Room-temperature quantum memories from nanoseconds to hours
Warm atomic vapor is one of the simplest quantum systems, offering real-life applications in deployable centimeter-size devices. It strongly couples to optical fields and exhibits superb coherence properties at or above room temperature. Notably, atomic vapors are at the heart of miniature atomic clocks and inside the most sensitive magnetometers and gyroscopes. We explore schemes for realizing optical quantum memories in alkali vapors and noble-gases. We realize a fast ladder-type memory (FLAME) by mapping the optical field onto the superposition between electronic orbitals in rubidium. FLAME demonstrates GHz-bandwidth and extremely low noise, suitable for quantum network synchronization. We consider the implementation of FLAME via tapered fibers, and its integration with Rydberg-level excitations for quantum nonlinear optics. On the other side of the scale, we report on a record memory lifetime approaching one second at room temperature. The long lifetime is achieved by mapping the optical field onto ground-state spin orientation of cesium, which is insensitive to spin-exchange collisions. The scheme paves the way towards relying on spin exchange for coupling light coherently to noble-gas nuclear spins, with an alkali vapor serving as a mediator. If successful, this could leverage the hour-long coherence time of noble-gas spins for extreme quantum optics and sensing applications.