Valentin Ivannikov

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.

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.

Low-Temperature Grown GaAsSb with Sub-Picosecond Photocarrier Lifetime for Continuous-Wave Terahertz Measurements

We report on continuous-wave optoelectronic terahertz (THz) measurements using low-temperature grown (LTG) GaAsSb as photomixer material. A broadband log-periodic antenna and a six interdigital finger photomixer with 1μm gap is fabricated on LTG-GaAsSb for THz generation and detection. At 0.37THz, the resonance frequency of the inner most antenna tooth, we obtained a power of 6.3nW. A Golay cell was used as detector. The photocarrier lifetime of the material was determined to be 700fs by pump-probe experiments with an optical wavelength close to the band gap of LTG-GaAsSb. The band gap was 1.0eV, measured by wavelength dependent pump-probe measurements.

Phase diffusion in trapped-atom interferometers

We evaluate the performance and phase diffusion of trapped

Ultracold atom interferometry with pulses of variable duration

^{87}

Ensemble master equation for a trapped-atom clock with one- and two-body losses

Rb atoms in an atom-chip sensor with Ramsey interferometry and Hahns spin echo in the time and phase domains. We trace out how the phase uncertainty of interference fringes grows with time. The phase-domain spin echo enables us to attain many-second-long phase diffusion with a low-cost local oscillator that otherwise seems unrealistic to obtain with such an oscillator. In the Ramsey experiment we record interference fringes with contrast decaying in

Long Coherence Time of an Interacting Bose-Einstein Condensate

12

Split spin-squeezed Bose-Einstein Condensates

s, and with a frequency uncertainty of

Adiabatic entangling gate of Bose-Einstein condensates based on the minimum function

80