Transcript Slowing Light with the Bose

The Bose-Einstein
Condensate
Jim Fung
Phys 4D
Bose-Einstein Condensate
(BEC)
• Postulated by Bose and Einstein in
1924.
• Forms when less than 500
billionths of a Kelvin above
Absolute Zero.
• Forms “superatom” in which no
individual atom can be identified.
BEC continued
 Previously, the coldest
temperatures able to be
produced were with
initial cooling with He
and then magnetic
cooling.
 In 1995, Bose
condensation was
observed when rubidium
was cooled to 100nK
Two BEC overlapping, interference pattern
How do you make it?
 Cool with laser light until
1/10000 degrees above absolute
zero.
 Bombard atoms from all sides,
forming an “Optical molasses”.
 Photons are absorbed by the
atoms and released with a blue
shift relative to the laser,
indicating that the photons
gained energy.
 Doppler Effect.
 Magnetic field assists the laser
trap.
So is that all we need?
No! The lowest temperature that
light can slow the atoms down to is
1/10000K.
Due to fact that a photon gives a
certain minimum kick to an atom
when it collides.
We need evaporative cooling.
Evaporative Cooling
Form a magnetic trap in which the
atoms are contained.
BEC atoms have one free valence atom
and thus have magnetic moment.
BEC cannot occur for atoms with odd
sum for p+n+e.
Allow more energetic atoms to escape
the collection.
High energy particles are accelerated
away by finely tuned E/M waves.
So what do you mean it
slows down light?
• Speed of photons is c.
• Light is macroscopically slowed
when passing through a medium.
• Light propagates through a
substance by atomic absorption
and reemission, thus slowing its
apparent speed.
Speed of Light
Substance
Vacuum
Air(0°C)
Water(20°C)
Glass
Diamond
Speed of light (m/s)
299792458
299704600
225000000
190000000
123900000
Bose-Einstein
Condensate
17
Properties/Applications
Optical communication (fiber
optics).
Quantum computing.
Study quantum interactions –
superatoms exhibiting observable
wave interference.
Atom lasers.
Atom laser accelerated by
gravity
 BEC is to matter as laser is to light.
 Expect to see great developments in BEC
technology and application.
 Lasers at first were thought to be too difficult
to use practically and it took 20 years to
become viable and look at the advances in
technology that have come about from it! BEC
has the potential to do the same in the future!