Coherence time of over a second in a telecom-compatible quantum memory storage material

TL;DR

This paper demonstrates a rare-earth quantum memory material with a hyperfine coherence time exceeding one second at telecom wavelengths, advancing the development of long-distance quantum communication.

Contribution

It introduces $^{167}$Er$^{3+}:$Y$_{2}$SiO$_{5}$ as a practical quantum memory candidate with record coherence times and efficient optical pumping capabilities.

Findings

Hyperfine coherence time of 1.3 seconds observed.

First demonstration of efficient optical pumping in a rare-earth system.

Material shows high absorption and suitable transitions for broadband spin-wave storage.

Abstract

Quantum memories for light will be essential elements in future long-range quantum communication networks. These memories operate by reversibly mapping the quantum state of light onto the quantum transitions of a material system. For networks, the quantum coherence times of these transitions must be long compared to the network transmission times, approximately 100 ms for a global communication network. Due to a lack of a suitable storage material, a quantum memory that operates in the 1550 nm optical fiber communication band with a storage time greater than 1 us has not been demonstrated. Here we describe the spin dynamics of $^{167}$Er$^{3+}:$Y$_{2}$SiO$_{5}$ in a high magnetic field and demonstrate that this material has the characteristics for a practical quantum memory in the 1550 nm communication band. We observe a hyperfine coherence time of 1.3 seconds. Further, we demonstrate efficient optical pumping of the entire ensemble into a single hyperfine state, the first such demonstration in a rare-earth system and a requirement for broadband spin-wave storage. With an absorption of 70 dB/cm at 1538 nm and $\Lambda$-transitions enabling spin-wave storage, this material is the first candidate identified for an efficient, broadband quantum memory at telecommunication wavelengths.