On-demand multimode optical storage in a laser-written on-chip waveguide

TL;DR

This paper demonstrates an integrated on-chip quantum memory in a laser-written waveguide capable of storing multiple optical modes with high coherence, bandwidth, and on-demand retrieval, advancing practical quantum network components.

Contribution

It introduces a novel on-chip waveguide in Eu-doped crystal with low insertion loss and a new pumping scheme for multimode quantum storage with high fidelity.

Findings

Stored 200 temporal modes with AFC scheme

Achieved conditional on-demand storage of 100 modes

Maintained high interference visibility indicating coherence

Abstract

Quantum memory is a fundamental building block for large-scale quantum networks. On-demand optical storage with a large bandwidth, a high multimode capacity and an integrated structure simultaneously is crucial for practical application. However, this has not been demonstrated yet. Here, we fabricate an on-chip waveguide in a $\mathrm {^{151}Eu^{3+}:Y_2SiO_5}$ crystal with insertion losses of 0.2 dB, and propose a novel pumping scheme to enable spin-wave atomic frequency comb (AFC) storage with a bandwidth of 11 MHz inside the waveguide. Based on this, we demonstrate the storage of 200 temporal modes using the AFC scheme and conditional on-demand storage of 100 temporal modes using the spin-wave AFC scheme. The interference visibility between the readout light field and the reference light field is $99.0\% \pm 0.6\%$ and $97\% \pm 3\%$ for AFC and spin-wave AFC storage, respectively, indicating the coherent nature of this low-loss, multimode and integrated storage device.