# Quantum Brownian motion at strong dissipation probed by superconducting tunnel junctions

## TL;DR

This study experimentally investigates quantum Brownian motion in a strongly dissipative regime using superconducting tunnel junctions, confirming the quantum Smoluchowski equation's predictions at ultra-low temperatures.

## Contribution

It provides the first experimental validation of the quantum Smoluchowski equation describing quantum Brownian motion under strong dissipation.

## Key findings

- Quantum systems exhibit quasi-classical dynamics with quantum corrections.
- Experimental data aligns with the quantum diffusion model.
- Strong dissipation allows quantum effects to be leading corrections.

## Abstract

We have studied the temporal evolution of a quantum system subjected to strong dissipation at ultra-low temperatures where the system-bath interaction represents the leading energy scale. In this regime, theory predicts the time evolution of the system to follow a generalization of the classical Smoluchowski description, the quantum Smoluchowski equation, thus, exhibiting quantum Brownian motion characteristics. For this purpose, we have investigated the phase dynamics of a superconducting tunnel junction in the presence of high damping. We performed current-biased measurements on the small-capacitance Josephson junction of a scanning tunneling microscope placed in a low impedance environment at milli-Kelvin temperatures. We can describe our experimental findings by a quantum diffusion model with high accuracy in agreement with theoretical predications based on the quantum Smoluchowski equation. In this way we experimentally demonstrate that quantum systems subjected to strong dissipation follow quasi-classical dynamics with significant quantum effects as the leading corrections.