Measuring the Charge Parity of an InAs Double Quantum Dot

We have fabricated tunable, few electron InAs nanowire double quantum dots (DQDs) which support rapid electrically driven single spin rotations.\footnote{M. D. Schroer, K. D. Petersson, M. Jung and J. R. Petta, Phys. Rev. Lett. \textbf{107}, 176811 (2011).} However, the measurement of nanowire DQDs presents an outstanding problem, typically relying on transport through the sample due to the lack of a local quantum point contact charge detector. We demonstrate a non-invasive charge sensing method based on a radio frequency measurement of the sample's complex admittance, which yields a fast and sensitive determination of the charge state.\footnote{M. Jung, M. D. Schroer, K. D. Petersson and J. R. Petta, Appl. Phys. Lett. \textbf{100}, 253508 (2012).} We show that this measurement is also sensitive to the spin state of the DQD, allowing a simple determination of the total charge parity in the sample.\footnote{M. D. Schroer, M. Jung, K. D. Petersson and J. R. Petta, Phys. Rev. Lett. \textbf{109}, 166804 (2012).} Radio frequency charge parity measurement may prove useful in high effective mass systems, such as Si/SiGe quantum dots, where the determination of the absolute charge number is not always feasible.