Ultrastrong magnon–magnon coupling dominated by antiresonant interactions

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Makihara, Takuma
Hayashida, Kenji
Noe, G. Timothy II
Li, Xinwei
Marquez Peraca, Nicolas
Ma, Xiaoxuan
Jin, Zuanming
Ren, Wei
Ma, Guohong
Katayama, Ikufumi

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Springer Nature Limited


Exotic quantum vacuum phenomena are predicted in cavity quantum electrodynamics sys- tems with ultrastrong light-matter interactions. Their ground states are predicted to be vacuum squeezed states with suppressed quantum fluctuations owing to antiresonant terms in the Hamiltonian. However, such predictions have not been realized because antiresonant interactions are typically negligible compared to resonant interactions in light-matter sys- tems. Here we report an unusual, ultrastrongly coupled matter-matter system of magnons that is analytically described by a unique Hamiltonian in which the relative importance of resonant and antiresonant interactions can be easily tuned and the latter can be made vastly dominant. We found a regime where vacuum Bloch-Siegert shifts, the hallmark of anti- resonant interactions, greatly exceed analogous frequency shifts from resonant interactions. Further, we theoretically explored the system’s ground state and calculated up to 5.9 dB of quantum fluctuation suppression. These observations demonstrate that magnonic systems provide an ideal platform for exploring exotic quantum vacuum phenomena predicted in ultrastrongly coupled light-matter systems.



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Makihara, T., Hayashida, K., Noe II, G.T. et al. Ultrastrong magnon–magnon coupling dominated by antiresonant interactions. Nat Commun 12, 3115 (2021). https://doi.org/10.1038/s41467-021-23159-z