Counting Individual Electrons on Liquid Helium
  We show that small numbers of electrons, including a single electron, can be held in a novel electrostatic trap above the surface of superfluid helium. A potential well is created using microfabricated electrodes in a 5 micron diameter pool of helium. Electrons are injected into the trap from an electron reservoir on a helium microchannel. They are individually detected using a superconducting single-electron transistor (SET) as an electrometer. A Coulomb staircase is observed as electrons leave the trap one-by-one until the trap is empty. A design for a scalable quantum information processor using arrays of electron traps is presented 
G. Papageorgiou (1), P. Glasson (1), K. Harrabi (1), V.Antonov (1),   E.Collin (2), P.Fozooni (1), P.G.Frayne (1), M.J.Lea (...