Observation of coherent oscillations in molecular association from ultra cold thermal gasץ

A coherently driven 2-level system is well known to exhibit Rabi oscillations as a function of excitation duration. But if we replace one of the levels with a continuum, these oscillations will be smeared out by decoherence. The latter example is realized in molecular association from ultra cold free atoms.

Here we use an external magnetic field modulation technique to stimulate transition from the free 7Li two-atom continuum into a dimer bound state. We show that despite the significant thermal energy present in the system, certain parameter space of the external field leads to the observation of the molecular conversion efficiency (MCE) oscillations. We also show that these oscillations can be switched on or off by changing the pulse parameters.

Our experimental results are in agreement with the recent theoretical study done in ref. [1]. They shed light on the old dispute related to the observation of similar coherent oscillations in ref. [2], which were consequently questioned in a theoretical treatment [3]. This is also a demonstration of nonadiabatic effects, related to the pulse envelope, so far only known from ionization with ultrashort pulses [4].

References:

[1] P. Giannakeas, L. Khaykovich, J. M. Rost, and C. H. Greene. Nonadiabatic molecular association in thermal gases driven by radio-frequency pulses. Physical Review Letters, 123(4):043204, 2019.

[2] S. T. Thompson, E. Hodby, and C. E. Wieman. Ultracold molecule production via a resonant oscillating magnetic field. Physical Review Letters, 95(19):190404, 2005.

[3] T. M. Hanna, T. Köhler, and K. Burnett. Association of molecules using a resonantly modulated magnetic field. Physical Review A, 75(1):013606, 2007.

[4] Q. C. Ning, U. Saalmann, and J. M. Rost. Electron dynamics driven by light-pulse derivatives. Phys. Rev. Lett., 120:033203, Jan 2018.