Lattice field theory for superconducting circuits

TL;DR

This paper introduces a novel ab-initio lattice field theory method for analyzing large superconducting quantum circuits, providing accurate predictions without systematic errors from Hilbert space truncation.

Contribution

It presents a new lattice field theory approach for superconducting circuits that improves accuracy and avoids truncation errors compared to existing techniques.

Findings

The method accurately predicts fluxonium qubit properties.

Impedance and capacitance effects on fluxonium are systematically analyzed.

Charge noise and dephasing rates are statistically characterized.

Abstract

Large superconducting quantum circuits have a number of important applications in quantum computing. Accurately predicting the performance of these devices from first principles is challenging, as it requires solving the many-body Schr\"odinger equation. This work introduces a new, general ab-initio method for analyzing large quantum circuits based on lattice field theory, a tool commonly applied in nuclear and particle physics. This method is competitive with state-of-the-art techniques such as tensor networks, but avoids introducing systematic errors due to truncation of the infinite-dimensional Hilbert space associated with superconducting phases. The approach is applied to fluxonium, a specific many-component superconducting qubit with favorable qualities for quantum computation. A systematic study of the influence of impedance on fluxonium is conducted that parallels previous experimental studies, and ground capacitance effects are explored. The qubit frequency and charge noise dephasing rate are extracted from statistical analyses of charge noise, where thousands of instantiations of charge disorder in the Josephson junction array of a fixed fluxonium qubit are explicitly averaged over at the microscopic level. This is difficult to achieve with any other existing method.