Abstract

Quantised charge transport devices have been studied over the last two decades, mainly for their promising application as standards for electrical current in the field of quantum metrology. The ability to transport a precise number of electrons (holes) from a source to a drain at a well-known frequency allows for the redefinition of the SI base unit for current, the ampere, in terms of a clock cycle and the elementary charge; a fundamental invariant of nature (or so we have good reason to believe).

For a practical standard based on quantised charge transport, it is necessary for the magnitude of generated current to be greater than a nanoampere with an accuracy of one part in ten billion. These goals have not yet been reached simultaneously.

I will, in a roughly chronological order, list the different types of quantised charge transport devices that have been developed since the early ‘90s. In each case, I will highlight their specific strengths and weaknesses in the race to redefine the ampere. I will then discuss in detail the high-frequency fixed-barrier GaAs/AlGaAs electron pump, first developed within our group several years ago. I will present results from our recent measurements using a perpendicular magnetic field where we demonstrate the most accurate source of quantised current above 50pA. I will show that our pumps are parallelisable, increasing the output current without significant loss of quantisation. I will also present experimental data and results from simulations by Dr Adam Thorn with the aim to argue the case that our electron pump devices may prove to be extremely useful tools for probing fundamental charge interactions in dynamic quantum dot potentials.