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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.
05/2013;
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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.
Physical Review Letters 04/2013; 110(16):163902. · 7.37 Impact Factor
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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.
06/2012;
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ABSTRACT: We investigate the relationship between stability, adiabaticity and transfer
efficiency in a \Lambda-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.
12/2011;
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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.
Physical Review Letters 05/2011; 106(21):210403. · 7.37 Impact Factor
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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.
Faraday Discussions 01/2009; 142:311-8; discussion 319-34. · 5.00 Impact Factor
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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
10/2008;
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ABSTRACT: We investigate the deceleration and bunching of cold molecules in a pulsed supersonic jet using a far-off-resonant optical lattice traveling with a constant velocity. Using an analytical treatment, we show that by choosing the lattice velocity equal to half the supersonic beam velocity and by optimizing the pulse duration, a significant fraction (∼33%) of translationally cold (1 K) CO molecules from a supersonic molecular beam can be decelerated to zero velocity, and simultaneously bunched in velocity space. Due to the large difference of polarizability to mass ratio between the buffer gas and the CO molecules in the pulsed jet, the buffer gas can be precluded from the fraction of stationary molecules by choosing a suitable pulse duration. Furthermore, we find that spatial bunching within the optical lattice is induced and the position of the bunch within the lattice can be chosen by varying the lattice velocity.
Phys. Rev. A. 01/2004; 69(1).
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ABSTRACT: We present an analytical solution to the collisionless Boltzmann equation for describing the distribution function of molecular ensembles subject to an external periodic traveling force of pulsed optical fields. We apply our solution to study a pulsed standing wave mirror for neutral molecules, recently proposed [P. Ryytty et al., Phys. Rev. Lett. 84, 5074 (2000)]. Using our analytical solution we study the effects of the anharmonicity of optical potential on the reflectivity of the molecular mirror and the corresponding optimal pulse duration. We demonstrate that the reflectivity of the molecular mirror can be significantly improved by optimizing the pulse duration of the external optical fields when taking into account the anharmonicity of molecular motion.
Physical Review E 08/2003; 68(1 Pt 2):016607. · 2.26 Impact Factor
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ABSTRACT: We investigate the dynamics of untrapped molecules within a far-off resonant accelerating optical lattice. Our analysis shows that untrapped molecules can be temporarily transported by the lattice, and those that are transported for the longest time reach a unique, well-defined critical velocity that depends on the mass to polarizability ratio of the molecular species. We show that this species-dependent critical velocity leads to a velocity dispersion for different species within a gas mixture. Our numerical simulations show that the velocity distribution of a multicomponent gas evolves to form well-separated peaks in velocity space for each species. We propose a time-of-flight analysis technique that transforms the velocity dispersion to a temporal separation of different species, even for small differences in the mass to polarizability ratio. Separation utilizing this concept is demonstrated for atmospheric species and isotopes of nitrogen. Finally, we present an extension of this concept for both temporal and angular dispersion. © 2003 American Institute of Physics.
The Journal of Chemical Physics 01/2003; 118(4):1729-1734. · 3.33 Impact Factor
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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.
Phys. Rev. A. 74(6).
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ABSTRACT: A matter wave mirror using a single, pulsed, super-Gaussian (SG) optical beam for specular reflection of neutral ground-state molecules is studied. The mirror has a high reflectivity close to 100% and nearly perfect specular reflection over a large incident angle. This mirror avoids the usual problems due to surface roughness and the van der Waals interactions that occur in conventional atomic mirrors. Further, it is capable of reflectance and transmittance with applications to velocity filtering and deceleration of cold molecules.
Phys. Rev. A. 72(3).
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ABSTRACT: We review recent theoretical studies on the dynamics of molecules in pulsed optical lattices. These lattices are periodic potential wells formed by the interaction between two counter propagating far-off resonant optical fields and the molecules. We show that the molecules can be manipulated in both constant velocity and accelerating lattices for a number of applications. We first study a molecular optical mirror through the reflections of molecules by a stationary optical lattice and show that the reflectivity can be significantly improved by optimizing the pulse duration. When reflection occurs from a moving lattice, we show that molecules can brought to rest when the lattice velocity is half the molecular velocity, demonstrating a new and efficient method for creating slow cold molecules. We further describe a microlinear accelerator for molecules produced by an accelerating optical lattice, which is achieved by frequency chirping one of the two optical fields. The molecules trapped by the potential wells of the lattice are accelerated to high velocities (10–100 km/s) over micron-size distance within nanosecond time scales. When the lattice is decelerated, the trapped molecules can be slowed to zero velocity, offering an alternate method for producing slow cold molecules. Molecules that are not trapped in the accelerating lattice can be temporarily localized around a characteristic velocity, which is uniquely dependent on the mass-to-polarizability ratio. We show that this feature can be used for a new form of time-of-flight mass spectrometry for chemical analysis of a mixture.
Progress in Quantum Electronics.
