The emerging field of cavity spintronics utilizes the cavity magnon polariton (CMP) induced by magnon Rabi oscillations. In contrast to a single-spin quantum system, such a cooperative spin dynamics in the linear regime is governed by the classical physics of harmonic oscillators. It makes the magnon Rabi frequency independent of the photon Fock state occupation, and thereby restricts the quantum application of CMP. Here we show that a feedback cavity architecture breaks the harmonic-oscillator restriction. By increasing the feedback photon number, we observe an increase in the Rabi frequency, accompanied with the evolution of CMP to a cavity magnon triplet and a cavity magnon quintuplet. We present a theory that explains these features. Our results reveal the physics of cooperative polariton dynamics in feedback-coupled cavities, and open up new avenues for exploiting the light-matter interactions.
The emerging field of cavity spintronics utilizes the cavity magnon polariton (CMP) induced by magnon Rabi oscillations. In contrast to a single-spin quantum system, such a cooperative spin dynamics in the linear regime is governed by the classical physics of harmonic oscillators. It makes the magnon Rabi frequency independent of the photon Fock state occupation, and thereby restricts the quantum application of CMP. Here we show that a feedback cavity architecture breaks the harmonic-oscillator restriction. By increasing the feedback photon number, we observe an increase in the Rabi frequency, accompanied with the evolution of CMP to a cavity magnon triplet and a cavity magnon quintuplet. We present a theory that explains these features. Our results reveal the physics of cooperative polariton dynamics in feedback-coupled cavities, and open up new avenues for exploiting the light-matter interactions.
Magnons, the quanta of spin waves, have significant potential for use in modern technologies, especially when strongly coupled to another mode for read-out and control. However, while magnons strongly interact with microwave photons via the magnetic-dipole interaction to form hybrid cavity-magnon polariton modes, the weak magnetostrictive magnon-phonon interaction, together with large polariton linewidths dominated by magnon dissipation, has so far restricted magnonic-spheres to the weak-coupling regime. The material-limited magnon dissipation rate in particular has been regarded as an unavoidable limitation in these systems. Here, we surpass this long-standing limitation by implementing an active microwave feedback loop to suppress the linewidth of cavity-magnon polaritons and strongly suppress their effective decay rate below the magnon-limited linewidth, thereby enhancing the polariton-phonon cooperativity from C=1 to C=150. As a key milestone, we achieve normal-mode splitting between a cavity-magnon polariton and a mechanical mode, providing direct evidence of three-mode hybridization among photons, magnons, and phonons. Our results establish feedback as a general route to accessing strong-coupling regimes in systems previously thought to be limited by material properties and hence open new opportunities for coherent control in hybrid quantum systems.
Investigation of the spin-cavity polaritons (SCP) is important since they play a decisive role in creating long-storage quantum memories and optical interfaces, polaritonic chemistry, and masers, especially those which operate at room temperature, being of great significance for a lot of different applications. In this report, we suggest an almost completely classical model for the description of the polaritonic peaks conditioned both by free and forced Rabi oscillations of the SCP system. Our investigation is based on the linearized coupled differential equations we derived semi-classically for the magnetization component of the transition of the spin triplet states and the varying field in a cavity when the empty cavity is exactly tuned to the transition. The normal frequencies of this system of equations were found, and the corresponding graphs were constructed for the appropriate values of the parameters. It is shown that the increase in the spin-photon coupling can cause both the pushing apart of normal frequencies at a mutual decay rate (which is the known effect) and the merging together of normal decay rates at a mutual frequency (which is the predicted effect here). Polariton peaks, observable by the cavity transmission function and by EPR in the form of absorption and dispersion signals, were also investigated, and corresponding graphs were constructed. At that, instead of a transition of spin triplet states, a variety of other two-level systems (atoms, molecules, excitons, and so on) can act as emitters. Since the value of the spin-photon coupling is of great interest for applied scientists, obtaining this value by comparing our results with experimental data is of great importance.
