Hybrid Light-Matter Particles Unlock Potential for Terahertz Quantum Technology
Summarize this article with:
Scientists have predicted the emergence of ferron-polaritons, novel quasiparticles formed by the interaction of ferroelectric excitations and light, within superconductor/ferroelectric/superconductor heterostructures. M. Nursagatov, Xiyin Ye, and G. A. Bobkov, alongside Tao Yu and I. V. Bobkova, demonstrate that this coupling not only provides direct evidence for the existence of ferrons but also achieves an ultrastrong-coupling regime with a terahertz-range spectral gap. This gap is significantly larger than observed in magnetic systems, highlighting the potent nature of electric dipole interactions. Their work establishes these heterostructures as a promising new platform for investigating extreme light-matter coupling and potentially enabling the development of rapid, terahertz-frequency quantum technologies based on ferroelectric materials. Ultrastrong coupling between ferroelectric ferrons and superconducting photons Scientists have predicted the formation of ferron-polaritons within superconductor/ferroelectric/superconductor heterostructures, representing a novel hybrid quasiparticle arising from the interaction between collective ferroelectric excitations, termed ferrons, and Swihart photons. This coupling provides direct evidence for the existence of ferrons and reaches the ultrastrong-coupling regime, characterised by a spectral gap in the terahertz range, significantly exceeding that of magnetic counterparts due to the inherent strength of electric dipole interactions. The research establishes these heterostructures as a promising platform for investigating extreme light-matter coupling and developing high-speed, terahertz-frequency quantum technologies based on ferroelectric materials. This work demonstrates that the ferron mode, polarized normal to the film interfaces within the heterostructure, couples to the Swihart photon mode of the superconducting resonator, ultimately forming ferron-polaritons. This interaction, a direct consequence of the ferroelectric material’s electric polarization, occurs under conditions of extreme electric field confinement between the superconducting electrodes. Consequently, the resulting coupling reaches the ultrastrong regime, with the characteristic energy scale, the ferron-polariton gap, being orders of magnitude larger than in analogous magnetic systems. The study considers a thin ferroelectric film sandwiched between two superconducting layers, analysing the collective electrodynamics of this configuration. Calculations reveal that the electric polarization fluctuations drive the formation of these hybrid quasiparticles, providing unambiguous experimental evidence for ferrons and their dynamic properties. The predicted ultrastrong coupling and terahertz-scale energy gap open possibilities for manipulating electric polarization at high speeds and exploring novel quantum phenomena. Furthermore, these findings establish a clear pathway towards the development of ferroelectric-based quantum optics and signal processing capabilities operating at microwave and terahertz frequencies. By bridging the gap between magnonics and ferronics, this research highlights the potential of superconductor/ferroelectric heterostructures for advancing quantum technologies and exploring fundamental aspects of light-matter interactions. The theoretical framework presented details the conditions necessary for observing these effects, paving the way for future experimental verification and device fabrication. Landau-Lifshitz-Gilbert modelling of ferroelectric free energy and spontaneous polarisation A superconducting/ferroelectric/superconducting trilayer heterostructure served as the foundation for investigating collective electrodynamics and the emergence of ferron-polaritons. The study employed planar geometry, fabricating thin films of ferroelectric material between two semi-infinite superconducting layers, as depicted in a schematic illustration. This configuration facilitated coupling between the ferron mode, polarized normal to the film interfaces, and the Swihart photon mode within the superconducting resonator. The free energy density was modelled using a Landau expansion, incorporating terms for uniaxial anisotropy and electric field dependence to describe the ferroelectric behaviour. Specifically, the free energy was defined as F = α1/2 P2y + α2/4 P4y + α3/2 (Px2 + Pz2) − 1/2Ed · P, where α1, α2, and α3 represent Landau parameters and P denotes the total electric polarization. The static spontaneous polarization, P0, was determined to be {0.746, 0.753, 0.265} C/m2 for LiNbO3, PbTiO3, and BaTiO3 respectively, minimizing the free energy