Measuring the quantum states of a mesoscopic SQUID using a small Josephson junction

TL;DR

This paper experimentally investigates the energy levels of a mesoscopic SQUID by coupling it to a small Josephson junction, revealing how dissipation influences energy band formation and localization.

Contribution

It introduces a novel method for energy level spectroscopy of a SQUID using inelastic Cooper-pair tunneling in a small Josephson junction.

Findings

Strong quasiparticle dissipation leads to localized energy states.

Weak dissipation allows observation of energy band formation.

Experimental results align with theoretical models of particle localization and band structure.

Abstract

We have experimentally studied the energy levels of a mesoscopic SQUID using inelastic Cooper-pair tunneling. The tunneling in a small Josephson junction depends strongly on its electromagnetic environment. We use this fact to do energy level spectroscopy of a SQUID-loop by coupling it to a small junction. Our samples with strong quasiparticle dissipation are well described by a model of a particle localized in one of the dips in a cosine-potential, while in the samples with weak dissipation we can see formation of energy bands.