Short-time dynamics of an ultracold Fermi gas in radio-frequency spectroscopy

André Schirotzek

John T. Stewart, John Gaebler, Deborah Jin

Kaijun Jiang, Hua Luo, Li Kai +3 more

André Schirotzek, Cheng-Hsun Wu, Ariel Sommer +1 more

黄良辉, 王鹏军, 付正坤 +1 more

We create weakly bound Feshbach molecules in ultracold Fermi gas 4~K by sweeping a magnetic field across a broad Feshbach resonance point 202.2 G with a rate of 20 ms/G and perform the dissociation process using radio-frequency （RF） technology. From RF spectroscopy, we obtain the binding energy of the weakly bound molecules in the vicinity of Feshbach resonance. Our measurement also shows that the number of atoms generated from the dissociation process is different at various magnetic fields with the same RF amplitude, which gives us a deeper understanding of weakly bound Feshbach molecules.

Chun Kit Chung, C. K. Law

We employ a time-dependent variational approach to investigate the dynamics of a fermionic atomic gas driven by a radio-frequency (rf) field at zero temperature. Starting from an initial Bardeen-Cooper-Schrieffer (BCS) state with pairing of atoms of two internal levels, an rf field transfers atoms to a third level. Dynamical equations derived from the variational principle are shown to be consistent with the time-dependent Bogoliubov--de Gennes equation. In particular, we show that the short-time dynamics is governed by a set of linear equations, in which an eigenvector associated with a discrete eigenvalue can be identified as the formation of a pair bound state in the final scattering channel. Such a bound state induces characteristic oscillations in the time evolution of the order parameter. At longer times numerical solutions demonstrate complicated dynamics where linear theory breaks down.