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Published byRegina Rowson Modified about 1 year ago

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Bose-Einstein Condensation Ultracold Quantum Coherent Gases

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What’s Ultra-Cold Matter ? Very Cold Very Dense … in Phase Space Typically nanoKelvin – microKelvin Atoms/particles have velocity ~ mm/s – cm/s x p x p x p Different temperatures Same phase space density Higher phase space density mK μKμK nK

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Ultra-cold Quantum Mechanics x p xx pp fundamental unit of phase space volume Quantum mechanics requires Quantum physics is important when Equivalent: deBroglie wavelength ~ inter-particle separation Quantum régime Boltzmann régime

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EiEi NiNi 1 EFEF Quantum Statistics Bosons Fermions symmetric symmetric multi-particle wavefunction. Integer spin: photons, 87 Rb. probability of occupying a state |i> with energy E i. anti-symmetric anti-symmetric multi-particle wavefunction. ½-integer spin: electrons, protons, neutrons, 40 K. probability of occupying a state |i> with energy E i. EiEi NiNi N BEC

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Bose-Einstein Condensation of 87 Rb Evaporation Efficiency BEC thermal atoms magnetic trapping evap. cooling MOT PSD

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87 Rb BEC MHz: N = 7.3x10 5, T>T c MHz: N = 6.4x10 5, T~T c MHz: N=1.4x10 5, T

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87 Rb BEC Surprise! Reach T c with only a 30x loss in number. (trap loaded with 2x10 7 atoms) Experimental cycle = seconds MHz: N = 7.3x10 5, T>T c MHz: N = 6.4x10 5, T~T c MHz: N=1.4x10 5, T

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Fermions: Sympathetic Cooling Problem: Cold identical fermions do not interact due to Pauli Exclusion Principle. No rethermalization. No evaporative 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. Solution: add non-identical particles Pauli exclusion principle does not apply. We cool our fermionic 40 K atoms sympathetically with an 87 Rb BEC. Fermi Sea “Iceberg” BEC

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The Problem with Fermions At very low temperatures, If, then two atoms must scatter as an s-wave: s-wave is symmetric under exchange of particles: Identical ultra-cold fermions do not interact a s = 0 for fermions

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Sympathetic Cooling Cooling Efficiency

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Below T F 0.9 T F 0.35 T F For Boltzmann statistics and a harmonic trap, For ultra-cold fermions, even at T=0,

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Fermi Boltzmann Gaussian Fit Pauli Pressure

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