# Statistics of radiation due to non-degenerate Josephson parametric down conversion

## TL;DR

This paper provides a theoretical analysis of the photon statistics and correlations in non-degenerate Josephson parametric down-conversion, revealing how asymmetries and thermal effects influence radiation properties.

## Contribution

It introduces a comprehensive theoretical framework for the full counting statistics and coherence properties of non-degenerate Josephson parametric oscillators, including effects of asymmetry and thermal noise.

## Key findings

- Photon pair emission is affected by mode linewidth asymmetry.
- Strong violation of Cauchy-Schwarz inequality occurs at specific driving strengths.
- Thermal effects modify the radiation statistics and coherence properties.

## Abstract

In a process called parametric down-conversion, a dc-biased Josephson junction coupled to two microwave resonators emits photon pairs when the Josephson frequency matches the sum of the two resonance frequencies. Recent experiments have shown that such a setup permits analyzing the correlation of the radiation. Motivated by these results, we study theoretically the full counting statistics of a non-degenerate parametric oscillator below the threshold of instability. Furthermore, we analyze the second-order coherences of the radiation and discuss thermal effects on the radiation statistics. We provide results for the driving strength at which the Cauchy-Schwarz inequality is most strongly violated. Additionally, we study the impact of asymmetry in the linewidth of the modes---a distinctive property of the non-degenerate resonance effect. In particular, we find that the radiation from the mode with the larger linewidth preferably takes the total detuning, while the other mode emits photons at its resonance frequency.