Quantum Research Institute Seminar | Cavity electrodynamics of integrated quantum materials

Abstract.
Quantum materials embedded into devices have been observed to host a wide variety of quantum phases that can exhibit intriguing properties, like dissipationless transport, magnetism, or fractionalized carriers. Understanding the conditions under which these phenomena emerge is of great fundamental interest and important for deterministically designing materials for new applications. In these device-integrated quantum materials, the macroscopic responses are not solely due to the intrinsic interactions of the materials. Instead, these interactions, and the resulting ground state physics, are modified by the specifics of the device integration.

In this talk, I will discuss how integrated quantum materials form sub-wavelength cavities due to their micron-size, confining low-energy light into the near field. I will introduce time-domain on-chip THz spectroscopy as a technique to capture the cavity electrodynamics, probing the response of integrated materials to light on their natural frequency (~THz/meV) scales. This technique overcomes the mismatch between free-space THz wavelengths (~300 um) and sample size (~10 um) by measuring the optical conductivity on-chip, in the near field, and at finite momenta. I will illustrate how the properties of integrated quantum materials, such as gate-tunable van der Waals heterostructures, can be modified and controlled due to cavity effects. Using on-chip THz spectroscopy, I observed light-matter hybridization in a gate-tunable van der Waals heterostructure, between plasmonic self cavity modes in monolayer graphene and a graphite electrostatic gate. This hybridization can be tuned into the ultrastrong coupling regime using electrostatic gating and the cavity geometry. In this regime, light-matter coupling can be wielded to engineer new thermodynamic ground states. Together, these results lay a path for utilizing integrated quantum materials in novel THz quantum technologies.


Bio.
Hope Bretscher is currently a Marie Skłodowska-Curie postdoctoral fellow at the Max Planck Institute for the Structure and Dynamics of Matter, in Hamburg Germany, where she investigates the low-energy electrodynamics of 2D materials. Originally from St. Louis Missouri, Hope received her BA in physics from the University of Chicago. Funded by a Marshall Scholarship, she pursued a master’s degree in Science and Technology studies from the University of Edinburgh, before attaining her PhD in 2021 on ultrafast dynamics in vdW materials from the University of Cambridge.