Observation of Perfect Absorption in Hyperfine Levels of Molecular Spins with Hermitian Subspaces

TL;DR

This paper demonstrates perfect absorption in molecular spin systems coupled to microwave resonators, revealing how Hermitian subspaces influence spectra and enabling potential quantum device applications like switches and modulators.

Contribution

It introduces a method to engineer Hermitian subspaces in non-Hermitian Hamiltonians for molecular spins coupled to resonators, controlling absorption and spectral properties.

Findings

Perfect absorption achieved in molecular spin-resonator system

Hermitian subspaces can be engineered via detuning control

Potential applications as single-photon switches and modulators

Abstract

We investigate Perfect Absorption (PA) of radiation, in which incoming energy is entirely dissipated, in a system consisting of molecular spin centers coherently coupled to a planar microwave resonator operated at milliKelvin temperature and in the single photon regime. This platform allows us to fine tune the spin-photon coupling and to control the effective dissipation of the two subsystems towards the environment, thus giving us the opportunity to span over a wide space of parameters. Our system can be effectively described by a non-Hermitian Hamiltonian exhibiting distinct Hermitian subspaces. We experimentally show that these subspaces, linked to the presence of PA, can be engineered through the resonator-spin detuning, which controls the composition of the polaritons in terms of photon and spin content. In such a way, the required balance between the feeding and the loss rates is effectively recovered even in the absence of PT-symmetry. We show that Hermitian subspaces influence the overall aspect of coherent spectra of cavity QED systems and enlarge the possibility to explore non-Hermitian effects in open quantum systems. We finally discuss how our results can be potentially exploited for applications, in particular as single-photon switches and modulators.