Mean-field theory of Feshbach-resonant interactions in 85Rb condensates

Recent Feshbach-resonance experiments with 85Rb Bose-Einstein condensates have led to a host of unexplained results: dramatic losses of condensate atoms for an across-resonance sweep of the magnetic field, a collapsing condensate with a burst of atoms emanating from the remnant condensate, increased losses for decreasing interaction times, and coherent oscillations between remnant and burst atoms. Using a simple yet realistic mean-field model, we find that rogue dissociation, molecular dissociation to noncondensate atom pairs, is strongly implicated as the physical mechanism responsible for these observations.     

Giant optical nonlinearity of an atomic Bose-Einstein condensate and low-threshold bistability

The polarization of an atomic Bose-Einstein condensate weakly excited by laser radiation at a nearly resonance frequency is determined. The coefficient of nonlinearity (cubic in field) in the refractive index of the condensate is calculated for the slow decay mode due to the spontaneous emission of excited atoms, as well as for the stationary mode, when the loss of atoms is compensated by the injection of atoms into the trap. In both cases, the cubic nonlinearity coefficients of the condensate are several orders of magnitude larger than the corresponding values for known nonlinear media. The conditions for observing hysteresis in an interferometer containing the condensate in the stationary state in the presence of an incident laser beam are specified.     

Elastic scattering loss of atoms from colliding bose-einstein condensate wave packets

Bragg diffraction of atoms by light waves can create high momentum components in a Bose-Einstein condensate. Collisions between atoms from two distinct momentum wave packets cause elastic scattering that can remove a significant fraction of atoms from the wave packets and cause the formation of a spherical shell of scattered atoms. We develop a slowly varying envelope technique that includes the effects of this loss on the condensate dynamics described by the Gross-Pitaevski equation. Three-dimensional numerical calculations are presented for two experimental situations: passage of a moving daughter condensate through a nonmoving parent condensate, and four-wave mixing of matter waves.     

Oscillations of a Bose-Einstein condensate in a rapidly contracting circular box

A Bose-Einstein condensate will evolve almost adiabatically if the number of atoms is large enough, even though the trap parameters may be changing rapidly. We demonstrate this by examining a Bose-Einstein condensate in a two-dimensional rapidly contracting circular box. We show that as a result of the contraction the condensate will oscillate about the instantaneous ground state. These oscillations will be small though when the number of atoms is large. Approximate analytic expressions are found for the evolving condensate wavefunction, both before and after the contraction has begun.     

Optimized production of a cesium Bose–Einstein condensate

We report on the optimized production of a Bose–Einstein condensate of cesium atoms using an optical trapping approach. Based on an improved trap loading and evaporation scheme we obtain more than 10⁵ atoms in the condensed phase. To test the tunability of the interaction in the condensate we study the expansion of the condensate as a function of scattering length. We further excite strong oscillations of the trapped condensate by rapidly varying the interaction strength. PACS 03.75.Kk; 32.80.Pj     

Amplification of light and atoms in a bose-einstein condensate

A Bose-Einstein condensate illuminated by a single off-resonant laser beam ("dressed condensate") shows a high gain for matter waves and light. We have characterized the optical and atom-optical properties of the dressed condensate by injecting light or atoms, illuminating the key role of long-lived matter wave gratings produced by the condensate at rest and recoiling atoms. The narrow bandwidth for optical gain gave rise to an extremely slow group velocity of an amplified light pulse ( approximately 1 m/s).     

Efimov states in a Bose-Einstein condensate near a Feshbach resonance

Recent experiments with Bose-Einstein condensates of 85Rb atoms near a Feshbach resonance have produced evidence for a condensate of diatomic molecules coexisting with the atom condensate. It should also be possible to create condensates of the triatomic molecules predicted by Efimov coexisting with the atom and dimer condensates. The smoking gun for the trimer condensate would be oscillatory dependence of observables on the binding energy of the trimer. It may also be possible to deduce the existence of the trimer condensate from the spectra of the bursts of atoms and dimers created in the disappearance of the trimers.     

