CAREER: Hybrid Systems of Al/AlOx/Al Tunnel Junctions Coupled to Semiconductor Heterostructures

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

The project centers on hybrid systems of Al/AlOx/Al tunnel junctions coupled with semiconductor heterostructures. Arrays of Al/AlOx/Al tunnel junctions are known to form a system with macroscopic degrees of freedom that behave quantum mechanically. By fabricating such a system of tunnel junctions on a GaAs/AlGaAs heterostructure with an electron gas located near the top surface of the heterostructure, we can directly control the dissipation independently of other parameters, something not previously possible in any quantum system. One of the goals of this project is to implement this control over dissipation in various structures in order to study fundamental tunneling processes and quantum phase transitions. On the semiconductor side, the hybrids also make feasible many unique and potentially important experiments. In particular, we will use the hybrids to study two of the most basic aspects, the charge and the statistics, of the excitations of fractional quantum Hall liquids (FQHLs). Remarkably, the excitations of the FQHLs, also called Laughlin quasiparticles, are predicted to carry fractional charge and obey unusual fractional statistics different from that for fermions or bosons. Measurement of fractional statistics, which we hope to tackle using Al/AlOx/Al tunnel junctions, has been a longstanding challenge in the field of fractional quantum Hall effect. The research will be accompanied by a nationwide outreach program, in which high school students across the country will do collaborative measurements to determine the position of the North magnetic pole. Doing a measurement on such a global scale will provide an interesting and genuine scientific experience, which we hope will excite students about science in general. %%% Typically macroscopic objects, such as dust particles, billiard balls, and planets, obey Newtonian, or classical mechanics. Microscopic objects, such as electrons, atoms, and molecules, on the other hand, obey a different set of rules and behave quantum mechanically. Tunnel junctions composed of aluminum and aluminum oxide layers are unique, in that they are macroscopic objects, yet they have certain macroscopic features that behave quantum mechanically. By coupling such tunnel junctions to semiconductors, we can control the environment to which this quantum system is coupled to, something not previously possible in any quantum system. One of the goals of this project is to implement this control over the environment in various structures in order to study fundamental quantum processes that are relevant to a rich variety of systems. Tunnel junctions can also be used to make a new a kind of detector, known as a single electron transistor (SET), which are million times more charge sensitive than commercially available transistors. This extreme charge sensitivity of SETs makes feasible many unique and potentially important experiments. In particular, we will use the hybrids with SETs to study some of the remarkable properties of a new state of matter, known as a fractional quantum Hall liquid. New kinds particles arise in this new state matter with very unusual properties. Our research will take advantage of the extreme charge sensitivity of SETs to investigate these unusual properties of these new particles, which have been a longstanding challenge in the field of fractional quantum Hall effect. The research will be accompanied by a nationwide outreach program, in which high school students across the country will do collaborative measurements to determine the position of the North magnetic pole. Doing a measurement on such a global scale will provide an interesting and genuine scientific experience, which we hope will excite students about science in general. ***