Interference of multi-mode photon echoes generated in spatially separated solid-state atomic ensembles

TL;DR

This paper demonstrates high-visibility interference of photon echoes from spatially separated solid-state ensembles, showing phase-preserving multimode storage and retrieval, relevant for quantum repeater architectures.

Contribution

It presents the first experimental demonstration of interference of photon echoes from separate solid-state memories with preserved phase coherence.

Findings

Photon echoes from separate ensembles interfere with high visibility.

Storage and retrieval of multiple temporal modes achieved.

Interference visibility not limited by atomic decoherence.

Abstract

High-visibility interference of photon echoes generated in spatially separated solid-state atomic ensembles is demonstrated. The solid state ensembles were LiNbO$_3$ waveguides doped with Erbium ions absorbing at 1.53 $\mu$m. Bright coherent states of light in several temporal modes (up to 3) are stored and retrieved from the optical memories using two-pulse photon echoes. The stored and retrieved optical pulses, when combined at a beam splitter, show almost perfect interference, which demonstrates both phase preserving storage and indistinguishability of photon echoes from separate optical memories. By measuring interference fringes for different storage times, we also show explicitly that the visibility is not limited by atomic decoherence. These results are relevant for novel quantum repeaters architectures with photon echo based multimode quantum memories.