Polariton Band Gap Research Articles

Waveguide bandgap engineering with an array of superconducting qubits

Waveguide quantum electrodynamics offers a wide range of possibilities to effectively engineer interactions between artificial atoms via a one-dimensional open waveguide. While these interactions have been experimentally studied in the few qubit limit, the collective properties of such systems for larger arrays of qubits in a metamaterial configuration has so far not been addressed. Here, we experimentally study a metamaterial made of eight superconducting transmon qubits with local frequency control coupled to the mode continuum of a waveguide. By consecutively tuning the qubits to a common resonance frequency we observe the formation of super- and subradiant states, as well as the emergence of a polaritonic bandgap. Making use of the qubits quantum nonlinearity, we demonstrate control over the latter by inducing a transparency window in the bandgap region of the ensemble. The circuit of this work extends experiments with one and two qubits toward a full-blown quantum metamaterial, thus paving the way for large-scale applications in superconducting waveguide quantum electrodynamics.

Observation and Active Control of a Collective Polariton Mode and Polaritonic Band Gap in Few-Layer WS2 Strongly Coupled with Plasmonic Lattices.

Two-dimensional semiconductors host excitons with very large oscillator strengths and binding energies due to significantly reduced carrier screening. Two-dimensional semiconductors integrated with optical cavities are emerging as a promising platform for studying strong light-matter interactions as a route to explore a variety of exotic many-body effects. Here, in few-layered WS2 coupled with plasmonic nanoparticle lattices, we observe the formation of a collective polaritonic mode near the exciton energy and the formation of a complete polariton band gap with energy scale comparable to the exciton-plasmon coupling strength. A coupled oscillator model reveals that the collective mode arises from the cooperative coupling of the excitons to the plasmonic lattice diffraction orders via exciton-exciton interactions, leading to ultrastrong coupling. The emergence of the collective mode is accompanied by a superlinear increase of the polariton mode splitting as a function of the square root of the exciton oscillator strength. The presence of these many body effects, which are enhanced in systems which lack bulk polarization, not only allows the formation of a collective mode with periodically varying field profiles, but also further enhances the exciton-plasmon coupling. By integrating the hybrid WS2-plasmonic lattice device with a field-effect transistor, we demonstrate active tuning of the collective mode and the polariton band gap. We also report electrically tunable waveguiding in the polariton band gap region through a line defect, which can be turned off with gate bias that can extinguish the collective mode and the polariton band gap. These systems provide new opportunities for obtaining a deeper and systematic understanding of many body cooperative phenomena in two-dimensional materials coupled with periodic photonic systems and for designing more complex and actively controllable polaritonic devices including switchable polariton lasers, waveguides, and optical logical elements.

Topological Phases of Polaritons in a Cavity Waveguide.

We study the unconventional topological phases of polaritons inside a cavity waveguide, demonstrating how strong light-matter coupling leads to a breakdown of the bulk-edge correspondence. We observe an ostensibly topologically nontrivial phase, which unexpectedly does not exhibit edge states. Our findings are in direct contrast to topological tight-binding models with electrons, such as the celebrated Su-Schrieffer-Heeger (SSH) model. We present a theory of collective polaritonic excitations in a dimerized chain of oscillating dipoles embedded inside a photonic cavity. The added degree of freedom from the cavity photons upgrades the system from a typical SSH SU(2) model into a largely unexplored SU(3) model. Tuning the light-matter coupling strength by changing the cavity size reveals three critical points in parameter space: when the polariton band gap closes, when the Zak phase changes from being trivial to nontrivial, and when the edge state is lost. These three critical points do not coincide, and thus the Zak phase is no longer an indicator of the presence of edge states. Our discoveries demonstrate some remarkable properties of topological matter when strongly coupled to light, and could be important for the growing field of topological nanophotonics.

Field Tunable Polaritonic Band Gaps in Fibonacci Piezoelectric Superlattices**Supported by the National Natural Science Foundation of China under Grant No 11705155, the Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province, the Projects of Hunan Provincial Education Office under Grant Nos 16B243, 17B244 and 16A199, and the Chenzhou City Science and Technology Project under Grant Nos

The Fibonacci piezoelectric superlattices (FPSs) with an external dc electric field is presented, in which the dc electric field can tune the bandwidth of polaritonic band gaps (PBGs) continuously and reversibly via the electro-optic effect. The absolute bandwidths of two major PBGs of the FPSs around ω = 7.5 GHz and ω = 12.5 GHz can be broadened from 0.022 GHz to 0.74 GHz and from 0.02 GHz to 0.82 GHz with the dc electric field increasing from 0 to 1.342 × 106 V/m, respectively. The corresponding relative bandwidths of the two major PBGs are widened from 0.28% to 9.2% and from 0.18% to 6.35%, respectively. The general mechanism for the bandwidth tunability is that the coupling strength between the lattice vibration and electromagnetic waves is capable of being altered by the dc electric field via the electro-optic effect. Thus the properties can be applied to construct microwave switchings or field tunable bulk acoustic filters.

