Electron transport on thin helium film across mm long transport line*

Using the spins of surface state electrons on liquid helium as qubits is a promising quantum computing platform which leverages the clean vacuum-helium interface to achieve high coherence times. Qubit initialization for such a system will require the movement of electrons from bulk to thin films of helium, which provides accelerated thermalization due to Johnson noise currents. Here, we demonstrate the efficient transport of high densities of electrons across a ~50 nm thick van der Waals helium film. Electrons are transferred between two regions of bulk helium consisting of 600 nm tall, 10 um wide channels patterned above three electrodes, allowing for the use of the Sommer-Tanner method to determine electron density. Connecting these two regions is a 5.6 um wide, 4 mm long transport line fabricated with resistive (.0056 ohm-cm at 1.8 K), amorphous NbSi which allows for reduced variations in work function and an ultrasmooth surface. When a voltage is applied along this thin, resistive gate we establish a constant electric field on the electrons. Furthermore, by pulsing underlying gates positive and negative at each end of the transport region, the movement of electrons in and out of the thin film region can be timed to determine a time-of-flight electron mobility.