Strongly correlated photons generated by coupling a three- or four-level system to a waveguide

TL;DR

This paper investigates how coupling multi-level atomic systems to a waveguide can generate strongly correlated photons, enabling nonclassical light sources and high-capacity quantum communication through photon bound states and entanglement.

Contribution

It introduces a model for generating correlated photons using three- or four-level atoms in waveguides, highlighting new mechanisms for photon blockade, tunneling, and entanglement.

Findings

Photon-photon bound states observed.

Controlled photon blockade and tunneling demonstrated.

High spectral entanglement in photon pairs achieved.

Abstract

We study the generation of strongly correlated photons by coupling an atom to photonic quantum fields in a one-dimensional waveguide. Specifically, we consider a three-level or four-level system for the atom. Photon-photon bound states emerge as a manifestation of the strong photon-photon correlation mediated by the atom. Effective repulsive or attractive interaction between photons can be produced, causing either suppressed multiphoton transmission (photon blockade) or enhanced multiphoton transmission (photon-induced tunneling). As a result, nonclassical light sources can be generated on demand by sending coherent states into the proposed system. We calculate the second-order correlation function of the transmitted field and observe bunching and antibunching caused by the bound states. Furthermore, we demonstrate that the proposed system can produce photon pairs with a high degree of spectral entanglement, which have a large capacity for carrying information and are important for large-alphabet quantum communication.