In cold atom experiments, the state of the atoms is determined by using an optical detection system, whose central element is a laser beam. Either we measure its absorption by the atoms using a CCD camera, or we collect on a photodiode the fluorescence of the atoms induced by the beam. This detection method uses complex optical systems, and it is destructive : once the state of the atoms is detected, the cloud cannot be reused.
Researchers of the laboratory Systèmes de Référence Temps-Espace (SYRTE) [Unité CNRS/Observatoire de Paris-PSL/Sorbonne Université/LNE] have developed a non-destructive detection solution of the quantum state of cold atoms based on microwave radiation. The microwave power emitted by an antenna depends on the radiation resistance of the medium towards which the antenna is transmitting. By measuring the microwave power of a horn antenna, the researchers were able to detect the internal state of cold atoms of rubidium 87. They also observed, in near real time, coherent quantum dynamics on a cloud of atoms from a single cooling process.
After validating this new detection method by measuring the atomic spectrum around the hyperfine clock transition, the researchers demonstrated its non-destructive character by observing Rabi oscillations in stroboscopic mode on the same sample of cold atoms. In this proof-of-principle experiment, the physicists used cold atoms in free fall because this is the operating configuration of conventional atomic interferometers and inertial sensors. However, for the realization of compact quantum sensors it is possible to use a microfabricated coplanar waveguide as a microwave antenna. This opens a promising way for a new technology of non-destructive, local, broadband, and microcircuit integrated detection of cold atoms.
Bibliography
- Nondestructive microwave detection of a coherent quantum dynamics in cold atoms – Communications Physics 4, article numéro 35 (2021)
William Dubosclard, Seungjin Kim et Carlos L. Garrido Alzar