= Observation of Fermi pressure in trapped lithium
In 2001, <Andrew G. Truscott>, <Randall G. Hulet>, and collaborators observed <degeneracy pressure> in trapped <lithium>. A <Zeeman slower> fed a dual <magneto-optical trap>; <optical pumping> prepared atoms for a cloverleaf apparatus for <magnetic trapping of neutral atoms>. Microwave evaporation removed energetic lithium-7 <bosons>; elastic <collisions> cooled lithium-6 <fermions> by <sympathetic cooling>.<Observation of Fermi Pressure in a Gas of Trapped Atoms by Andrew G. Truscott and others>[Truscott et al., Observation of Fermi Pressure in a Gas of Trapped Atoms (2001), p. 2570, preparation and cooling]{ref}
Sequential <absorption imaging> recorded both trapped clouds on a camera. Fits to axial profiles used the <boson> cloud as a <thermometer>. At common <temperature>, the nearly equal magnetic trapping potentials provided a comparison: the clouds had similar sizes near $T/T_F=1$, but the <fermion> cloud remained broader as cooling reached $T/T_F=0.25$. Figure 3 compared its radius with ideal <Fermi gas> and classical predictions.<Observation of Fermi Pressure in a Gas of Trapped Atoms by Andrew G. Truscott and others>[pp. 2570–2572, Figs. 1–3, imaging, thermometry, and radius comparison]{ref}
Varying the wait before imaging tested <thermal equilibrium>. Finite imaging resolution restricted the analysis to the axial direction; fits neglected interaction-induced density shifts. Cooling eventually suffered from the dwindling <boson> <heat capacity>. The result supports quantum occupation effects, without directly resolving individual occupied states or reaching zero <temperature>.<Observation of Fermi Pressure in a Gas of Trapped Atoms by Andrew G. Truscott and others>[p. 2571, axial resolution and negligible-interaction approximation; p. 2572, equilibration test and cooling limit]{ref}
These were neutral alkali atoms in a spatially varying trap. The <Fermi energy of a model electron gas> instead uses uniform <Electrons>, two equally populated <spin> states, and the <Electron> <mass>. The measured trapped-atom radii are not measurements of that electron model's $p_F$ or $E_F$; comparing their numerical <Fermi energies> requires the appropriate particle <mass>, internal-state populations, and confining potential.
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