Gates, Readout, and Simulation with Spin Qubits

Electron cotunneling in semiconductor quantum dots refers to higher-order transport processes in which two or more charge carriers tunnel simultaneously. These phenomena have been typically studied in the context of direct transport measurements and have been utilized for fundamental purposes such as quantum dot energy-level spectroscopy with enhanced resolution [1]. Here, we expand this picture to alternating cotunneling events through quantum dot systems subject to radiofrequency excitation. We theoretically explore and experimentally demonstrate these AC cotunneling events in multi-quantum dot systems and exploit them for charge polarizability measurements with enhanced sensitivity with respect to more established techniques such as in-situ dispersive readout [2]. Particularly, we introduce a new charge polarizability detection method, which we dub the radio-frequency electron cascade, that leverages the synchronised single-electron AC currents in a three-quantum dot system to produce signal enhancement of interdot charge transitions. Our discovery expands the portfolio of rf readout methods in semiconductor nanostructures and provides a route to increased dispersive readout fidelity in semiconductor quantum computing architectures.

[1] De Franceschi, S., et al. "Electron cotunneling in a semiconductor quantum dot." Physical review letters 86.5 (2001): 878.

[2] Gonzalez-Zalba, M. F., et al. "Probing the limits of gate-based charge sensing." Nature communications 6.1 (2015): 1-8.