Nonadiabatic Molecular Association in Thermal Gases Driven by Radio-Frequency Pulses.

The molecular association process in a thermal gas of ^{85}Rb is investigated where the effects of the envelope of the radio-frequency field are taken into account. For experimentally relevant parameters our analysis shows that with increasing pulse length the corresponding molecular conversion efficiency exhibits low-frequency interference fringes which are robust under thermal averaging over a wide range of temperatures. This dynamical interference phenomenon is attributed to Stückelberg phase accumulation between the low-energy continuum states and the dressed molecular state which exhibits a shift proportional to the envelope of the radio-frequency pulse intensity.

Lifetime of the Bose gas with resonant interactions.

We study the lifetime of a Bose gas at and around unitarity using a Feshbach resonance in lithium 7. At unitarity, we measure the temperature dependence of the three-body decay coefficient L(3). Our data follow a L(3)=λ(3)/T(2) law with λ(3)=2.5(3)(stat)(6)(syst)×10(-20) (µK)(2) cm(6) s(-1) and are in good agreement with our analytical result based on zero-range theory. Varying the scattering length a at fixed temperature, we investigate the crossover between the finite-temperature unitary region and the previously studied regime where |a| is smaller than the thermal wavelength. We find that L(3) is continuous across the resonance, and over the whole a<0 range our data quantitatively agree with our calculation.

Experimental study of the BEC-BCS crossover region in lithium 6.

We report Bose-Einstein condensation of weakly bound 6Li2 molecules in a crossed optical trap near a Feshbach resonance. We measure a molecule-molecule scattering length of 170(+100)(-60) nm at 770 G, in good agreement with theory. We study the 2D expansion of the cloud and show deviation from hydrodynamic behavior in the BEC-BCS crossover region.

Measurement of the interaction energy near a Feshbach resonance in a 6Li Fermi gas.

We investigate the strongly interacting regime in an optically trapped 6Li Fermi mixture near a Feshbach resonance. The resonance is found at 800(40) G in good agreement with theory. Anisotropic expansion of the gas is interpreted by collisional hydrodynamics. We observe an unexpected and large shift (80 G) between the resonance peak and both the maximum of atom loss and the change of sign of the interaction energy.

Formation of a matter-wave bright soliton.

We report the production of matter-wave solitons in an ultracold lithium-7 gas. The effective interaction between atoms in a Bose-Einstein condensate is tuned with a Feshbach resonance from repulsive to attractive before release in a one-dimensional optical waveguide. Propagation of the soliton without dispersion over a macroscopic distance of 1.1 millimeter is observed. A simple theoretical model explains the stability region of the soliton. These matter-wave solitons open possibilities for future applications in coherent atom optics, atom interferometry, and atom transport.

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.

Anamorphic concentration of solar radiation beyond the one-dimensional thermodynamic limit.

We propose and demonstrate a new scheme for anamorphic concentration of a big (40 cm x 40 cm) diffuse light source to achieve an extremely high concentration in one lateral direction at the expense of that in the other direction, to preserve the total (two-dimensional) optical brightness. Such anamorphic concentration is achieved by a combination of two conventional two-dimensional concentrators and a properly designed retroreflector array. Our experiments in search of a diffuse white-light source with properties comparable with those of solar radiation have yielded 28-fold improvement of the one-dimensional concentration ratio compared with those of conventional concentrators and 14-fold improvement compared with the one-dimensional thermodynamic limit.

Tunable and frequency-stabilized diode laser with a Doppler-free two-photon zeeman lock.

We describe frequency locking of a diode laser to a two-photon transition of rubidium using the Zeeman modulation technique. We locked and tuned the laser frequency by modulating and shifting the two-photon transition frequency with ac and dc magnetic fields. We achieved a linewidth of 500 kHz and continuous tunability over 280 MHz with no laser frequency modulation.

High-resolution spectrometry for diffuse light by use of anamorphic concentration.

A new scheme to improve the spectral resolution of grating-based spectrometers for diffuse light is proposed and demonstrated. It exploits an anamorphic transformation that reduces the beam divergence in the direction of the grating grooves while increasing the divergence in the orthogonal direction to improve the spectral resolution without any loss of light. Up to 12-fold improvement in the spectral resolution was obtained.

Concentration of diffuse linear light sources with continuous optical elements.

A new technique for geometric transformation of a diffuse linear light source into a two-dimensional symmetric virtual source is proposed and demonstrated. It involves two cylindrical lenses and a single holographic element that is optically recorded with a simple and single step. The results for a specific arrangement that transforms a 40 mm x 0.4 mm source, with diffusive angle of 0.1 rad, into a 1 mm x 1.2 mm nearly symmetric spot are presented. The lack of sharp boundaries in either the beam or the optical elements suppresses any diffraction losses, relaxes alignment tolerances, and improves stability.