Search

Conventional transport methods provide quantitative information on spin, orbital, and valley states in quantum dots but lack spatial resolution. Scanning tunneling microscopy, on the other hand, provides exquisite spatial resolution at the expense of speed. Working to combine the spatial resolution and energy sensitivity of scanning probe microscopy with the speed of microwave measurements, we couple a metallic tip to a Si/SiGe double quantum dot (DQD) that is integrated with a charge detector. We first demonstrate that the dc-biased tip can be used to change the occupancy of the DQD. We then apply microwaves through the tip to drive photon-assisted tunneling (PAT). We infer the DQD level diagram from the frequency and detuning dependence of the tunneling resonances. These measurements allow the resolution of ∼65 μeV excited states, an energy consistent with valley splittings in Si/SiGe. This work demonstrates the feasibility of scanning gate experiments with Si/SiGe devices.

This paper describes a solid state system in which a qubit is realized as the spin of a single trapped electron in a quantum dot and read functionality is via an adjacent quantum wire with a single or a small number of conductive states. Because of the limited design window for this system, simulation is an important guide to an experimental search for successful designs. We use a semianalytic approximation that is accurate enough to provide meaningful results and computationally simple enough to allow high throughput, as needed for design and optimization. In particular, we find designs that achieve double pinchoff (i.e., a single trapped electron in the dot and a single conductive state in the wire). After relaxing the design requirements to allow for a small number of conductive states in the wire, we find successful designs that are optimally robust, in the sense that their success is unlikely to be affected by fabrication errors. [ABSTRACT FROM AUTHOR]