Molecules as Sources

T. J. Gay

Stefan Truppe, M. Hambach, Sarah M. Skoff +6 more

Experiments with cold molecules usually begin with a molecular source. We describe the construction and characteristics of a cryogenic buffer gas source of CaF molecules. The source emits pulses with a typical duration of 240 μs, a mean speed of about 150 m/s, and a flux of 5×1010 molecules per steradian per pulse in a single rotational state.

N. Poli

Andreas H. Trabesinger

Kaiya Wilson, Ebram Youssef, Lo\"ıc Anderegg

Molecular magneto-optical traps (MOTs) are loaded from cryogenic buffer gas beam (CBGB) sources, which produce a large flux of cold molecules. However, only a small fraction of this flux is slowed and captured. Here, we investigate and optimize one of these CBGB sources through a combination of experiment and simulation to maximize the number of molecules loaded into a MOT of CaF molecules. We experimentally determine the range of molecule velocities from the source that are successfully slowed and captured in the MOT, and perform a systematic study of buffer gas source geometries to identify designs that maximize MOT loading. Our observations agree well with Monte Carlo simulations, which provide physical insight into the dynamics within the source and explain how source geometry influences the subset of molecules that are ultimately trapped. These results provide practical design guidelines for optimizing cryogenic buffer gas beam sources used in laser cooling experiments.

W. E. Moerner

Single molecules in suitable host crystals have been demonstrated to be useful single-photon emitters both at liquid-helium temperatures and at room temperature. The low-temperature source achieved controllable emission of single photons from a single terrylene molecule in p -terphenyl by an adiabatic rapid passage technique. In contrast with almost all other single-molecule systems, terrylene single molecules show extremely high photostability under continuous, high-intensity irradiation. A room-temperature source utilizing this material has been demonstrated, in which fast pumping into vibrational sidebands of the electronically excited state achieved efficient inversion of the emissive level. This source yielded a single-photon emission probability p (1) of 0.86 at a detected count rate near 300 000 photons s −1 , with very small probability of emission of more than one photon. Thus, single molecules in solids can be considered as contenders for applications of single-photon sources such as quantum key distribution.