Non-Technical Abstract -- A key research problem in condensed-matter physics is the investigation of quantum coherence at the scale of circuits on a chip. Progress in this area could accelerate the pace of improvements necessary for implementing large-scale quantum computers and advance fundamental understanding of quantum mechanics at large scales. The goal of this Faculty Early Career Development project at Syracuse University is to build and measure circuits which can probe the quantum coherent properties of vortices that are guided through nanofabricated superconducting structures. Vortices are quantized bundles of magnetic flux which thread many different superconductors over a particular range of applied magnetic fields. The research project will make extensive use of the nearby, NSF-funded Cornell Nanoscale Facility. Quantum coherent circuits are currently outside the realm of the standard undergraduate curriculum and are unfamiliar topics to the general public, but are becoming highly relevant because of the emerging field of quantum information. Therefore, a new course on applied topics in quantum mechanics will be developed for the undergraduate physics program which will treat important modern problems. New experimental projects involving investigations of quantum coherence will be built for the upper-level undergraduate lab courses. Several public lectures on quantum coherent circuits will be given as part of an ongoing series at Syracuse.
-- A key research problem in condensed-matter physics is the investigation of quantum coherence at the scale of circuits on a chip. Progress in this area could accelerate the pace of improvements necessary for implementing large-scale quantum computers and advance fundamental understanding of quantum mechanics at large scales. The goal of this Faculty Early Career Development project at Syracuse University is to probe the quantum coherent properties of vortices that are guided through nanofabricated superconducting structures with feature sizes down to 100 nm. The research project will make extensive use of the nearby, NSF-funded Cornell Nanoscale Facility. Experiments will be developed to measure the quantum interference of a vortex that is permitted to follow two different paths and detect the tunneling of a single vortex by coupling the vortex to another quantum coherent superconducting device. Quantum coherent circuits are currently outside the realm of the standard undergraduate curriculum and are unfamiliar topics to the general public. Therefore, a new course on applied topics in quantum mechanics will be developed for the undergraduate physics program which will treat important modern topics, including the emerging field of quantum information. New experimental projects involving investigations of quantum coherence will be built for the upper-level undergraduate lab courses. Several public lectures on quantum coherent circuits will be given as part of an ongoing series at Syracuse.
My NSF CAREER research project has been directed at studying vortex dynamics and quantum coherent behavior at the scale of circuits on a chip. With these investigations, I have aimed to address fundamental issues, including the decoherence of macroscopic objects. From a technological standpoint, quantum coherent circuits could serve as the basic elements of a quantum computer, potentially capable of solving key problems that are intractable on the most powerful classical computers. Microfabricated superconducting structures for guiding vortices, quantized bundles of magnetic flux that penetrate through singularities in a superconducting condensate, provide a novel system to attack these problems. We have performed an extensive investigation of the behavior of these vortices at microwave frequencies and low temperatures using a system of superconducting resonators. At low temperatures, it is possible that quantum tunneling influences the vortex dynamics in the resonators. Most recently we have explored the dependence of the microwave response on the resonator geometry and microwave drive power. This work has resulted in a more complete understanding of the dynamics of vortices at high frequencies, something that is crucial to developing structures for observing and utilizing quantum coherent effects in vortex systems and other superconducting circuits. We have also developed nanostructured channels for constructing artificial ratchets where we have demonstrated the rectified motion of vortices in response to an oscillatory drive, thus providing an important model system for exploring ratchet phenomena. Artificial ratchets form a fundamental tool for exploring certain aspects of non-equilibrium statistical mechanics. In addition, ratchet dynamics may be important for understanding the behavior of certain molecular motors and could lead to a new class of microelectronic circuits based on the controlled motion of vortices. Throughout the course of this project, we have embarked on multiple collaborations, both international and domestic, for various aspects of device fabrication and analysis of experiments. We have also made extensive use of the NSF-funded Cornell NanoScale Facility, a one-hour drive from Syracuse, for fabricating the various superconducting devices that we have used in our experiments. This NSF CAREER project has served as the primary funding for two graduate students to complete their doctoral research and successfully defend their theses. In addition, this has provided funding for two more graduate students to begin experimental research on vortex dynamics in my lab. My research group members and I have given numerous conference and workshop presentations on this research and we have published seven papers on this work during the course of this project, including an invited review article that I wrote on the field of vortex ratchets in superconductors. Since the start of the project, I have given multiple public lectures on quantum coherent superconducting circuits and tours of our low-temperature laboratory for a variety of visiting groups. I have also incorporated various aspects of my research from this project into the different laboratory and introductory lecture courses that I have taught over the past several years.
