Cavity-based control of quantum vortices in superconductors

• Applicant: Vadim Plastovets, Ph.D.
• Subject Area: Theoretical Condensed Matter Physics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 566401345

Despite being a well-established field, superconductivity remains a hot topic, both from a fundamental perspective and for its applications in microelectronics. Naturally, the key properties of a superconducting material — its ability to carry dissipationless current and exhibit perfect diamagnetism — are determined by its microscopic structure. The primary way to control them is by altering the material's chemical composition. In addition, due to its quantum nature, the superconducting ground state is highly sensitive to external factors such as temperature and magnetic field. These dependencies have been thoroughly studied over the past decades as they fundamentally determine the material’s phase diagram. I consider here a new "degree of freedom" for controlling the superconducting state — the interaction with the quantum fluctuations of the electromagnetic vacuum. Typically, such effects are negligible, but they become significant in optically confined systems, such as cavities. This proposal belongs to the broader research field of cavity quantum materials, which has been recently attracting a lot of attention from different communities ranging from condensed matter to quantum optics. In the context of the present proposal, this enhanced interaction between light and matter has two major consequences: on the one hand, it can modify the mechanism of electron-pair formation that underlies superconductivity and on the other hand it can alter the properties of the superconducting state and thus provide an alternative to the standard “control knobs” like temperature or magnetic field. The former consequence has been explored in recent theoretical and experimental studies, while the latter remains largely unexplored and is the focus of the present proposal. Specifically, I will focus on cavity-based control of the superconducting state in the presence of geometrical inhomogeneities or impurities, as well as the superconductor’s response to external electromagnetic perturbations. Special attention will be devoted to the magnetic vortex phase, which is of paramount significance for superconducting microelectronics. These vortices are macroscopic topological objects that have proven to be highly controllable and useful excitations with promising applications in quantum devices and quantum computing. The possibility of cavity-based control over the inhomogeneous phases of a superconductor could open new research avenues and stimulate experimental studies in this direction. The project is well balanced as it touches on my area of expertise in superconductivity and provides me with excellent opportunities to explore a new area of cavity-quantum-materials, supported by the expertise of my host.

• DFG Programme: WBP Position