Quantum state transfer between atomic ensembles trapped in separate cavities via adiabatic passage

We propose a new approach for quantum state transfer（QST） between atomic ensembles separately trapped in two distant cavities connected by an optical fiber via adiabatic passage. The three-level Λ-type atoms in each ensemble dispersively interact with the nonresonant classical field and cavity mode. By choosing appropriate parameters of the system, the effective Hamiltonian describes two atomic ensembles interacting with ＂the same cavity mode＂ and has a dark state. Consequently, the QST between atomic ensembles can be implemented via adiabatic passage. Numerical calculations show that the scheme is robust against moderate fluctuations of the experimental parameters. In addition, the effect of decoherence can be suppressed effectively. The idea provides a scalable way to an atomic-ensemble-based quantum network, which may be reachable with currently available technology.

Vacuum induced transparency and slow light phenomena in a two-level atomic ensemble controlled by a cavity

We study the optical properties of a two-level atomic ensemble controlled by a high-finesse cavity. Even though the cavity is initially in the vacuum state in the absence of external driving, the probe response of the atomic ensemble can be dramatically modified. When the collectively enhanced atom–cavity coupling is strong enough and the cavity decay rate is much smaller than the atomic damping rate, an electromagnetically induced transparency-like coherent phenomenon emerges with a dip absorption for the response of the two-level atoms in the cavity without driving, and thus is called vacuum induced transparency. We also show the slow light with very low group velocity in such an atomic ensemble.

Scheme for preparation of multi-partite entanglement of atomic ensembles

We show a scheme of preparing multipartite W type of maximally entangled states among many atomic ensembles with the generation time increasing with the party number only polynomially. The scheme is based on laser manipulation of atomic ensembles and single-photon detection, and fits well the status of the current experimental technology. We also show one of the applications of this kind of W state, demonstrating Bell theorem without inequalities.

Entangling Two Atomic Ensembles Trapped in Separated Cavities

We propose a scheme for the generation of two collections of atoms trapped in distant cavities connected by an optical fiber.The virtual photon exchange leads to the entanglement between these two atomic ensembles.During the operation the atomic system,cavity modes,and fiber are not excited,which is important in view of decoherence.

Probabilistic and robust preparation of a GHZ-types tate via atomic ensembles and linear optics

This paper proposes two simple and robust schemes to generate an atomic-ensemble Greenberger-Horne--Zeilinger-type （GHZ-type） entangled state via linear optics and single photon detection. These schemes are based on two-photon Hong-Ou-Mandel-type interference, therefore they are insensitive to the phase fluctuation. This advantage will make the realizations of these two schemes easier. One scheme can scale efficiently with the number of ensembles because of the used quantum memory. Both schemes are also robust to the noise and within the reach of current technology.

Controlled Coherent Quantum Tunneling of Atomic Ensembles

We investigate the coherent tunneling phenomenon of the laser-driven atomic ensembles confined in a well-separated double-well potential. By generalizing the Frohlich canonical transformation to adiabatically eliminate the light field variable, a BCS-like effective Hamiltonian is obtained to depict the residual interaction between the two atomic ensembles. The number of the tunneling collective low excitations and its relationship to the ratios gr/gl and Nr/Nl are given.

Photonic graphene with reconfigurable geometric structures in coherent atomic ensembles

Photonic graphene,possesses a honeycomb-like geometric structure,provides a superior platform for simulating photonic bandgap,Dirac physics,and topological photonics.Here,the photonic graphene with reconfigurable geometric structures is demonstrated in a 5S_(1/2)–5P_(3/2)–5D_(5/2) cascade-type 85Rb atomic ensembles.A strong hexagonal-coupling field,formed by the interference of three identical coupling beams,is responsible for optically inducing photonic graphene in atomic vapor.The incident weak probe beam experiences discrete diffraction,and the observed pattern at the output plane of vapor cell exhibits a clear hexagonal intensity distribution.The complete photonic graphene geometries from transversely stretched to longitudinally stretched are conveniently constructed by varying the spatial arrangement of three coupling beams,and the corresponding diffraction patterns are implemented theoretically and experimentally to map these distorted geometric structures.Moreover,the distribution of lattice sites intensity in photonic graphene is further dynamically adjusted by two-photon detuning and the coupling beams power.This work paves the way for further investigation of light transport and graphene dynamics.

Efficient generation of non-classical photon pairs in a hot atomic ensemble

We demonstrate the generation of non-classical photon pairs in a warm S-Rb atomic vapor （＇ell with no buffer gas or polarization preserving coatings via spontaneous four-wave mixing. We obtain the photon pairs with a 1/e correlation time of 40 ns and the violation of Cauchy-Sehwartz inequality by a factor of 23 - 3. This provides a convenient and efficient method to generate photon pair sources based on an atomic ensemble.

Scheme for the preparation of macroscopic W-type state of atomic ensembles in cavity QED coulped with optical fibers

We propose a potentially practical scheme to generate macroscopic W-type state of N atomic ensembles in cavity QED system consisting of N atomic ensembles trapped in N single-mode cavities connected by(N 1)optical fibers.We show that the N-qubit W-type state of atomic ensembles can be realized with high success probabilities if the coulping strength of the cavity-fiber is much stronger than that of cavity-atom.We also show that both the growth of atomic number in each ensemble and the increase of the number of atomic ensembles can diminish the detrimental influence from dissipative processes.This idea provides a scalable way to an atomic-ensemble-based quantum network,which is plausible with current available technology.

