Fluctuation Phenomena and Measurement Theory in Mesoscopic Electronic and Optical Systems

Yale University, New Haven CT

Investigators

Abstract

This theoretical research has two different focus areas: nanoelectronic devices for ultrasensitive detection and amplification, and microcavity resonators and lasers, typically on the size scale of 10-100 microns. The electronic aspect of the project will analyze the conditions under which a mesoscopic detector achieves quantum-limited detection, which refers to a measurement with the minimum degree of backaction on the measured quantum system allowed by the uncertainty principle. Such questions are of relevance in quantum information physics where the measured quantum system would be a quantum bit and the detector is the read-out device. The same condition determines the minimum noise associated with any quantum system that acts as an amplifier due to the presence of zero point fluctuations. Earlier work analyzing mesoscopic scattering detectors without electron-electron interactions found a simple condition for reaching the quantum limit which can be expressed information-theoretically: There should be no information about the measured system imprinted in the input variable to the detector which is not extracted by measuring the output variable. In the current project the quantum limit condition will be analyzed for interacting detectors, specifically mesoscopic scattering detectors (resonant tunneling structures) in the presence of dephasing, and semiconducting quantum dots near the charge degeneracy points. It is hoped that general information-theoretic principles will also be developed to understand qualitatively the approach to the quantum limit of detection in wider classes of quantum amplifiers such as metallic and superconducting single-electron transistors and superconducting quantum interference devices. The optics aspect of the project treats dielectric microcavity resonators and lasers, which, due to their asymmetric shape, generate complex, and at least partially chaotic, ray dynamics. Despite the presence of ray chaos, such resonators have high-Q resonances with directional emission, making them potentially useful for integrated optical devices when compared to standard whispering gallery resonators with circular symmetry. The project will analyze the predicted enhancement of the rate of evanescent leakage (tunneling of photons) out of such high-Q resonances due to the effect of ray chaos. It will also analyze the mode-locking behavior, which is expected to occur in the non-linear regime of such resonators, specifically focusing on the case of stable orbit multiplets which can be calculated analytically. A more general theory of lasing in such complex resonators will be developed with the aim of understanding mode competition and the enormous increase in output power such lasers display in comparison to microcylinder lasers. The photon statistics of such resonators and lasers is predicted to be very different from conventional lasers and will be studied in detail during this project with the goal of proposing novel and interesting experiments. Both of these focus areas of research have a broader impact on current science and technology. The properties of quantum amplifiers have become of great importance in the field of quantum information physics and quantum computation. As is now well known, quantum information processors are predicted to have revolutionary properties such as an exponential speed-up of factoring algorithms for decoding. Solid-state superconducting qubits are a reality and the measuring devices to manipulate them and read them out are being developed worldwide; this has brought the abstract topic of quantum measurement theory into the real world of the physics of nanostructures. This research addresses several important questions in this field. The optics area relates to several problems of current technological interest. First, it relates to the development of integrated optical technology for communication applications; and second it relates to the development of novel blue and ultraviolet semiconductor light sources which will be important for lithographic, sensing, display and data storage applications. Three inventions relating to these areas have been patented based on earlier stages of this research. %%% This theoretical research has two different focus areas: nanoelectronic devices for ultrasensitive detection and amplification, and microcavity resonators and lasers, typically on the size scale of 10-100 microns. With both topics, the research blends fundamental research with possible technological applications. Besides the fundamental nature of the research, the technological applications touch on quantum information systems and novel light sources for application in advanced computers. Both graduate students and postdoctoral associates will participate in the project. ***