Gate Dispersive Charge Detection in Ge/SiGe Quantum Dots

Abstract

Spin qubits are an attractive platform for scalable quantum information processing, and recently, laterally gated quantum dots (QDs) in Ge heterostructures have emerged as a leading implementation of spin qubits. To date, RF single-hole transistors (SHT) and integrated superconducting resonators have been used for spin and charge readout, but their size can pose challenges. Here we demonstrate compact RF gate-dispersive charge readout of a Ge double QD (DQD), and a single hole box (SHB)-DQD system. We resolve QD loading and interdot transitions with both techniques. We find that the SHB enhances the interdot signal-to-noise ratio (SNR) of our 540 MHz circuit by a factor of 20 for a DQD coupling $t_c \approx 5$ GHz, providing a unity-SNR at 135 microseconds, c.f. for 2.7 miliseconds for the direct detection. Power- and temperature-dependent measurements verify that SNR is limited by dielectric loss which compromises impedance matching. These results establish a compact readout approach based on gate-dispersive detection for Ge/SiGe heterostructure QDs.