chua’s scheme, our teleportation scheme has significantly reduced the measuring difficulty.

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.