Nonlocal collective ultrastrong interaction of plasmonic metamaterials and photons in a terahertz photonic crystal cavity

Abstract

Light-matter interaction in the strong coupling regime is of profound interest for fundamental quantum optics, information processing and the realization of ultrahighresolution sensors. Here, we report a new way to realize strong light-matter interaction, by coupling metamaterial plasmonic "quasi-particles" with photons in a photonic cavity, in the terahertz frequency range. The resultant cavity polaritons exhibit a splitting which can reach the ultra-strong coupling regime, even with the comparatively low density of quasi-particles, and inherit the high Q-factor of the cavity despite the relatively broad resonances of the Swiss-cross and split-ring-resonator metamaterials used. We also demonstrate nonlocal collective interaction of spatially separated metamaterial layers mediated by the cavity photons. By applying the quantum electrodynamic formalism to the density dependence of the polariton splitting, we can deduce the intrinsic transition dipole moment for singlequantum excitation of the metamaterial quasi-particles, which is orders of magnitude larger than those of natural atoms. These findings are of interest for the investigation of fundamental strong-coupling phenomena, but also for applications such as ultra-low-threshold terahertz polariton lasing, voltage-controlled modulators and frequency filters, and ultra-sensitive chemical and biological sensing. IntroductionStrong light-matter interaction in a resonant cavity is at the core of quantum electrodynamics (cavity QED) research. It has been intensively studied for several decades, as it both reveals and exploits fascinating quantum-optical phenomena such as entanglement, and provides a promising approach to quantum computing and quantum information processing [1][2][3][4][5]. While the strong coupling regime of cavity QED was initially explored with atoms, it was later realized with a range of fermionic solid-state material systems, involving, for instance, interband (excitonic) or inter-subband transitions in quantum wells [6][7][8] and quantum dots [9,10]. It was also demonstrated with a bosonic superconducting two-level system coupled to a microwave superconducting transmission line resonator [11], and, most recently, with cyclotron transitions in 2D electron gases [12,13], spin resonances in magnetic materials [14][15][16] and molecular vibrational transitions in polymers [17,18]. Strong interaction between localized surface plasmons and photons in either waveguide or metallic cavity was also investigated in the visible/infrared spectral range [19][20][21]. However, the fundamental research and applications are limited in these experiments due to the nano-scale size of the required structures. In the terahertz frequency range, on the other hand, it is difficult to realize a cavity with simple metallic reflectors due to the strong Drude absorption of free-carriers in metal.Here, by employing a dielectric photonic crystal cavity [13], we realize the strong interaction between photons and plasmonic quasi-particles consisting of electromagnetic metamat...

Superradiant Ensembles of Terahertz Polaritonic Meta-Atoms

“…an entity of strongly coupled systems. A comparable density dependent response of the vacuum Rabi frequency has been observed in a slightly different experiment using split ring resonator ensembles on a metamaterial surface placed in a THz photonic cavity [28]. Therefore, we state that for a surface consisting of subwavelengthly arranged polaritonic meta-atoms, the independent cavity assumption, as the state of the art approach for describing strongly coupled systems in the THz regime, is not valid.…”

“…Secondly, the array of (in this case metamaterial) cavities, which is usually treated to be without self-interaction. Nevertheless, it has been shown, that this assumption is not always valid depending on the chosen arrangement [26]- [28].…”

Room-temperature passive terahertz imaging based on high sensitivity field-effect transistor detectors

“…This work shows that TeraFETs can be used for various applications, such as spectroscopy [15,35,38,40,46,47], imaging [35,37,48], technical vision [15,18,35,37,47] as well as research-related applications [18,47,49]. The intended aim of this work was to explore and present the direct detection schemes.…”

“…This section presents a new approach of dielectric photonic crystal cavity for the research on strong coupling between photons and localized surface plasmons. This study was published in [49].…”

“…Here, the split-ring resonator (SRR) study is summarized which was also presented in more detail together with Swiss ring metamaterial experiments in [49]. The research on SRRs has been conducted using a continuous-wave Toptica system which has a few times better resolution than the TDS system used for Swiss ring MM experiments.…”