Open Access
Spatiotemporal symmetries and energy-momentum conservation in uniform spacetime metamaterials
(American Chemical Society, 2024-11-13) Liberal Olleta, Íñigo; Ganfornina Andrades, Antonio; Vázquez Lozano, Juan Enrique; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Spacetime metamaterials are opening new regimes of light-matter interactions based on the breaking of temporal and spatial symmetries, as well as intriguing concepts associated with synthetic motion. In this work, we investigate the continuous spatiotemporal translation symmetry of spacetime metamaterials with uniform modulation velocity. Using Noether's theorem, we demonstrate that such symmetry entails the conservation of the energy momentum. We highlight how energy-momentum conservation imposes constraints on the range of allowed light-matter interactions within spacetime metamaterials, as illustrated with examples of the collision of electromagnetic and modulation pulses. Furthermore, we discuss the similarities and differences between the conservation of energy-momentum and relativistic effects. We believe that our work provides a step forward in clarifying the fundamental theory underlying spacetime metamaterials.
Open Access
Symmetries in time-varying media: on the conservation of spin angular momentum, helicity, and chirality
(IEEE, 2024) Mohammadi Jajin, Mohsen; Vázquez Lozano, Juan Enrique; Liberal Olleta, Íñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
Our results demonstrate that time-varying media exacerbate the differences between the symmetries and conserved quantities associated with dynamical properties associated with the circular polarization of light. In this manner, we provide further insights into the physical meaning of helicity and chirality, including their similarities and differences, as well as the fundamental role played by the symmetries of the electromagnetic Lagrangian in time-varying media.
Open Access
Shaping the quantum vacuum with anisotropic temporal boundaries
(De Gruyter, 2022) Vázquez Lozano, Juan Enrique; Liberal Olleta, Íñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
Temporal metamaterials empower novel forms of wave manipulation with direct applications to quantum state transformations. In this work, we investigate vacuum amplification effects in anisotropic temporal boundaries. Our results theoretically demonstrate that the anisotropy of the temporal boundary provides control over the angular distribution of the generated photons. We analyze several single and multi-layered configurations of anisotropic temporal boundaries, each with a distinct vacuum amplification effect. Examples include the inhibition of photon production along specific directions, resonant and directive vacuum amplification, the generation of angular and frequency photon combs and fast angular variations between inhibition and resonant photon production.
Open Access
Orthogonal thermal noise and transmission signals: a new coherent perfect absorption's feature
(American Physical Society, 2024-09-06) Oña Valladares, Douglas; Ortega Gómez, Ángel; Hernández Martínez, Osmery; Liberal Olleta, Íñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
Coherent perfect absorption (CPA) is an interference process associated with the zeros of the scattering matrix of interest for optical computing, data processing, and sensing. However, the noise properties of CPA remain relatively unexplored. Here, we demonstrate that CPA thermal noise signals exhibit a unique property: they are orthogonal to the signals transmitted through the network. In turn, such property enables a variety of thermal noise management effects, such as the physical separability of thermal noise and transmitted signals, and "externally lossless"networks that internally host radiative heat transfer processes. We believe that our results provide a new perspective on the many CPA technologies currently under development.
Open Access
Optomagnonics in dispersive media: magnon-photon coupling enhancement at the epsilon-near-zero frequency
(American Physical Society, 2022) Bittencourt, V.A.S.V.; Liberal Olleta, Íñigo; Viola Kusminskiy, Silvia; Ingeniaritza Elektrikoa eta Elektronikoa; Institute of Smart Cities - ISC; Ingeniería Eléctrica y Electrónica
Reaching strong light-matter coupling in solid-state systems has long been pursued for the implementation of scalable quantum devices. Here, we put forward a system based on a magnetized epsilon-near-zero (ENZ) medium, and we show that strong coupling between magnetic excitations (magnons) and light can be achieved close to the ENZ frequency due to a drastic enhancement of the magneto-optical response. We adopt a phenomenological approach to quantize the electromagnetic field inside a dispersive magnetic medium in order to obtain the frequency-dependent coupling between magnons and photons. We predict that, in the epsilon-near-zero regime, the single-magnon single-photon coupling can be comparable to the magnon frequency for a small magnetic volume and perfect mode overlap. For state-of-the-art illustrative values, this would correspond to achieving the single-magnon strong coupling regime, where the coupling rate is larger than all the decay rates. Finally, we show that the nonlinear energy spectrum intrinsic to this coupling regime can be probed via the characteristic multiple magnon sidebands in the photon power spectrum.
