Tunneling and Bulk Resistance Measurements in the Fractional Quantum Hall States

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

Technical Abstract The properties of the quasiparticles in the fractional quantum Hall states are different from those of non-interacting particles, which are either Fermions or Bosons. It is predicted that in most fractional quantum Hall states the interchange of quasiparticles results in a change of the wave function by a phase factor that is a complex number, with magnitude one, but different from +/-1, as for Fermions and Bosons. Even more surprising is the possibility, for a special state at filling fraction i= 5/2, that interchange of the particles does not simply change the wave function's phase, but results in a completely different wave function. For this case, the statistics are called non-Abelian. To determine the statistics of quasiparticles requires building an interferometer, in which the quasiparticles can travel on two distinct paths to the detector. Experiments are proposed to study the tunneling process by which the particles access the two paths, and, once it is understood, to create an interferometer to test the ideas about non-Abelian statistics. This research could contribute to the development of strategies for quantum computing. The education of graduate students and postdoctoral scientists in the kind of research proposed here is very valuable. By learning nano-fabrication techniques, ultra-low temperature physics techniques, as well as thinking deeply about fundamental physics issues, young people become extremely valuable to small and large businesses, as well as to academia. Non-Technical Abstract Research is proposed to study a novel system, which might be the basis of a quantum computer. It has been shown that such a computer could solve problems that conventional computers cannot. For example, a classical computer cannot factor very large numbers into its prime factors. This fact is used to protect our bank accounts and many of the Nation's defense secrets. However, a quantum computer could do this. No one has built such a quantum computer yet, but if it can be done, it is important for us to do it in the US first, so that new approaches to security can be found. The work proposed here is to study a system, which might be useful for quantum computing. When electrons are forced to move in only two dimensions inside semiconductors and are placed in a strong magnetic field, they form a kind of liquid, with special properties. The liquid acts as though it is made of new particles, instead of electrons, and these new particles may be used for quantum computing. Graduate students and postdoctoral researchers working on this project will learn semiconductor technology as well as learning the deep physics of quantum mechanics. This will prepare them to work in small and large corporations on forefront technologies that will make the Nation more competitive.