Quantum optics with giant atoms in imperfect waveguides

Abstract

The rapid advancement of quantum technologies has driven the exploration of novel regimes in quantum light-matter interactions to overcome fundamental limits in coherence and control. Giant atoms, characterized by their ability to couple to a waveguide at multiple points separated by distances comparable to the wavelength of the guided light, have emerged as a promising platform for quantum optics. The phase shifts accumulated by photons traveling between these coupling points give rise to both self-interference and collective interference effects. Self-interference allows a single giant atom to decouple from its environment, preventing relaxation into the waveguide. For multiple giant atoms, the interference effects provide two mechanisms for decoherence suppression: the formation of dark states in driven and undriven systems and decoherence-free interaction (DFI) in a certain configuration. Previous studies in this emerging field have assumed the waveguide to be lossless. In this thesis, we investigate the impact of two realistic imperfections: losses in the waveguide and asymmetric coupling, where the relaxation rates at each coupling point are unequal. Utilizing the SLH formalism for cascaded quantum systems, we derive the Lindblad master equation to model the dynamics of the system. Through numerical simulations, we quantify the extent to which these imperfections influence giant-atom phenomena. Our results determine the upper bounds of losses per distance in recent experiments and also the tolerances of losses in forming a highly entangled state. The results presented in the report introduce essential, realistic considerations for topology designs and driven configurations in future giant-atom experiments, laying the foundation for realizing implementations in quantum technologies.