Nanophotonic quantum phase switch with a single atom

TL;DR

This paper demonstrates a nanophotonic quantum phase switch using a single atom coupled to a photonic crystal cavity, enabling nonlinear photon interactions and routing at the quantum level for quantum network applications.

Contribution

It introduces a novel system where a single atom controls photon phase and routing, advancing integrated quantum nanophotonics and quantum network technology.

Findings

Achieved atom-induced optical phase shift nonlinear at two-photon level

Demonstrated photon number routing separating photons and pairs

Implemented single-photon switch controlled by a gate photon

Abstract

In analogy to transistors in classical electronic circuits, a quantum optical switch is an important element of quantum circuits and quantum networks. Operated at the fundamental limit where a single quantum of light or matter controls another field or material system, it may enable fascinating applications such as long-distance quantum communication, distributed quantum information processing and metrology, and the exploration of novel quantum states of matter. Here, by strongly coupling a photon to a single atom trapped in the near field of a nanoscale photonic crystal cavity, we realize a system where a single atom switches the phase of a photon, and a single photon modifies the atom's phase. We experimentally demonstrate an atom-induced optical phase shift that is nonlinear at the two-photon level, a photon number router that separates individual photons and photon pairs into different output modes, and a single-photon switch where a single "gate" photon controls the propagation of a subsequent probe field. These techniques pave the way towards integrated quantum nanophotonic networks involving multiple atomic nodes connected by guided light.