Bistability of material waves in an atomic Bose-Einstein condensate in a magnetic interferometer

It is shown theoretically that, upon filling a ring cavity (a loop magnetic waveguide) with an atomic Bose-Einstein condensate (BEC), a hysteresis dependence of the atomic number density inside the cavity on the atomic flux introduced into the cavity from the outside appears. Main parameters of the measuring system being proposed are determined: the reflectance of the magnetic mirror through which the condensate is introduced, the length of the ring cavity, and the strength of the constant magnetic field governing the BEC velocity in the cavity.     

Bose–Einstein condensation of metastable helium in a bi-planar quadrupole Ioffe configuration trap

Using a novel magnetic trapping geometry we have evaporatively cooled metastable helium atoms to form a Bose–Einstein condensate containing approximately one million atoms. This is only the fourth demonstration of a metastable condensate and the first realisation of a BEC in a bi-planar quadrupole Ioffe configuration magnetic trap.     

Effective Minkowski-to-Euclidean signature change of the magnon BEC pseudo-Goldstone mode in polar <Superscript>3</Superscript>He

We discuss the effective metric experienced by the Nambu–Goldstone mode propagating in the broken symmetry spin-superfluid state of coherent precession of magnetization. This collective mode represents the phonon in the RF driven or pulsed out-of-equilibrium Bose–Einstein condensate (BEC) of optical magnons. We derive the effective BEC free energy and consider the phonon spectrum when the spin superfluid BEC is formed in the anisotropic polar phase of superfluid ³He, experimentally observed in uniaxial aerogel ³He-samples. The coherent precession of magnetization experiences an instability at a critical value of the tilting angle of external magnetic field with respect to the anisotropy axis. From the action of quadratic deviations around equilibrium, this instability is interpreted as a Minkowski-to-Euclidean signature change of the effective phonon metric. We also note the similarity between the magnon BEC in the unstable region and an effective vacuum scalar “ghost” condensate.     

Quasipure Bose-Einstein condensate immersed in a Fermi sea

We report the observation of coexisting Bose-Einstein condensate (BEC) and Fermi gas in a magnetic trap. With a very small fraction of thermal atoms, the 7Li condensate is quasipure and in thermal contact with a 6Li Fermi gas. The lowest common temperature is 0.28 microK approximately 0.2(1)T(C) = 0.2(1)T(F) where T(C) is the BEC critical temperature and T(F) the Fermi temperature. The 7Li condensate has a one-dimensional character.     

Geometric Phase and Bose-Einstein Condensate

We show that a geometric phase may appear in the Bose-Einstein condensate (BEC) in which an adiabatic procedure happens, then a perturbation expression of geometric phase is obtained for the case of time-averaged orbiting potential trap. The phase caused by the adiabatic bias magnetic field in one BEC may interfere with another, which is similar to the phase interference of Aharonov-Susskind effect, and can be observed by experiments.     

Topological creation of a multiply charged quantized vortex in the Rb Bose-Einstein condensate

A quadruply-charged quantized vortex has been created successfully in the ⁸⁷Rb Bose-Einstein Condensate (BEC). The condensate was confined in a cloverleaf magnetic trap, and the vortex was formed by the reversal of the axial magnetic field. The vortex could be observed only in a holding time of about 1 ms, which was much shorter than that reported in the Na BEC, and the vortex position was also unstable in the BEC. To overcome these experimental difficulties, we took the following two measures and improved the vortex formation: (i) axial confinement with a FORT, which prevents the BEC from axial expansion after the field reversal, and (ii) compensation of gravity with a blue-detuned laser beam, which removes the gravitational sag.     

Screening of magnetic fields by charged Bose condensate

The space-space component of the photon polarization operator is calculated in zero frequency limit for a medium with Bose-Einstein condensate (BEC) of electrically charged particles. It is found that the polarization operator tends to a finite value at vanishing photon 3-momentum, as it happens in superconducting media. It means that magnetic fields are exponentially screened in such a medium analogously to the Debye screening of electric charges. At non-zero temperature the screened magnetic field oscillates and contains a contribution which drops only as a power of distance. This phenomenon is unknown for superconductors, even in BEC phase and can be potentially observable.     

