An ingenius magneto-optic trap using a magnetic mirror created with audio tapes and floppy disks - mightfacilitate the possibility ofstorage and observation of cold rubidium atoms
A NOVEL technique for storing and
studying cold atoms using audio
tapes and floppy disks has recently
been developed. E Hinds and his
colleagues at Yale University, US, have
reported creating a magneto-optic trap
alongwith a magnetic mirror, with
which they have managed to trap
rubidium atoms (Physical Review
Letters, 75, 1995, and Nature, Vol 377,
September 28, 1995).
Non-uniform magnetic fields have
been used to deflect atoms for ages. The
magnetic moment of the atom interacts
with the magnetic field producing a
deflection. Ordinary methods produce a
very slight deflection. To get a larger
deflection, strongly varying magnetic
fields and methods for slowing down
(or cooling) the atoms before deflecting
them were necessary. The Yale group,
working on an old idea enunciated by
the Soviet physicist V V Vladimirskii in
196 1, created a magnetic mirror with an
ordinary audio tape. They recorded a
five kHz (kilohertz) audio tone on a cassette tape. The process of recording
magnetises the tape, which is then cut
into strips. The magnetisation oil the
tape had a period of 9.5 micrometre and
the strips were then glued to a flat glass
plate to form a magnetic mirror.
The particular configuration of the
magnetic field reflects the atoms when it
interacts with their magnetic moments.
In the actual experiment, rubidium
atoms were trapped in a magneto-optic trap which had a non-uniform
magnetic field and three pairs of mutually perpendicular laser beams. The
atoms are cooled by the lasers to an
extremely low temperature (20
microkelvins) and then allowed to drop
from a height of about 80 cm onto the
mirror created with the audio tape. The
atoms are observed while they undergo
multiple bounces for a duration of
about 0.6 seconds.
In an improved version of the mirror with a floppy disk instead of audio
tape, the researchers have managed to
obtain more bounces for a longer time
(around one second). Though the use of
such magnetic storage devices for atoms
is still a distant dream, scientists are
excited about the possibilities Of using
this simple and effective technique for
making magnetic mirrors.
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