Minute-Scale Photonic Quantum Memory

TL;DR

This paper demonstrates a photonic quantum memory capable of storing single photons for over a minute with high fidelity, using a novel integration of photon echo protocols and dynamical decoupling in Eu-yttrium silicate crystals.

Contribution

It introduces a new method combining noiseless photon echo and dynamical decoupling to achieve minute-scale quantum storage in rare-earth crystals.

Findings

Achieved a 5.6 second quantum storage with 88% fidelity.

Extended the storage lifetime to 27.6 seconds with a 42-second single-photon-level storage.

Surpassed classical fidelity limits for quantum memory.

Abstract

Long-lived storage of single photons is a fundamental requirement for enabling quantum communication and foundational tests of quantum physics over extended distances. While the implementation of a global-scale quantum network requires quantum storage times on the order of seconds to minutes, existing photonic quantum memories have so far been limited to subsecond lifetimes. Although $^{151}$Eu$^{3+}$:Y$_2$SiO$_5$ crystals exhibit substantially extended spin coherence times at the `magic' magnetic field, the concomitant weak optical absorption has until now prevented single-photon storage. Here, we overcome this challenge by integrating a noiseless photon echo protocol--which makes full use of the crystal's natural absorption for photonic storage--with a universally robust dynamical decoupling sequence incorporating adiabatic pulses to efficiently protect delocalized spin-wave excitation, enabling long-lived quantum storage at the `magic' magnetic field. At a storage time of 5.6 s, we achieve a time-bin qubit storage fidelity of 88.0 $\pm$ 2.1%, surpassing the maximum fidelity attainable via classical strategies. Our device reaches a $1/e$ storage lifetime of 27.6 $\pm$ 0.5 s, enabling single-photon-level storage for 42 s with a signal-to-noise ratio greater than unity. This work establishes photonic quantum memory in the minute-scale regime, laying a solid foundation for global-scale quantum network and deep-space quantum experiments.