I shall present a series of frontier experiments hunting X rays coming from exotic atoms produced at the DAFNE collider of LNF-INFN (Italy) and from processes violating the standard Quantum Mechanics at the Italian Gran Sasso underground laboratory.

In the first part of the talk I shall introduce the studies of kaonic atoms in the framework of the SIDDHARTA collaboration at the DAFNE Collider at the LNF-INFN, Frascati (Roma) laboratory. Combining the excellent quality kaon beam delivered by the DAFNE collider with new experimental techniques, as fast and very precise X ray detectors, like the Silicon Drift Detectors, we have performed unprecedented measurements on kaonic hydrogen and helium. Presently, a major upgrade of the setup, SIDDHARTA-2 is being realized to perform the first ever kaonic deuterium measurement. Kaonic atoms studies represent an opportunity to unlock the secrets of the strong interaction in the strangeness sector and understand the role of strangeness in the Universe, from nuclei to the stars.

In the second part of the talk I shall present the VIP experiment at the LNGS underground laboratory searching for impossible atoms, i.e. atoms prohibited by the Pauli Exclusion principle, which might exist in some theories beyond the Standard Model (Wuantum Gravity). Also, I shall briefly discuss the search of the so called spontaneous radiation linked with collapse models dealing with the measurement problem (Schroedinger cat paradox) and the interplay with gravity.