QUAPT

In 1998, one of the fundamental assumptions in quantum mechanics, that the Hamiltonian describing a quantum system has to be Hermitian, was overturned. The existence of an entire class of Hamiltonians that are non-Hermitian yet still possess real eigenvalues was discovered. These non-Hermitian Hamiltonians describe PT-symmetric systems, which are systems that are invariant under the combined operations of parity-inversion and time-reversal. Currently, it is still under debate what implications PT-symmetry has for quantum physics. Yet in photonics, PT-symmetry can be readily realized by a proper distribution of gain and loss in the system, making photonics the ideal platform for studying the physics of PT-symmetric systems. Indeed, various effects of PT-symmetry such as non-orthogonal eigenmodes, non-reciprocal evolution of light, and diffusive coherent transport have been demonstrated on a photonic platform, and inspired applications in lasers and optical diodes. So far, these photonic experiments have been purely classical and the full impact of PT-symmetry on the evolution of light is still unclear. Quantum evolution of light in PT-symmetric systems is completely unexplored territory with lots of new physics to be unravelled. Therefore, the objective of this proposal is to for the first time experimentally investigate the evolution of quantum states in non-Hermitian systems. In particular, the project will study the quantum evolution of multiple correlated photons injected in PT-symmetric integrated photonic structures fabricated using direct laser-writing technology. The aim is to investigate how modifying the non-Hermitian Hamiltonian of the system influences photon correlations, expecting to demonstrate novel behaviour and unravel new physics. It is expected to find that quantum correlations fundamentally change: for example, correlated photons that should naturally bunch might anti-bunch, show a mixed bunching-antibunching, or even uncorrelated behaviour.