Bistability of Cavity Magnon Polaritons

Abstract

We report the first observation of the magnon-polariton bistability in a cavity magnonics system consisting of cavity photons strongly interacting with the magnons in a small yttrium iron garnet (YIG) sphere. The bistable behaviors are emerged as sharp frequency switchings of the cavity magnon-polaritons (CMPs) and related to the transition between states with large and small number of polaritons. In our experiment, we align, respectively, the [100] and [110] crystallographic axes of the YIG sphere parallel to the static magnetic field and find very different bistable behaviors (e.g., clockwise and counter-clockwise hysteresis loops) in these two cases. The experimental results are well fitted and explained as being due to the Kerr nonlinearity with either positive or negative coefficient. Moreover, when the magnetic field is tuned away from the anticrossing point of CMPs, we observe simultaneous bistability of both magnons and cavity photons by applying a drive field on the lower branch.

Entangling two magnon modes via magnetostrictive interaction

“…In general, the magnetostrictive interaction is of different types depending on the resonance frequencies of the magnon and phonon modes [32], but the dispersive magnon-phonon interaction becomes dominant when the mechanical frequency is much smaller than the magnon frequency [13], which is the case to be considered in the present work. This magnon-phonon coupling is currently small [13], but it can be efficiently enhanced by driving the sphere with a strong microwave field [14,20]. The magnomechanical coupling strength is sensitive to the direction of the bias magnetic field [13], and we adjust the directions of the two bias magnetic fields (see figure 1(a)) such that only in one sphere the magnetostrictive interaction is effectively activated 2 .…”

“…This strong coupling offers a possibility to enable coherent information transfer between drastically different information carriers, and thus may find potential applications in quantum information processing, especially when the system becomes hybrid [10], such as by coupling magnons to a superconducting qubit [11,12], to phonons [13,14], or to both microwave and optical photons [15]. Furthermore, various interesting phenomena have been explored in the system of cavity-magnon polaritons, such as the observation of magnon gradient memory [16], the exceptional point [17,18], manipulation of distant spin currents [19], and bistability [20], to name but a few.…”

“…The intense magnon drive may bring about unwanted nonlinear effects due to the Kerr nonlinear term  † † m mm m in the Hamiltonian[20,42]. The Kerr coefficient  is inversely proportional to the volume of the sphere.…”

“…The Kerr coefficient  is inversely proportional to the volume of the sphere. For a 1 mm diam YIG sphere used in[20,42],  p »…”

Level attraction and level repulsion of magnon coupled with a cavity anti-resonance

“…Although the coupling strength between a single spin and a microwave photon is very weak, stronger coupling can be achieved by the use of collective excitations (also called as magnons) in ferrimagnetic materials such as yttrium iron garnet (YIG, Y 3 Fe 5 O 12 ) [4][5][6][7][8][9]. Various interesting phenomena, including the manipulation of spin current [10,11], the magnon quintuplet state [12], the exceptional point [13] and the bistability of cavity magnon polaritons [14] have been demonstrated in strongly coupled magnonphoton systems. In addition to the fundamental uniform mode, coupling between photons and higher order non-uniform modes has also been studied, with coupling strength depending on the overlap between the magnon and caity modes [15,16].…”