Two groups of physicists have devised quantum memories from crystals laced with rare earth elements that are capable of storing an entangled photon and then releasing it a short time later. That kind of memory would be useful for long-distance quantum cryptography, for instance, in which individual photons from an entangled pair are sent to two parties who wish to share a unique and secure link. The photons would act as a kind of shared cryptographic key, but the problem is that the individual photons have a maximum range of about 100 kilometers in an optical fiber.
See: Entangling Appliance: Solid-State Memories Pave the Way to Practical Quantum Communication. Two groups of physicists have managed to shift the quantum entanglement between two photons onto an entangled state between one photon and a quantum memory
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