under specific conditions. Analysis focused on the linear-response regime, assuming a dominant spontaneous polarization component, P0y, significantly larger than fluctuations in the x and z directions. The dynamics of the electric polarization were then governed by Newton’s Law, relating acceleration to the effective electric field derived from the total free energy. This approach allowed researchers to predict the formation of a spectral gap in the terahertz range, indicative of ultrastrong coupling between the ferron and Swihart photon modes, and providing direct evidence for the existence of ferrons as collective excitations of the ferroelectric order. Ultrastrong coupling and terahertz gap formation in ferroelectric heterostructures Researchers demonstrate the formation of ferron-polaritons within /ferroelectric/ heterostructures, establishing a hybrid light-matter quasiparticle arising from the coupling between ferroelectric excitations and Swihart photons. This coupling reaches the ultrastrong-coupling regime, evidenced by a spectral gap in the terahertz range, which is orders of magnitude larger than observed in magnetic analogues due to the superior strength of electric dipole interactions. The characteristic energy scale of this interaction is on the scale of terahertz frequencies, signifying a substantial advancement in light-matter coupling strength. The study focuses on thin ferroelectric films of thickness 2dP sandwiched between superconducting layers, utilising materials such as LiNbO3, PbTiO3, and BaTiO3 with static spontaneous polarization values of 0.746, 0.753, and 0.265 C/m2 respectively. Small fluctuations in electric polarization around a static value are described by a linearized Landau-Khalatnikov-Tani equation, revealing an ionic plasma frequency governing the dynamics of polarization. Analysis of these fluctuations indicates that the electric polarization fluctuation of frequency ω is uniform across the ferroelectric film, fulfilling the condition kdP ≪1 for thin-film behaviour. Calculations of the dynamical electric and magnetic fields radiated by ferronic excitations within the heterostructure utilise Maxwell’s equations and constitutive relations. Solutions to these equations in both superconducting and ferroelectric layers reveal that the superconducting layer exhibits a conductivity described by σS(ω) = i/(ωμ0λ2 eff) at frequencies around 1 terahertz, with an effective penetration depth λeff exceeding 100 nanometres. The resulting depolarization field, Ed, is expressed as −N δp, where N(k, ω) = ω2 ε0[ω2 −c2k2dP /(dP + λeff)] defines the coupling strength and demonstrates that fluctuations of electric polarization along the film normal radiate the electric field.
Terahertz Spectral Gaps and Isotropic Coupling in Ferron-Polariton Heterostructures Scientists have predicted the formation of ferron-polaritons within superconductor/ferroelectric/superconductor heterostructures, representing a novel hybrid quasiparticle. These entities arise from the interaction between collective ferroelectric excitations, termed ferrons, and Swihart photons, demonstrating a direct observation of ferrons themselves. The coupling between these components reaches the ultrastrong-coupling regime, characterised by a terahertz-range spectral gap significantly larger than that observed in comparable magnetic systems. This substantial gap reflects the inherent strength of electric dipole interactions relative to magnetic ones, highlighting a fundamental difference in their energy scales. The resulting ferron-polariton spectrum exhibits isotropy, differing markedly from the anisotropic behaviour of magnonic counterparts. These findings establish these heterostructures as a promising platform for investigating extreme light-matter coupling at terahertz frequencies and potentially enabling the development of high-speed, low-loss signal processing and quantum technologies utilising ferroelectric excitations. The authors acknowledge that the observed interaction is highly selective, with only ferron modes polarised perpendicular to the film actively participating, while in-plane modes remain unaffected. Future research may focus on exploring the potential of manipulating these ferron-polaritons for practical applications in terahertz signal processing and quantum devices, building upon the established platform for extreme light-matter interactions. Further investigation into the limitations of the plane-wave ansatz and the impact of dynamic polarization fluctuations could refine the theoretical model and broaden its applicability. 👉 More information 🗞 Ferron-Polaritons in Superconductor/Ferroelectric/Superconductor Heterostructures 🧠 ArXiv: https://arxiv.org/abs/2602.05473 Tags: