The Bose-Einstein Condensate

The Bose-Einstein Condensate

Jim FungPhys 4DJim FungPhys 4D

Bose-Einstein Condensate (BEC)

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.

• 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 continuedBEC 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

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?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.

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?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.

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 CoolingEvaporative 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.

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?

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 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 LightSpeed of Light

Substance Speed of light (m/s)Vacuum 299792458Air(0°C) 299704600Water(20°C) 225000000Glass 190000000Diamond 123900000

Bose-Einstein Condensate 17

Substance Speed of light (m/s)Vacuum 299792458Air(0°C) 299704600Water(20°C) 225000000Glass 190000000Diamond 123900000

Bose-Einstein Condensate 17

Properties/ApplicationsProperties/Applications

Optical communication (fiber optics).

Quantum computing.Study quantum interactions –

superatoms exhibiting observable wave interference.

Atom lasers.

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!

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!