Quantum interference and phonon-mediated back-action in lateral quantum-dot circuits

Abstract

Spin qubits have been successfully realized in electrostatically defined, lateral few-electron quantum-dot circuits. Qubit readout typically involves spin to charge information conversion, followed by a charge measurement made using a nearby biased quantum point contact (QPC). It is critical to understand the back-action disturbances resulting from such a measurement approach. Previous studies have indicated that QPC detectors emit phonons which are then absorbed by nearby qubits. We report here the observation of a pronounced back-action effect in multiple dot circuits, where the absorption of detector-generated phonons is strongly modified by a quantum interference effect, and show that the phenomenon is well described by a theory incorporating both the QPC and coherent phonon absorption. Our combined experimental and theoretical results suggest strategies to suppress back-action during the qubit readout procedure. © 2012 Macmillan Publishers Limited. All rights reserved.