When the coupling between a confined electromagnetic mode and the electronic degrees of freedom of a solid-state system becomes large enough, the interaction can modify the electronic wavefunctions and the related material properties. These effects become more dramatic in systems with continuum electronic degrees of freedom, in which the gapless spectra enhance the electronic malleability.

Solid-state cavity quantum electrodynamics can thus become a tool for quantum material engineering, allowing us to drastically enrich the catalogue of materials available for scientific and technological applications.

In this talk I will present the first experimental demonstration of cavity-induced single-photon wavefunction modification in which we measured a change of 30% for the Bohr radius in microcavity embedded quantum wells [1]. Using doped quantum wells characterised by a continuum spectrum we then predicted [2] and demonstrated [3] the formation of novel excitons bound by photon exchange. We also observed related polaritonic nonlocal effects [4] reducing the achievable field enhancement and thus the achievable strength of the light-matter coupling.

[1] Experimental verification of the very strong coupling regime in a GaAs quantum well microcavity. S. Brodbeck et al., Phys. Rev. Lett. 119, 027401 (2017)

[2] Strong coupling of ionising transitions. E. Cortese et al., Optica 6, 354 (2019)

[3] Excitons bound by photon exchange. E. Cortese et al., Nature Physics 17, 31 (2021)

[4] Polaritonic nonlocality in light-matter interaction.S. Rajabali et al., Nature Photonics 15, 690 (2021).