Molecular Probe of Pairing in the BEC-BCS Crossover

Abstract

We have used optical molecular spectroscopy to probe the many-body state of paired 6 Li atoms near a broad Feshbach resonance. The optical probe projects pairs of atoms onto a vibrational level of an excited molecule. The rate of excitation enables a precise measurement of the closed-channel contribution to the paired state. This contribution is found to be quite small, supporting the concept of universality for the description of broad Feshbach resonances. The dynamics of the excitation provide clear evidence for pairing across the BEC-BCS crossover, and into the weakly interacting BCS regime.

Thermodynamics of Ultracold Fermi Gases

“…The contact coe cient was also measured through other microscopic observables, such as the photo-association amplitude [38,194], the high-k tail of the momentum distribution [189,195], the high-ν tail of the radio-frequency spectrum [196,197,195,198], the photo-emission spectroscopy spectrum [156], and other macroscopic observables, namely the potential energy and the release energy [18,62,190,191,195]. These results are gathered in Table 5.1.…”

“…The connection with Bose-Einstein condensation was characterized by a direct measurement of the condensate fraction [35,36,47], and the importance of many-body e ects was established through the measurement of the single-particle excitation energy gap [50,51] and closed-channel fraction [38].…”

Stability of a Fermionic N + 1 Particle System with Point Interactions

“…These can be experimentally tested, see [16,25,26,29,36]. In this section, we shall present a rigorous version of the Tan relations for the Hamiltonian H α constructed in the last subsection.…”

Functional renormalization for the Bardeen–Cooper–Schrieffer to Bose–Einstein condensation crossover

“…We briefly discuss the example of 6 Li [3], which besides 40 K has been realized in current experiments [4][5][6][7][8][9] (figure 1a).…”

“…However, the quantitatively precise understanding of BCS-BEC crossover physics requires non-perturbative methods. The experimental realization of molecule condensates and the subsequent crossover to a BCS-like state of weakly attractive fermions [4][5][6][7][8][9] pave the way to future experimental precision measurements and provide a testing ground for non-perturbative methods. An understanding of the crossover on a quantitative level at and near the resonance has been developed through numerical quantum Monte Carlo (QMC) methods [12][13][14][15][16].…”