Quantum Information with Photonic Crystal Fibres

Anticipated technologies that harness uniquely quantum mechanical effects include quantum computing, quantum lithography, and quantum metrology. However, the only quantum technology in existence today is quantum cryptography, where any attempt to measure information encoded in the state of a photon results in a detectable disturbance. More sophisticated quantum networks will require multiple nodes with the ability to implement small-scale quantum processing. Such networks will rely on optical fibre links, making fibre-based photon generation and information processing of key technological importance. Here we demonstrate both elements in an all-fibre realization of a CNOT gate using two heralded photonic crystal fibre single photon sources. We measure an average logical fidelity of 90% and an average process fidelity of 0.83 < F < 0.91. Using a simple model we find the remaining discrepancy to be due almost entirely to spectral properties of the photon sources, demonstrating near-perfect operation of the fibre CNOT gate itself.

(Color online) An all-optical fiber quantum CNOT gate operated with heralded photonic crystal fiber single-photon sources. A ps 708 nm Ti:sapphire laser pumps two PCFs creating a nondegenerate pair of photons at 583 and 900 nm. These are separated at dichroic mirrors (DMs) and pass through interference filters F1 and F2 with bandwidths of 0.2 and 0.8 nm, respectively. Detection of the 583 nm photons heralds the arrival of the 900 nm control c and target t photons at the inputs to the CNOTgate. HWPs are used to create logical and diagonal input states. The gate consists of three PPFCs with the reflectivities for horizontal and vertical photons as shown. The polarizations of the idler photons are then analyzed using a HWP and a PBS cube for each arm. Note that the Hadamard operations before and after the gate are integrated into the encoding and analysis wave plates. Also inserted here are quarter-wave plates (QWPs) which may be tilted to correct for any phase accumulated through the gate. All four photons are then detected using Perkin Elmer silicon avalanche photodiodes (APDs) and sent to an electronic fourfold coincidence counting circuit for analysis.

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