Quantum Fluctuations in the Chirped Pendulum

TL;DR

This paper investigates quantum and classical noise effects on autoresonance in a superconducting resonator with a Josephson junction, revealing unique scaling behaviors due to quantum fluctuations at low temperatures.

Contribution

It demonstrates for the first time how quantum noise influences the threshold width in autoresonance of a superconducting circuit, highlighting a novel quantum scaling law.

Findings

Threshold width decreases with temperature as sqrt(T).

Zero point motion causes saturation below 150 mK.

Quantum and classical fluctuations set initial conditions, not dynamics.

Abstract

An anharmonic oscillator when driven with a fast, frequency chirped voltage pulse can oscillate with either small or large amplitude depending on whether the drive voltage is below or above a critical value-a well studied classical phenomenon known as autoresonance. Using a 6 GHz superconducting resonator embedded with a Josephson tunnel junction, we have studied for the first time the role of noise in this non-equilibrium system and find that the width of the threshold for capture into autoresonance decreases as the square root of T, and saturates below 150 mK due to zero point motion of the oscillator. This unique scaling results from the non-equilibrium excitation where fluctuations, both quantum and classical, only determine the initial oscillator motion and not its subsequent dynamics. We have investigated this paradigm in an electrical circuit but our findings are applicable to all out of equilibrium nonlinear oscillators.