SIGNIFICANT EVENTS - SCIENCE EVENTS
03/08/02
Ketterle Group Reports Observation of Vortex Phase Singularities in BEC
Bose-Einstein condensates of dilute atomic gases offer a unique opportunity to study
quantum hydrodynamics. The low density of the gas allows direct comparison with first
principle theories.
Recently, vortices in a Bose-Einstein condensate have been realized experimentally
and are currently under intensive study. In most of this work, vortices were identified
by observing the density depletion at the cores. The flow field of a vortex can be
directly observed when the phase of the macroscopic wavefunction is measured using
interferometric techniques. In the MIT work, Ketterle's group created one or several
vortices in a condensate by moving a laser beam through it, and then imaged its phase
by interfering that condensate with a second unperturbed condensate that served as a
local oscillator. The characteristic signature of vortices was dislocations in the
interference fringes. The "extra" fringe that terminates at the vortex core corresponds
to one quantum of circulation h/m (where m is the atomic mass and h Planck's constant)
or a phase change of 2
These results are described in the paper "Observation of Vortex Phase Singularities in
Bose-Einstein Condensates" with authors S. Inouye, S. Gupta, T. Rosenband, A.P. Chikkatur,
A. Grlitz, T.L. Gustavson, A.E. Leanhardt, D.E. Pritchard, and W. Ketterle, published
in Physical Review Letters 87, 080402 (2001).
integrated along a path around the vortex core.
Observation of the phase singularities
of vortices created by sweeping a laser beam through a condensate. Without the sweep,
straight fringes of about 20 µm spacings were observed (upper image), while after the
sweep, fork-like dislocations appeared (lower image). The speed of the sweep was 1.1 µm/ms
corresponding to a Mach number of 0.1. The field of view of each image is 1.1 mm x
0.38 mm.
