Kyongmo An
The ability to adjust the cooperativity between distinct waveforms is an important feature of quantum information devices. The coupling between spin and phonon is of particular interest, which allows for long-range communication at GHz frequencies [1,2]. I will first demonstrate using local light scattering that one can maximize this attribute in thin films by adjusting the orientation and strength of an external magnetic field. We found a factor of 2 enhancement by coupling the Kittel mode to circularly polarized acoustic waves instead of linearly polarized ones [3]. Beyond local interactions, we investigate nonlocal transport mediated by lattice waves. We report that the damping of ferromagnetic resonance generates coherent ballistic phonons that propagate through the substrate with minimal scattering. Using a distant platinum sensor, we detect a nonlocal energy dissipation that bypasses the conventional diffusive thermal bath. Finally, I will demonstrate a long-range spin coupling enabled by these standing wave phonons. In the experiment, two thin ferromagnets sit on either side of a 0.5-mm-thick crystal and communicate with one another by acting as “speakers” and “microphones” for sound waves in the crystal. The system can be brought into tripartite hybridization by carefully tuning the two ferromagnetic resonance frequencies to an acoustic resonance of the whole crystal. There, the entire system of magnetization and lattice can oscillate only coherently. At low temperatures, we expect quantum information exchange and distant entanglement of magnons, phonons, and microwave photons.
[1] K. An et al., Physical Review B 101, 060407 (2020)
[2] K. An et al., Physical Review X 12, 011060 (2022)
[3] K. An et al., Physical Review Applied 20, 014046 (2023)