Synchronization of optical photons for quantum information processing



Kenzo Makino, Yosuke Hashimoto, Jun-ichi Yoshikawa, Hideaki Ohdan, Takeshi Toyama, Peter Van Loock & Akira Furusawa



A fundamental element of quantum information processing with photonic qubits is the nonclassical quantum interference between two photons when they bunch together via the Hong-Ou-Mandel (HOM) effect. Ultimately, many such photons must be processed in complex interferometric networks. For this purpose, it is essential to synchronize the arrival times of the flying photons and to keep their purities high. On the basis of the recent experimental success of single-photon storage with high purity, we demonstrate for the first time the HOM interference of two heralded, nearly pure optical photons synchronized through two independent quantum memories. Controlled storage times of up to 1.8 μs for about 90 events per second were achieved with purities that were sufficiently high for a negative Wigner function confirmed with homodyne measurements.



Synchronization of optical photons.
(A) Independent statistical photon sources without memories.
(B) Independent photon sources with memories. τmax, the maximum storage time.
In principle, the synchronization window could be further increased beyond 1.8 μs; however,
in our present performance of memories, this would be at the expense of the negativity of the
Wigner function.

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