Non-perturbative treatment of giant atoms using chain transformations

TL;DR

This paper presents a numerically exact method for analyzing giant superconducting atoms strongly coupled to acoustic waveguides, capturing non-Markovian effects beyond the rotating-wave approximation using chain transformations and matrix-product states.

Contribution

It introduces a chain transformation approach combined with matrix-product state simulations to study non-perturbative effects in giant atoms beyond the rotating-wave approximation.

Findings

Access to a wide range of system-bath observables

Exploration of previously inaccessible parameter regimes

Demonstration of non-Markovian effects in giant atoms

Abstract

Superconducting circuits coupled to acoustic waveguides have extended the range of phenomena that can be experimentally studied using tools from quantum optics. In particular giant artificial atoms permit the investigation of systems in which the electric dipole approximation breaks down and pronounced non-Markovian effects become important. While previous studies of giant atoms focused on the realm of the rotating-wave approximation, we go beyond this and perform a numerically exact analysis of giant atoms strongly coupled to their environment, in regimes where counterrotating terms cannot be neglected. To achieve this, we use a Lanczos transformation to cast the field Hamiltonian into the form of a one-dimensional chain and employ matrix-product state simulations. This approach yields access to a wide range of system-bath observables and to previously unexplored parameter regimes.