Phase-noise limitations on single-photon cross-phase modulation with differing group velocities

"Phase-noise limitations on single-photon cross-phase modulation with differing group velocities. Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. A framework is established for evaluating CPHASE gates that use single-photon cross-phase modulation (XPM) originating from the Kerr nonlinearity. that the control and target pulses propagated at the same group velocity, showed that the causality-induced phase noise required by a noninstantaneous XPM response function precluded the possibility of high-fidelity π-radian conditional phase shifts. The framework presented herein incorporates the more realistic case of group-velocity disparity between the control and target pulses, as employed in existing XPM-based fiber-optical switches. Nevertheless, the causality-induced phase noise identified (2006)] still rules out high-fidelity π-radian conditional phase shifts. This is shown to be so for both a reasonable theoretical model for the XPM response function and for the experimentally measured XPM response function of silica-core fiber.