# Dispersive Gate Sensing the Quantum Capacitance of a Point Contact

## TL;DR

Dispersive gate sensing (DGS) is extended to detect quantum capacitance changes in open quantum systems, revealing detailed electronic features and potential for qubit tuning and charge configuration probing beyond traditional transport methods.

## Contribution

The paper introduces the extension of DGS to open regimes, enabling the detection of quantum features in systems with many electrons and providing new insights into quantum device characterization.

## Key findings

- DGS can resolve Van Hove singularities in ballistic systems.
- DGS probes potential landscapes not accessible by dc transport.
- DGS has potential applications in qubit tuning and charge state detection.

## Abstract

The technique of dispersive gate sensing (DGS) uses a single electrode to readout a qubit by detecting the change in quantum capacitance due to single electron tunnelling. Here, we extend DGS from the detection of discrete tunnel events to the open regime, where many electrons are transported via partially- or fully-transmitting quantum modes. Comparing DGS with conventional transport shows that the technique can resolve the Van Hove singularities of a one-dimensional ballistic system, and also probe aspects of the potential landscape that are not easily accessed with dc transport. Beyond readout, these results suggest that gate-sensing can also be of use in tuning-up qubits or probing the charge configuration of open quantum devices in the regime where electrons are delocalized.