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Register a new userPiezoacoustics for precision control of electrons floating on helium
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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.
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The system of electrons trapped in vacuum above the liquid helium surface displays the highest mobilities known in condensed matter physics. We provide a brief summary of the experimental and theoretical results obtained for this system. We then show that a quasi-2D set of N > 10^8 electrons in vacuum trapped in 1D hydrogenic levels above a micron-thick helium film can be used as an easily manipulated strongly interacting set of quantum bits. Individual electrons are laterally confined by micron sized metal pads below the helium. Information is stored in the lowest hydrogenic levels. Using electric fields at temperatures of 10 mK, changes in the wave function can be made in nanoseconds. Wave function coherence times are .1 millisecond. The wave function is read out using an inverted dc voltage which releases excited electrons from the surface, or using SETs attached to the metal pads which control the electrons.
We consider the application of a small in-plane magnetic field to electrons on a helium surface in a perpendicular magnetic field. Certain states that were bound to the helium surface then dissolve into the continuum turning into long-lived resonances. As a result microwave absorption lines acquire an asymmetric Fano lineshape that is tunable by varying the microwave polarisation or the in-plane magnetic field. Electrons trapped in a formerly bound state will tunnel off the surface of helium; we show that under suitable circumstances this ``radioactive decay can show damped oscillations rather than a simple exponential decay. The mechanism for oscillatory exponential decay is not specific to electrons on Helium and this effect may also be relevant elsewhere in physics.
Single electrons can be conceived as the simplest quantum nodes in a quantum network. Between electrons, single photons can act as quantum channels to exchange quantum information. Despite this appealing picture, in conventional materials, it is extremely difficult to make individual electrons and photons coherently interact with each other at the visible-infrared wavelengths suitable for long-distance communication. Here we theoretically demonstrate that the self-confined single-electron structure in condensed helium-4 can be a fascinating candidate for single-electron quantum nodes. Each electron in helium forms a bubble of 1 to 2 nm radius and coherently interacts with mid-infrared photons. A parametrically amplified femtosecond laser can drive the electrons into any superposition between the ground and excited states. An electron inside a slot-waveguide cavity can strongly couple with cavity photons and exhibits vacuum Rabi oscillations. Two electrons in the cavity naturally generate entanglement through their respective coupling to the lossy cavity. The electron-in-helium system offers unique insight in understanding nonequilibrium quantum dynamics.
We report on an unconventional $macroscopic$ field effect transistor composed of electrons floating above the surface of superfluid helium. With this device unique transport regimes are realized in which the charge density of the electron layer can be controlled in a manner not possible in other material systems. In particular, we are able to manipulate the collective behavior of the electrons to produce a highly non-uniform, but precisely controlled, charge density to reveal a negative source-drain current. This behavior can be understood by considering the propagation of damped charge oscillations along a transmission line formed by the inhomogeneous sheet of two-dimensional electrons above, and between, the source and drain electrodes of the transistor.
Quantum annealing machines based on superconducting qubits, which have the potential to solve optimization problems faster than digital computers, are of great interest not only to researchers but also to the general public. Here, we propose a quantum annealing machine based on a semiconductor floating gate (FG) array. We use the same device structure as that of the commercial FG NAND flash memory except for small differences such as thinner tunneling barrier. We theoretically derive an Ising Hamiltonian from the FG system in its single-electron region. Recent high-density NAND flash memories are subject to several problems that originate from their small FG cells. In order to store information reliably, the number of electrons in each FG cell should be sufficiently large. However, the number of electrons stored in each FG cell becomes smaller and can be countable. So we utilize the countable electron region to operate single-electron effects of FG cells. Second, in the conventional NAND flash memory, the high density of FG cells induces the problem of cell-to-cell interference through their mutual capacitive couplings. This interference problem is usually solved by various methods using a software of error-correcting codes. We derive the Ising interaction from this natural capacitive coupling. Considering the size of the cell, 10 nm, the operation temperature is expected to be approximately that of a liquid nitrogen. If a commercial 64 Gbit NAND flash memory is used, ideally we expect it to be possible to construct 2 megabytes (MB) entangled qubits by using the conventional fabrication processes in the same factory as is used for manufacture of NAND flash memory. A qubit system of highest density will be obtained as a natural extension of the miniaturization of commonly used memories in this society.
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