Achievement

Single-photon qubits are encoded in principal modes of the electromagnetic field. High-fidelity, cascadable photonic gates must map input principal modes to the same principal modes at their outputs. To date, deterministic and cascadable universal two-qubit photonic logic gates have not been realized. Cross-phase modulation (XPM) has been proposed for constructing such a gate, the conditional π-phase gate. Single-mode XPM analyses are encouraging, but continuous-time treatments have shown that fidelity-degrading noise precludes high-fidelity operation. iQuiSE Trainee Christopher Chudzicki has performed continuous-time analysis of a single-photon conditional-phase gate that, for sufficiently small nonzero phase shifts, has high fidelity. His gate exploits the quantum Zeno effect to make it cascadable, so that a sequence of such gates can realize a high-fidelity conditional π-phase gate. Christopher has presented his work at the March 2012 Meeting of the American Physical Society.