High-Sensitivity Charge Detection with a Single-Lead Quantum Dot for Scalable Quantum Computation*

We report the development of a high sensitivity semiconductor charge sensor based on a quantum dot coupled to a single lead, designed to minimize the geometric requirements of a charge sensor for scalable quantum computing architectures. The quantum dot is fabricated in Si:P using atomic precision lithography and its charge transitions are measured with rf reflectometry. A second quantum dot with two leads placed 42\,nm away serves as both a charge for the sensor to measure and as a conventional rf single electron transistor (rf-SET) with which to make a comparison of the charge detection sensitivity. We demonstrate sensitivity equivalent to an integration time of 550\,ns to detect a single charge with a signal-to-noise ratio of 1, compared with an integration time of 55\,ns for the rf-SET. This level of sensitivity is suitable for fast ($<15\,\mu$s) single-spin readout in quantum information applications, with a significantly reduced geometric footprint compared to the rf-SET. [Phys. Rev. Applied 6, 044016 (2016)]