On-Demand Millisecond Storage of Spectro-Temporal Multimode Telecom Photons

The realization of scalable quantum networks for distribution of entanglement over long distances hinges on quantum repeaters. To outperform the exponential transmission loss in optical fibers, quantum repeaters must employ multiplexing schemes in the temporal, spectral, or spatial domain. The performance of such a multiplexed scheme is contingent on efficient quantum memories offering both extended storage times and large multimode capacities. In this work, we experimentally demonstrate such a memory operating at telecom wavelength using an Er$^{3+}$:Y$_{2}$SiO$_{5}$ crystal. Using single-photon detectors, we record on-demand storage and recall of weak coherent pulses for up to $1$ ms, exceeding that of previously reported quantum memories based on Er$^{3+}$. The memory exhibits an efficiency of 10.36\% at 300 $\mu$s storage time with a signal-to-noise ratio of $10.9$. We further showcase its multimode capacity by storing 20 temporal and 3 spectral modes simultaneously with on-demand and selective recall capabilities, essential for a scalable quantum repeater architecture.