All-optical switching at the two-photon limit with interference-localized states

TL;DR

This paper introduces a novel all-optical switch that operates at the single-photon level using interference-localized states, enabling high-contrast, ultrafast switching with potential applications in quantum photonics.

Contribution

It presents a new concept of a single-photon switch based on interference-localized states and their interaction-induced delocalization, modeled with Bose-Hubbard Hamiltonians.

Findings

Achieves picosecond switching times at single-photon energies.

Provides high ON/OFF contrast for photon control.

Demonstrates feasibility with photonic lattices and ultracold atoms.

Abstract

We propose a single-photon-by-single-photon all-optical switch concept based on interference-localized states on lattices and their delocalization by interaction. In its 'open' operation, the switch stops single photons while allows photon pairs to pass the switch. Alternatively, in the 'closed' operation, the switch geometrically separates single-photon and two-photon states. We demonstrate the concept using a three-site Stub unit cell and the diamond chain. The systems are modeled by Bose-Hubbard Hamiltonians, and the dynamics is solved by exact diagonalization with Lindblad master equation. We discuss realization of the switch using photonic lattices with nonlinearities, superconductive qubit arrays, and ultracold atoms. We show that the switch allows arbitrary 'ON'/'OFF' contrast while achieving picosecond switching time at the single-photon switching energy with contemporary photonic materials.