E. Rowen

Spectroscopy of strong-pulse superradiance in a Bose-Einstein condensate

We study experimentally superradiance in a Bose-Einstein condensate using a two-frequency pump beam. By controlling the frequency difference between the beam components, we measure the spectrum of the backward (energy-mismatched) superradiant atomic modes. In addition, we show that the populations of these modes display coherent time dynamics. These results are compared to a semiclassical model based on coupled Schroedinger-Maxwell equations.

Short-time Enhancement of the Decay of Coherent Excitations in Bose-Einstein Condensates

We study, both experimentally and theoretically, short-time modifications of the decay of excitations in a Bose-Einstein Condensate (BEC) embedded in an optical lattice. Strong enhancement of the decay is observed compared to the Golden Rule results. This enhancement of decay increases with the lattice depth. It indicates that the description of decay modifications of few-body quantum systems also holds for decay of many-body excitations of a BEC.

Energy-dependent damping of excitations over an elongated Bose-Einstein condensate

We report the measurement of Beliaev damping of bulk excitations in cigar shaped Bose Einstein condensates of atomic vapor. By using post selection, excitation line shapes of the total population are compared with those of the undamped excitations. We find that the damping depends on the initial excitation energy of the decaying quasi particle, as well as on the excitation momentum. We model the condensate as an infinite cylinder and calculate the damping rates of the different radial modes. The derived damping rates are in good agreement with the experimentally measured ones. The damping rates strongly depend on the destructive interference between pathways for damping, due to the quantum many-body nature of both excitation and damping products.

Collisional Decay of a Strongly Driven Bose-Einstein Condensate

We study the collisional decay of a strongly driven Bose-Einstein condensate oscillating between two momentum modes. The resulting products of the decay are found to strongly deviate from the usual s-wave halo. Using a stochastically seeded classical field method we simulate the collisional manifold. These results are also explained by a model of colliding Bloch states.

Decoherence and dephasing in strongly driven colliding Bose-Einstein condensates

We report on a series of measurements of decoherence and wave-packet dephasing between two colliding, strongly coupled, identical Bose-Einstein condensates. We measure, in the strong-excitation regime, a suppression of the mean-field shift, compared to the shift which is observed for a weak excitation. This suppression is explained by applying the Gross-Pitaevskii energy functional. By selectively counting only the nondecohered fraction in a time-of-flight image we observe oscillations for which both inhomogeneous and Doppler broadening are strongly suppressed. If no post-selection is used, the decoherence rate due to collisions can be extracted and is in agreement with the local density average calculated rate.

Three-wave mixing of bogoliubov quasiparticles in a Bose-Einstein condensate

A dressed basis is used to calculate the dynamics of three-wave mixing between Bogoliubov quasiparticles in a Bose condensate. Because of the observed oscillations between different momentum modes, an energy splitting, analogous to the optical Mollow triplet, appears in the Beliaev damping spectrum of the excitations from the oscillating modes.

Control of decoherence of many-body excitations in a Bose-Einstein Condensate

We measure the effects of reservoir engineering on the decay of a coherent, many-body excitation in a BEC loaded into an optical lattice. We show both enhancement and suppression of decoherence vs. lattice depth.

Ultra cold bosons in incommensurate optical lattices

We study the quantum phase diagram of ultra cold bosons in 1D incommensurate optical lattices, as compared to commensurate lattices. We also examine the experimental implications of incommesurability and one spatial dimension.

Changes in excitation line shapes due to beliaev damping in a BEC

We quantitatively study the Beliaev decay of Bogoliubov quasi-particles of different energies and momenta in an elongated BEC. The structure of the continuum leads to a momentum dependent collisional shift of the excitation spectrum.

Spectroscopic and collisional splitting in the spectrum of a strongly driven Bose condensate

The paper studies the spectrum of a /sup 87/Rb BEC in the presence of a dressing traveling optical lattice. The dressing Rabi frequency /spl Omega//sub d/ is determined by performing Rabi oscillations in the time domain. The spectrum of the dressed condensate is measured with a perturbative Bragg probe and presented without and with the dressing lattice beams, where splitting in frequency with magnitude similar to /spl Omega//sub d/ clearly seen for the latter.