Piezoacoustics for precision control of electrons floating on helium

Piezoelectric surface acoustic waves (SAWs) are powerful for investigating and controlling elementary and collective excitations in condensed matter. In semiconductor two-dimensional electron systems SAWs have been used to reveal the spatial and temporal structure of electronic states, produce quantized charge pumping, and transfer quantum information. In contrast to semiconductors, electrons trapped above the surface of superfluid helium form an ultra-high mobility, two-dimensional electron system home to strongly-interacting Coulomb liquid and solid states, which exhibit non-trivial spatial structure and temporal dynamics prime for SAW-based experiments. Here we report on the coupling of electrons on helium to an evanescent piezoelectric SAW. We demonstrate precision acoustoelectric transport of as little as ~0.01% of the electrons, opening the door to future quantized charge pumping experiments. We also show SAWs are a route to investigating the high-frequency dynamical response, and relaxational processes, of collective excitations of the electronic liquid and solid phases of electrons on helium.

Coupling a single electron on superfluid helium to a superconducting resonator

Electrons on helium form a unique two-dimensional system on the interface of liquid helium and vacuum. A small number of trapped electrons on helium exhibits strong interactions in the absence of disorder, and can be used as a qubit. Trapped electrons typically have orbital frequencies in the microwave regime and can therefore be integrated with circuit quantum electrodynamics (cQED), which studies light–matter interactions using microwave photons. Here, we experimentally realize a cQED platform with the orbitals of single electrons on helium. We deterministically trap one to four electrons in a dot integrated with a microwave resonator, allowing us to study the electrons’ response to microwaves. Furthermore, we find a single-electron-photon coupling strength of $$g/2\pi =4.8\pm 0.3$$g∕2π=4.8±0.3 MHz, greatly exceeding the resonator linewidth $$\kappa /2\pi =0.5$$κ∕2π=0.5 MHz. These results pave the way towards microwave studies of Wigner molecules and coherent control of the orbital and spin state of a single electron on helium.

Single-File Transport of Classical Electrons on the Surface of Liquid Helium

Electrons trapped on the surface of liquid helium form a model two-dimensional system. Because the electron density is low (~ 109 cm-2) and the Coulomb interaction between the electrons is essentially unscreened, the system can be regarded as a classical analogue of the degenerate Fermi gas. Electrons on helium have therefore long been used to study many-body transport phenomena in two dimensions. Here we review recent experiments investigating the transport of electrons on helium through microscopic constrictions formed in microchannel devices. Two constriction geometries are studied; short saddle-point constrictions and long constrictions in which the length greatly exceeds the width. In both cases, the constriction width can be tuned electrostatically so that the electrons move in single file. As the width of the short constriction is increased, a periodic suppression of the electron current is observed due to pinning for commensurate states of the electron lattice. A related phenomenon is observed for the long constriction whereby the quasi-one-dimensional Wigner lattice exhibits reentrant melting as the number of electron chains increases. Our results demonstrate that electrons on helium are an ideal system in which to study many-body transport in the limit of single-file motion. [Formula: see text] Special Issue Comments: This article presents experimental results on the dynamics of classical electrons moving on the surface of liquid helium in narrow channels with constrictions, with a focus on the "quantum wire", i.e. single file, regime. This article is related to the Special Issue articles about advanced statistical properties in single file dynamics34 and the mathematical results on electron dynamics in liquid helium.35