Non-invasive detection of single-electron processes

Electrical transport measurement can be made 'non-invasively' by capacitively coupling a detector circuit with known behaviour to a quantum device. This allows much more sensitive measurements to be performed; since no electrons are exchanged with the device, the amount of disturbance can be reduced. The sensing circuit is still operational in regimes of extreme low current in the quantum device. This article is a review of work with two non-invasive probes: a voltage probe capable of sensing single-electron effects at currents of order 10(-17) A, and a capacitance detector which is able to detect the localization of electrons where no electrons move on a timescale of seconds.