B. V. Hall

Long-lived periodic revivals of coherence in an interacting Bose-Einstein condensate

We observe the coherence of an interacting two-component Bose-Einstein condensate (BEC) surviving for seconds in a trapped Ramsey interferometer. Mean-field-driven collective oscillations of two components lead to periodic dephasing and rephasing of condensate wave functions with a slow decay of the interference fringe visibility. We apply spin echo synchronous with the self-rephasing of the condensate to reduce the influence of state-dependent atom losses, significantly enhancing the visibility up to 0.75 at the evolution time of 1.5 s. Mean-field theory consistently predicts higher visibility than experimentally observed values. We quantify the effects of classical and quantum noise and infer a coherence time of 2.8 s for a trapped condensate of 5.5x10{sup 4} interacting atoms.

Spatially inhomogeneous phase evolution of a two-component Bose-Einstein condensate

We investigate the spatially dependent relative phase evolution of an elongated two-component Bose-Einstein condensate. The pseudospin-1/2 system is comprised of the |F=1,m_F=-1> and |F=2,m_F=+1> hyperfine ground states of 87Rb, which we magnetically trap and interrogate with radio-frequency and microwave fields. We probe the relative phase evolution with Ramsey interferometry and observe a temporal decay of the interferometric contrast well described by a mean-field formalism. Inhomogeneity of the collective relative phase dominates the loss of interferometric contrast, rather than decoherence or phase diffusion. We demonstrate a technique to simultaneously image each state, yielding subpercent variations in the measured relative number while preserving the spatial mode of each component. In addition, we propose a spatially sensitive interferometric technique to image the relative phase.

Doppler-free two-photon resonances for atom detection and sum frequency stabilization

We investigate the excitation of the 5D5/2 level in Rb atoms using counter-propagating laser beams, which are nearly resonant to the one-photon 5S1/2 → 5P3/2 and 5P3/2 → 5D5/2 transitions, ensuring that a sum of the optical frequencies corresponds to the 5S1/2 → 5D5/2 transition. The excitation produced by two-photon and stepwise processes is detected via spontaneously emitted fluorescence at 420 nm arising from the 6P3/2 → 5S1/2 transition. The dependences of blue fluorescence intensity on atomic density and laser detuning from the intermediate 5P3/2 level have been investigated. The sensitivity of the frequency-detuned bi-chromatic scheme for atom detection has been estimated. A novel method for sum-frequency stabilization of two free-running lasers has been suggested and implemented using two-photon Doppler-free fluorescence and polarization resonances.

Precision Measurements of s-wave Scattering Lengths in a Two-Component Bose-Einstein Condensate

We developed a new method of measuring s-wave scattering lengths with a high precision (a12 = 97:993(20) a0 and a22 = 95:41(7) a0 in 87Rb) using collective oscillations and Ramsey interferometry in a two-component Bose-Einstein condensate.

Long Coherence Time of an Interacting Bose-Einstein Condensate

Mean-field induced self-rephasing and the synchronized application of spin echo allow us to preserve coherence of an interacting Bose-Einstein condensate for a long time (> 4 s) in a trapped Ramsey interferometer on an atom chip.

Dynamics of Bose-Einstein condensates in an asymmetric double-well

In this paper, we report on experiments that have used double well system. For example, we have investigated the dynamic splitting of a single BEC by transforming a single well into an asymmetric double-well potential. In this experiment the relative population of the two wells is extremely sensitive to the presence of small gravitational or magnetic field gradients.