Protected Polarization Symmetry Breaking in Kerr Resonators for Random Number Generation and Photonic Ising Machines
Liam Quinn
Abstract
This thesis experimentally and theoretically investigates the applications of spontaneous symmetry breaking in nonlinear resonators. Symmetry breaking refers to the transition of an initially symmetric system into a pair of asymmetric states. In a resonator with two equally driven polarization components, the intensities of the two fields would typically be expected to remain equal. However, this symmetry can spontaneously break as a result of small changes to the input conditions, causing one polarization component to increase in intensity while the other decreases. In practice, the selection enacted by symmetry-breaking is not entirely random, due to experimental asymmetries that bias the outcome. In this thesis we will experimentally and numerically explore a remarkable technique which can eliminate said biases through a nonlinear symmetry protection mechanism. Operation in this symmetry protected regime allows for a truly random selection of states, even in the presence of experimental imperfections. We experimentally verified the efficacy of the symmetry-protection mechanism by constructing an all-optical random number generator. Using an optical fiber resonator coherently driven with a train of pulses, we have achieved optical random bit generation at rates exceeding 3 Mbit/s without post-processing. We evaluated the randomness of the system with a variety of metrics, demonstrating the high fidelity of the random number generator. We extended this platform further to develop a novel optical Ising machine, a computational platform demonstrated to offer efficient solutions to combinatorial optimization problems which arise in a variety of contexts. Our proof-of-concept experimental results demonstrate continuous operation with up to 100 coupled spins for over an hour, enabled by the symmetry-protection protocol that ensures highly robust operation. Furthermore, the ability to measure artificial spins through optical intensity offers advantages over existing phase-based Ising implementations. We support our experimental findings with numerical simulations, which highlight the platform’s future potential for scaling to larger systems, with all-to-all coupling.