Thanks to the great advances in quantum systems generation, manipulation and measurement, the new millennium witnessed the passage from the first to the second quantum revolution. Today, fundamental aspects of quantum theory, such as entanglement and the superposition principle, are at the core of many technologies able to outperform their classical counterparts (e.g., quantum information and metrology).
However, our comprehension of reality remains partial and veiled; a long debate is still ongoing on the peculiar aspects of quantum theory foundational axioms, like the non-locality of quantum correlations, the ontological nature of the wave function and its collapse, the measurement process, the macro-objectivation problem (i.e., the transition from a microscopic probabilistic world to a macroscopic deterministic one).
Hence, although quantum mechanics looks almost mature, fundamental questions are still open, with implications also on quantum technologies. We address these topics by performing advanced quantum optics experiments, ranging from the simulation of quantum particles undergoing time travel to the reconciliation of macroscopic irreversibility with the time-reversible quantum laws of the microscopic world.