Radio-Frequency-Detected Fast Charge Sensing in Undoped\nSilicon Quantum Dots

Abstract

Spin\nqubits in silicon quantum dots offer a promising platform\nfor a quantum computer as they have a long coherence time and scalability.\nThe charge sensing technique plays an essential role in reading out\nthe spin qubit as well as tuning the device parameters, and therefore,\nits performance in terms of measurement bandwidth and sensitivity\nis an important factor in spin qubit experiments. Here we demonstrate\nfast and sensitive charge sensing by radio frequency reflectometry\nof an undoped, accumulation-mode Si/SiGe double quantum dot. We show\nthat the large parasitic capacitance in typical accumulation-mode\ngate geometries impedes reflectometry measurements. We present a gate\ngeometry that significantly reduces the parasitic capacitance and\nenables fast single-shot readout. The technique allows us to distinguish\nbetween the singly- and doubly occupied two-electron states under\nthe Pauli spin blockade condition in an integration time of 0.8 μs,\nthe shortest value ever reported in silicon, by the signal-to-noise\nratio of 6. These results provide a guideline for designing silicon\nspin qubit devices suitable for the fast and high-fidelity readout.