Probing the limits of gate-based charge sensing

TLDR

Quantum computation demands qubit‑specific readout, and solid‑state designs use external electrometers, but an in‑situ gate sensor can replace them by coupling the qubit to a resonant circuit to probe its radiofrequency polarizability. We investigate the ultimate performance of resonant gate‑based readout and the noise sources that limit it. We discuss experimental factors limiting gate detection and highlight ways to optimize its sensitivity. We achieve a charge sensitivity of 37 µe Hz⁻¹/², the best reported for this technique, and show that resonant gate‑based readout offers higher sensitivity and fewer circuit elements than external electrometers. The authors are Gonzalez‑Zalba et al.

Abstract

Quantum computation requires a qubit-specific measurement capability to readout the final state of individual qubits. Promising solid-state architectures use external readout electrometers but these can be replaced by a more compact readout element, an in situ gate sensor. Gate-sensing couples the qubit to a resonant circuit via a gate and probes the qubit's radiofrequency polarizability. Here we investigate the ultimate performance of such a resonant readout scheme and the noise sources that limit its operation. We find a charge sensitivity of 37 μe Hz−1/2, the best value reported for this technique, using the example of a gate sensor strongly coupled to a double quantum dot at the corner states of a silicon nanowire transistor. We discuss the experimental factors limiting gate detection and highlight ways to optimize its sensitivity. In total, resonant gate-based readout has advantages over external electrometers both in terms of reduction of circuit elements as well as absolute charge sensitivity. Reading out the state of quantum bits is an essential requirement that any quantum computer implementation must satisfy. Gonzalez-Zalba et al. now show that in situresonant gate-based detection can be a more sensitive approach than external electrometers while reducing the qubit architecture's complexity.