Light narrowing over broad temperature range with paraffin-coated vapor cells

This letter reports light narrowing in paraffin-coated vapor cells from room temperature 27℃ to 59℃, where spin-exchange relaxation is suppressed. By means of a coating lock and eliminating the reservoir effect, an ultra-narrow magnetic resonance linewidth of 0.36 Hz and an atomic coherence lifetime of T₂ = 0.9 s are achieved. In cells free of buffer gas, the narrow linewidth over this broad temperature range is a result of enhanced spin polarization, which is facilitated by the effective suppression of radiation trapping benefiting from the stability of the vapor density. Using such cells in atomic magnetometers, the photon shot noise limit is estimated as 0.2 fT/rtHz and the spin-projection noise limit is estimated as 1.1 fT/rtHz. Also, a magnetometer system with the stable coated cell is identified, which demonstrates the potential for achieving relatively stable magnetometer sensitivity without precisely controlling the cell temperature. The long coherence lifetime and broad operating temperature range expand the potential applications of quantum memory and other quantum sensors such as atomic clocks.