One-Electron Occupation, Charge Sensing, and Spectroscopy in Si/SiGe Double Quantum Dots
A key missing ingredient on the path towards silicon quantum dot spin qubits has been a double quantum dot with one electron in each dot. I will discuss the demonstration of such a quantum dot and its verification using charge-sensing measurements with integrated quantum point contacts. One of the important features of silicon quantum dots is the strong energy-dependence of tunnel rates between the dots and the leads. I will show signatures of both very slow and very fast rates, and I will discuss the extent to which such rates can be tuned in-situ with gate voltages. The energy-dependence of tunneling enables measurements that would be much more difficult without it, including excited state spectroscopy and calibration of the relationship between gate voltage and energy in quantum dots. I will discuss data acquired using three quite different approaches to charge-sensing spectroscopy: dc-charge sensing, time-averaged charge sensing in the presence of rapid pulsed gate voltages, and real-time counting of individual electron tunneling events. The last of these methods is an essential ingredient for strong measurement in semiconductor quantum dot spin qubits. This work is supported by ARO and LPS, NSF, DOD, and DOE.