All-optical-fiber polarization-based quantum logic gate

We report an experimental demonstration of a quantum controlled-NOT gate constructed entirely in optical fiber and operating on polarization-encoded single-photon qubits. We operated this gate using two heralded optical fiber single-photon sources and found an average logical fidelity of 90% and an average process fidelity of 0.83 <= (F) over bar <= 0.91. On the basis of a simple model we are able to conclude that imperfections are primarily due to the photon sources, meaning that the gate itself works with very high fidelity. Such all fiber quantum information processing will likely have important applications in future quantum networks.