Coherent dynamics and decoherence in a superconducting weak link

TL;DR

This paper demonstrates coherent quantum flux dynamics in a superconducting loop with a nanobridge, exploring decoherence mechanisms and achieving quantum state control without a tunnel junction.

Contribution

It introduces a superconducting weak link system with a nanobridge, enabling quantum control and coherence studies without traditional tunnel junctions.

Findings

Coherent oscillations observed in the nanobridge system

Decoherence likely caused by inductance fluctuations

Energy relaxation characterized via microwave spectroscopy

Abstract

We demonstrate coherent dynamics of quantized magnetic fluxes in a superconducting loop with a weak link - a nanobridge patterned from the same thin NbN film as the loop. The bridge is a short rounded shape constriction, close to 10 nm long and 20 - 30 nm wide, having minimal width at its center. Quantum state control and coherent oscillations in the driven time evolution of the tunnel-junctionless system are achieved. Decoherence and energy relaxation in the system are studied using a combination of microwave spectroscopy and direct time-domain techniques. The effective flux noise behavior suggests inductance fluctuations as a possible cause of the decoherence.