Distillation of bose-einstein condensates in a double-well potential

Bose-Einstein condensates of sodium atoms, prepared in an optical dipole trap, were distilled into a second empty dipole trap adjacent to the first one. The distillation was driven by thermal atoms spilling over the potential barrier separating the two wells and then forming a new condensate. This process serves as a model system for metastability in condensates, provides a test for quantum kinetic theories of condensate formation, and also represents a novel technique for creating or replenishing condensates in new locations.     

Entangled spin states of a Bose condensate in an electromagnetic field

We consider the formation of entangled quantum states for an atomic Bose condensate interacting with an external electromagnetic field in a single-particle state under conditions of change in various regimes for exchange interaction processes. These states of the Bose system have high phase coherence and are accompanied by the generation of squeezed states of a new type in terms of the parameters defined by a combination of transition operators for the condensate atoms and external-field photons with an appropriate polynomial deformation of the algebra SU(2). We show that localized quantum structures corresponding to stable elementary excitations of the atoms and the field in the condensate can be formed in principle. We also analyze the purely quantum effects of collapse and revival for the level populations of the Bose condensate and the change in atomic statistics as well as determine the conditions for the formation of superstructure of these unsteady states for the Bose system.     

Normal mode splitting in hybrid BEC-optomechanical system

We consider an opto-mechanical cavity system consisting of Bose-Einstein condensate (BEC), trapped inside the optical cavity and driven by single mode laser field. The intracavity field acts as nonlinear spring which couples the condensate mode with moving end mirror of the cavity. We study the occurrence of normal mode splitting in the position spectra of the mechanical oscillator and condensate mode as a consequence of hybridization of the fluctuations of intracavity field, mechanical mode and condensate mode. We also discuss the modification in the dynamics of the mechanical oscillator due to frequency of the collective oscillations of cold atoms and the back action of the atoms on the mechanical mirror. Moreover, we investigate the normal mode splitting in the transmission spectrum of cavity field.     

Quantum tweezer for atoms

We propose a quantum tweezer for extracting a desired number of neutral atoms from a reservoir. A trapped Bose-Einstein condensate is used as the reservoir, taking advantage of its coherent nature, which can guarantee a constant outcome. The tweezer is an attractive quantum dot, which may be generated by red-detuned laser light. By moving at certain speeds, the dot can extract a desired number of atoms from the condensate through Landau-Zener tunneling. The feasibility of our quantum tweezer is demonstrated through realistic and extensive model calculations.     

Spontaneous Formation of Antiferromagnetic Vortex Lattice in a Fast Rotating BEC with Dipole Interactions

When a Bose-Einstein condensate is set to rotate,superfluid vortices will be formed,which finally condense into a vortex lattice as the rotation frequency further increases.We show that the dipole-dipole interactions renormalize the short-range interaction strength and result in a distinction between interactions of parallel-polarized atoms and interactions of antiparallel-polarized atoms.This effect may lead to a spontaneous breakdown of the rapidly rotating Bose condensate into a novel anti-ferromagnetic-like vortex lattice.The upward-polarized Bose condensate forms a vortex lattice,which is staggered against a downward-polarized vortex lattice.A phase diagram related to the coupling strength is obtained.     

Tunneling Dynamics of Two-Species Bose-Einstein Condensates with Feshbach Resonances

We investigate tunneling dynamics of atomic group consisting of three atoms in Bose-Einstein condensateswith Feshbach resonance. It is shown that the tunneling of the atom group depends not only on the inter-atomicnonlinear interactions and the initial number of atoms in these condensates, but also on the tunneling coupling betweenthe atomic condensate and the three-atomic molecular condensate. It is found that besides oscillating tunneling currentbetween the atomic condensate and the molecular condensate, the nonlinear atomic group tunneling dynamics sustains aself-maintained population imbalance: a macroscopic quantum self-trapping effect. The influence of de-coherence causedby non-condensate atoms on the tunneling dynamics is studied. It is indicated that de-coherence suppresses the atomicgroup tunneling.     