Optical quantum states based on hot atomic ensembles and their applications

The four-wave mixing process in atomic ensembles has many important applications in quantum information.We review recent progress on the generation of optical quantum states from the four-wave mixing process in hot atomic ensembles,including the production of two-beam,multi-beam,and multiplexed quantum correlated or entangled states.We also review the applications of these optical quantum states in implementing quantum information protocols,constructing SU(1,1)quantum interferometers,and realizing quantum plasmonic sensing.These applications indicate that the four-wave mixing process in hot atomic ensembles is a promising platform for quantum information processing,especially for implementing alloptical quantum information protocols,constructing SU(1,1)interferometers,and realizing quantum sensing.

Tunable magnomechanically induced transparency and fast-slow light in a hybrid cavity magnomechanical system

We theoretically explore the tunability of magnomechanically induced transparency(MMIT) phenomenon and fastslow light effect in a hybrid cavity magnomechanical system in which a high-quality yttrium iron garnet(YIG) sphere and an atomic ensemble are placed inside a microwave cavity. In the probe output spectrum, we can observe magnoninduced transparency(MIT) and MMIT due to the photon-magnon and phonon-magnon couplings. We further investigate the effect of atomic ensemble on the absorption spectrum. The results show that better transparency can be obtained by choosing appropriate atomic ensemble parameters. We give an explicit explanation for the mechanism of the Fano resonance phenomenon. Moreover, we discuss phenomena of slow-light propagation. The maximum group delay increases significantly with the increasing atom–cavity coupling strength, and the conversion between slow light and fast light can also be achieved by adjusting the atom–cavity coupling strength. These results may have potential applications for quantum information processing and high precision measurements.

Generation of Multiple-Photon GHZ State via Cavity-Assisted Interaction

We propose a scheme for preparing multiple-photon GHZ state via cavity-assisted interaction. There are n-pair single-photon pulses successively injected and reflected from two sides of the cavity, which traps one atom. After the atomic state is measured, a 2n-photon GHZ state is produced. In the ideal case, the successful probability of the scheme is close to unity.

Experimental study of the dependences of retrieval efficiencies on time delay between magneto-optical-trap being turned off and optical storage

We report an experimental study of electromagnetically induced transparency（EIT）-based light storage in a cloud of cold atoms loaded into a magneto-optical-trap（MOT）. After the MOT is turned off, the retrieval efficiencies of rightand left-circularly polarized signal light fields each as a function of storage time are measured for different time delays between MOT off and the storage event, respectively. The results show that in the delay ranging from 0.015 ms to 3.5 ms,the retrieval efficiency for a zero-storage time（0.2 μs） and the storage lifetime can exceed 15% and 1.4 ms, respectively.The measured results will provide important help for optimizing the storage of the polarized entanglement photons in cold atomic ensembles.

Controllable four-wave mixing response in a dual-cavity hybrid optomechanical system

We systematically investigate the four-wave mixing(FWM)spectrum in a dual-cavity hybrid optomechanical system,which is made up of one optical cavity with an ensemble of two-level atoms and another with a mechanical oscillator.In this work,we propose that the hybrid dual-cavity optomechanical system can be employed as a highly sensitive mass sensor due to the fact that the FWM spectrum generated in this system has a narrow spectral width and the intensity of the FWM can be easily tuned by controlling the coupling strength(cavity-cavity,atom-cavity).More fascinatingly,the dual-cavity hybrid optomechanical system can also be used as an all-optical switch in view of the easy on/off control of FWM signals by adjusting the atom-pump detuning to be positive or negative.The proposed schemes have great potential applications in quantum information processing and highly sensitive detection.

Efficient Excitation of a Symmetric Collective Atomic State with a Single-Photon Through Dipole Blockade

In the famous quantum communication scheme developed by Duan et al.[L.M.Duan,M.D.Lukin,J.I.Cirac,and P.Zoller,Nature(London) 414(2001) 413],the probability of successful generating a symmetric collective atomic state with a single-photon emitted have to be far smaller than 1 to obtain an acceptable entangled state.Based on strong dipole-dipole interaction between two Rydberg atoms,two simultaneous excitations in an atomic ensemble are greatly suppressed,which makes it possible to excite a mesoscopic cold atomic ensemble into a near-ideal singly-excited symmetric collective state accompanied by a signal-photon with near unity success probability.

Shape-preserving storage of elegant Ince-Gaussian modes in warm atomic vapor

Multimode photonic quantum memory could enhance the information processing speed in a quantum repeater-based quantum network. A large obstacle that impedes the storage of the spatial multimode in a hot atomic ensemble is atomic diffusion, which severely disturbs the structure of the retrieved light field. In this paper, we demonstrate that the elegant InceGaussian(eIG) mode possesses the ability to resist such diffusion. Our experimental results show that the overall structure of the eIG modes under different parameters maintains well after microseconds of storage. In contrast, the standard IG modes under the same circumstance are disrupted and become unrecognizable. Our findings could promote the construction of quantum networks based on room-temperature atoms.

Narrowband photon pair generation and waveform reshaping

In this article, we review on narrowband photon pairs produced in nonlinear crystals, and especially in atomic ensembles. In atomic ensembles, ＂write-read＂ process in pulse mode and spontaneous four-wave mixing process （SFWM） in continuous mode are two popular photon pair generation schemes. We specifically discuss the experimental works with continuous SFWM scheme in cold atomic ensembles. Photon pairs produced in these systems are characteristic of controllable long coherence time, and therefore are accessible with direct temporal modulation. We elaborate on the recent techniques on modulation and waveform reshaping of narrow-band paired photons.

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.