Particle Production in Ultra-Strong Coupling Waveguide QED

TL;DR

This paper investigates particle production in ultra-strong coupling waveguide QED, revealing broadband emission phenomena and their signatures, with implications for quantum simulation and complex quantum systems.

Contribution

It introduces a quantum superposition-based approach to analyze particle production in many-body quantum optics, especially in circuit QED at ultrastrong coupling.

Findings

Broadband particle production dominates off-resonant emission lineshape.

Frequency conversion processes produce distinctive time correlation signatures.

Results are experimentally testable in quantum waveguide setups.

Abstract

Understanding large-scale interacting quantum matter requires dealing with the huge number of quanta that are produced by scattering even a few particles against a complex quantum object. Prominent examples are found from high energy cosmic ray showers to the optical or electrical driving of degenerate Fermi gases. We tackle this challenge in the context of many-body quantum optics, as motivated by the recent developments of circuit quantum electrodynamics at ultrastrong coupling. The issue of particle production is addressed quantitatively with a simple yet powerful concept rooted in the quantum superposition principle. This key idea is illustrated by the study of multi-photon emission from a single two-level artificial atom coupled to a high impedance waveguide. We find surprisingly that the off-resonant inelastic emission lineshape is dominated by broadband particle production, due to the large phase space associated with contributions that do not conserve the number of excitations. Such frequency conversion processes produce striking signatures in time correlation measurements, which can be tested experimentally in quantum waveguides. These ideas open new directions for the simulation of a variety of physical systems, from polaron dynamics in solids to complex superconducting quantum architectures.