Quantum cavity modes in spatially extended Josephson systems

TL;DR

This paper presents a theoretical analysis of quantum cavity modes in spatially extended Josephson systems, showing how quantum states of photons influence measurable junction properties, enabling quantum state detection.

Contribution

It introduces a theoretical framework linking quantum photon states in Josephson junction cavities to observable macroscopic junction characteristics.

Findings

Photon number affects critical current and escape rate.

Quantum states like squeezing and entanglement influence junction dynamics.

Proposes using junction measurements to detect quantum photon states.

Abstract

We report a theoretical study of the macroscopic quantum dynamics in spatially extended Josephson systems. We focus on a Josephson tunnel junction of finite length placed in an externally applied magnetic field. In such a system, electromagnetic waves in the junction are excited in the form of cavity modes manifested by Fiske resonances, which are easily observed experimentally. We show that in the quantum regime various characteristics of the junction as its critical current $I_c$, width of the critical current distribution $\sigma$, escape rate $\Gamma$ from the superconducting state to a resistive one, and the time-dependent probability $P(t)$ of the escape are influenced by the number of photons excited in the junction cavity. Therefore, these characteristics can be used as a tool to measure the quantum states of photons in the junction, e.g. quantum fluctuations, coherent and squeezed states, entangled Fock states, etc.