[Show abstract][Hide abstract] ABSTRACT: It was recently found that the electric local-field effect (LFE) can lead to
strong coupling of atomic Bose-Einstein condensates (BECs) to off-resonant
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 short-range attractive interaction between two components of
the (pseudo) spinor, and a long-range 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
long-range interaction gives rise to modulational instability of the spatially
uniform state, and creates the stable ground state in the form of hybrid
matter-wave - microwave solitons (which seem like one-dimensional magnetic
monopoles), with a size much smaller than the MW wavelength, even in the
presence of arbitrarily strong contact inter-component 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 dissipation-less, making
them excellent candidates even for classical information processing. We propose
to use an array of large-spin quantum magnets for realizing a device which has
two modes of operation: memory and data-bus. While the weakly interacting
low-energy levels are used as memory to store classical information (bits), the
high-energy levels strongly interact with neighboring magnets and mediate the
spatial movement of information through quantum dynamics. Despite the fact that
memory and data-bus 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 spin-orbit
(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 Goos-H\"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.
Physical Review A 10/2014; 91(3). DOI:10.1103/PhysRevA.91.031603 · 2.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The system of quantum degenerate atomic gases coupled to an optical
cavity offers the opportunity to explore the light-matter strong
interaction in a new quantum regime beyond the conventional cavity
quantum electrodynamics. We review recent progress made in the cavity
quantum optics with Bose-Einstein condensates (BECs). Special emphasis
focuses on cavity mediated atomic dynamics and cavity-assisted quantum
measurement. First we explicitly explain how to exploit the cavity
coupling to the atomic centre-of-mass 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 principle-proof-experiment of a magneto-optical
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
quadrupole-Ioffe-configuration trap can generate a residual magnetic force to
drive a Bose-Einstein 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 matter-wave self-imaging 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 well-developed magnetic trapping techniques.
[Show abstract][Hide abstract] ABSTRACT: We have performed a principle-proof experiment of a magneto-optical
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 quadrupole-Ioffe-configuration trap can
generate a residual magnetic force to drive a Bose-Einstein 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 matter-wave self-imaging 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 well-developed magnetic
trapping techniques.
Physical Review A 11/2013; 88(5):53629-. DOI:10.1103/PhysRevA.88.053629 · 2.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigate the ground state (GS) of a collisionless Bose-Einstein condensate (BEC) trapped in a soft one-dimensional optical lattice (OL), which is formed by two counterpropagating optical beams perturbed by the BEC density profile through the local-field effect (LFE). We show that LFE gives rise to an envelope-deformation potential, a nonlocal potential resulting from the phase deformation, and an effective self-interaction of the condensate. As a result, stable photon-atomic (polaritonic) lattice solitons, including an optical component, in the form of the deformation of the soft OL, in a combination with a localized matter-wave component, are generated in the blue-detuned setting, without any direct interaction between atoms. These self-trapped 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 Bose-Einstein
condensate (BEC) trapped in a soft one-dimensional optical lattice (OL), which
is formed by two counterpropagating optical beams perturbed by the BEC density
profile through the local-field effect (LFE). We show that LFE gives rise to an
envelope-deformation potential, a nonlocal potential resulting from the phase
deformation, and an effective self-interaction of the condensate. As a result,
stable photon-atomic lattice solitons, including an optical component, in the
form of the deformation of the soft OL, in a combination with a localized
matter-wave component, are generated in the blue-detuned setting, without any
direct interaction between atoms. These self-trapped 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 single-layer array of high electric permittivity (high-ε) 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 high-ε particles. The effect offers the possibility to improve the optical elements integration level in on-chip optical circuits.
[Show abstract][Hide abstract] ABSTRACT: We study the quantum nonequilibrium dynamics of ultracold three-level atoms
trapped in an optical lattice, which are excited to their Rydberg states via a
two-photon 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 two-photon detuning to the Rydberg interaction strength.
