Publications (27)77.94 Total impact
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ABSTRACT: It was recently found that the electric localfield effect (LFE) can lead to strong coupling of atomic BoseEinstein condensates (BECs) to offresonant optical fields. We demonstrate that the magnetic LFE gives rise to a previously unexplored mechanism for coupling a (pseudo)spinor BEC or fermion gas to microwaves (MWs). We present a theory for the magnetic LFE, and find that it gives rise to a shortrange attractive interaction between two components of the (pseudo) spinor, and a longrange interaction between them. The latter interaction, resulting from deformation of the magnetic field, is locally repulsive but globally attractive, in sharp contrast with its counterpart for the optical LFE, produced by phase modulation of the electric field. Our analytical results, confirmed by the numerical computations, show that the longrange interaction gives rise to modulational instability of the spatially uniform state, and creates the stable ground state in the form of hybrid matterwave  microwave solitons (which seem like onedimensional magnetic monopoles), with a size much smaller than the MW wavelength, even in the presence of arbitrarily strong contact intercomponent repulsion. One interesting extension of the analysis may be the consideration of molecular BECs with rotational states coupled by the electric MW field, instead of its magnetic component.  [Show abstract] [Hide abstract]
ABSTRACT: Tackling heat dissipation in electronic devices is an ultimate goal of information technology. Quantum systems are inherently dissipationless, making them excellent candidates even for classical information processing. We propose to use an array of largespin quantum magnets for realizing a device which has two modes of operation: memory and databus. While the weakly interacting lowenergy levels are used as memory to store classical information (bits), the highenergy levels strongly interact with neighboring magnets and mediate the spatial movement of information through quantum dynamics. Despite the fact that memory and databus require different features, which are usually prerogative of different physical systems  well isolation for the memory cells, and strong interactions for the transmission  our proposal avoids the notorious complexity of hybrid structures. The proposed mechanism can be realized with different setups. We specifically show that molecular magnets, as the most promising technology, can implement hundreds of operations within their coherence time, while adatoms on surfaces probed by a scanning tunneling microscope is a future possibility.  [Show abstract] [Hide abstract]
ABSTRACT: We consider a matter wave packet of cold atom gas impinging upon a step potential created by the optical light field. In the presence of spinorbit (SO) coupling, the atomic eigenstates contain two types of evanescent states, one of which is the ordinary evanescent state with pure imaginary wave vector while the other possesses complex wave vector and is recognized as oscillating evanescent state. We show that the presence and interplay of these two types of evanescent states can give rise to two different mechanisms for total internal reflection (TIR), and thus lead to unusual GoosH\"anchen (GH) effect. As a result, not only large positive but also large negative GH shift can be observed in the reflected atomic beam. The dependence of the GH shift on the incident angle, energy and height of the step potential is studied numerically.  [Show abstract] [Hide abstract]
ABSTRACT: The system of quantum degenerate atomic gases coupled to an optical cavity offers the opportunity to explore the lightmatter strong interaction in a new quantum regime beyond the conventional cavity quantum electrodynamics. We review recent progress made in the cavity quantum optics with BoseEinstein condensates (BECs). Special emphasis focuses on cavity mediated atomic dynamics and cavityassisted quantum measurement. First we explicitly explain how to exploit the cavity coupling to the atomic centreofmass motion of a BEC to implement cavity optomechanics, simulate Dicke quantum phase transition and study the interplay between nonlinearity and disorder. Then, we consider the cavity coupling to the internal spin degree of a BEC to implement the spin analogue of cavity optomechanics. Finally we introduce how to implement nondestructive measurement via the cavity and discuss the effect of measurement backaction.  [Show abstract] [Hide abstract]
ABSTRACT: We have performed a principleproofexperiment of a magnetooptical diffraction (MOD) technique that requires no energy level splitting by homogeneous magnetic field and a circularly polarized optical lattice, avoiding system errors in an interferometer based on the MOD. The principle for this new MOD is that asynchronized switching of quadrupole trap and Ioffe trap in a quadrupoleIoffeconfiguration trap can generate a residual magnetic force to drive a BoseEinstein condensate (BEC) to move. We have observed asymmetric atomic diffraction resulting from the asymmetric distribution of the Bloch eigenstates involved in the diffraction process when the condensate is driven by such a force, and matterwave selfimaging due to coherent population oscillation of the dominantly occupied Bloch eigenstates. We have classified the mechanisms that lead to symmetric or asymmetric diffraction, and found that our experiment presents a magnetic alternative to a moving optical lattice, with a great potential to achieve a very large momentum transfer ($>110 \hbar k$) to a BEC using welldeveloped magnetic trapping techniques.  [Show abstract] [Hide abstract]
