Shot-Noise-Driven Macroscopic Vibrations and Displacement Transduction in Quantum Tunnel Junctions

Abstract

Back-action is an inevitable result of quantum measurement. Although the microscopic impacts of shot-noise back-action have been explored, macroscopic evidence is seldom documented, especially in the field of electrical transport. Tunneling shot-noise has been shown to excite the fundamental flexural mode of the host crystal using a sub-GHz lumped-element radio-frequency quantum point contact (QPC). In this study, this aspect of shot-noise back-action is examined at much higher operational frequencies and wider bandwidths by employing a GaAs QPC integrated into a planar superconducting cavity within the circuit-QED framework, leading to the observation of the excitation of multiple mechanical modes. The device operates in the shot-noise-limited regime. Constructed on a piezoelectric platform, there is positive feedback between the electrical and mechanical degrees of freedom within the QPC. Shot-noise excites piezoelectric vibrational modes; concurrently the resulting polarization charges enhance tunneling and develop peaks in the shot-noise spectra at the modal frequencies. The excitation of vibrational modes is a macroscopic demonstration of measurement back-action, and the amplitudes of the noise-peaks enable us to calibrate the displacement sensitivity of the QPC-resonator systems, which is in the range $\approx 35fm/\surd Hz$, making it an excellent sensor for ultra-sensitive and rapid strain/displacement detection.