When the two-photon detuning is blue-shifted and the latter ratio is less than
1, bistability exists among the phases. Actually, this ratio controls the
Rydberg-blockade and antiblockade effect, thus the phase transition in this
system can be considered as a possible approach to study both effects.
Physical Review A 06/2012; 85(6). DOI:10.1103/PhysRevA.85.065401 · 2.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We review our recent experimental progress in quantum technology employing amplification effect of four-wave 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 non-classical light source, we have further developed a nonlinear Mach-Zehnder (MZ) interferometer, for which the maximum fringe intensity depends quadratically on the intensity of the phase-sensing field at the high-gain regime, leading to much better sensitivity than a linear MZ interferometer in which the beam splitters have the same phase-sensing intensity. The quantum technologies developed by our group could have great potential in areas such as precision measurement and quantum information.
Chinese Science Bulletin 06/2012; 57(16). DOI:10.1007/s11434-012-5101-7 · 1.58 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigate the relationship between stability, adiabaticity and transfer efficiency in a Λ-type 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 intra-atomic collision. Our results could be useful for efficiently photoassociating ground-state molecules from a cold atomic gas with strong atom–atom collisional interaction.
Journal of Physics B Atomic Molecular and Optical Physics 01/2012; 45(1). DOI:10.1088/0953-4075/45/1/015301 · 1.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We study a recent experiment [K. Li et al., Phys. Rev. Lett. 101, 250401 (2008)] on diffracting a Bose-Einstein condensate by two counterpropagating optical fields. Including the local-field effect, we explain the asymmetric momentum distribution and self-imaging of the Bose-Einstein condensate self-consistently. Moreover, we find that the two counterpropagating optical fields could not produce a perfect optical lattice, which is actually deformed by the local-field effect. Our work implies that the local-field 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 Bose-Einstein condensate by two counterpropagating optical fields. Including the local field effect, we explain asymmetric momentum distribution and self-imaging of the BEC in a self-consistent way, and find that the self-imaging is not dependent on the intensity difference of the two optical fields, but on the light-condensate 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 analyze a model of a double-well pseudopotential (DWPP), based in the 1D Gross-Pitaevskii equation with a spatially modulated
self-attractive nonlinearity. In the limit case when the DWPP structure reduces to the local nonlinearity coefficient represented
by a set of two delta-functions, analytical solutions are obtained for symmetric, antisymmetric and asymmetric states. In
this case, the transition from symmetric to asymmetric states, i.e., a spontaneous-symmetry-breaking (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 delta-function model. In a general model, which features
a finite width of the nonlinear-potential 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 finite-width 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 present an investigation of the dynamics of centre-of-mass of a neutral particle cloud in a cavity pumped by an optical field. We derive an expression for the pump threshold for spatial self-organization 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 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 double-well potential (NDWP), alias a double-well pseudopotential, with the objective to study an alternative implementation of the spontaneous symmetry breaking (SSB) in Bose-Einstein 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 delta-functions, 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 delta-functions. In the general model with a finite width of the nonlinear-potential 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
Physical Review A 10/2008; 78(5). DOI:10.1103/PhysRevA.78.053601 · 2.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigate the effect of the position-dependent s-wave scattering length (SSL) on Bose-Einstein 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 matter-wave 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 position-dependent tuning of the SSL has the potential to result in novel properties of ultracold atomic gases.
Physical Review A 01/2007; 75(1). DOI:10.1103/PhysRevA.75.013625 · 2.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper, we explore a scheme to tackle a challenging problem of stable Bose-Einstein condensates (BECs) with attractive atom interactions. In this scheme, the s-wave scattering length is tuned in space, rather than in time as previously studied, by a far-off-resonant 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 ground-state properties of the tuned BECs and show them to exhibit a strikingly different spatial density distribution from a conventional one with a positive s-wave 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.
Physical Review A 12/2006; 74(6). DOI:10.1103/PhysRevA.74.063601 · 2.81 Impact Factor