Quantum Dynamics of Nonlinear Cavity Systems

TL;DR

This paper explores the quantum dynamics of nonlinear cavity systems, including a SQUID-based displacement detector, an analogue Hawking radiation setup, and a quantum parametric amplifier modeling black hole evaporation, revealing new quantum effects and deviations from classical predictions.

Contribution

It introduces novel quantum analyses of nonlinear cavity configurations, demonstrating enhanced displacement detection, analogue Hawking radiation effects, and deviations in Hawking spectrum linked to black hole energy release.

Findings

Closer approach to quantum-limited displacement detection

Observation of analogue Hawking radiation with backreaction effects

Deviations from thermal Hawking spectrum during black hole energy loss

Abstract

We investigate the quantum dynamics of three different configurations of nonlinear cavity systems. To begin, we carry out a quantum analysis of a dc superconducting quantum interference device (SQUID) mechanical displacement detector comprised of a SQUID with a mechanically compliant loop segment. The SQUID is approximated by a nonlinear current-dependent inductor, inducing a flux tunable nonlinear Duffing term in the cavity equation of motion. Expressions are derived for the detector signal and noise response where it is found that a soft-spring Duffing self-interaction enables a closer approach to the displacement detection standard quantum limit, as well as cooling closer to the ground state. Next, we make use of a superconducting transmission line formed from an array of dc-SQUIDs for investigating analogue Hawking radiation. Biasing the array with a space-time varying flux modifies the propagation velocity of the transmission line, leading to an effective metric with a horizon. This setup allows for quantum effects such as backreaction and analogue space-time fluctuations on the Hawking process. Finally, we look at a quantum parametric amplifier with dynamical pump mode, viewed as a zero-dimensional model of Hawking radiation from an evaporating black hole. The conditions are derived under which the spectrum of particles generated from vacuum fluctuations deviates from the thermal spectrum predicted for the conventional parametric amplifier. We find that significant deviation occurs once the pump mode (black hole) has released nearly half of its initial energy in the signal (Hawking radiation) and idler (in-falling particle) modes. As a model of black hole dynamics, this finding lends support to the view that late-time Hawking radiation contains information about the quantum state of the black hole and is entangled with the black hole's quantum gravitational degrees of freedom.