Signatures of Hong-Ou-Mandel Interference at Microwave Frequencies

TL;DR

This paper models and analyzes Hong-Ou-Mandel interference signatures at microwave frequencies, demonstrating how quantum interference manifests in correlation functions for different microwave photon sources and matching experimental results.

Contribution

It provides detailed calculations of correlation functions for microwave photons, including effects of finite detection bandwidth, and compares them with experimental data.

Findings

Correlation functions show suppression indicating quantum interference

Good agreement between calculations and experimental data

Finite bandwidth effects are significant in the analysis

Abstract

Two-photon quantum interference at a beam splitter, commonly known as Hong-Ou-Mandel interference, was recently demonstrated with \emph{microwave-frequency} photons by Lang \emph{et al.}\,\cite{lang:microwaveHOM}. This experiment employed circuit QED systems as sources of microwave photons, and was based on the measurement of second-order cross-correlation and auto-correlation functions of the microwave fields at the outputs of the beam splitter. Here we present the calculation of these correlation functions for the cases of inputs corresponding to: (i) trains of \emph{pulsed} Gaussian or Lorentzian single microwave photons, and (ii) resonant fluorescent microwave fields from \emph{continuously-driven} circuit QED systems. The calculations include the effects of the finite bandwidth of the detection scheme. In both cases, the signature of two-photon quantum interference is a suppression of the second-order cross-correlation function for small delays. The experiment described in Ref. \onlinecite{lang:microwaveHOM} was performed with trains of \emph{Lorentzian} single photons, and very good agreement between the calculations and the experimental data was obtained.