The Gilbert equation and the optical Bloch equations have a similar mathematical form. The analogies can be used to apply concepts from quantum optics on spintronic systems and vice versa, thereby bring new possibilities for exciting new applications.

 

The most fundamental effect in coherent quantum optics is the process of Rabi oscillations for which the electromagnetic radiation and 2-level systems interact coherently. Surprisingly, Rabi nutations have not been shown in one of the most abundant 2-state systems in nature: spins in ferromagnets, even in the classical limit.

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Here we developed a new technique which we can refer to as the pump-probe ferromagnetic resonance experiment and used it to show that Rabi’s formula is equally suitable to describe spins of ferromagnets [Nature Commun. 8, 16004 (2017)].

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Using this experimental method, we further reached the regime of spin mode-locking and showed that the microwave signal acts to overcome the inhomogeneous broadening by operating on a sub-ensemble. Hence, extended effective coherence times of the ensemble result.