Predictive simulations of the dynamical response of mesoscopic devices: Part II

The dynamical response of mesoscopic devices, such as topological qubits, can often be qualitatively understood by considering simple phenomenological low-energy effective models involving only a few degrees of freedom. However, more quantitative simulations require connecting these effective models to more complete microscopic models that can involve hundreds or even thousands of degrees of freedom leading to a Hilbert space much larger than can be efficiently simulated. In this talk, we present a method to tackle the challenge of identifying the relevant low-energy states from microscopic models in a systematic and controlled fashion. We describe a method that incorporates ideas from tensor network theory and quantum chemistry to reduce an initially large Hilbert space to a few many-body states that accurately capture the low-energy quantum dynamics of the system. We illustrate this new method by simulating the dynamical response of a microscopic model of the fermion parity readout device experimentally studied in arxiv 2401.09549.