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arXiv · 1204.6428

Time-Reversal Symmetry and Universal Conductance Fluctuations in a Driven Two-Level System

Simon Gustavsson·Jonas Bylander·William D. Oliver
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Abstract

In the presence of time-reversal symmetry, quantum interference gives strong corrections to the electric conductivity of disordered systems. The self-interference of an electron wavefunction traveling time-reversed paths leads to effects such as weak localization and universal conductance fluctuations. Here, we investigate the effects of broken time-reversal symmetry in a driven artificial two-level system. Using a superconducting flux qubit, we implement scattering events as multiple Landau-Zener transitions by driving the qubit periodically back and forth through an avoided crossing. Interference between different qubit trajectories give rise to a speckle pattern in the qubit transition rate, similar to the interference patterns created when coherent light is scattered off a disordered potential. Since the scattering events are imposed by the driving protocol, we can control the time-reversal symmetry of the system by making the drive waveform symmetric or asymmetric in time. We find that the fluctuations of the transition rate exhibit a sharp peak when the drive is time-symmetric, similar to universal conductance fluctuations in electronic transport through mesoscopic systems.

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Simon Gustavsson, Jonas Bylander, William D. Oliver. 2012-04-28. Time-Reversal Symmetry and Universal Conductance Fluctuations in a Driven Two-Level System. https://doi.org/10.1103/physrevlett.110.016603

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