Electrostatically-defined semiconductor quantum dot arrays offer a promising platform for quantum computation and quantum simulation. However, crosstalk of gate voltages to inter- dot tunnel couplings and dot potentials, and a limited sensing range of a charge sensor based on Coulomb repulsion, pose challenges for the control and readout of large-scale quantum dot arrays.

In this talk I will briefly introduce the basics of quantum-dot spin qubits, and then I will discuss two new techniques to overcome the challenges in scalability. First, while crosstalk to the dot potentials is routinely and efficiently compensated using virtual gates, due to exponential dependence of tunnel couplings on gate voltages, crosstalk to the tunnel couplings is currently compensated through a slow iterative process. Nevertheless, we show that the crosstalk on tunnel couplings can be efficiently characterized and compensated for, using the fact that the same exponential dependence applies to all gates [1]. We demonstrate efficient calibration of crosstalk in a quadruple quantum dot array and define a set of virtual barrier gates, with which we show orthogonal control of all inter-dot tunnel couplings. Next, we report on cascade- based fast, high-fidelity and scalable spin readout [2]. The cascade consists of an initial charge transition, far from the sensor, and subsequent charge transitions induced by Coulomb repulsion, with the final transition nearby the sensor. Combined with spin-to-charge conversion a cascade enables the readout of charge and spin occupation of quantum dots remote from the charge sensor. We demonstrate fast and high-fidelity spin readout by performing Pauli spin blockade with a cascade in a quadruple dot. Our work marks a key step forward in the control and readout of large-scale quantum dot arrays.

References
[1]T.-K. Hsiao, C. J. van Diepen et al, Efficient orthogonal control of tunnel couplings in a quantum dot array. Physical Review Applied 13, 054018 (2020).
[2]C. J. van Diepen, T.-K. Hsiao et al, Electron cascade for distant spin readout . Nature Communications (accepted). arXiv:2002.08925 (2020).