Our manuscript „Single-atom quantum probes for ultracold gases boosted by nonequilibrium spin dynamics“ is published in Physical Review X (DOI:10.1103/PhysRevX.10.011018).
Pressure or temperature are gas properties reflecting microscopic collisions between atoms. Collisions of the atoms can moreover change the quantum properties of the colliding atoms. Together with our college Prof. E. Tiemann of the university Hannover, we have succeeded in using single atomic impurities as quantum probes in an ultracold gas.
Collisions between ultracold atoms modify the quantum properties of our impurities and allow deducing the temperature of the gas.
Experimentally, we immerse individual neutral cesium (Cs) atoms in an ultracold rubidium (Rb) gas. Subsequent collisions lead to an exchange of quantized angular momentum. The energy associated with such a change is different for the two atomic species. Consequently, two types of processes can occur. In exothermal collisions, excess energy is dissipated in the gas, while endothermal processes are only possible if sufficient additional energy can is available from the thermal (kinetic) energy in a collision. The latter process effectively couples the quantum spin distribution of the Cs probes with the temperature of the gas. Hence, it is possible to extract the system's temperature from the Cs spin distribution.
Moreover, we found that the sensitivity of the thermometer increases, considering the spin dynamic instead of the steady-state distribution. Based on the additional magnetic field dependency of the system, it is also possible to use this physical effect as a multimeter to measure the present magnetic field. Our work is an important step to pave the way for non-destructive quantum many-body system measurements and to operate and optimize new quantum sensors.