We report integrated charge sensing measurements on a Si/SiGe double quantum dot. The quantum dot is shown to be tunable from a single, large dot to a well-isolated double dot. Charge sensing measurements enable the extraction of the tunnel coupling t between the quantum dots as a function of the voltage on the top gates defining the device. Control of the voltage on a single such gate tunes the barrier separating the two dots. The measured tunnel coupling is an exponential function of the gate voltage. The ability to control t is an important step toward controlling spin qubits in silicon quantum dots.

We report the fabrication and measurement of one-electron single and double quantum dots with fast tunnel rates in a Si/SiGe heterostructure. Achieving fast tunnel rates in few-electron dots can be challenging, in part due to the large electron effective mass in Si. Using charge sensing, we identify signatures of tunnel rates in and out of the dot that are fast or slow compared to the measurement rate. Such signatures provide a means to calibrate the absolute electron number and verify single electron occupation. Pulsed gate voltage measurements are used to validate the approach.Comment: 4 pages, double column, 3 figure

We investigate the tunnel rates and energies of excited states of small numbers of electrons in a quantum dot fabricated in a Si/SiGe heterostructure. Tunnel rates for loading and unloading electrons are found to be strongly energy dependent, and they vary significantly between different excited states. We show that this phenomenon enables charge sensing measurements of the average electron occupation that are analogous to Coulomb diamonds. Excited-state energies can be read directly from the plot, and we develop a rate model that enables a quantitative understanding of the relative sizes of different electron tunnel rates.

Quantum dots in Si have attracted recent interest due to the possibility of long spin relaxation and spin dephasing times in this material. Si/SiGe heterostructures are a particularly promising host for Si quantum dots, because the epitaxial interfaces that define the quantum well are believed to have very low defect density. Here we discuss recent results demonstrating that gatetunable quantum dots containing individual electrons can be reproducibly produced in the Si/SiGe materials system. We discuss the tunability of the tunnel rates to the leads, the role of such tunnel rates in the determination of the absolute number of electrons in the quantum dots, and the role of the interdot tunnel rate in double quantum dots.