  Quantum network with a current telecom photonic infrastructure is deficient
in quantum storages that keep arbitrary quantum state in sufficient time
duration for a long-distance quantum communication with quantum repeater
algorithms. Atomic quantum storages have achieved subsecond storage time
corresponding to 1000 km transmission time for a telecom photon through a
quantum repeater algorithm. However, the telecom photon is not directly
accessible to typical atomic storages. Solid state quantum frequency
conversions fill this wavelength gap and add more abilities, for example, a
frequency multiplex. Here we report on the experimental demonstration of a
polarization-insensitive solid-state quantum frequency conversion to a telecom
photon from a short-wavelength photon entangled with an atomic ensemble.
Atom-photon entanglement has been generated with a Rb atomic ensemble and the
photon has been translated to telecom range while retaining the entanglement by
our nonlinear-crystal-based frequency converter in a Sagnac interferometer.
