The dynamical Casimir effect in superconducting microwave circuits

TL;DR

This paper theoretically explores the dynamical Casimir effect in superconducting microwave circuits with tunable boundary conditions, analyzing photon generation and quantum properties to distinguish it from other radiation sources.

Contribution

It proposes a method to implement rapid boundary condition modulation in superconducting circuits and analyzes the resulting quantum radiation signatures.

Findings

Photon flux density shows signatures of the dynamical Casimir effect.

Output field exhibits quadrature squeezing characteristic of the effect.

Distinct correlation functions differentiate the effect from other radiation types.

Abstract

We theoretically investigate the dynamical Casimir effect in electrical circuits based on superconducting microfabricated waveguides with tunable boundary conditions. We propose to implement a rapid modulation of the boundary conditions by tuning the applied magnetic flux through superconducting quantum interference devices (SQUIDs) that are embedded in the waveguide circuits. We consider two circuits: (i) An open waveguide circuit that corresponds to a single mirror in free space, and (ii) a resonator coupled to a microfabricated waveguide, which corresponds to a single-sided cavity in free space. We analyze the properties of the dynamical Casimir effect in these two setups by calculating the generated photon-flux density, output-field correlation functions, and the quadrature squeezing spectra. We show that these properties of the output field exhibit signatures unique to the radiation due to the dynamical Casimir effect, and could therefore be used for distinguishing the dynamical Casimir effect from other types of radiation in these circuits. We also discuss the similarities and differences between the dynamical Casimir effect, in the resonator setup, and downconversion of pump photons in parametric oscillators.