Radio-frequency point-contact electrometer

We fabricate and characterize a radio-frequency semiconductor point-contact electrometer (RF-PC) analogous to radio-frequency single-electron transistors [RF-SETs, see Science {\bf 280}, 1238 (1998)]. The point contact is formed by surface Schottky gates in a two-dimensional electron gas (2DEG) in an AlGaAs/GaAs heterostructure. In the present setup, the PC is operating as a simple voltage-controlled resistor rather than a quantum point contact (QPC) and demonstrates a charge-sensitivity about $2\times 10^{-1} \mathrm{e/\sqrt{Hz}}$ at a bandwidth of $30 \mathrm{kHz}$ without the use of a cryogenic RF preamplifier. Since the impedance of a typical point-contact device is much lower than the impedance of the typical SET, a semiconductor-based RF-PC, equipped with practical cryogenic RF preamplifiers, could realize an ultra-fast and ultra-sensitive electrometer.