Quantum point contact galvanically coupled to planar superconducting resonator for ultra-sensitive broad-band electrical amplification

Abstract

\n Probing single charge dynamics in solids can give insights into various quantum transport phenomena, most of which are fragile and short-time-scaled. Detection of these events in real-time requires a mesoscopic electrical amplifier with unprecedented sensitivity and operational bandwidth. In this work, we explore a hybrid electrical amplifier consisting of a semiconducting quantum point contact galvanically coupled to a superconducting λ/2 transmission-line resonator for ultra-fast and ultra-sensitive charge amplification. The resonator, made of Aluminium with a coplanar waveguide geometry, is designed to operate at its first harmonic resonant mode ~ 3.4 GHz, where the reflected power from the resonator is amplitude-modulated by the conductance changes in the quantum point contact channel. From the sidebands of the amplitude modulated reflected signal we extract a conductance sensitivity of 2.85×10-7 (e2/h)/√Hz (11.05 pS∕√Hz). This sensitivity translates to a unit signal-to-noise measurement time ~ 1.62 ns for a variation of 0.01 (e2/h) in the conductance. The optimization of various operational parameters of the device reveals a bandwidth of ~ 155 MHz which corresponds to a rise-time ~ 2.2 ns. Both the sensitivity and bandwidth that we obtain are greater by an order compared to the existing reports. In addition, the device also exhibits very good sensitivities ~ 3.58×10-4 (e2/h)/√Hz up to a measurable frequency of 240 MHz. The extremely high sensitivity, ultra-fast operation reaching the nanosecond time-scales, and the circuit QED architecture makes this scheme an attractive choice for single charge detection and counting experiments for spin-qubit readout and quantum electrical metrology.