Quantum Cooperation and Superfluids

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Lecture 18

• Quantum Cooperation and Superfluids

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Quantum Mechanics Operating on a Large Scale

• Lasers
• Superfluidity
• Superconductivity
• Bose-Einstein condensate
• Future technologies?

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Lasers Light Amplification by Stimulated
Emission of Radiation

• Monochromatic one specific wavelength (colour)
  of light
• Coherent every wave is moving in step
• Directional beam is tight, strong and
  concentrated

Normal light many wavelengths,non-coherent,
non-directional
Laser light monochromatic,coherent, directional
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Absorption and Emission of Photons
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Stimulated Emission of Photons in a Metastable
State
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Basic Operation of a Laser

• Lasing medium is pumped to get electrons to an
  excited state (e.g., using a very intense flash
  of light)
• Electrons rapidly fall to a metastable state
• Population inversion achieved when most electrons
  are in the metastable state
• Stimulated emission occurs in a cascade effect

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Ruby Laser
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Ruby Laser Animation
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Other Types of Lasers

• Solid-state lasers
• ruby laser
• Liquid lasers
• dye laser
• Gas lasers
• argon laser, for eye surgery, laser-light shows
  (blue-green)
• carbon dioxide laser, for cutting steel
• Semiconductor lasers
• diode laser, in laser pointers, CD players,
  bar-code readers

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Superfluid Helium

• Helium becomes a liquid at 4 Kelvin, the lowest
  boiling point of any element
• First achieved by Onnes in 1908
• Becomes a superfluid at 2.2 Kelvin

Kamerlingh Onnes (1853-1926)
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Viscosity and Superfluids

• Resistance of a liquid to flow
• E.g., honey has more viscosity than water
• A superfluid has no viscosity, in effect it
  experiences no friction and is able to flow
  forever!
• Recall interior of a neutron star is thought to
  consist of neutron superfluid

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Strange Behaviour of Superfluid Helium
Superfluid helium can creep up the sides of a
container and flow out of it, all by itself!
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Superconductivity

• At very low temperatures (lt 9 Kelvin), most
  metals carry electricity with almost zero
  resistance
• Discovered by Onnes in 1911, using mercury
• Once a current is started, it flows
  indefinitely!

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Meissner Effect in Superconductors

• A magnet is able to levitate over a
  superconductor
• because magnetic fields cannot penetrate a
  superconductor

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Bose-Einstein Condensate (BEC)

• If we concentrate a large number of identical
  bosons in a small region and at low temperature,
  their wave functions would start to overlap
• The bosons lose their individual identities and
  become a single object
• Like water vapour condensing to form a drop of
  water

Satyendranath Bose (1894-1974)
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Formation of a BEC
High temperature
Low temperature
Bose-Einstein condensation
Absolute zero Pure Bose-Einstein condensate
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Examples of BECs

• Helium atoms superfluidity
• Cooper pairs superconductivity
• Super-atoms at extremely low temperatures(0.000
  000 1 Kelvin)
• Achieved using laser cooling

Laser Cooling Animation
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2000 Rubidium Atoms Forming a BEC
Discoverers won the 2001 Nobel Prize in Physics