Limitations of two-level emitters as non-linearities in two-photon controlled phase gates

TL;DR

This paper analyzes the fundamental limitations of two-level emitter-based non-linearities in two-photon controlled-phase gates, showing that conflicting spectral requirements restrict maximum fidelity to 84%.

Contribution

It identifies the conflicting spectral conditions for one- and two-photon scattering that limit gate fidelity in passive two-level emitter systems.

Findings

Maximum fidelity limited to 84% for Gaussian pulses.

Fidelity constrained by opposing spectral requirements.

Passive system performance without external modulation.

Abstract

We investigate the origin of imperfections in the fidelity of a two-photon controlled-phase gate based on two-level-emitter non-linearities. We focus on a passive system that operates without external modulations to enhance its performance. We demonstrate that the fidelity of the gate is limited by opposing requirements on the input pulse width for one- and two-photon scattering events. For one-photon scattering, the spectral pulse width must be narrow compared to the emitter linewidth, while two-photon scattering processes require the pulse width and emitter linewidth to be comparable. We find that these opposing requirements limit the maximum fidelity of the two-photon controlled-phase gate for Gaussian photon pulses to 84%.