An AC Stark Gradient Echo Memory in Cold Atoms

TL;DR

This paper proposes a novel quantum memory scheme using the ac Stark effect in cold atoms, achieving high efficiency, fast switching, and long coherence times suitable for quantum computing and communication.

Contribution

It introduces a new ac Stark gradient mechanism for quantum memory in cold atoms, enhancing flexibility and performance over existing methods.

Findings

Memory bandwidths of MHz achievable with realistic laser powers

Nanosecond precision in gradient switching

Coherence times of tens of milliseconds possible

Abstract

The burgeoning fields of quantum computing and quantum key distribution have created a demand for a quantum memory. The gradient echo memory scheme is a quantum memory candidate for light storage that can boast efficiencies approaching unity, as well as the flexibility to work with either two or three level atoms. The key to this scheme is the frequency gradient that is placed across the memory. Currently the three level implementation uses a Zeeman gradient and warm atoms. In this paper we model a new gradient creation mechanism - the ac Stark effect - to provide an improvement in the flexibility of gradient creation and field switching times. We propose this scheme in concert with a move to cold atoms (~1 mK). These temperatures would increase the storage times possible, and the small ensemble volumes would enable large ac Stark shifts with reasonable laser power. We find that memory bandwidths on the order of MHz can be produced with experimentally achievable laser powers and trapping volumes, with high precision in gradient creation and switching times on the order of nanoseconds possible. By looking at the different decoherence mechanisms present in this system we determine that coherence times on the order of 10s of milliseconds are possible, as are delay-bandwidth products of approximately 50 and efficiencies over 90%.