Exploring non-equilibrium Andreev modes in graphene Josephson junctions

Nontechnical Abstract: Modern semiconductor and quantum technologies rely on devices that operate out of equilibrium—that is, their state changes over time. This research aims to develop innovative quantum devices that take advantage of nonequilibrium behavior using graphene Josephson junctions. Traditionally, Josephson junctions consist of two superconductors separated by a non-superconducting region, enabling them to conduct electricity without resistance or energy loss. This project explores a new type of Josephson junctions by leveraging the extraordinary properties of graphene—a single layer of carbon atoms—as the non-superconducting region. By integrating multiple superconducting terminals, these devices are predicted to display remarkable electrical properties under nonequilibrium conditions. This project enriches our understanding of these emergent properties and has the potential to pave the way for developing devices that are highly efficient and resilient to noise—addressing a key challenge in quantum technology. Beyond technical innovations, this project also contributes to workforce development by training students at all levels. Additionally, it features a strong focus on education and outreach, including course development and engaging the local STEM community through summer camps. Technical Abstract: This research builds upon recent advances in graphene Josephson junctions to explore the nonequilibrium properties of emergent Andreev bound states in these systems. The project aims to develop ballistic, dual-gated Josephson junctions on graphene heterostructures to minimize disorder and enable independent control over carrier density and contact transparency. A central focus is on manipulating and probing the energy-phase relationship of Andreev modes under nonequilibrium conditions, achieved by applying microwave radiation and/or voltage bias. The project also aims to identify topological properties of these nonequilibrium states by directly examining the Andreev band structure using tunneling spectroscopy. This research intends to deepen our understanding of Andreev modes, topological phases, and superconductivity, paving the way for their use in superconducting spintronics and quantum information processing. Finally, the project aims to train the next generation of quantum scientists and engineers by equipping them with expertise in nanolithography and low-temperature measurement techniques—key skills for the future quantum workforce. 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.