Storage of photonic time-bin qubits for up to 20 ms in a rare-earth doped crystal

TL;DR

This paper demonstrates long-duration quantum storage of photonic time-bin qubits in a rare-earth crystal, achieving up to 20 ms storage with high fidelity, advancing quantum network capabilities.

Contribution

It introduces a method combining dynamical decoupling and magnetic fields to extend quantum memory storage times in rare-earth crystals.

Findings

Stored six temporal modes for up to 100 ms

Achieved 85% fidelity in qubit storage after 20 ms

Verified quantum coherence with time-bin qubits

Abstract

Long-duration quantum memories for photonic qubits are essential components for achieving long-distance quantum networks and repeaters. The mapping of optical states onto coherent spin-waves in rare earth ensembles is a particularly promising approach to quantum storage. However, it remains challenging to achieve long-duration storage at the quantum level due to read-out noise caused by the required spin-wave manipulation. In this work, we apply dynamical decoupling techniques and a small magnetic field to achieve the storage of six temporal modes for 20, 50 and 100 ms in a $^{151}$Eu$^{3+}$:Y$_2$SiO$_5$ crystal, based on an atomic frequency comb memory, where each temporal mode contains around one photon on average. The quantum coherence of the memory is verified by storing two time-bin qubits for 20 ms, with an average memory output fidelity of $F=(85\pm 2)\%$ for an average number of photons per qubit of $\mu_\text{in}$ = 0.92$\pm$0.04. The qubit analysis is done at the read-out of the memory, using a type of composite adiabatic read-out pulse we developed.