An international team around scientist from the Moscow Institute of Physics and Technology MIPT have developed and tested a new platform for reali­zation of the ultrastrong photon-to-magnon coupling. The proposed system is on-chip and is based on thin-film hetero-structures with super­conducting, ferro­magnetic and insulating layers. This discovery solves a problem that has been on the agenda of research teams from different countries for the last 10 years, and opens new oppor­tunities in implementing quantum technologies. 

The last decade has seen significant progress in the development of artificial quantum systems. Scientists are exploring different platforms, each with its own advantages and disad­vantages. The next critical step for advancing quantum industry requires an efficient method of information exchange between platform hybrid systems that could benefit from distinct platforms. For example, hybrid systems based on collective spin exci­tations, or magnons, are being developed. In such systems, magnons must interact with photons, standing electro­magnetic waves trapped in a resonator. The main limiting factor for developing such systems is the funda­mentally weak interaction between photons and magnons. They are of different sizes, and follow different dispersion laws. This size difference of a hundred times or more considerably complicates the interaction.

The scientists managed to create a system with a ultrastrong photon-to-magnon coupling. Vasily Stolyarov, deputy head of the MIPT Labora­tory of Topo­logical Quantum Phenomena in Superconducting Systems, commented: “We created two subsystems. In one, being a sandwich from superconductor/­insulator/­superconductor thin films, photons are slowed down, their phase velocity is reduced. In another one, which is also a sandwich from superconductor/­ferromagnetic/­superconductor thin films, super­conducting proximity at both interfaces enhances the collective spin eigen-frequencies. The ultra strong photon-to-magnon coupling is achieved thanks to the suppressed photon phase velocity in the electro­magnetic subsystem.”

Igor Golovchanskiy, senior researcher at the MIPT, explained: “Photons interact very weakly with magnons. We managed to create a system in which these two types of exci­tations interact very strongly. With the help of super­conductors, we have significantly reduced the electromagnetic resonator. This resulted in a hundred times reduction of the phase velocity of photons, and their interaction with magnons increased by several times.” This discovery will accelerate the implem­entation of hybrid quantum systems, as well as open up new possi­bilities in super­conducting spintronics and magnonics. (Source: MIPT / MISIS)

Reference: I. A. Golovchanskiy et al.: Ultrastrong photon-to-magnon coupling in multilayered heterostructures involving superconducting coherence via ferromagnetic layers, Sci. Adv. 7, eabe8638 (2021); DOI: 10.1126/sciadv.abe8638

Link: Laboratory of Topological Quantum Phenomena in Superconducting Systems, Moscow Institute of Physics and Technology MIPT, State University, Moscow, Russia