TERRA

The THz part of the electromagnetic spectrum is important for real world applications but devices are difficult to elaborate due to the lack of available materials with well adapted properties. One way to overcome these difficulties is by using metamaterials, consisting of an array of nanofabricating sub-wavelength resonators, that allow the realization of components operating in the THz range. Characterization of THz metamaterials can be performed by far-field transmittance and reflectance measurements but becomes challenging in the near-field, within micrometric distances away from the resonator surface. Scanning Near-field Optical Microscopy can be used for this purpose but it is normally slow and influenced by the finite size of the scanning AFM tip. Here, we propose to interface THz resonators (metamaterials) with Rydberg atoms that strongly interact with THz radiation subsequently converting it to visible photons (THz to visible conversion). This strong interaction can be utilized as a novel near-field imaging technique mapping the electric field of the resonators with a sub-wavelength resolution, defined by visible photons. Beyond its applications in instrumentation sensing, coupling Rydberg atoms with THz resonators provides a platform to study the modification of the atomic energy levels and radiative properties (lifetime) in the vicinity of a metasurface. Indeed, metasurfaces modify the vacuum modes of the electromagnetic field proving a unique way to tune the atomic properties and the Casimir-Polder interaction of Rydberg atoms, with applications in hybrid systems, interfacing atoms with photonics platforms, and quantum technologies. Finally, the possibility of ultra-fast switching the THz resonator properties via an external light field (by use of an active semiconductor medium) could provide a unique testbed for dynamical QED experiments that are paramount for quantum physics but extremely difficult to probe with tabletop experiments.