Natural orbits of atomic Cooper pairs in a nonuniform Fermi gas (6 pages)

Marvin Holten, Luca Bayha, Keerthan Subramanian +5 more

Ramon Carbó‐Dorca, Debraj Nath

Y. H. Pong, C. K. Law

We examine the basic mode structure of atomic Cooper pairs in an inhomogeneous Fermi gas. Based on the properties of Bogoliubov quasiparticle vacuum, the single particle density matrix and the anomalous density matrix share the same set of eigenfunctions. These eigenfunctions correspond to natural pairing orbits associated with the BCS ground state. We investigate these orbits for a Fermi gas in a spherical harmonic trap and construct the wave function of a Cooper pair in the form of Schmidt decomposition. The issue of spatial quantum entanglement between constituent atoms in a pair is addressed.

А. V. Avdeenkov

M. Dzero, E. A. Yuzbashyan, B. L. Altshuler

We investigate under what conditions a uniform quench of a superfluid atomic Fermi gas leads to the emergence of spatial inhomogeneities. We demonstrate that, if the system is larger than the coherence length, the superfluid order parameter becomes spatially nonuniform. Spatial modulations develop through a parametric excitations of pairing modes with opposite momenta. Their growth is eventually suppressed by nonlinear effects resulting in a state characterized by a random superposition of wave packets of the superfluid order parameter. This state can be probed by measuring the molecular momentum distribution following a fast sweep to the BEC side of the Feshbach resonance.

Tomasz Świsłocki, Tomasz Karpiuk, Mirosław Brewczyk

We investigate the ground state properties of normal and superfluid phases of a mixture of Fermi atoms at zero temperature in a quasi-one-dimensional harmonic trap. Assuming pairing occurs in the Hartree-Fock single-particle states (obtained using atomic orbitals approach) we calculate the spectrum of elementary excitations of the system. We find that for strong enough attraction between different kinds of fermions the state consisting of Cooper pairs becomes energetically favorable. For even stronger attraction a discontinuity located at the Fermi surface appears in the spectrum of elementary excitations. At the same time the chemical potential changes its sign and the system goes from the gas of Cooper pairs to the condensed phase of molecular dimers realizing the BCS to Bose-Einstein condensate crossover in one-dimensional space.