Towards highly multimode optical quantum memory for quantum repeaters

TL;DR

This paper demonstrates a new method to enhance the multimode capacity of atomic frequency comb quantum memories, enabling storage of up to 100 modes, which is crucial for advancing long-distance quantum communication via quantum repeaters.

Contribution

The authors introduce a novel comb preparation technique that significantly increases multimode capacity in atomic frequency comb memories without reducing efficiency.

Findings

Stored 100 modes for 51 microseconds using AFC echo scheme

Stored 50 modes for 0.541 milliseconds with AFC spin-wave memory

Discussed the fundamental multimode limit set by optical decoherence

Abstract

Long-distance quantum communication through optical fibers is currently limited to a few hundreds of kilometres due to fiber losses. Quantum repeaters could extend this limit to continental distances. Most approaches to quantum repeaters require highly multimode quantum memories in order to reach high communication rates. The atomic frequency comb memory scheme can in principle achieve high temporal multimode storage, without sacrificing memory efficiency. However, previous demonstrations have been hampered by the difficulty of creating high-resolution atomic combs, which reduces the efficiency for multimode storage. In this article we present a comb preparation method that allows one to increase the multimode capacity for a fixed memory bandwidth. We apply the method to a $^{151}$Eu$^{3+}$-doped Y$_2$SiO$_5$ crystal, in which we demonstrate storage of 100 modes for 51 $\mu$s using the AFC echo scheme (a delay-line memory), and storage of 50 modes for 0.541 ms using the AFC spin-wave memory (an on-demand memory). We also briefly discuss the ultimate multimode limit imposed by the optical decoherence rate, for a fixed memory bandwidth.