Modular Multi-formalism Mixed-signal Simulator of Quantum Hardware*

There is an unmet need for multi-physics modeling of quantum information processors at the system scale, quantitatively coupled to experimental measurements of subsystem components.  Similarly to mixed-signal classical electronics simulators, we need to address the "analog" dynamics of noise (e.g., a Lindblad master equation), while simultaneously modeling the discrete digital infrastructure built on top of the low level analog model. Tools derived from both SPICE and Verilog do so in the classical domain. We showcase a tool addressing many of the problems faced by such mixed-signal simulations in the quantum domain. To limit the exponential cost of low-level quantum simulations, we introduce a multi-formalism "quantum state allocator" and "garbage collector" that ensures the simulation tracks only the minimally sized Hilbert space of interest. The allocator is agnostic to the formalism used, permitting on-the-fly transitions between Lindblad Master Equation, Noisy Stabilizer Tableaux, and other models, depending on how fast the problem grows. The analog simulator is integrated with a discrete event simulator, permitting easy simulation of quantum circuits and quantum networks with arbitrary classical feedback. We demonstrate a case study where we design and optimize a small color-center-based cluster-state quantum computer.