Lithium ferrite (LiFe) is a promising material for cavity magnonics because its large spin density enables strong coupling between magnons and microwave photons. Its potential for cavity magnomechanics, however, has remained unexplored. Here, we observe magnomechanical interactions in a single-crystal LiFe sphere using coherent microwave feedback to suppress dissipation of the cavity--magnon polariton. In the absence of sufficient feedback, the narrow mechanical response is difficult to resolve against the much broader polariton background. Increasing the feedback gain reduces the polariton linewidth and correspondingly increases the magnomechanical cooperativity, revealing a clear magnomechanically induced transparency feature. In the measurements presented here, the effective upper-polariton linewidth is reduced from 3.53MHz without feedback to 5.8kHz in the presence of feedback, while the measured cooperativity increases from C=1.9×10−3 to C=0.15. These measurements provide, to our knowledge, the first observation of cavity magnomechanics in LiFe and demonstrate coherent feedback as a practical route for accessing weak interactions that would otherwise be obscured by dissipation.
Investigation of the spin-cavity polaritons (SCP) is important since they play decisive role for the creating long-storage quantum memories and optical interfaces, polaritonic chemistry and for the elaborating of masers, especially those which operate at room temperature being of the great significance for a lot of different applications. In this report, we suggest almost completely classical model for the description of the polaritonic peaks conditioned both by free and forced Rabi oscillations of the SCP system. Our investigation is based on the linearized coupled differential equations we derived semi-classically for the magnetization component of the transition of the spin triplet states and the varying field in a cavity, when the empty cavity is exactly tuned to the transition. The normal frequencies of this system of equations were found and the corresponding graphs were constructed for the appropriate values of the parameters. It is shown that the increase of the spin-photon coupling can cause both pushing apart normal frequencies at a mutual decay rate (which is the known effect), and merging together normal decay rates at a mutual frequency (which is the predicted here effect). Polariton peaks observable by the cavity transmission function and by electron paramagnetic resonance (EPR) in the form of absorption and dispersion signals were also investigated and corresponding graphs were constructed. At that, instead of a transition of spin triplet states, a variety of other two-level systems (atoms, molecules, excitons and so on) can act as emitters. Since the value of the spin-photon coupling is of great interest for applied scientists, obtaining this value by comparing our results with experimental data is of great importance.
Manipulating the cavity-magnon polariton blockade is significant for achieving precise, on-demand control of individual photons (magnons) and has particular applications in realizing multifunctional quantum technologies, quantum information processing, and hybrid quantum networks. In this paper, we theoretically propose a scheme to realize an n-cavity-magnon polariton blockade in a cavity-magnon system by utilizing Kerr nonlinearity. We demonstrate that the Kerr nonlinearity introduces anharmonicity into the polariton energy spectrum, which in turn enables the blockade effect. When the external driving frequency is resonant with the transition to the nth polariton excited state, a perfect n-polariton blockade is achieved. Moreover, increasing the driving strength can enhance the higher-order blockade while maintaining high fidelity in a dissipative environment. Our work pioneers the field of cavity-magnon polariton blockade, opens a new avenue for the preparation of controllable quantum resources, and holds significant potential for applications in quantum communication and quantum information processing.
Cavity quantum electrodynamics provides an ideal platform to engineer and control light-matter interactions with polariton quasiparticles. In this work, we investigate collective phenomena in a system of many particles in a harmonic trap coupled to a homogeneous cavity vacuum field. The system couples collectively to the cavity field, through its center of mass, and collective polariton states emerge. The cavity field mediates pairwise long-range interactions and enhances the effective mass of the particles. This leads to an enhancement of localization in the matter ground state density, which features a maximum when light and matter are on resonance, and demonstrates a Dicke-like, collective behavior with the particle number. The light-matter interaction also modifies the photonic properties of the polariton system, as the ground state is populated with bunched photons. In addition, it is shown that the diamagnetic A^2 A 2 term is necessary for the stability of the system, as otherwise the superradiant ground state instability occurs. We demonstrate that coherent transfer of polaritonic population is possible with an external magnetic field and by monitoring the Landau-Zener transition probability.