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Andrew G. Truscott measured Fermi pressure in a trapped dilute atomic gas. The experiment compared the spatial distributions of fermionic and bosonic lithium under conditions where their different quantum statistics become important.

Even at low temperature, the Pauli exclusion principle prevents identical fermions from all occupying the lowest one-particle state. Filling higher states gives the trapped cloud a finite extent beyond a classical thermal expectation. The distribution therefore probes degeneracy pressure through the size of a controllable atomic sample.^[ref]

An experimental researcher whose joint work studied the spatial distribution of ultracold atoms obeying Fermi-Dirac statistics. The team’s 2001 measurement of degeneracy pressure compared trapped atomic clouds as they cooled, using the difference between bosonic and fermionic behavior to expose the effect of quantum statistics. The measurement connects a macroscopic cloud shape with the allowed occupation of single-particle states.^[ref]

An experimental atomic physicist who coauthored a measurement of degeneracy pressure in trapped lithium. Collisions with a cooled bosonic component lowered the fermionic component's temperature; its spatial extent then revealed the pressure caused by the Pauli exclusion principle. The experiment connected a microscopic occupancy rule to the visible size of an atomic cloud.^[ref]

Institutional profile: physics.rice.edu/graduate-awards

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.^[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.^[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.^[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.

Randall G. Hulet developed experiments with quantum-degenerate atomic gases, including the observation of Fermi pressure in trapped lithium. The comparison of bosonic and fermionic isotopes made their different population statistics experimentally accessible.

A degenerate fermionic cloud remains spread over many occupied one-particle states because of the Pauli exclusion principle. Its size and distribution therefore reflect quantum statistics as well as temperature and confinement. The experiment connected the same pressure mechanism important in dense astrophysical matter to a dilute laboratory gas.^[ref]

An experimental researcher whose team observed degeneracy pressure in a trapped gas of atoms obeying Fermi-Dirac statistics. Cooling a fermionic cloud alongside a bosonic one lets their sizes be compared under common experimental conditions. The fermionic distribution resists the concentration expected for a classical gas because the Pauli exclusion principle prevents identical fermions from all occupying the same low-energy state. The cloud’s spatial profile therefore makes a consequence of quantum statistics directly measurable.^[ref]