Confining photons to atomic length scales

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Localizing photons to atomic length scales offers fascinating possibilities in terms of high-resolution scanning optical microscopy, as well as in terms of strong light-matter coupling. Atomic-scale resolution spectroscopic imaging is expected to have a huge impact in life science as well as in nano science in general. On the other hand, strong coupling in a nanoscale optical resonator with atomic scale mode volume will be of great interest for large scale integration of quantum computation schemes and the implementation of nonlinearities for all-optical data manipulation in the single-photon regime. However, so far light localization has been limited to the >10 nm range. The present project will synergistically combine both groundbreaking aspects of atomic scale light localization by implementing a new type of scanning microscopy which uses atomically confined MIM cavity resonances as optical probes. We recently succeeded in fabricating single-crystal metal-insulator-metal (MIM) nano resonators with sub-1nm insulating gaps and demonstrated the corresponding sub-1nm light confinement. Lateral scanning of probe and/or sample on the one hand will afford spectroscopic mapping with near-atomic spatial resolution by recording luminescence and Raman scattering of nano objects, such as individual quantum dots, (bio)molecules, and novel 2D-materials. The strong gradients of the probe field are expected to open multipolar spectroscopic channels due to modified selection rules. On the other hand, probe scanning also varies the coupling strength between probe and quantum emitters, causing a smooth transition from the perturbative into the strong and possibly even ultrastrong interaction regime. It is further expected that the quantum mechanical entanglement of probe and quantum emitter in the strong coupling regime will lead to new imaging modalities.