Microscopic dynamics in a strongly interacting Bose-Einstein condensate

An initially stable 85Rb Bose-Einstein condensate (BEC) was subjected to a carefully controlled magnetic field pulse near a Feshbach resonance. This pulse probed the strongly interacting regime for the BEC, with the diluteness parameter (na(3)) ranging from 0.01 to 0.5. Condensate number loss resulted from the pulse, and for triangular pulses shorter than 1 ms, decreasing the pulse length actually increased the loss, until very short time scales (approximately 10 micros) were reached. The observed time dependence is very different from that expected in traditional inelastic loss processes, suggesting the presence of new microscopic BEC physics.     

Spin current in a spinor Bose-Einstein condensate induced by a gradient magnetic field

We develop a research of spin currents in a ²³Na spinor Bose-Einstein condensate (BEC) by applying a magnetic field gradient. The spin current is successfully induced by the spin-dependent force arising from the magnetic field gradient. The dynamics of the spin components under the magnetic force is investigated. The study is promising to be extended to produce a longer spin-coherence and to enhance the sensitivity of the spin-mixing interferometry in a spinor BEC.     

Observation of reduced three-body recombination in a correlated 1D degenerate Bose gas

We investigate the correlation properties of a one-dimensional interacting Bose gas by loading a magnetically trapped 87Rb Bose-Einstein condensate (BEC) into a deep two-dimensional optical lattice. We measure the three-body recombination rate for both the BEC in the magnetic trap and the BEC loaded into the optical lattice. The recombination rate coefficient is a factor of 7 smaller in the lattice, which we interpret as a reduction in the local three-body correlation function in the 1D case. This is a signature of correlation intermediate between that of the uncorrelated, phase coherent, 1D, mean-field regime and the strongly correlated Tonks-Girardeau regime.     

Cyclotron dynamics of a Bose–Einstein condensate in a quadruple-well potential with synthetic gauge fields

We investigate the cyclotron dynamics of Bose–Einstein condensate (BEC) in a quadruple-well potential with synthetic gauge fields. We use laser-assisted tunneling to generate large tunable effective magnetic fields for BEC. The mean position of BEC follows an orbit that simulated the cyclotron orbits of charged particles in a magnetic field. In the absence of atomic interaction, atom dynamics may exhibit periodic or quasi-periodic cyclotron orbits. In the presence of atomic interaction, the system may exhibit self-trapping, which depends on synthetic gauge fields and atomic interaction strength. In particular, the competition between synthetic gauge fields and atomic interaction leads to the generation of several discontinuous parameter windows for the transition to self-trapping, which is obviously different from that without synthetic gauge fields.     

Estimating optical lattice alignment by RF spectroscopy

A method that uses radio frequency (RF) spectroscopy to evaluate the alignment of an optical lattice is proposed and demonstrated. A one-dimensional (1D) optical lattice is applied along the long axis of a cigar-shaped Bose-Einstein condensate (BEC) in a magnetic trap. The RF spectra of condensates with and without the optical lattice are analyzed, measured, and compared with the condition in which the lattice is misaligned with the BEC. The proposed method greatly optimizes the optical alignments of the lattices.     

Observation of the BEC-BCS crossover in a degenerate Fermi gas of lithium atoms

We observe characteristic atomic behaviors in the Bose-Einstein-condensation-Bardeen-Cooper-Schrieffer(BEC-BCS)crossover,by accurately tuning the magnetic field across the Feshbach resonance of lithium atoms.The magnetic field is calibrated by measuring the Zeeman shift of the optical transition.A non-monotonic anisotropic expansion is observed across the Feshbach resonance.The density distribution is explored in different interacting regimes,where a condensate of diatomic molecules forms in the BEC limit with the indication of a bimodal distribution.We also measure the three-body recombination atom loss in the BEC-BCS crossover,and find that the magnetic field of the maximum atom loss is in the BEC limit and gets closer to the Feshbach resonance when decreasing the atom temperature,which agrees with previous experiments and theoretical prediction.This work builds up a controllable platform for the study on the strongly interacting Fermi gas.     

