Transport measurements of electrons above shallow helium-filled microchannels

The spins of electrons floating on superfluid helium constitute a promising platform for quantum computation. Quantum devices for electrons on helium, such as electrostatically defined quantum dots, require gate electrodes that are patterned beneath thin helium films. This can be particularly challenging at helium depths below 1 μm, since the electrons can be trapped by potential fluctuations on the surface of the gate electrode resulting from surface roughness and variations in the work function.

In this talk, we report transport measurements of electrons on helium in a microchannel device where the channels are 200 nm deep and 3 μm wide. The channels are fabricated above amorphous metallic TaWSi, which has surface roughness below 1 nm and minimal variations in work function across the surface due to the absence of polycrystalline grains. We are able to set the electron density in the channels using a ground plane, obtaining electron densities as high as 2.56×10⁹ cm^-2. We also demonstrate control of the transport using a barrier which enables pinchoff at a central microchannel connecting two reservoirs. The mobility of electron transport through the central microchannel is at least 300 cm²/Vs.