ABSTRACT: We have performed a principleproof experiment of a magnetooptical diffraction (MOD) technique that requires no energy level splitting by a homogeneous magnetic field and a circularly polarized optical lattice, avoiding system errors in an interferometer based on the MOD. The principle for this MOD is that asynchronized switching of the quadrupole trap and the Ioffe trap in a quadrupoleIoffeconfiguration trap can generate a residual magnetic force to drive a BoseEinstein condensate (BEC) to move. We have observed asymmetric atomic diffraction resulting from the asymmetric distribution of the Bloch eigenstates involved in the diffraction process when the condensate is driven by such a force, and matterwave selfimaging due to coherent population oscillation of the dominantly occupied Bloch eigenstates. We have classified the mechanisms that lead to symmetric or asymmetric diffraction and found that our experiment presents a magnetic alternative to a moving optical lattice, with a great potential to achieve a very large momentum transfer (>110ℏk) to a BEC using welldeveloped magnetic trapping techniques.  [Show abstract] [Hide abstract]
ABSTRACT: We investigate the ground state (GS) of a collisionless BoseEinstein condensate (BEC) trapped in a soft onedimensional optical lattice (OL), which is formed by two counterpropagating optical beams perturbed by the BEC density profile through the localfield effect (LFE). We show that LFE gives rise to an envelopedeformation potential, a nonlocal potential resulting from the phase deformation, and an effective selfinteraction of the condensate. As a result, stable photonatomic (polaritonic) lattice solitons, including an optical component, in the form of the deformation of the soft OL, in a combination with a localized matterwave component, are generated in the bluedetuned setting, without any direct interaction between atoms. These selftrapped modes, which realize the system's GS, are essentially different from the gap solitons supported by the interplay of the OL potential and collisional interactions between atoms. A transition to tightly bound modes from loosely bound ones occurs with the increase of the number of atoms in the BEC.  [Show abstract] [Hide abstract]
ABSTRACT: We investigate the ground state (GS) of a collisionless BoseEinstein condensate (BEC) trapped in a soft onedimensional optical lattice (OL), which is formed by two counterpropagating optical beams perturbed by the BEC density profile through the localfield effect (LFE). We show that LFE gives rise to an envelopedeformation potential, a nonlocal potential resulting from the phase deformation, and an effective selfinteraction of the condensate. As a result, stable photonatomic lattice solitons, including an optical component, in the form of the deformation of the soft OL, in a combination with a localized matterwave component, are generated in the bluedetuned setting, without any direct interaction between atoms. These selftrapped modes, which realize the system's GS, are essentially different from the gap solitons supported by the interplay of the OL potential and collisional interactions between atoms. A transition to tightly bound modes from loosely bound ones occurs with the increase of the number of atoms in the BEC.  [Show abstract] [Hide abstract]
ABSTRACT: It is shown that a singlelayer array of high electric permittivity (highε) rods with a radius smaller than λ/10 is capable of reflecting more than 97% of the energy of optical waves with an arbitrary incident angle. Here, λ is the incident wavelength. The occurrence of the phenomenon depends on the construction of two particular grating modes (GMs) in the array which result in two corresponding transmitted wave components that cancel each other. The construction of the dominant GMs in the array benefits from the highly independent manipulability of the angular momenta components with opposite signs in highε particles. The effect offers the possibility to improve the optical elements integration level in onchip optical circuits.  [Show abstract] [Hide abstract]
ABSTRACT: We study the quantum nonequilibrium dynamics of ultracold threelevel atoms trapped in an optical lattice, which are excited to their Rydberg states via a twophoton excitation with nonnegligible spontaneous emission. Rich quantum phases including uniform phase, antiferromagnetic phase and oscillatory phase are identified. We map out the phase diagram and find these phases can be controlled by adjusting the ratio of intensity of the pump light to the control light, and that of twophoton detuning to the Rydberg interaction strength. When the twophoton detuning is blueshifted and the latter ratio is less than 1, bistability exists among the phases. Actually, this ratio controls the Rydbergblockade and antiblockade effect, thus the phase transition in this system can be considered as a possible approach to study both effects.  [Show abstract] [Hide abstract]
