Observation of Co-tunneling in Pairs of Coupled Flux Qubits

TL;DR

This paper demonstrates the direct observation of co-tunneling between two coupled flux qubits, revealing details about their joint quantum dynamics and local environmental interactions through resonant tunneling measurements.

Contribution

It provides the first direct measurement of co-tunneling in coupled flux qubits and characterizes their environmental couplings.

Findings

Gaussian line shape of tunneling rate matches theory

Uncorrelated local environmental fluctuations for each qubit

Evidence of two-qubit quantum dynamics through resonant tunneling

Abstract

We report measurements of macroscopic resonant tunneling between the two lowest energy states of a pair of magnetically coupled rf-SQUID flux qubits. This technique provides a direct means of observing two-qubit dynamics and a probe of the environment coupled to the pair of qubits. Measurements of the tunneling rate as a function of qubit flux bias show a Gaussian line shape that is well matched to theoretical predictions. Moreover, the peak widths indicate that each qubit is coupled to a local environment whose fluctuations are uncorrelated with that of the other qubit.