Entanglement of light-shift compensated atomic spin waves with telecom light

Entanglement of a 795 nm light polarization qubit and an atomic Rb spin wave qubit for a storage time of 0.1 s is observed by measuring the violation of Bell's inequality (S = 2.65 \pm 0.12). Long qubit storage times are achieved by pinning the spin wave in a 1064 nm wavelength optical lattice, with a magic-valued magnetic field superposed to eliminate lattice-induced dephasing. Four-wave mixing in a cold Rb gas is employed to perform light qubit conversion between near infra red (795 nm) and telecom (1367 nm) wavelengths, and after propagation in a telecom fiber, to invert the conversion process. Observed Bell inequality violation (S = 2.66 \pm 0.09), at 10 ms storage, confirms preservation of memory/light entanglement through the two stages of light qubit frequency conversion.

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