Development of a displacement sensor towards detecting quantum fluctuations in nanoelectromechanical systems

Abstract

In condensed matter physics, it has been a long-standing goal to detect quantum mechanical behavior in macroscopic systems. Theoretically, a macroscopic system reveals its quantum dynamics when the mechanical quanta (hw) are not obscured by thermal fluctuations (kBT). The mechanical quanta will be observable if a mechanical resonator vibrates at GHz frequencies while kept at sub-Kelvin temperatures. Such a resonator's displacement fluctuations will be approximately a few femto-meters. Therefre, an ultra-sensitive and ultra-fast displacement sensor is desired to monitor the resonator's motion. Several research groups have been working at the edge of nanotechnology to develop such a high-performance resonator-sensor system. Despite the great effort, it has not been experimentally realized yet. In this thesis, we propose a new experimental methodology that has a major potential to approach the quantum limit. The method comprises of fabrication of a high frequency resonator with a built-in tunneling junction. Theoretical analyses reveal the clear advantage of a tunneling sensor over the presently applied capacitance based sensors. However, apparent complexities have detained their application to this problem. Here, we have developed and tested a new fabrication method that can overcome the major obstacles leading to application of this measurement scheme.