Quantum memories play a crucial role in creating large-scale quantum networks by enabling the connection of multiple short-distance entanglements into long-distance entanglements. This approach helps to overcome photon transmission losses effectively. Rare-earth ion-doped crystals are a promising candidate for implementing high-performance quantum memories, and integrated solid-state quantum memories have already been successfully demonstrated using advanced micro- and nano-fabrication techniques.
However, previous implementations of integrated quantum memories for light have been limited to storing information in optically excited states. This method does not allow for on-demand retrieval with adjustable storage times, as the storage duration is fundamentally constrained by the lifetime of the excited states.
Spin-wave storage, which transfers photons into spin-wave excitations in ground states, offers a solution by enabling on-demand retrieval with storage times extended to the spin coherence lifetime. Despite its potential, the integration of spin-wave storage faces a significant challenge: separating single-photon-level signals from the substantial noise generated by strong control pulses in integrated structures.
To date, spin-wave quantum storage has not been successfully demonstrated in integrated solid-state devices, posing a major obstacle to the practical application of this promising technology.
Recently, the group led by Chuan-Feng Li and Zong-Quan Zhou at the University of Science and Technology of China has successfully demonstrated an integrated spin-wave quantum memory, by implementing spin-wave quantum storage protocols using a specially developed device.
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