Energy Down Conversion between Classical Electromagnetic Fields via a Quantum Mechanical SQUID Ring

TL;DR

This paper demonstrates energy transfer between a classical resonator and a quantum SQUID ring driven by microwaves, highlighting non-linear quantum-classical interactions at large frequency ratios.

Contribution

It introduces a model showing energy exchange between a quantum SQUID ring and a classical circuit, emphasizing non-perturbative and non-linear quantum effects.

Findings

Energy transfer occurs at large frequency ratios.

Quantum SQUID maintains its quantum nature during interaction.

Non-perturbative, non-linear coupling enables energy exchange.

Abstract

We consider the interaction of a quantum mechanical SQUID ring with a classical resonator (a parallel $LC$ tank circuit). In our model we assume that the evolution of the ring maintains its quantum mechanical nature, even though the circuit to which it is coupled is treated classically. We show that when the SQUID ring is driven by a classical monochromatic microwave source, energy can be transferred between this input and the tank circuit, even when the frequency ratio between them is very large. Essentially, these calculations deal with the coupling between a single macroscopic quantum object (the SQUID ring) and a classical circuit measurement device where due account is taken of the non-perturbative behaviour of the ring and the concomitant non-linear interaction of the ring with this device.