Storage of photonic time-bin qubits for up to 20\u2009ms in a rare-earth doped crystal

Antonio Ortu,Adrian Holzäpfel,Mikael Afzelius,Jean Etesse

doi:10.1038/s41534-022-00541-3

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 151Eu3+:Y2SiO5 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 ± 2)% for an average number of photons per qubit of μin = 0.92 ± 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.

Highlights

The realization of quantum repeaters[1–3], and more generally quantum networks, is a long-standing goal in quantum communication
In this article we report on an atomic frequency comb (AFC) spin-wave memory in 151Eu3+:Y2SiO5, in which we demonstrate storage of 6 temporal modes with mean photon occupation number μin = 0.711 ± 0.006 per mode for a duration of 20 ms using a XY-4 dynamical decoupling (DD) sequence with 4 pulses
The photons to be stored are sent along the input path and are absorbed by the AFC on the jgi $ jei transition, leading to a coherent superposition in the atomic ensemble

Summary

Introduction

The realization of quantum repeaters[1–3], and more generally quantum networks, is a long-standing goal in quantum communication. It will enable long-range quantum entanglement distribution, long-distance quantum key distribution, distributed quantum computation, and quantum simulation[4]. The introduction of atomic ensembles as repeater nodes, and the use of linear optics for the entanglement swapping, stems from the seminal DLCZ proposal[2]. A key advantage of atomic ensembles is their ability to store qubits in many modes through multiplexing[6–12], which is crucial for distributing entanglement efficiently and with practical rates[13]. Rare-earth-ion (RE) doped crystals provide a solid-state approach for ensemble-based quantum nodes. RE doped crystals can provide multiplexing in different degrees of freedom[8,9,11,14–16], efficient storage[17,18], long optical coherence times[19,20], and long coherence times of hyperfine states[21–24] that allows long-duration and on-demand storage of optical quantum states. We focus on repeaters employing time-multiplexing and on-demand read-out in time[13], which require the long storage times provided by hyperfine states[25]

Methods

Results

Conclusion