Optical isolator based on highly efficient optical pumping of Rb atoms in a miniaturized vapor cell

We demonstrate both numerically and experimentally the important role of buffer gas in achieving optical isolator based on efficient hyperfine-structure optical pumping of Rubidium (87Rb) atoms in miniaturized vapor cells. It is observed that the increase in the buffer gas pressure allows achieving highly efficient optical pumping. Specifically, at a buffer gas pressure of 40 Torr, it is possible to pump about 85% of the atoms out of the pumped state into the other ground state. While optical pumping has been reported for conventional centimeter-scale cells, we show that in miniaturized cells the role of buffer gas is crucial, as the higher collision rate with the walls diminishes the effect of optical pumping, posing a stringent limitation on the applicability of optical pumping in miniaturized systems. Following the results reported herein, we demonstrate an optical isolator with isolation ratio better than 20 dB at a relatively low temperature of about 80 °C, and with a low magnetic field (∼800 Gauss). The obtained results provide another step forward in the quest for miniaturizing quantum devices. The demonstrated device shows that such miniaturized vapor cells can be considered for applications such as all-optical switching, optical quantum memory, frequency references, and magnetometry to name a few.