# Strong coupling of microwave photons to antiferromagnetic fluctuations in an organic magnet

## TL;DR

This study demonstrates strong coupling between microwave photons and antiferromagnetic fluctuations in an organic magnet within a circuit QED setup, revealing potential for coherent control and probing of spin correlations.

## Contribution

It introduces the use of organic crystals with multispin modes in circuit QED, showing strong coupling and anisotropic exchange interactions at low temperatures.

## Key findings

- Strong coupling achieved at base temperature
- Magnetic resonance shows field angle dependence
- Organic crystals suitable for coherent spin manipulation

## Abstract

Coupling between a crystal of di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium radicals and a superconducting microwave resonator is investigated in a circuit quantum electrodynamics (circuit QED) architecture. The crystal exhibits paramagnetic behavior above 4~K, with antiferromagnetic correlations appearing below this temperature, and we demonstrate strong coupling at base temperature. The magnetic resonance acquires a field angle dependence as the crystal is cooled down, indicating anisotropy of the exchange interactions. These results show that multispin modes in organic crystals are suitable for circuit QED, offering a platform for their coherent manipulation. They also utilize the circuit QED architecture as a way to probe spin correlations at low temperature.