Weak localization and conductance fluctuations-like effects in Qubits driven by biharmonic signals

Alejandro Ferrón,Daniel Domínguez,María José Sánchez

doi:10.1088/1742-6596/568/5/052028

Abstract

We investigate the effect of broken time reversal symmetry in flux qubits driven by a biharmonic magnetic flux signal with a phase lag. In the regime of large relaxation times, we explicitly compute the transition rate between the ground and the excited state, accounting for decoherence as a classical noise. Through a direct analogy between interference effects at the avoided level crossing and scattering events in weakly disordered electronic mesoscopic systems, the transition rate plays the role of an effective transmittance while the phase lag acts as a time reversal control parameter. Clear signatures of both weak localization and conductance fluctuations-like effects are predicted. Their behavior is studied as a function of the coherence rate, and a comparison with recent experimental results is performed. Our study shows that it is decoherence, and not the driving protocol, what limits the experimental detection of weak localization effects.

Highlights

Flux qubits (FQ) can be considered as artificial atoms whose energy levels are sensitive to an external magnetic flux. [1, 2] Its energy spectrum exhibits, as a function of the static magnetic flux, a rich structure of avoided crossings that can be explored by driving the FQ with a strong ac magnetic flux
Each avoided crossing acts as an effective beam splitter in where a scattering event takes place. This analogy has been discussed in extent for FQ under weak driving, when the lowest two energy levels are explored and a single avoided crossing is attained by the amplitude of the ac flux.[3, 7]
In this work we have tested fluctuation effects associated to broken time reversal symmetry in FQ driven by a biharmonic ac magnetic flux

Summary

Introduction

Flux qubits (FQ) can be considered as artificial atoms whose energy levels are sensitive to an external magnetic flux. [1, 2] Its energy spectrum exhibits, as a function of the static magnetic flux, a rich structure of avoided crossings that can be explored by driving the FQ with a strong ac magnetic flux. This analogy has been discussed in extent for FQ under weak driving, when the lowest two energy levels are explored and a single avoided crossing is attained by the amplitude of the ac flux.[3, 7]

Results

Conclusion