Ultrahigh cooperativity interactions between magnons and resonant photons in a YIG sphere

Abstract

Resonant photon modes of a 5mm diameter YIG sphere loaded in a cylindrical cavity in the 10-30GHz frequency range are characterised as a function of applied DC magnetic field at millikelvin temperatures. The photon modes are confined mainly to the sphere, and exhibited large mode filling factors in comparison to previous experiments, allowing ultrastrong coupling with the magnon spin wave resonances. The largest observed coupling between photons and magnons is 2g/2π = 7.11 GHz for a 15.5 GHz mode, corresponding to a cooperativity of C = 1.51±0.47×10 7 . Complex modifications beyond a simple multi-oscillator model, of the photon mode frequencies were observed between 0 and 0.1 Tesla. Between 0.4 to 1 Tesla, degenerate resonant photon modes were observed to interact with magnon spin wave resonances with different couplings strengths, indicating time reversal symmetry breaking due to the gyrotropic permeability of YIG. Bare dielectric resonator mode frequencies were determined by detuning magnon modes to significantly higher frequencies with strong magnetic fields. By comparing measured mode frequencies at 7 Tesla with Finite Element modelling, a bare dielectric permittivity of 15.96 ± 0.02 of the YIG crystal has been determined at about 20mK.

Entangling two magnon modes via magnetostrictive interaction

“…Such a system of two YIG spheres (without involving the mechanical mode) has been used to study magnon dark modes [16] and high-order exceptional points [18]. The magnetic dipole interaction mediates the coupling between magnons and cavity photons (see figure 1(b)), and this coupling can be very strong [1][2][3][4][5][6][7][8]. The mechanical mode is represented by the vibrations of the YIG sphere caused by the magnetostrictive force, which leads to the deformation of the geometry structure of the sphere and establishes the magnon-phonon coupling.…”

“…Ferrimagnetic systems, for example yttrium iron garnet (YIG), provide a unique platform for the study of the strong interactions between light and matter. Owing to their high spin density (several orders of magnitude larger than those of previous spin ensembles) and low dissipation rate, in recent years the strong [1][2][3][4][5][6] and ultrastrong [7,8] coupling between the Kittel mode [9] in the YIG sphere and the microwave cavity photons have been realized leading to cavity-magnon polaritons. 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].…”

Macroscopic entanglement of two magnon modes via quantum correlated microwave fields

“…In recent years, ferrimagnetic systems, like yttrium iron garnet (YIG), become an active and important platform for the study of strong interaction between light and matter, owing to their high spin density and low damping rate. Magnons, as collective excitations of a large number of spins, can strongly couple to cavity microwave photons [1][2][3][4][5][6][7][8] leading to cavity-magnon polaritons. The strong coherent interaction allows one to observe many interesting phenomena in cavity-magnon systems, such as the exceptional point [9], remote manipulation of spin currents [10], bistability [11], etc.…”

Experimental implementations of cavity-magnon systems: from ultra strong coupling to applications in precision measurement

“…Where the perturbative approach to solving dynamical equations breaks down in the USC and DSC regimes, new theoretical approaches have appeared [26,28,29]. The USC regime has been explored experimentally in various applications from coupled photons and superconducting qubits [30,31], to cavity-magnonic systems [8,10,32,33], to other forms of light matter coupling [34][35][36][37][38]. The DSC regime has also now been demonstrated experimentally in superconducting circuits [39,40], and terahertz light-Landau polariton couplings in nanostructure metamaterials [41].…”