ABSTRACT: We review our recent experimental progress in quantum technology employing amplification effect of fourwave mixing in a rubidium vapor. We have produced an intensity difference squeezed light source at frequencies as low as 1.5 kHz which is so far the lowest frequency at which squeezing has been observed in an atomic system. Moreover, we find that the bandwidth of our squeezed light source can be controlled with light intensity pumping. Using our nonclassical light source, we have further developed a nonlinear MachZehnder (MZ) interferometer, for which the maximum fringe intensity depends quadratically on the intensity of the phasesensing field at the highgain regime, leading to much better sensitivity than a linear MZ interferometer in which the beam splitters have the same phasesensing intensity. The quantum technologies developed by our group could have great potential in areas such as precision measurement and quantum information.  [Show abstract] [Hide abstract]
ABSTRACT: We investigate the relationship between stability, adiabaticity and transfer efficiency in a Λtype atom–molecule coupling system via a nonlinear stimulated Raman adiabatic passage. We find that only when the pump and control lasers overlap in time domain, the coherent population trapping (CPT) state could become unstable. If the overlapping time of the two lasers is short so that unstable growth of the deviation from the CPT state is negligible, then good adiabaticity of the CPT state could be maintained even in the unstable region. In this case, a high atom–molecule transfer efficiency could be obtained by chirping applied laser pulses to elegantly compensate the frequency shift induced by intraatomic collision. Our results could be useful for efficiently photoassociating groundstate molecules from a cold atomic gas with strong atom–atom collisional interaction.  [Show abstract] [Hide abstract]
ABSTRACT: We study a recent experiment [K. Li et al., Phys. Rev. Lett. 101, 250401 (2008)] on diffracting a BoseEinstein condensate by two counterpropagating optical fields. Including the localfield effect, we explain the asymmetric momentum distribution and selfimaging of the BoseEinstein condensate selfconsistently. Moreover, we find that the two counterpropagating optical fields could not produce a perfect optical lattice, which is actually deformed by the localfield effect. Our work implies that the localfield effect could be essential for getting a better quantitative analysis of other optical lattice experiments. In particular, the intensity imbalance of the two optical fields could act as a new means to tailor both cold atom dynamics and light propagation.  [Show abstract] [Hide abstract]
ABSTRACT: We study a recent experiment (K. Li et al., Phys. Rev. Lett. 101, 250401 (2008)) on diffracting a BoseEinstein condensate by two counterpropagating optical fields. Including the local field effect, we explain asymmetric momentum distribution and selfimaging of the BEC in a selfconsistent way, and find that the selfimaging is not dependent on the intensity difference of the two optical fields, but on the lightcondensate interaction time. We show further that the local field effect leads to deformation of an optical lattice, and thus is essential for getting better quantitative analysis of other current optical lattice experiments of cold atoms. Moreover, intensity imbalance of the two optical fields could be applied as a new means to tailor both cold atom dynamics and optical propagation.  [Show abstract] [Hide abstract]
ABSTRACT: We present an investigation of the dynamics of centreofmass of a neutral particle cloud in a cavity pumped by an optical field. We derive an expression for the pump threshold for spatial selforganization of the particles and analyze its scaling laws in terms of the system parameters. Using a newly developed statistical model, we simulate the dynamics of the particles and numerically obtain the scaling laws. We show good agreement between the analytic formulae and simulations. We further use the scaling relation to discuss the operating conditions for cavity cooling a large ensemble of particles. Finally, we study cavity cooling of an ensemble of molecules with an initial temperature of around 10 mK. We show that 35% of the molecules are trapped by the optical field intensity in the cavity and a final temperature below 1 mK is reached.  [Show abstract] [Hide abstract]
