We present the first quantum controlled-NOT (CNOT) gate realized using a fiber-based indistinguishable photon-pair source in the 1.55 μm telecommunications band. Using this free-space CNOT gate, all four Bell states are produced and fully characterized by performing quantum state tomography, demonstrating the gate's unambiguous entangling capability and high fidelity. Telecom-band operation makes this CNOT gate particularly suitable for quantum information processing tasks that are at the interface of quantum communication and linear optical quantum computing.
@article{arxiv.0802.1441,
title = {Demonstration of a Quantum Controlled-NOT Gate in the Telecom Band},
author = {Jun Chen and Joseph B. Altepeter and Milja Medic and Kim Fook Lee and Burc Gokden and Robert H. Hadfield and Sae Woo Nam and Prem Kumar},
journal= {arXiv preprint arXiv:0802.1441},
year = {2009}
}