Distribution of light-matter quantum correlations with a temporally multiplexed solid-state quantum memory array
Multiplexed quantum memories increase the entanglement distribution rate in long-distance quantum repeater architectures by harnessing storage in several degrees of freedom. Here, we report on the distribution of light-matter quantum correlations using an array of time-multiplexed solid-state quantum memories. We store telecom-heralded single photons sequentially in up to ten memory cells using the full atomic frequency comb protocol with on-demand read-out in a Pr$^{3+}$:Y$_2$SiO$_5$ crystal. Leveraging both spatial and temporal multiplexing, we demonstrate quantum correlations between the telecom photon and up to 60 spatio-temporal modes of the quantum memory array. We then transmit the heralding telecom photon over 39.1 km of deployed optical fiber in the Metropolitan Area of Barcelona. In a realistic scenario where the generation rate is limited by the two-way communication time, we show that up to 15 % of the $393 \mu s$ round-trip communication time is filled with communication trials, leading to a 60-fold enhancement in the rate of detected telecom photons correlated with the quantum memory array, compared to a single-mode memory. With increased storage times and efficiencies, our multiplexed quantum memory array will constitute the backbone of a long-distance quantum network, establishing remote entanglement at high rates.