Gate-Sensing the Potential Landscape of a GaAs Two-Dimensional Electron Gas

In situ dispersive gate sensors hold potential as a means of enabling the scalable readout of quantum dot arrays. Sensitive to quantum capacitance, dispersive sensors have been used to detect inter- and intra-dot transitions in GaAs double quantum dots [1], and can distinguish the spin states of singlet triplet qubits [2]. In addition, the gate-sensing technique is likely of value in probing the physics of Majorana zero modes in nanowire devices [3]. Beyond the readout signatures associated with charge and spin configurations of qubits, gate-sensing is sensitive to trapped charge in the potential landscape. Here, we report gate-sensing signals arising from tunnelling of electrons between puddles of trapped charge in a GaAs 2DEG. We examine these signals in a family of different devices with varying mobilities, and as a function of temperature and bias. Implications for qubit readout using the gate-sensing technique are discussed. [1] Colless, J. et al. PRL 110, 046805 (2013), [2] House, M.G. et al, Nat. Comms. 6, 8848 (2015), [3] Karzig, T. et al, arXiv:1610.05289v2 (2016)