Tunneling Dynamics of Two-Species Bose-Einstein Condensates with Feshbach Resonances

We investigate tunneling dynamics of atomic group consisting of three atoms in Bose-Einstein condensates with Feshbach resonance. It is shown that the tunneling of the atom group depends not only on the inter-atomic nonlinear interactions and the initial number of atoms in these condensates, but also on the tunneling coupling between the atomic condensate and the three-atomic molecular condensate. It is found that besides oscillating tunneling current between the atomic condensate and the molecular condensate, the nonlinear atomic group tunneling dynamics sustains a self-maintained population imbalance: a macroscopic quantum self-trapping effect. The influence of de-coherence caused by non-condensate atoms on the tunneling dynamics is studied. It is indicated that de-coherence suppresses the atomic group tunneling.     

简谐势阱中具有吸引相互作用原子体系的玻色-爱因斯坦凝聚

给出了简谐势阱中具有吸引相互作用原子体系的非线性定态薛定谔方程的基态解,得到了凝 聚原子数随能量本征值变化的双稳态曲线.并由此得到与实验报道相符的吸引型玻色-爱因斯 坦凝聚体所能包含的最大原子数. 关键词： 玻色-爱因斯坦凝聚 双稳态     

Stable 85Rb bose-einstein condensates with widely tunable interactions

Bose-Einstein condensation has been achieved in a magnetically trapped sample of 85Rb atoms. Long-lived condensates of up to 10(4) atoms have been produced by using a magnetic-field-induced Feshbach resonance to reverse the sign of the scattering length. This system provides new opportunities for the study of condensate physics. The variation of the scattering length near the resonance has been used to magnetically tune the condensate self-interaction energy over a wide range, extending from strong repulsive to large attractive interactions. When the interactions were switched from repulsive to attractive, the condensate shrank to below our resolution limit, and after approximately 5 ms emitted a burst of high-energy atoms.     

Spatially periodic structures of an atomic Bose-Einstein condensate

The conditions providing the formation of periodic vortex lattices of an interference nature in an atomic Bose-Einstein condensate (i.e., in the absence of rotation of the condensate) are determined. Spatially periodic exact solutions of the nonlocal nonlinear Schrödinger equation (the generalized Gross-Pitaevskii equation) that describes the Bose-Einstein condensate of a dilute gas of alkali metal atoms with due regard for the nonlocality of interatomic interactions are obtained in the form of a set of two or three plane waves. It is shown that periodic vortex lattices can be produced in interference experiments with a Bose-Einstein condensate of a dilute gas of alkali metal atoms.     

Transition to instability in a kicked bose-einstein condensate

A periodically kicked ring of a Bose-Einstein condensate is considered as a nonlinear generalization of the quantum kicked rotor. For weak interactions between atoms, periodic motion (antiresonance) becomes quasiperiodic (quantum beating) but remains stable. There exists a critical strength of interactions beyond which quasiperiodic motion becomes chaotic, resulting in an instability of the condensate manifested by exponential growth in the number of noncondensed atoms. Similar behavior is observed for dynamically localized states (essentially quasiperiodic motions), where stability remains for weak interactions but is destroyed by strong interactions.     

Effect of the weak interaction on the in situ radii of condensate boson atoms in one or two-dimensional deep optical lattices

In this letter we suggest a theoretical model to investigate the weak interaction dependence of the in situ radii of condensate boson atoms in a combined harmonic with one or two-dimensional deep optical lattice. The semiclassical approximation is employed to calculate the above mentioned parameters. The calculated results showed that the in situ radii depends crucially on the interatomic interaction. Our results can be extended to investigate the moment of inertia of condensate boson atoms in combined harmonic-optical potential as well as superfluidity nature of synthetically charged boson atoms in combined potential.