Long-Lived Circular Rydberg States Of Laser-Cooled Rubidium Atoms In A Cryostat

The exquisite properties of Rydberg levels make them particularly appealing for emerging quantum technologies. The lifetime of low-angular-momentum laser-accessible levels is however limited to a few 100 mu s by optical transitions and microwave blackbody radiation (BBR) induced transfers at room temperature. A considerable improvement would be obtained with the few 10 ms lifetime of circular Rydberg levels in a cryogenic environment reducing the BBR temperature. We demonstrate the preparation of long-lived circular Rydberg levels of laser-cooled rubidium atoms in a cryostat. We observe a 3.7 ms lifetime for the circular level of principal quantum number n = 52. By monitoring the transfers between adjacent circular levels, we estimate in situ the microwave BBR temperature to be (11 +/- 2) K. The measured atomic coherence time (270 mu s) is limited here only by technical magnetic field fluctuations. This work opens interesting perspectives for quantum simulation and sensing with cold circular Rydberg atoms.