Observation of prolonged coherence time of the collective spin wave of atomic ensemble in a paraffin coated Rb vapor cell

TL;DR

This paper demonstrates a significantly prolonged coherence time of collective spin waves in a paraffin-coated Rb vapor cell, enhancing quantum memory potential for long-distance quantum communication.

Contribution

It reports the first observation of a 300 microsecond coherence time in a thermal atomic ensemble with paraffin coating, surpassing previous results by two orders of magnitude.

Findings

Coherence time extended to 300 microseconds.

Prolonged spin lifetime achieved with paraffin coating.

Reduced fluorescence background without buffer gas.

Abstract

We report a prolonged coherence time of the collective spin wave of a thermal 87Rb atomic ensemble in a paraffin coated cell. The spin wave is prepared through a stimulated Raman Process. The long coherence time time is achieved by prolonging the lifetime of the spins with paraffin coating and minimize dephasing with optimal experimental configuration. The observation of the long time delayed-stimulated Stokes signal in the writing process suggests the prolonged lifetime of the prepared spins; a direct measurement of the decay of anti-Stokes signal in the reading process shows the coherence time is up to 300 us after minimizing dephasing. This is one hundred times longer than the reported coherence time in the similar experiments in thermal atomic ensembles based on the Duan-Lukin-Cirac-Zoller (DLCZ) and its improved protocols. This prolonged coherence time sets the upper limit of the memory time in quantum repeaters based on such protocols, which is crucial for the realization of long-distance quantum communication. The previous reported fluorescence background in the writing process due to collision in a sample cell with buffer gas is also reduced in a cell without buffer gas.