Spatial distribution of electrons on a superfluid helium charge-coupled   device
  Electrons floating on the surface of superfluid helium have been suggested as promising mobile spin qubits. Three micron wide channels fabricated with standard silicon processing are filled with superfluid helium by capillary action. Photoemitted electrons are held by voltages applied to underlying gates. The gates are connected as a 3-phase charge-coupled device (CCD). Starting with approximately one electron per channel, no detectable transfer errors occur while clocking $10^9$ pixels. One channel with its associated gates is perpendicular to the other 120, providing a CCD which can transfer electrons between the others. This perpendicular channel has not only shown efficient electron transport but also serves as a way to measure the uniformity of the electron occupancy in the 120 parallel channels. 
Maika Takita, F.R. Bradbury, T.M. Gurrieri, K.J. Wilkel, Kevin Eng,   M.S. Carroll, S.A. Lyon
cond-mat.mes-hall