Collective quantum effects in nonreciprocal systems

Interactions heavily influence collective behavior across all scales, from atoms to animals. Studying the transition from single-body over few-body to many-body dynamics provides insights into when responses become truly collective. Research on collective effects explains fundamental concepts like self-organization, self-assembly, and phase transitions, and has many applications. For instance, tunable interactions in many-body quantum systems have driven advancements in quantum computation, simulation, and metrology. In active systemssuch as chemical, biological, and socially influenced systemsinteractions become fundamentally nonreciprocal as the components modify and adjust their responses over time. Unlike these macroscopic systems, the concept of closed quantum systems, which are isolated from the environment, relies on reciprocal interactions. In practice, quantum systems always experience decoherence due to information loss to the environment. In these open quantum systems, interactions mediated by the environment can exhibit nonreciprocity, drastically altering collective dynamics. This project will utilize optically trapped and controlled chains of glass nanoparticles, which are approximately 1000 times smaller than a grain of sand, to explore the effects of nonreciprocal interactions in open quantum systems. The motion of these nanoparticles can now be readily prepared in a quantum state, while several nanoparticles can be simultaneously trapped and made to interact through light. Using our system, we aim to study how nonreciprocity induces stress in self-assembled nanoparticle crystals. Additionally, we plan to leverage nonreciprocal interactions facilitated by an optical resonator to design entangled and protected states of motion of multiple nanoparticles. These experiments will allow us to investigate the decoherence mechanisms in macroscopic solid-state objects. Moreover, the collective enhancement in response to external perturbations is expected to lead to more precise sensing of forces and momentum kicks.