Abstract
The transition from the weakly interacting BCS regime to the strongly interacting unitary regime is explored for ultracold trapped Fermi gases assuming a normal mode description of the gas instead of the conventional Cooper pairing. The Pauli principle is applied “on paper” using specific normal mode assignments. Energies, entropies, critical temperatures, and an excitation frequency are studied and compared with existing results in the literature. These normal modes have been derived analytically for N identical, confined particles from a first-order \(L=0\) group theoretic solution of a three-dimensional Hamiltonian with a general two-body interaction. In previous studies, normal modes were able to describe the unitary regime obtaining ground-state energies comparable to benchmark results and thermodynamic quantities in excellent agreement with experiment. As a precurser to this work, the behavior of the normal mode frequencies was investigated across the BCS to unitarity transition, and a microscopic basis of the large excitation gaps and universal behavior at unitarity was proposed. The current study now explores the ability of these normal mode frequencies to determine various properties along this transition, testing the ability of the microscopic dynamics of these normal modes to produce observable behavior away from unitarity. The results suggest that the physics of superfluidity can be described using normal modes across a wide range of interparticle interaction strengths and thus offers a clear microscopic alternative to the two-body pairing models commonly used to describe superfluidity along this transition.
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This research was funded by the National Science Foundation under Grant No. PHY-2011384.
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Watson, D.K. Exploring the Transition from BCS to Unitarity Using Normal Modes: Energies, Entropies, Critical Temperatures and Excitation Frequencies. J Low Temp Phys 212, 1–21 (2023). https://doi.org/10.1007/s10909-023-02966-2
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DOI: https://doi.org/10.1007/s10909-023-02966-2