Speaker
Description
Large-scale quantum networks require a scalable, mass-producible memory platform. Ground-state atomic vapor memories are a promising candidate: room-temperature operation makes them experimentally simple, and they have been shown to perform well across a range of figures of merit. Their noise performance is compatible with preserving the non-classical photon-number statistics of retrieved photons, and their acceptance bandwidth can be matched to high-quality single-photon sources such as semiconductor quantum dots or SPDC sources. Additionally, vapor cells can be microfabricated, using the same techniques already applied to compact quantum sensors such as atomic clocks, magnetometers, and gyroscopes. However, so far, no quantum memory has been realized in a MEMS vapor cell. Recently, we demonstrated for the first time an optical memory in a microfabricated vapor cell compatible with wafer-scale fabrication techniques, representing a crucial step towards scalability.
Our result relies on a novel memory scheme that engineers a ''clean'' atom-light interaction. A tesla-order static magnetic field brings the atomic vapor into the hyperfine Paschen-Back regime, where Zeeman degeneracies are lifted and the nuclear and total electronic spin are decoupled. This spectrally isolates a single $\Lambda$-system in the hot ensemble, enabling efficient, low-noise storage in the atomic ground states. In this proof-of-principle experiment, we stored and retrieved weak coherent pulses attenuated to the single-photon level, reaching an end-to-end efficiency of $3.12(17)\%$ at an $80\,\mathrm{ns}$ storage time, with a $\mathrm{SNR} = 7.9(8)$. The memory preserves the pulses over a $1/e$ lifetime of $224(8)\,\mathrm{ns}$. The SNR is currently limited by poor initial atomic polarization caused by radiation trapping. To address this, the cell geometry and filling have been optimized to improve state preparation, and a custom-built permanent magnet now provides the tesla-order field with ppm-level homogeneity on the centimeter scale. With these upgrades, we will attempt to interface the memory with a single-photon source. Such an optical interconnect, built from miniaturized room-temperature memories, would pave the way to more complex networking applications.