25 research outputs found
Confirmation of stimulated Hawking radiation, but not of black hole lasing
Stimulated Hawking radiation in an analogue black hole in a Bose-Einstein
condensate was reported seven years ago, and it was claimed that the
stimulation was of the black hole lasing variety. The study was based on
observation of rapidly-growing negative-energy waves. We find that the Hawking
particles are directly observable in the experimental plots, which confirms the
stimulated Hawking radiation. We further verify this result with new
measurements. Also, the observed Hawking particles provide a sensitive,
background-free probe of the underlying mechanism of the stimulation. The
experiment inspired the prediction of the Bogoliubov-Cherenkov-Landau (BCL)
mechanism of stimulated Hawking radiation. By computing the Bogoliubov
coefficient for Hawking radiation, we find that the stimulation was of the BCL
type, rather than black-hole lasing. We further confirm the results with
numerical simulations of both black hole lasing and BCL stimulation
Direct observation of number squeezing in an optical lattice
We present an in-situ study of an optical lattice with tunneling and single
lattice site resolution. This system provides an important step for realizing a
quantum computer. The real-space images show the fluctuations of the atom
number in each site. The sub-Poissonian distribution results from the approach
to the Mott insulator state, combined with the dynamics of density-dependent
losses, which result from the high densities of optical lattice experiments.
These losses are clear from the shape of the lattice profile. Furthermore, we
find that the lattice is not in the ground state despite the momentum
distribution which shows the reciprocal lattice. These effects may well be
relevant for other optical lattice experiments, past and future. The lattice
beams are derived from a microlens array, resulting in lattice beams which are
perfectly stable relative to one another
Direct observation of the phonon energy in a Bose-Einstein condensate by tomographic imaging
The momentum and energy of phonons in a Bose-Einstein condensate are measured
directly from a time-of-flight image by computerized tomography. We find that
the same atoms that carry the momentum of the excitation also carry the
excitation energy. The measured energy is in agreement with the Bogoliubov
spectrum. Hydrodynamic simulations are performed which confirm our observation.Comment: Letter, 5 figure