Coupled polaritonic band gaps in the anisotropic piezoelectric superlattices

Anisotropic piezoelectric superlattices (APSs) with the periodic arrangement of polarized anisotropic piezoelectric domains in a certain direction are presented, in which the coupled polaritonic band gaps (CPBGs) can be obtained in the whole Brillouin Zone and the maximum relative bandwidth (band-gap sizes divided by their midgap frequencies) of 5.1% can be achieved. The general characteristics of the APSs are similar to those of the phononic crystals composed of two types of materials, with the main difference being the formation mechanism of the CPBGs, which originate from the couplings between lattice vibrations along two different directions and electromagnetic waves rather than from the periodical modulation of density and elastic constants. In addition, there are no lattice mismatches because the APSs are made of the same material. Thus, the APSs can also be extended to the construction of novel acousto-optic devices.

Light propagation in two-dimensional photonic crystals based on uniaxial polar materials: results on polaritonic spectrum

The dispersion relations of two-dimensional photonic crystals made of uniaxial polaritonic cylinders arranged in triangular lattice are calculated. The particular case of the transverse magnetic polarization is taken into account. Three different uniaxial materials showing transverse phonon-polariton excitations are considered: aluminum nitride, gallium nitride, and indium nitride. The study is carried out by means of the finite-difference time-domain technique for the solution of Maxwell equations, together with the method of the auxiliary differential equation. It is shown that changing the filling fraction can result in the modification of both the photonic and polaritonic bandgaps in the optical dispersion relations. Wider gaps appear for smaller filling fraction values, whereas a larger number of photonic bandgaps will occur within the frequency range considered when a larger filling fraction is used. The effect of including the distinct wurtzite III–V nitride semiconductors as core materials in the cylinders embedded in the air on the photonic properties is discussed as well, highlighting the effect of the dielectric anisotropy on the properties of the polaritonic part of the photonic spectrum.

Multiple Rabi Splittings under Ultrastrong Vibrational Coupling.

From the high vibrational dipolar strength offered by molecular liquids, we demonstrate that a molecular vibration can be ultrastrongly coupled to multiple IR cavity modes, with Rabi splittings reaching 24% of the vibration frequencies. As a proof of the ultrastrong coupling regime, our experimental data unambiguously reveal the contributions to the polaritonic dynamics coming from the antiresonant terms in the interaction energy and from the dipolar self-energy of the molecular vibrations themselves. In particular, we measure the opening of a genuine vibrational polaritonic band gap of ca. 60meV. We also demonstrate that the multimode splitting effect defines a whole vibrational ladder of heavy polaritonic states perfectly resolved. These findings reveal the broad possibilities in the vibrational ultrastrong coupling regime which impact both the optical and the molecular properties of such coupled systems, in particular, in the context of mode-selective chemistry.

Scaling the Artificial Polariton Bandgap at Infrared Frequencies Using Indium Tin Oxide Nanorod Arrays

Artificial polariton bandgaps at infrared frequencies are investigated by exploiting the strong coupling of electromagnetic waves with induced electric dipoles in two‐dimensional (2D) indium tin oxide nanorod arrays (ITO‐NRAs). The electric dipoles originate from the collective oscillations of free electrons within the individual ITO nanorods undergoing plasmonic resonance. Controlling the near‐field interactions among the neighboring electric dipoles allows for manipulation of the collective polariton modes that are manifested as a polariton bandgap. A theoretical model is developed to understand the coupled phenomena underlying the unique characteristics of plasmon–polariton bandgaps. With high‐degree geometric control of the ITO‐NRAs, it is experimentally demonstrated that reducing the spacing between ITO nanorods in a square array strengthens the near‐field interactions and thus results in a redshift as well as broadening of the polariton bandgap. Furthermore, arranging ITO‐NRAs in a rectangular lattice breaks the symmetry with respect to the principle axis, which leads to a splitting of the collective polariton modes owing to the competition between the quasi‐longitudinally and quasi‐transversely coupled plasmon–polariton modes. The work highlights the use of a classical dipole coupling method for scaling polariton bandgaps to the infrared in artificial plasmonic lattices, thereby offering a new design dimension for infrared sensing, absorbers, and optical communications.

