Finite sizes and smooth cutoffs in superconducting circuits

TL;DR

This paper examines the impact of finite size effects and smooth cutoff models on the accuracy of superconducting circuit simulations, especially in ultra-strong coupling regimes, highlighting potential inaccuracies from common modeling assumptions.

Contribution

It demonstrates that traditional assumptions about pointlike qubits and UV cutoff neglect can lead to significant errors in superconducting circuit models.

Findings

Sharp or no cutoff models cause inaccuracies in ultra-strong coupling regimes.

Finite size effects are relevant for short timescales in experiments.

Smooth cutoff models improve modeling accuracy.

Abstract

We investigate the validity of two common assumptions in the modelling of superconducting circuits: first, that the superconducting qubits are pointlike, and second, that the UV behaviour of the transmission line is not relevant to the qubit dynamics. We show that in the experimentally accessible ultra-strong coupling regime and for short (but attainable) times, the use of an inaccurate cutoff model (such as sharp, or none at all) could introduce very significant inaccuracies in the model's predictions.