A passive CPHASE gate via cross-Kerr nonlinearities

TL;DR

This paper proposes a passive CPHASE gate using atom-mediated cross-Kerr nonlinearities, demonstrating high fidelity with multiple interaction sites and narrow photon spectra, advancing quantum photonic gate design.

Contribution

It introduces a novel passive CPHASE gate design based on discrete atom-mediated cross-Kerr sites with quantifiable fidelity improvements.

Findings

Fidelity exceeds 99% with 12 interaction sites

Fidelity improves as the number of sites increases

Narrower photon spectral width enhances gate performance

Abstract

A fundamental and open question is whether cross-Kerr nonlinearities can be used to construct a controlled-phase (CPHASE) gate. Here we propose a gate constructed from a discrete set of atom-mediated cross-Kerr interaction sites with counter-propagating photons. We show that the average gate fidelity $F$ between a CPHASE and our proposed gate increases as the number of interaction sites increases and the spectral width of the photon decreases, e.g. with 12 sites we find $F > 99\%$.