In a study published on 24/02/2021 in the journal Communications Physics of the Nature group, a SYRTE team (Observatoire de Paris-PSL, CNRS, SU, LNE) has just demonstrated a new technology for the detection of a laser-cooled atom gas based on the magnetic properties of polarized gas.

The technique has been demonstrated on a molasses of cold, untrapped, atoms, which is the most widely used configuration among conventional atom interferometers and inertial sensors.

A horn (right, in blue) experiences a radiation resistance to its electromagnetic microwave field depending on the presence of laser-cooled atoms shown in red.

An optimal implementation would actually use waveguides placed on the same plane (called atom chips) as microwave radiation source. Such a device would thus allow a non-destructive, local, high bandwidth quantum detection, integrated on microcircuit. This is an important technological milestone that has just been overcome for the industrial manufacture of compact cold atom quantum sensors.

The method has been demonstrated on the experimental system Gyrachip of the team Atomic Interferometry and Inertial Sensors of the SYRTE. Copyright : Cyril FRESILLON / SYRTE / FIRST-TF / CNRS Photothèque.

Method
The method uses a microwave field emitted by a horn antenna. The principle is to measure the radiation resistance of the horn, which depends on the presence of cold atoms and their atomic spin state. Thus, by measuring the power of the reflected microwave signal, and therefore not emitted by the antenna, the researchers were then able to measure the atomic spectrum, i.e. the variation of the response of the gas of cold atoms as a function of the frequency detuning to the hyperfine clock transition.

Atomic spectrum by microwave reflection, and atomic spectrum by absorption imaging

Then, using two antennas, a horn and a monopole, the researchers observed Rabi oscillations in stroboscopic mode: in this configuration, the signal reflected at the horn was used to detect Rabi oscillations, and thus the state of the collective spin of the atoms, while the monopole antenna was used to drive the dynamics of the atomic spin. With this technique, the researchers finally showed the non-destructive nature of this method, as well as a detection bandwidth (around 30 kHz) much higher than that typically possible in cold atom experiments.

Learn more :
Read the article in Communications Physics "Nondestructive microwave detection of a coherent quantum dynamics in cold atoms", William Dubosclard, Seungjin Kim, Carlos L. Garrido Alzar

Read the article "Sensors, the other quantum revolution" in CNRS le journal

Researcher contact:
Carlos L. Garrido Alzar,
carlos.garrido@obspm.fr