Bose-Einstein Condensation

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Bose-Einstein Condensation Ultracold Quantum
Coherent Gases
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Whats Ultra-Cold Matter ?

• Very Cold

? Typically nanoKelvin microKelvin ?
Atoms/particles have velocity mm/s cm/s

• Very Dense in Phase Space

Different temperatures Same phase space density
Higher phase space density
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Ultra-cold Quantum Mechanics
? Quantum physics is important when
Equivalent deBroglie wavelength inter-particle
separation
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Quantum Statistics
Bosons
Fermions

• anti-symmetric multi-particle wavefunction.
• ½-integer spin electrons, protons, neutrons,
  40K.
• probability of occupying a state igt with
  energy Ei.

• symmetric multi-particle wavefunction.
• Integer spin photons, 87Rb.
• probability of occupying a state igt with
  energy Ei.

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Bose-Einstein Condensation of 87Rb
10-13
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10-6
105
PSD
BEC
thermal atoms
magnetic trapping
evap. cooling
MOT
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87Rb BEC
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87Rb BEC
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Fermions Sympathetic Cooling
Problem Cold identical fermions do not interact
due to Pauli Exclusion Principle. ? No
rethermalization. ? No evaporative cooling.
Solution add non-identical particles ? Pauli
exclusion principle does not apply.
We cool our fermionic 40K atoms sympathetically
with an 87Rb BEC.
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The Problem with Fermions
Identical ultra-cold fermions do not interact
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Sympathetic Cooling
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Below TF
0.9 TF
0.35 TF

• For Boltzmann statistics and a harmonic trap,
• For ultra-cold fermions, even at T0,

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Pauli Pressure