One-way electromagnetic waveguide using multiferroic Fibonacci superlattices

The multiferroic Fibonacci superlattices (MFSs) are composed of single-phase multiferroic domains with polarization and magnetization according to the rule of Fibonacci sequence. We propose to construct a one-way electromagnetic waveguide by the MFSs. The forbidden band structures of the MFSs for the forward and backward electromagnetic waves are not completely overlapped, and an obvious translation between them occurs around the fixed point ω¯=1 with broken time-reversal and space inversion symmetries (TRSIS), which indicates the existence of one-way electromagnetic modes in the MFSs. Transmission spectrum is utilized to present this property and to indicate further one-way electromagnetic modes lying within the polaritonic band gap. The maximum forbidden bandwidth (divided by midgap frequency) of 5.4% for the backward electromagnetic wave (BEW) is found, in which the forward electromagnetic wave (FEW) can pass. The functions of one-way propagation modes and polaritonic band gap integrated into the MFSs can miniaturize the one-way photonic devices. The properties can also be applied to construct compact microwave isolators.

Tunable plasmon polaritons in arrays of interacting metallic nanoparticles

We consider a simple cubic array of metallic nanoparticles supporting extended collective plasmons that arise from the near-field dipolar interaction between localized surface plasmons in each nanoparticle. We develop a fully analytical quantum theory of the strong-coupling regime between these collective plasmons and photons resulting in plasmon polaritons in the nanoparticle array. Remarkably, we show that the polaritonic band gap and the dielectric function of the metamaterial can be significantly modulated by the polarization of light. We unveil how such an anisotropic behavior in the plasmonic metamaterial is crucially mediated by the dipolar interactions between the nanoparticles despite the symmetry of the underlying lattice. Our results thus pave the way towards the realization of tunable quantum plasmonic metamaterials presenting interaction-driven birefringence.

Surface Plasmon Polariton Band Gap-Enabled Plasmonic Mach–Zehnder Interferometer: Design, Analysis, and Application

In this paper, we propose a design for surface plasmon polariton band gap (SPPBG)-enabled plasmonic Mach–Zehnder interferometer (PMZI) comprising of array of silver nanorods embedded upright into silicon on insulator (SOI) substrate and analyze its potential in sensing, intended for cancer therapy. Periodic arrangement of nanorods embedded into SOI substrate grants strong spatial confinement and assist waveguidance to the propagating plasmon mode due to the SPPBG effect. This arrayed system triggers local field enhancement promoting sensing proficiency of the device and is assessed in terms of wavelength and phase shift. Proposed design of SPPBG-enabled PMZI sensor is successfully employed for detection and classification of various cancerous cells. The structural parameters of PMZI are optimized in compliance with the plasmonic band gap in the range of 400–800 nm yielding exceptionally high sensitivity at input wavelength of 633 nm. Volumetric analysis of the analyte reveals that very small analyte volume of the order of 10−15 cc is sufficient to yield significant phase shift. Phase shift obtained for the breast adenocarcinoma and blood cancer cell lines are 1.2357radian and 0.3351radian, respectively, which read very high value of phase shifts to identify extremely small changes in refractive index of the analyte. Figure of merit calculated thereby expose impressive device performance outdoing preceding plasmonic sensors leading to validation of proposed ultra-compact-sensitive PMZI design.

Magnetoelectrically coupled polariton excitation in a plasmonic crystal composed of nanorod dimers

In this work, the long wavelength optical properties of a plasmonic crystal, composed of gold nanorod dimers arranged parallel, have been studied. Due to the strong coupling between incident light and the oscillation of free electrons inside nanorod dimers, the magnetically induced and/or magnetoelectrically coupled plasmonic polaritons can be excited. A theoretical demonstration has been proposed and coupled equations that show similar profiles to the Huang–Kun equations for ionic crystals have been deduced, indicating the constitutive abnormalities and polaritonic bandgap effect. The analogy between the magnetoelectrically coupled metamaterials and ionic crystals may shed light on physical explanations, as well as constitutive parameter retrieval, for the magnetoelectric metamaterials.

Coherent light emission from a nanosystem embedded within a polaritonic band-gap medium

This paper demonstrates how we can generate coherent light of lasing characteristics from a system made of a two-level system and a nanoparticle. The lasing is achieved by embedding the whole system in a polaritonic band-gap material. The study is conducted on silver nanoparticles embedded within silicon carbide.

Characterization of the surface plasmon polariton band gap in an Ag/SiO_2/Ag T-shaped periodical structure

In this study, the localized surface plasmon polariton (LSPP) band gap of an Ag/SiO(2)/Ag asymmetric T-shaped periodical structure is demonstrated and characterized. The Ag/SiO(2)/Ag asymmetric T-shaped periodical structure was designed and fabricated to exhibit the LSPP modes in an infrared wavelength regime, and its band gap can be manipulated through the structural geometry. The LSPP band gap was observed experimentally with the absorbance spectra and its angle dependence characterized with different incident angles. Such a T-shaped structure with a LSPP band gap can be widely exploited in various applications, such as emitters and sensors.

