(Phys.org) Physicists from Kaiserslautern and a colleague from Hanover have succeeded for the first time in using a single cesium atom as a sensor for ultracold temperatures. To determine the measured data, they used quantum states—the spin or angular momentum of the atom. With these spins, they measured the temperature of an ultra-cold gas and the magnetic field. The system is characterized by a particularly high sensitivity. Such sensors could be used in the future, for example, to investigate quantum systems without interference.
The special feature of the study was the high sensitivity of the measurement. In a typical measurement, it is necessary to bring the sensor into contact with the cold gas and wait until equilibrium is reached. “In fact, for quantum sensors, there is a fundamental limit to their sensitivity in equilibrium. However, we included information about the interactions between cesium and rubidium in advance, so we did not have to wait until the atom was in equilibrium with the rubidium gas.”
“This is the first time we have used a single atom as a sensor that uses quantum information and is significantly better than a classic sensor,” Widera points out. The physicists also conducted this experiment with magnetic fields and recorded the magnetic states. This novel and highly sensitive sensor is suitable, for example, for examining fragile quantum systems almost without destruction.

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