Interferometric precision measurements with Bose–Einstein condensate solitons formed by an optical lattice

We propose the precision measurement of both angular rotation and of the gradient magnetic of a field based on the use of matter wave interferometers with soliton states of a Bose-Einstein condensate (BEC). We consider the formation of these soliton states in a BEC with negative scattering length by an optical lattice produced by two counterpropagating laser beams. We determine the parameters of both the initial condensate and the optical radiation necessary for the formation of coherent solitons. We demonstrate that this interferometer can be used to measure magnetic field gradient with a precision of 10^-2 pT/cm. Our calculations show that the sensitivity of a gyroscope based on a ring, two-port matter wave interferometer can achieve 2.6×10^-7 rad s^-1. The precision of this method is more than ten times greater than in that of rotating interferometer with cooled atoms.     

Atom chip based fast production of Bose–Einstein condensate

We have developed a simple method for the fast and efficient production of a Bose–Einstein condensate (BEC) on an atom chip. By using a standard six-beam magneto-optical trap and light-induced atom desorption for loading, 3×10^{7 87}Rb atoms are collected within 1 s and loaded into a small-volume magnetic potential of the chip with high efficiency. With this method, a BEC of 3×10³ atoms is realized within a total time of 3 s. We can realize a condensate of up to 2×10⁴ atoms by reducing three-body collisions. The present system can be used as a fast and high-flux coherent matter-wave source for an atom interferometer. PACS 03.75.Be; 32.80.Pj; 39.25.+k     

The <Superscript>55</Superscript>Mn Spin Echo Test of Magnon BEC State in MnCO<Subscript>3</Subscript>

The coherent quantum state of magnons—Bose–Einstein condensate (BEC) has been observed in several types of antiferromagnets. According to the Bose statistics of magnons, BEC appears when the magnon density exceeds the critical density N _BEC and the magnon gas condenses to a quantum liquid. The BEC state is characterized by a coherent precession of the magnetization. In this paper, the first experiments showing the suppression of the spin echo signal by the magnon BEC is presented. These experiments confirm the coherence of magnetic excitations in the BEC state.     

Analytic Study of a Bose--Einstein Condensate in Waveguide with an Obstacle Potential

We investigate the exact solutions of one-dimensional (1D) time-independent Gross-Pitaevskii equation (GPE), which governs a Bose-Einstein condensate (BEC) in the magnetic waveguide with a square-Sech potential. Both the bound state and transmission state are found and the corresponding spatial configurations and transport properties of BEC are analyzed. It is shown that the well-known absolute transmission of the linear system can occur in the considered nonlinear system.     

Condensation of N interacting bosons: a hybrid approach to condensate fluctuations

We present a new method of calculating the distribution function and fluctuations for a Bose-Einstein condensate (BEC) of N interacting atoms. The present formulation combines our previous master equation and canonical ensemble quasiparticle techniques. It is applicable both for ideal and interacting Bogoliubov BEC and yields remarkable accuracy at all temperatures. For the interacting gas of 200 bosons in a box we plot the temperature dependence of the first four central moments of the condensate particle number and compare the results with the ideal gas. For the interacting mesoscopic BEC, as with the ideal gas, we find a smooth transition for the condensate particle number as we pass through the critical temperature.     

Landau Damping of Collective Modes in a Disc-Shaped Bose-Einstein Condensate

We investigate the Landau damping of collective modes in an anisotropic Bose Einstein condensate （BEC）, Based on divergence-free analytical solutions for the ground state wavefunction of the condensate and all eigenvalues and eigenfunctions for thermal excited quasiparticles, we make a detailed analytical calculation on coupling matrix elements. We evaluate the Landau damping of a quadrupole collective mode in the BEC with a disc-shaped trap and discuss its dependence on temperature and particle number of the system.