Cyclical quantum memory for photonic qubits

We have performed a proof-of-principle experiment in which qubits encoded in the polarization states of single photons from a parametric down-conversion source were coherently stored and read out from a quantum memory device. The memory device utilized a simple free-space storage loop, providing a cyclical readout that could be synchronized with the cycle time of a quantum computer. The coherence of the photonic qubits was maintained during switching operations by using a high-speed polarizing Sagnac interferometer switch.