Near quantum limited measurement in nanoelectromechanical systems

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Nanoelectromechanical systems have many potential applications in nanoelectronics as well as in fundamental studies of quantum mechanics in mesoscopic systems. Nanoelectromechanical systems have been touted as an extension of microelectromechanical systems which would operate at higher frequencies and consume far less power due their higher quality factors. Since these systems can be cooled close to their ground states with existing cryogenic techniques, they are useful tools to study the quantum effects like backaction, coherent states and superposition in mesoscopic mechanical systems. Also there have been proposals to use these systems as qubits and buses in quantum computing.

In this thesis I discuss the effects of the backaction of a superconducting single electron transistor that measures the position of a radio frequency nanomechanical resonator. One of the novel effects of this backaction is the cooling of the nanomechanical resonator. The fact that a system can be cooled by merely coupling it to noisy non-equilibrium device is a counterintuitive phenomenon. Although backaction effects have been used to produce ultra-cold atoms, our results are the first demonstration of this cooling effect in a mesoscopic system. For a linear continuous position detection scheme, quantum mechanics places a lower limit on the product of position shot noise, Sx, and the backaction force noise, SF, which is given by,

(S_x S_F)^(1/2)> hbar/2

As part of this work we demonstrate that our detection scheme is only 15 times away from this limit and only 4 times away from quantum limit for position sensitivity.