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A superfluid switch
In atomtronics scientists construct circuit elements using ultra-cold
atomic gases where the atoms take the role of electrons. PFC
scientists have developed an experiment that not only generates
persistent superfluid currents--frictionless flow; this quantum fluid
can be configured to switch atom-currents on and off.
The green laser is an tunable weak link in the
circuit that can switch off the atom current
This work spans condensed matter, atomic physics, and
specialized optics. The first step is to create long-lived superflow in
a ring-shaped Bose-Einstein condensate. They use special laser
beams to add rotational momentum to the atom cloud, thus
creating superflow. Generating persistent current-- in this case
lasting 40 seconds-- was not easy, as defects in the atom trap can
cause the current to disappear. The researchers designed their
atom trap to be completely made of laser light, producing an
extremely smooth all-optical donut-shaped potential in which to
study both the superflow and atomtronics.
A “weak link” was created by focusing a green
laser beam into the path of the superflow. The
scientists control the amplitude of the
obstruction by adjusting the laser power. The
barrier is analogous to a constriction in a pipe,
causing the flow in the narrow region to
speed-up and become turbulent. The
conditions for current flow cannot be
maintained when the local velocity near the
barrier becomes sufficiently fast. At this
critical value, the weak link abruptly shuts-off
the superflow, like a switch.
“Superflow in a toroidal Bose-Einstein condensate: an atom circuit
with a tunable weak link,” A. Ramanathan, K. C. Wright, S. R.
Muniz, M. Zelan, W. T. Hill III, C. J. Lobb, K. Helmerson, W. D. Phillips,
and G. K. Campbell, Phys. Rev. Lett. 106, 130401 (2011)
Images courtesy of K.C. Wright

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