Josephson photonics with a two-mode superconducting circuit

TL;DR

This paper studies the quantum behavior of two coupled electromagnetic modes in a superconducting circuit driven by a Josephson junction, revealing non-classical states with strong quantum correlations and squeezing.

Contribution

It provides a detailed analysis of the quantum dynamics of a two-mode superconducting circuit under Josephson driving, including analytical and numerical results on non-classical states.

Findings

Observation of strong anti-bunching and violation of classical inequalities.

Identification of regimes with number squeezing and non-classical photon states.

Enhanced number squeezing due to mode damping asymmetries.

Abstract

We analyze the quantum dynamics of two electromagnetic oscillators coupled in series to a voltage biased Josephson junction. When the applied voltage leads to a Josephson frequency across the junction which matches the sum of the two mode frequencies, tunneling Cooper pairs excite photons in both modes simultaneously leading to far-from-equilibrium states. These states display highly non-classical features including strong anti-bunching, violation of Cauchy-Schwartz inequalities, and number squeezing. The regimes of low and high photon occupancies allow for analytical results which are supported by a full numerical treatment. The impact of asymmetries between the two modes is explored, revealing a pronounced enhancement of number squeezing when the modes are damped at different rates.