Rabi-like splitting is one of the key concepts in modern quantum technology. Fully understanding it can help us advance our knowledge in quantum information processing. Assistant Professor Aakanksha Sud (Tohoku University), Dr. Kei Yamamoto (JAEA), Professor Shigemi Mizukami (Tohoku University), and collaborators discovered that Rabi-like splitting could be achieved using nonlinear coupling, which remarkably preserves the symmetries of the system. This result opens up various possibilities to deepen our understanding of nonlinear dynamics and coupling phenomena in artificial control.
In quantum physics, when there is a coupling between two harmonic oscillators with an ideal oscillation frequency, the oscillation frequency splits to two different frequencies in the coupled system. The difference in these two frequencies is referred to as Rabi splitting.
The physics behind Rabi-splitting and the coupling of oscillations arising from artificial magnets have been popular topics for research. The system possesses two spatially uniform magnon modes: an in-phase mode resembling ferromagnetic behavior and an anti-phase mode with characteristic antiferromagnetic properties. Although the frequencies of these two modes are identical under some conditions (fulfilled by an externally applied magnetic field), a symmetry breaking within the system is required to manifest Rabi-like splitting. However, the current research study found a way to bend the rules.
"Typically, you need to break the symmetry of the system to achieve Rabi-like splitting in artificial magnet," explains Shigemi Mizukami, "However, we were thrilled that both our experimental and theoretical studies showed that it could occur while still maintaining the symmetry of the system."
To achieve this, the researchers took advantage of nonlinear coupling. They induced nonlinear coupling with large radio-frequency currents, targeting an artificial magnet. This technique allows for the controlled manipulation of energy between modes.
These findings help deepen our understanding of nonlinear dynamics and coupling phenomena in artificial control, and may inform further research studies in this area. The research team plans to continue this project by directly applying this approach to devices that use high-speed signal processing.
The research was led by WPI Advanced Institute for Materials Research (AIMR), the Frontier Research Institute for Interdisciplinary Sciences (FRIS), the Research Institute of Electrical Communication (RIEC), the Center for Science and Innovation in Spintronics (CSIS), and the Graduate School of Engineering at Tohoku University, in collaboration with the Japan Atomic Energy Agency (JAEA) and University College London (UCL). The findings were published in Physical Review Letters on June 20, 2025.