A major challenge in quantum technologies is to build an efficient and long-lived quantum memory, particularly using solid-state devices. I will here report on an experiment where we combine the AFC optical memory with spin-echo techniques to extend the memory time from a few microseconds to about 1 ms, using an Europium-doped crystal. In general the spin-echo technique allows one to control the inhomogeneous spin dephasing which often sets the storage-time limit both in solid-state systems and laser-cooled gases. However, theoretically it is has been argued that spin-echo techniques would be extremely difficult to apply without creating noise in the case of a single quanta stored in a large spin ensemble. We here show how this noise can be limited and demonstrate high signal-to-noise ratio in the output mode when storing pulses at the single-photon level. Furthermore we stored polarization qubits encoded onto weak coherent , with fidelities surpassing a classical storage scheme.
Mikael Afzelius, "A long-lived and solid-state quantum memory for photons
(Conference Presentation)," Proc. SPIE 9900, Quantum Optics, 99000M (Presented at SPIE Photonics Europe: April 06, 2016; Published: 3 August 2016); https://doi.org/10.1117/12.2229369.5042345232001.
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