MACROSCOPIC PHASE COHERENCE FROM SYNTHETIC INTERLAYER COUPLING IN VAN DER WAALS FLAT BANDS

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

Non-technical description: Many spectacular physical phenomena—and useful device—rely on macroscopic quantum coherence. The most well known example are superconductors, where macroscopic coherence is directly tied both the absence of electrical resistance as well as the emergence of coherent degrees of freedom that form the basis for the best developed platforms for manipulating quantum information. However, macroscopic quantum coherence, in principle, a much broader phenomenon. This project aims to realize new modalities of macroscopic quantum coherence in a broad class of materials known as van der Waals heterostructures. Van der Waals heterostructures consist of successively laminated two dimensional atomic crystals such as graphene; their high crystalline perfection and broad range of tunability put a variety of new quantum coherent states in experimental range. By realizing new states characterized by macroscopic quantum coherence, this project furthers understanding of these phenomena and opens new avenues towards quantum information processing. Synergistic with the research effort is an educational initiative focused on technical workforce development, implemented through a summer school for graduate student across physics, chemistry and materials science working on quantum science related problems. Technical description: The ultimate goal of this project is to create a novel quantum bit based on interlayer coherence in a bilayer exciton condensate. This bit exploits the spontaneous phase coherence predicted to occur in these systems. Bilayer exciton condensates, first discovered in semiconductor quantum wells, have recently been shown to exist in graphene and chalcogenide heterostructures at higher temperatures and under less demanding experimental conditions—particularly in the absence of magnetic fields. The research team is using frequency-dependent interlayer tunneling spectroscopy to directly detect the emergence of macroscopic phase coherence through the excitonic analog of the AC Josephson effect. This new detection modality then allows a broad search for macroscopic coherence in a variety of double layer structures based on band-structure engineered two dimensional double layers. 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.