Ultrastrong coupling probed by Coherent Population Transfer

TL;DR

This paper proposes a new dynamical protocol using STIRAP to detect virtual photon pairs as evidence of ultrastrong light-matter coupling in superconducting circuits, advancing quantum technology applications.

Contribution

It introduces a novel method for unambiguously detecting ultrastrong coupling through dynamical photon production amplification in superconducting systems.

Findings

Protocol enables detection of virtual photons in USC regimes

Stimulated Raman Adiabatic Passage amplifies photon signals

Provides a benchmark for controlling USC dynamics

Abstract

Light-matter interaction, and the understanding of the fundamental physics behind, is the scenario of emerging quantum technologies. Solid state devices allow the exploration of new regimes where ultrastrong coupling (USC) strengths are comparable to subsystem energies, and new exotic phenomena like quantum phase transitions and ground-state entanglement occur. While experiments so far provided only spectroscopic evidence of USC, we propose a new dynamical protocol for detecting virtual photon pairs in the dressed eigenstates. This is the fingerprint of the violated conservation of the number of excitations, which heralds the symmetry broken by USC. We show that in flux-based superconducting architectures this photon production channel can be coherenly amplified by Stimulated Raman Adiabatic Passage (STIRAP). This provides a unique tool for an unambiguous dynamical detection of USC in present day hardware. Implementing this protocol would provide a benchmark for control of the dynamics of USC architectures, in view of applications to quantum information and microwave quantum photonics.