Fundamental Experimental Properties of Mesoscopic Systems

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This research is focused on investigations of the quantum mechanical phase coherence properties of mesoscopic devices. At low temperatures, most mesoscopic circuits only exhibit coherence times between 0.05 to 10 ns and it is believed that much longer times will be required to make functional quantum devices. This work will systematically explore the phase coherent transport and magnetic properties of mesoscopic systems on time scales much shorter and much longer than the phase coherence time. Studies of the effect of 0 to 26 GHz measurement currents on decoherence in metals (with and without magnetic impurities) and semiconductors will be made. Measurements of the thermodynamic electron temperature in a variety of mesoscopic samples will be made using SQUID based noise thermometer techniques in order to check the recent theoretical prediction that thermodynamics may break down in small devices. The goal of all this work is to understand how the high frequency, material, and geometrical properties effect the quantum coherence properties of small systems. The graduate students involved with this program will learn how to fabricate a variety of quantum devices using modern fabrication techniques, measure these devices using state-of-the-art techniques, and will comprehend a wide body of solid state theory. All these skills are necessary in order to become successful in an industrial, government, or university career.%%%The low temperature properties of all electrical circuits can be significantly changed when the dimensions of the elements are reduced below a few microns. Quantum effects such as electron interference and charge quantization are responsible for many of the large conductance fluctuations observed in these devices and have kindled hope that a revolutionary new class of fast coherent quantum devices can be built to help fuel the continuing progress in the microelectronics industry. Many of the proposed new devices require long electron coherence times in order to maximize the signal, yet most nano-scale circuits only exhibit coherence times between 0.05 to 10 nanoseconds. This proposed research is focused on understanding the underlying physics that controls the phase coherence time in small electrical circuits with the expectation that we will be able to discover ways to increase this time. We will systematically explore the phase coherent transport properties of small quantum systems on time scales much shorter and much longer than the phase coherence time in an attempt to understand if we can manipulate the quantum state without causing decoherence. The graduate students involved with this program will receive the training necessary to become a future generation of microelectronic scientists. They will learn how to fabricate a variety of quantum devices using modern fabrication techniques and measure these devices using state-of-the-art techniques. All these skills are necessary in order to become successful in an industrial, government, or university career.