Circuit quantum electrodynamics (cQED) with modular quasi-lumped models

TL;DR

This paper introduces a modular, quasi-lumped modeling method for circuit quantum electrodynamics that accurately captures complex interactions and renormalization effects, validated on large superconducting quantum processors.

Contribution

The paper presents a computationally-efficient, modular modeling approach for cQED systems that systematically includes non-perturbative effects without additional approximations.

Findings

Method improves experimental agreement by a factor of two.

Accurately models large-scale superconducting quantum processors.

Systematically accounts for couplings, constraints, and renormalizations.

Abstract

Extracting the Hamiltonian of interacting quantum-information processing systems is a keystone problem in the realization of complex phenomena and large-scale quantum computers. The remarkable growth of the field increasingly requires precise, widely-applicable, and modular methods that can model the quantum electrodynamics of the physical circuits, and even of their more-subtle renormalization effects. Here, we present a computationally-efficient method satisfying these criteria. The method partitions a quantum device into compact lumped or quasi-distributed cells. Each is first simulated individually. The composite system is then reduced and mapped to a set of simple subsystem building blocks and their pairwise interactions. The method operates within the quasi-lumped approximation and, with no further approximation, systematically accounts for constraints, couplings, parameter renormalizations, and non-perturbative loading effects. We experimentally validate the method on large-scale, state-of-the-art superconducting quantum processors. We find that the full method improves the experimental agreement by a factor of two over taking standard coupling approximations when tested on the most sensitive and dressed Hamiltonian parameters of the measured devices.