EEE research features on the cover of prestigious Physics journal

Research focused on the quanta of light (photons) strongly interacting with their magnetic counterpart, magnons in a microwave device to form a hybrid state, so-called magnon polariton. When the researchers turned on the nonlinear interaction in the magnet, they discovered a novel way of controlling the photon-magnon hybrid state.   
  
The present study has revealed a new and useful mechanism of controlling the coupling between photons and magnons in a simple solid state device. This might open a new avenue for developing future information transfer architectures.

Significance of research
In the past, magnon polaritons were studied in the linear excitation regime of both photons and magnons (the bottom figure). When they strongly interact, they show an avoided crossing as shown in the top panel (-20 dBm) of the figure set. This can be analogous to a coupled harmonic pendulums (oscillators) where the parameters to describe the dynamics are fixed. In the present study, the UCL EEE researchers within international collaboration took a step further to examine a simple question “what if one of the oscillators becomes an anharmonic oscillator?” The results are striking. They observed that the coupling strength between photons and magnons can be controlled by input power they used at the nonlinear regime. This can be represented by the power-dependent change of the observed spectra (in particular the gap size). They also developed a theoretical model to explain their experimental observation and the power dependence was found to originate from the saturation of magnons at that regime. Their discovery and developed theory might be used for creating an efficient switch for controlling coupling strength between photons and magnons, for future information transfer devices.
  
The present study – an international collaboration between UCL EEE, University of Tokyo, Japan Atomic Energy Agency, Tohoku University and University of the Chinese Academy of Sciences - has revealed a new and useful mechanism of controlling the coupling between photons and magnons in a simple solid-state device. This might open a new avenue for developing future information transfer architectures.   

EEE’s Oscar Lee, who is the leading author of this publication, stated:

“

My primary role involved finding the optimal conditions to demonstrate what remained as theory experimentally. The work involved measuring the magnet at different configurations and analysing its results, where new techniques had to be constantly implemented since existing solutions could not offer clear explanations.

It has been an incredibly fortunate journey for me to communicate with brilliant physicists from around the world and observe how new physics is evolved in real-time. Each step of the work had to be done with extra care, from collecting data to analysis, as every piece contributed to completing the theory.

Read the article 
Oscar Lee, Kei Yamamoto, Maki Umeda, Christoph W. Zollitsch, Mehrdad Elyasi, Takashi Kikkawa, Eiji Saitoh, Gerrit E. W. Bauer, and Hidekazu Kurebayashi
Phys. Rev. Lett. 130, 046703 – Nonlinear Magnon Polaritons

Further information 
Oscar Lee
Prof. Hide Hide Kurebayashi