Two-dimensionally multiplexed on-demand quantum memories

A long-distance quantum network requires quantum repeaters dispersed between the end nodes.

At intercity distances, the entangling rate of quantum repeaters may be limited by the photon travel time and the classical communication time.

Quantum repeaters and memories based on rare-earth-doped crystals overcome this limitation, as the atomic frequency comb (AFC) protocol preparing these memories allows for temporal multiplexing.

Besides temporal multiplexing, spatial and frequency multiplexing are also possibilities for rare-earth-doped crystals.Entanglement between these quantum memories is generated in a hybrid and heralded scheme by entangling each memory with a telecom photon and detecting a single photon after a beam splitter.

Thus, the key element for quantum repeaters with rare-earth-doped crystals is the quantum correlations between the telecom photons and the memories.In this project, I will extend the storage capabilities and the entanglement generation rate of rare-earth-doped crystals such that realistic quantum repeater applications at intercity distances are within reach.

The research project is divided into three research objectives: First, I will establish quantum correlations between a long-lived on-demand quantum memory and telecom photons. The correlations will be stored in spin waves for over milliseconds.

Second, I will implement spatial multiplexing and store quantum correlations between telecom photons and 100 spatial modes of a single crystal. The spatial multiplexing is realized with acousto-optical devices in a crossed configuration.

Third, I will entangle two on-demand quantum memories in 1700 modes with temporal and spatial multiplexing.I expect that spatial multiplexing will become a standard tool for solid-state crystal memories.

Entanglement of two on-demand memories in 1700 modes will mark a shift in paradigm, as this is the first demonstration of entanglement of two solid-state memories with multiplexing in two degrees of freedom.