A high-sensitivity gate-based charge sensor in silicon
  The implementation of a quantum computer requires a qubit-specific measurement capability to read-out the final state of a quantum system. The model of spin dependent tunneling followed by charge readout has been highly successful in enabling spin qubit experiments in all-electrical, semiconductor based quantum computing. As experiments grow more sophisticated, and head towards multiple qubit architectures that enable small scale computation, it becomes important to consider the charge read-out overhead. With this in mind, Reilly et al. demonstrated a gate readout scheme in a GaAs double quantum dot that removed the need for an external charge sensor. This readout, which achieved sensitivities of order me/$\sqrt(Hz)$, was enabled by using a resonant circuit to probe the complex radio-frequency polarisability of the double quantum dot. However, the ultimate performance of this technology and the noise sources that limit it remain to be determined. Here, we investigate a gate-based readout scheme using a radio-frequency resonant circuit strongly coupled to a double quantum at the corner states of a silicon nanowire transistor. We find a significantly improved charge sensitivity of 37 $\mu$e/$\sqrt(Hz)$. By solving the dynamical master equation of the fast-driven electronic transitions we quantify the noise spectral density and determine the ultimate charge and phase sensitivity of gate-based read-out. We find comparable performance to conventional charge sensors and fundamental limits of order ne/$\sqrt(Hz)$ and $\mu$rad/$\sqrt(Hz)$, with the gate-based sensor improving on standard detection for certain device parameters. Our results show that, especially in state-of-the-art silicon qubit architectures, charge detection by probing the complex polarisability has advantages in terms of reducing the readout overhead but also in terms of the absolute charge sensitivity. 
M. F. Gonzalez-Zalba, A. J. Ferguson, S. Barraud, A. C. Betz
cond-mat.mes-hall