NSF/DMR-BSF: Quantum Transport in a Helical One-Dimensional System

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Non-technical abstract: The invention of the silicon transistor and decades of research development by academia and industry led to the current era of rapid information processing and propagation characterized by computers and the internet. The silicon transistor is rapidly approaching its limit of performance. To go beyond the conventional silicon technology requires drastically different paradigms that are fundamentally quantum in nature and operate on new materials and device concepts that are yet to be discovered. Quantum wires that can carry current without dissipating energy and transport information-carrying quantum states without losing coherence are an important building block of the next-generation quantum computers and quantum networks. In prior research, the PI's lab discovered a new type of quantum wire that has the above potential. The objectives of this project are to further understand the fundamental properties of the wires and develop its technological potential by constructing nanoscale devices and performing measurements in such systems. Knowledge gained in this research is expected to have significant impact on the development of quantum electronics. The research activities aim to educate the next-generation workforce of quantum technologies. Technical abstract: The PI's lab recently pioneered a new one-dimensional helical system in bilayer graphene known as the kink states, where the valley degrees of freedom of an electron is locked to its direction of propagation. Electrons moving in opposite directions carry opposite valley indices. The valley-momentum locked quantum wires display excellent ballistic transport properties and support the operations of a topological valley valve, a waveguide and a tunable electron beam splitter, which the PI's lab demonstrated. This project seeks to further develop capabilities to manipulate and probe interactions of the kink states beyond conductance measurements. The research activities aim to construct a quantum point contact and utilize the versatile tunability of the platform to systematically examine the controlled coupling of the kink states at the quantum point contact, in particular signatures of interacting one-dimensional systems. The construction of a Mach-Zehnder interferometer enables the studies of phase coherence transport of the kink states. Research efforts also include coupling the kink states to a high upper-critical-field superconductor through superconductor-kink-superconductor junctions and understanding the supercurrent distribution carried by the kink states. These experiments lay the foundation of pursuing emergent phenomena in superconductor-kink hybrid structures. Experiments are aided by theoretical efforts in the interpretation and prediction of measurements. Experimental and theoretical knowledge obtained in this project fundamentally enrich the understandings of topology, superconductivity and one-dimensional physics. The research activities equip students of all levels with necessary skills to pursue careers in STEM fields and summer camp activities promote science leadership among high school students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.