ABSTRACT: We analyze a model of a doublewell pseudopotential (DWPP), based in the 1D GrossPitaevskii equation with a spatially modulated selfattractive nonlinearity. In the limit case when the DWPP structure reduces to the local nonlinearity coefficient represented by a set of two deltafunctions, analytical solutions are obtained for symmetric, antisymmetric and asymmetric states. In this case, the transition from symmetric to asymmetric states, i.e., a spontaneoussymmetrybreaking (SSB) bifurcation, is subcritical. Numerical analysis demonstrates that the symmetric states are stable up to the SSB point, while emerging asymmetric states (together with all antisymmetric solutions) are unstable in the deltafunction model. In a general model, which features a finite width of the nonlinearpotential wells, the asymmetric states quickly become stable, simultaneously with the switch of the bifurcation into the supercritical type. Antisymmetric solutions may also enjoy stabilization in the finitewidth DWPP structure, demonstrating a bistability involving the asymmetric states. The symmetric states require a finite norm for their existence. A full diagram for the existence and stability of the trapped states is produced for the general model.  [Show abstract] [Hide abstract]
ABSTRACT: We study optical cooling of a large ensemble of particles. We derive a new scaling law with respect to particle number and show a high density molecular cloud are cooled from 10 mK to 700 muK.  [Show abstract] [Hide abstract]
ABSTRACT: We propose a model of a nonlinear doublewell potential (NDWP), alias a doublewell pseudopotential, with the objective to study an alternative implementation of the spontaneous symmetry breaking (SSB) in BoseEinstein condensates (BECs) and optical media, under the action of a potential with two symmetric minima. In the limit case when the NDWP structure is induced by the local nonlinearity coefficient represented by a set of two deltafunctions, a fully analytical solution is obtained for symmetric, antisymmetric and asymmetric states. In this solvable model, the SSB bifurcation has a fully subcritical character. Numerical analysis, based on both direct simulations and computation of stability eigenvalues, demonstrates that, while the symmetric states are stable up to the SSB bifurcation point, both symmetric and emerging asymmetric states, as well as all antisymmetric ones, are unstable in the model with the deltafunctions. In the general model with a finite width of the nonlinearpotential wells, the asymmetric states quickly become stable, simultaneously with the switch of the SSB bifurcation from the subcritical to supercritical type. Antisymmetric solutions may also get stabilized in the NDWP structure of the general type, which gives rise to a bistability between them and asymmetric states. The symmetric states require a finite norm for their existence, an explanation to which is given. A full diagram for the existence and stability of the trapped states in the model is produced. Experimental observation of the predicted effects should be possible in BEC formed by several hundred atoms. Comment: submitted to Physical Review A  [Show abstract] [Hide abstract]
ABSTRACT: We investigate the effect of the positiondependent swave scattering length (SSL) on BoseEinstein condensate (BEC) dynamics. In particular, we study the propagation of a BEC within a finite regime where the SSL, tuned by a periodic magnetic or optical field, results in the Bragg scattering of the BEC. We have predicted a matterwave optical limiting process and bistability, which have potential applications like a matter wave limiter, a BEC mirror or cavity, and an atomic switch. The first phenomenon is a direct result of this periodic spatial tuning, showing that the positiondependent tuning of the SSL has the potential to result in novel properties of ultracold atomic gases. 
Article: Groundstate properties of a BoseEinstein condensate tuned by a faroffresonant optical field
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ABSTRACT: In this paper, we explore a scheme to tackle a challenging problem of stable BoseEinstein condensates (BECs) with attractive atom interactions. In this scheme, the swave scattering length is tuned in space, rather than in time as previously studied, by a faroffresonant Gaussian optical field, from negative to positive in the center region of the potential well. We find that this tuning leads to coexisting repulsive and attractive interactions within a single atomic gas and consequently a stable BEC in the repulsive region. We investigate the groundstate properties of the tuned BECs and show them to exhibit a strikingly different spatial density distribution from a conventional one with a positive swave scattering length. The tuned BEC is formed only when the condensed number is less than a critical number. We derive a formula for the critical number.
Publication Stats
237  Citations  
77.94  Total Impact Points  
Top Journals
Institutions

20082015

East China Normal University
 • State Key Laboratory of Precision Spectroscopy
 • Department of Physics
Shanghai, Shanghai Shi, China


2006

Hong Kong Baptist University
 Department of Physics
Chiulung, Kowloon City, Hong Kong


2005

Mid Sweden University
Härnösand, Västernorrland, Sweden


20032004

HeriotWatt University
 • School of Engineering and Physical Sciences
 • Department of Physics
Edinburgh, Scotland, United Kingdom
