Photonic quantum memory using an intra-atomic frequency comb. (arXiv:1810.07617v2 [quant-ph] UPDATED)

Photonic quantum memory, such as an atomic frequency comb (AFC), is essential
to make photonic quantum computation and long distance quantum communication
scalable and feasible. In standard AFC the frequency of different atoms must be
stable relative to each other which presents difficulties in realizing the
quantum memory. Here we propose a quantum memory using an intra-atomic
frequency comb which does not require frequency stabilization. We show that the
transitions between two degenerate energy levels of a single atom can be used
to construct the frequency comb. The spacing between the teeth of the comb is
controlled by applying an external magnetic field. Since the frequency comb is
constructed from individual atoms, these atoms can be used alone or in
ensembles to realize the quantum memory. Furthermore, the ensemble based
quantum memory with intra-AFC is robust against Doppler broadening which makes
it useful for high-temperature quantum memory. As an example, we numerically
show the intra-AFC in cesium atoms and demonstrate a photon echo which is
essential for quantum memory.

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