SURFACE PLASMON ENHANCED PHOTOLUMINESCENCE ON BIHARMONIC GRATING STRUCTURE

We compare the fluorescence enhancement from a conducting polymer film placed on top of a sinusoidal and biharmonic metallic grating. On the biharmonic grating, which possesses a surface plasmon polariton band-gap, the enhancement factor was larger than that on a sinusoidal grating, even though the coupling efficiency of the surface plasmon polariton was lower for the biharmonic grating. We investigate the mechanism of fluorescence enhancement numerically by finite difference time domain analyses and attribute the larger fluorescence enhancement to the electric field of the short wavelength band-edge mode extending longer into the dielectric region where the fluorophore is placed.

Spontaneous Emission Rate Enhancement of Silicon Nanocrystals by Plasmonic Bandgap on Copper Grating

The spontaneous emission (SE) rate enhancement due to surface plasmon polariton bandgap effect on copper grating was evaluated by calculating the dispersion relation and the electromagnetic field distribution simultaneously. Within the frequency range of silicon nanocrystals (Si-NC) luminescence ((h/2p)?=1.6 eV-1.9 eV), the calculated maximum averaged Purcell factors is about 30-163 for sinusoidal shaped Cu-Si3N4 grating. It is proved that copper can be adopted to enhance the SE of Si-NCs. Since copper is the most commonly adopted metal for silicon integrated-circuit manufacturing, such results pave a promising way for integrating Si emitters on microelectronics chips.

Calculated plasmonic enhancement of spontaneous emission from silicon nanocrystals with metallic gratings

The spontaneous emission rate (SER) enhancement due to the surface plasmon polariton (SPP) band gap effect of metallic gratings was evaluated by calculating the dispersion relation and electromagnetic field distribution simultaneously. Within the luminescence range of silicon nanocrystals (Si-NC) ( ℏω = 1.9 eV–1.6 eV), the calculated peak Purcell factors for Au-, Ag-, and Al-Si 3N 4 gratings are 266.9–30.1, 80.2–22.6, and 78.7–20.3, respectively. These results indicate that the common metals such as Au, Ag and Al, whose SPP resonance frequencies/energies are rather higher, can be adopted to enhance the SER of Si-NCs with the help of metallic gratings.

Phonon polaritons in photonic crystals at terahertz frequency range

We investigate the phonon-polariton band gaps in periodic and quasi-periodic (Fibonacci-type) multilayers made up of both positive (SiO2) and negative refractive index materials (metamaterials) following the Fibonacci sequence in the terahertz region. The behavior of the polaritonic band gaps as a function of the multilayer period is investigated systematically. Our theoretical model makes use of a transfer matrix approach to simplify the algebra involved and to set up analytical phonon-polariton dispersion relations (bulk and surface modes). We also present a quantitative analysis of the results, pointing out the distribution of the allowed polaritonic bandwidths for high Fibonacci generations, which gives good insight about their localization and power laws.

Localization and Scaling Behavior of Polariton-Gap in Fibonacci and Symmetric Fibonacci-Class Piezomagnetic Superlattices

A comparative study is made on the localization and scaling behavior in piezomagnetic Fibonacci and symmetric Fibonacci-class [SFC( n )] superlattices. For this photon–phonon coupled system, the polaritonic band-gap structures and transmission spectra both show a pattern of self-similarity, the fractal pattern in transmission spectra clearly demonstrates the (quasi)localization nature of polaritons. For Fibonacci superlattices self-similarity behavior takes place between the l th and the ( l +3)th generations, the scaling index α' = τ 3 = 4.236 with \(\tau = 0.5(\sqrt{5} + 1)\) denoting the golden mean. While for the generalized symmetric Fibonacci-class [SFC( n )] superlattices, self-similarity behavior occurs between the l th and the ( l +1)th generations and the scaling index \(\alpha'' = 0.5(n + \sqrt{n^{2} + 4})\). We conclude that the internal symmetric structure is responsible for the evolution of such scaling behavior.

One-dimensional photonic crystal based on nanocomposite of metal nanoparticles and dielectric

One-dimensional photonic crystal made of nanocomposite of metallic nanoparticles and dielectric is investigated. Splitting of photonic band gap into polaritonic and structure band gap and their fusion are predicted. The different behavior of structure gap with variation of nanoparticle concentration is observed. This behavior is determined by relative arrangement of structure and polaritonic gaps in frequency scale. Considered effects give new possibilities for creating photonic crystals with predefined properties.