Non-Hermitian quantum and classical integrated nonlinear photonics

Abstract

Integrated optical quantum circuits based on photonic waveguiding structures are increasingly gaining attention as a possible solution for scalable quantum technologies with important applications to quantum simulations. Quantum communication provides secure information transmission, but the distance over which quantum states of light can be distributed without significant disturbance is limited due to inescapable losses and noise in optical elements. Loss is the greatest challenge facing the implementation of integrated photonic technologies, and it is inescapable in experimental reality. In recent years there is a rise of interest in structures with spatially inhomogeneous losses. Light propagation in waveguiding structures with spatially distributed sections of loss can be used for implementation of quantum plasmonic circuits, which are able to strongly confine light to sub-wavelength dimensions, as well as for parity-time (PT) symmetric structures, with phase transition associated with PT-symmetry breaking, which opens new possibilities for light manipulation. The PhD thesis contains research on the controllable classical and quantum dynamics of optical frequency conversion processes in quadratically nonlinear photonic integrated circuites in the presence of losses. Namely, I discuss spontaneous parametric down-conversion (SPDC), sum-frequency generation (SFG) and optical parametric amplification (OPA) in nonlinear structures governed by non-Hermition Hamiltonians. I explore the fundamental features of multi-photon generation in integrated nonlinear waveguides. I have been shown that arrays of coupled nonlinear waveguides can serve as a robust integrated platform for the generation of entangled photon states with nonclassical spatial correlations through spontaneous parametric down-conversion (SPDC), and that the operation of such quantum circuit is tolerant even to relatively high losses. Furthermore, I have studied the bi-photon multimode quantum emission tomography in waveguide structures with spatially inhomegeneous losses. The PhD thesis also covers the research on the effect of these losses in waveguide couplers possessing parity-time (PT) symmetry. I have identified an anti-PT spectral symmetry of a parametric amplifier based on those couplers. Finally, I describe the single-photon conversion to a photon pair, and identify opportunities for the efficient enhancement of this process. Show more