Superstrong coupling of a microwave cavity to yttrium iron garnet magnons

Abstract

Multiple-post reentrant 3D lumped cavity modes have been realized to design the concept of discrete Whispering Gallery and Fabry-Pérot-like Modes for multimode microwave Quantum Electrodynamics experiments. Using a magnon spin-wave resonance of a submillimeter-sized Yttrium-IronGarnet sphere at milliKelvin temperatures and a four-post cavity, we demonstrate the ultra-strong coupling regime between discrete Whispering Gallery Modes and a magnon resonance with strength of 1.84 GHz. By increasing the number of posts to eight and arranging them in a D4 symmetry pattern, we expand the mode structure to that of a discrete Fabry-Pérot cavity and modify the Free Spectral Range (FSR). We reach the superstrong coupling regime, where spin-photon coupling strength is larger than FSR, with coupling strength in the 1.1 to 1.5 GHz range.Cavity Quantum Electrodynamics (QED) is a conceptual paradigm dealing with light-matter interaction at the quantum level that has been investigated in a number of various systems. There is a broad range of various problems that have to be solved by cavity QED including generation of nonclassical states[1], quantum memory [2], quantum frequency conversion [3,4], etc. For many of these applications, it is important to combine advantages of different approaches to QED in a Hybrid Quantum System (HQS) [5,6]. For example, combination of nonlinear properties of superconducting circuits based on Josephson Junction and large electron [7] or nuclearspin[8] ensembles can be used for new quantum protocols without single spin manipulation and is investigated in many physical implementations [9][10][11][12][13].In the process of HQS design, it is vital to be able to engineer photon modes by continuous adjustment of system parameters without reinventing a new cavity. It is important to have a single platform that can provide a broad range of spectra required for each particular purpose. Moreover, in order to achieve strong coupling with other elements of HQS, such a platform should guarantee reconfigurable high space localisation of both electrical and magnetic fields to achieve sufficient filling factors. Finally, such cavities are required to be adjustable in-situ in the wide range preferably at high speed rate. These features are lacking for traditional 3D cavities such as box resonators and microwave Whispering Gallery Mode resonators. Having only one or two free parameters to control, these platforms can be hard to modify for a particular set of requirements in terms of field patterns, spectra and tunability without significant change of their structure.All the described requirements are met by constructing designs based on the recently proposed multi-post reentrant cavity [14,15] that is based on a known 3D closed resonator with a central post gap [16,17]. For this platform, it has been demonstrated that by an a priori rearrangement of the post, one can easily engineer the device resonance frequencies and field patterns to achieve high frequency and space localisation [14] that guarantees strong coupli...

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].…”

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].…”

Ground-state cooling of a magnomechanical resonator induced by magnetic damping

“…3, we have N bs ≃ 0.257 by Eq. (13). Under the same parameters, the numerical solution of the mean phonon number obtained from the quantum master equation is shown in Fig.…”