Condensed Matter Seminar Series

Controlling the Shot Noise of a Quantum Point Contact via Coupling to a Mechanical Resonance

Alex Rimberg

Dartmouth College

Thursday May 14,  11:00,  Room 298,  Physics Building

A canonical one-dimensional system, the quantum point contact (QPC) has been extensively studied for almost twenty years.  Shot noise in QPCs, which is subtle probe providing information about the system’s quantum nature, has been measured for more than ten.  Nonetheless, this simplest of quantum systems continues to surprise.  We have recently performed the first broadband frequency resolved measurements of shot noise in a radio frequency QPC. Our measurements reveal a remarkable frequency dependence entirely absent from over two decades of theoretical investigation.  Our data suggest a piezoelectric mediated feedback loop in which shot noise drives resonant mechanical vibrations of the sample that in turn create correlations in the tunnelling of electrons.  The feedback loop concentrates the initially white noise in a narrow band around the sample’s resonant frequency.  This allows us to not only clearly observe the faint shot noise signal but also to engineer the spectrum to suppress the shot noise in an approximately 1 MHz detection bandwidth.  As the ultimate sensitivity and quantum mechanical backaction of a QPC charge sensor is determined by its shot noise, our ability to control the shot noise spectrum likely has important implications for how closely a QPC sensor can approach the quantum limit for charge detection.  Our results also suggest application to extremely sensitive displacement detection as we show that our ability to measure the weak shot noise signal corresponds to sensing vibrations at the sample edge of only a few angstroms.

Host: Gleb Finkelstein

Return to Condensed Matter Seminars Main Page

Return to Physics Main Page