Dougal Main

Abstract:

We demonstrate coherent storage and retrieval of pulsed light using the atomic frequency comb protocol in a room temperature alkali vapor. We utilize velocity-selective optical pumping to prepare multiple velocity classes in the 𝐹=4 hyperfine ground state of cesium. The frequency spacing of the classes is chosen to coincide with the 𝐹′=4−𝐹′=5 hyperfine splitting of the 62P3/2 excited state, resulting in a broadband periodic absorbing structure consisting of two usually Doppler-broadened optical transitions. Weak coherent states of duration 2ns are mapped into this atomic frequency comb with pre-programmed recall times of 8ns and 12ns, with multi-temporal mode storage and recall demonstrated. Utilizing two transitions in the comb leads to an additional interference effect upon rephasing that enhances the recall efficiency.

Abstract:

Quantum memories are a crucial technology for enabling large-scale quantum networks through synchronization of probabilistic operations. Such networks impose strict requirements on quantum memory, such as storage time, retrieval efficiency, bandwidth, and scalability. On- and off-resonant ladder protocols on warm atomic vapor platforms are promising candidates, combining efficient high-bandwidth operation with low-noise on-demand retrieval. However, their storage time is severely limited by motion-induced dephasing caused by the broad velocity distribution of atoms composing the vapor. In this paper, we demonstrate velocity selective optical pumping to overcome this decoherence mechanism. This will increase the achievable memory storage time of vapor memories. This technique can also be used for preparing arbitrarily shaped absorption profiles, for instance, preparing an atomic frequency comb absorption feature.

Abstract:

We present the first demonstration of velocity-selective pumping in an atomic vapour to preserve light-matter coherence. Control is illustrated by a subsequent demonstration of an atomic frequency comb quantum memory realised in the vapour.