Photon-photon quantum phase gate in a photonic molecule with $\chi^{(2)}$ nonlinearity

TL;DR

This paper proposes a high-fidelity photon-photon quantum phase gate using a microcavity with strong $$ nonlinearity acting as an artificial atom, enabling scalable quantum information processing with minimal noise.

Contribution

It introduces a novel scheme employing a photonic molecule with a microcavity as an artificial atom for deterministic photon-photon gates, reducing spectral entanglement and phase noise.

Findings

Achieves high-fidelity control-phase gate via artificial atom in a photonic molecule.

Avoids two-photon emission, reducing spectral entanglement.

Potential for room-temperature, integrated quantum photonic devices.

Abstract

The construction of photon-photon quantum phase gate based on photonic nonlinearity has long been a fundamental issue, which is vital for deterministic and scalable photonic quantum information processing. It requires not only strong nonlinear interaction at the single-photon level, but also suppressed phase noise and spectral entanglement for high gate fidelity. In this paper, we propose that high-quality factor microcavity with strong $\chi^{(2)}$ nonlinearity can be quantized to anharmonic energy levels and be effectively treated as an artificial atom. Such artificial atom has a size much larger than the photon wavelength, which enables passive and active ultra-strong coupling to traveling photons. High-fidelity quantum control-phase gate is realized by mediating the phase between photons with an intermediate artificial atom in a photonic molecule structure. The scheme avoids the two-photon emission and thus eliminates the spectral entanglement and quantum phase noises. Experimental realization of the artificial atom can be envisioned on the integrated photonic chip and holds great potential for single-emitter-free, room-temperature quantum information processing.