Real-time detection of single-electron tunneling using a quantum point contact

We observe individual tunnel events of a single electron between a quantum dot and a reservoir, using a nearby quantum point contact (QPC) as a charge meter. The QPC is capacitively coupled to the dot, and the QPC conductance changes by about 1% if the number of electrons on the dot changes by one. The QPC is voltage biased and the current is monitored with a current–voltage $(I–V)$ convertor at room temperature. We can resolve tunnel events separated by only $8\mu \mathrm{s}$ , limited by noise from the $I–V$ convertor. Shot noise in the QPC sets a $25\mathrm{ns}$ lower bound on the accessible timescales.