Author: Joel Stettenheim

Publisher:

Published: 2012

Total Pages: 262

ISBN-13:

Mesoscopic physics is a fascinating realm in which classical descriptions are usefully applied but wherein quantum behavior is strongly manifest. As such, it is an ideal arena for exploring the interplay between the classical and quantum worlds and the ways in which we can effectively control and coherently manipulate quantum systems with macrosopic inputs. Focusing on coupling between macroscopic and quantum systems, the first area of research presented in this thesis is our discovery and exploration of a naturally occurring feedback loop in which the mechanical motion of a macroscopic semiconductor crystal is controlled by the statistical fluctuations of tunneling electrons [1]. The second area of research presented in this thesis is a decription of our implementation of a system for the coherent manipulation of electronic spins using electron spin resonance. Consisting of a one-dimensional conduction channel and a tunable tunnel barrier, (quantum point contacts) QPCs are canonical quantum systems that display a rich array of physics [2-6]. In our GaAs system through piezoelectric coupling, the QPC current I probes the deformation of the host crystal and generates a naturally occurring feedback loop. Such systems with coupled mechanical and optical or electrical degrees of freedom [7], [8] have fascinating dynamics that, through macroscopic manifestations of quantum behavior [9], provide new insights into the transition between the classical and quantum worlds. The feedback, which is naturally associated with backaction, has been predicted to have significant consequences for the noise of a detector coupled to a mechanical oscillator [10], [11]. In our case the souce of the backaction is shot noise, and intrinsic noise source due to the stochastic partitioning of discrete charge flow by the QPC tunnel barrier. While ESR is conceptually relatively straight-forward, it is technically challenging to generate an ac magnetic field B[subscript ac] large enough to manipulate spins fast enough to perform meaningful quantum computation operations. In addition it is important to minimize the ac electric field E[subscript ac] which can cause sample heating and induce unwanted photon assisted transitions. As described in Chapter 3 in our ESR system, we address these issues by create a standing wave in a stripline and place the sample at a peak in B[subscript ac] and node in E[subscript ac].