Pulsed two-photon scattering from a single atom in a waveguide with delay-modified temporal correlations

TL;DR

This paper investigates how two-photon pulses interact with a single atom in a waveguide, revealing how delay-controlled correlations influence quantum nonlinearities and photon-photon interactions.

Contribution

It introduces a theoretical analysis of two-photon nonlinearities with delay-controlled correlations using matrix product states and scattering theory in a waveguide-QED system.

Findings

Different nonlinear features for correlated and uncorrelated photon pairs.

Significant impact of delay on photon correlation functions.

Demonstration of quantum correlations in experimentally accessible regimes.

Abstract

Quantum nonlinearity is an essential ingredient for many quantum technologies, but often the nonlinearity is too weak to be exploited at the few-photon level. However, few photons interacting strongly with single quantum emitters in a waveguide environment can impact a significant nonlinear response, opening up a wide range of photon-photon correlations. Using a waveguide-QED system containing a single atom (treated as a two-level system) chirally coupled to a waveguide, we theoretically investigate two-photon nonlinearities with delay-controlled temporal correlations. We use both matrix product states (MPS) and a frequency-dependent scattering theory approach to analyze the exact population dynamics, as well as the first-order and second-order photon correlation functions in transmission of the system, when pumped by a two-photon Fock-state pulse with a bimodal temporal pulse envelope. The two-photon Fock-state pulses are considered to be either two single photons localized to each peak of the pulse, or both photons delocalized (but correlated) between the two peaks. We consider the regimes of a short, moderate, and (relatively) long distance between the two pulse peaks, comparing the important differences in the temporal correlations with the two types of two-photon pulses. We demonstrate the strikingly different nonlinear features and quantum correlations that occur for uncorrelated and correlated two-photon pairs in experimentally accessible regimes.