Electrometer

Abstract: The mechanical detection of charge has a long history, dating back more than 200 years to Coulomb's torsion-balance electrometer. The modern analogues of such instruments are semiconductor-based field-effect devices, the most sensitive of which are cryogenically cooled single-electron transistors. But although these latter devices have extremely high charge sensitivity, they suffer from limited bandwidth and must be operated at millikelvin temperatures in order to reduce thermal noise. Here we report the fabrication and characterization of a working nanometre-scale mechanical electrometer. We achieve a charge sensitivity of 0.1 e Hz^(-0.5), competitive with conventional semiconductor field-effect transistors; moreover, thermal noise analysis indicates that the nanometre-scale electrometer should ultimately reach sensitivities of the order of 10^(-6) e Hz^(-0.5), comparable with charge-detection capabilities of cryogenic single-electron transistors. The nanometre-scale electrometer has the additional advantages of high temperature (≥4.2 K) operation and response over a larger bandwidth, from which a diversity of applications may result.

Abstract: A new method is described for the measurement of electron mobilities in gases. An electrical shutter method is employed in which the shutters take the form of two fine wire grids, alternate wires of which are connected to a high frequency alternating potential. Electrons pass through the grids only when the potential between adjacent grid wires is zero, and only electrons which cross the gas space in one half-cycle are received at the collecting electrode. A sharp maximum is thus observed in the electrometer current when the drift velocity of the electron multiplied by the time of one half-cycle is equal to the distance between the grids. The theoretical shape of the current curve is compared with experiment and good agreement observed. Measurements have been made between $\frac{X}{p}$ of 0.03 and 20, and the values obtained are compared with the Compton mobility equation.

Abstract: State readout is a key requirement for a quantum computer. For semiconductor-based qubit devices it is usually accomplished using a separate mesoscopic electrometer. Here we demonstrate a simple detection scheme in which a radio frequency resonant circuit coupled to a semiconductor double quantum dot is used to probe its charge and spin states. These results demonstrate a new noninvasive technique for measuring charge and spin states in quantum dot systems without requiring a separate mesoscopic detector.