Open Access
Amorphous glass-coated ferromagnetic wires in microwave engineering
(2013) Liberal Olleta, Íñigo; Gonzalo García, Ramón; Ederra Urzainqui, Íñigo; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
En esta tesis se ha estudiado el uso de hilos ferromagnéticos recubiertos de vidrio en ingeniería de microondas. Para este fin, se han formulado modelos analíticos y equivalentes circuitales de la interacción entre un hilo ferromagnético y campos electromagnéticos. Dichos modelos se han utilizado para estudiar los fenómenos más relevantes relacionados con la interacción entre un hilo ferromagnético y campos electromagnéticos, incluyendo la transición de efectos superficiales a volumétricos, y las múltiples peculiaridades del espectro de absorción. Además, se han investigado los límites fundamentales en el equilibrio de potencias presente en interacciones de un hilo ferromagnético con campos electromagnéticos, así como sus implicaciones tecnológicas. Estructuras consistentes en varios hilos ferromagnéticos se han modelado como materiales electromagnéticos artificiales (los cuales pertenecen a la clase de materiales dieléctricos con permitividad controlada por las propiedades magnéticas de los hilos) y superficies artificiales. Basado en estos estudios fundamentales, absorbentes electromagnéticos reconfigurables y sensores de estrés mecánico basados en técnicas de radar se han identificado como las aplicaciones más prometedoras. A este respecto, se han presentado diseños de prueba de concepto de un absorbente de banda ancha con una banda estrecha de reflexión, y un absorbente de banda estrecha. Dichos dispositivos podrían utilizarse en la práctica para monitorizar objetos ocultos a observadores externos, y para mitigar interferencias en comunicaciones inalámbricas. En lo concerniente a sensores de estrés mecánico basados en técnicas de radar, se ha presentado un procedimiento para caracterizar los hilos bajo estreses mecánicos. Utilizando dicha técnica se han caracterizado hilos en los que la posición en frecuencia de la resonancia ferromagnética natural aumenta en función del estrés aplicado. Estos resultados sugieren el uso de hilos ferromagnéticos para monitorizar estructuras arquitectónicas e implantes.
Open Access
Silicon carbide as a material-based high-impedance surface for enhanced absorption within ultra-thin metallic films
(Optical Society of America, 2020) Pérez Escudero, José Manuel; Buldain, Iban; Beruete Díaz, Miguel; Goicoechea Fernández, Javier; Liberal Olleta, Íñigo; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
The absorption of infrared radiation within ultra-thin metallic films is technologically relevant for different thermal engineering applications and optoelectronic devices, as well as for fundamental research on sub-nanometer and atomically-thin materials. However, the maximal attainable absorption within an ultra-thin metallic film is intrinsically limited by both its geometry and material properties. Here, we demonstrate that material-based high-impedance surfaces enhance the absorptivity of the films, potentially leading to perfect absorption for optimal resistive layers, and a fourfold enhancement for films at deep nanometer scales. Moreover, material-based high-impedance surfaces do not suffer from spatial dispersion and the geometrical restrictions of their metamaterial counterparts. We provide a proof-of-concept experimental demonstration by using titanium nanofilms on top of a silicon carbide substrate.
Open Access
Thermal emission in temporal metamaterials: fundamentals and novel phenomena
(IEEE, 2023) Vázquez Lozano, Juan Enrique; Liberal Olleta, Íñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
Thermal emission is a fundamental issue that customarily has been fueled by the developments carried out in nanophotonics. Given such a parallelism and the latest advances bringing forward the realization of temporal metamaterials, in this work we combine both topics to sketch out an original theoretical formulation for rigorously addressing thermal emission in time-modulated media. Upon this ground, we find new physics and thermal phenomena, highlighting the emergence of non-local correlations, the possibility to overcome the black-body spectrum by temporal means, as well as the role of ENZ bodies as genuine platforms to enhance thermal emission, and the conception of innovative thermal emitters dual to spatial gratings.
Open Access
Magnetic dipole super-resonances and their impact on mechanical forces at optical frequencies
(Optical Society of America, 2014) Liberal Olleta, Íñigo; Ederra Urzainqui, Íñigo; Gonzalo García, Ramón; Ziolkowski, Richard W.; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
Artificial magnetism enables various transformative optical phenomena, including negative refraction, Fano resonances, and unconventional nanoantennas, beamshapers, polarization transformers and perfect absorbers, and enriches the collection of electromagnetic field control mechanisms at optical frequencies. We demonstrate that it is possible to excite a magnetic dipole super-resonance at optical frequencies by coating a silicon nanoparticle with a shell impregnated with active material. The resulting response is several orders of magnitude stronger than that generated by bare silicon nanoparticles and is comparable to electric dipole super-resonances excited in spaser-based nanolasers. Furthermore, this configuration enables an exceptional control over the optical forces exerted on the nanoparticle. It expedites huge pushing or pulling actions, as well as a total suppression of the force in both far-field and near-field scenarios. These effects empower advanced paradigms in electromagnetic manipulation and microscopy.
Open Access
Superbackscattering antenna arrays
(IEEE, 2015) Liberal Olleta, Íñigo; Ederra Urzainqui, Íñigo; Gonzalo García, Ramón; Ziolkowski, Richard W.; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
This article discusses the theory, design and practical implementation of superbackscattering antenna arrays. In analogy with Uzkov’s maximal directivity theorem, it is demonstrated that the maximal backscattering cross-section, normalized to the wavelength squared, of a linear array of N isotropic scatterers whose separation tends to zero is N2(N + 1)2=(4pi). This analytical result is validated via numerical optimization of the excitation coefficients, and the same procedure is utilized to assess the maximal backscattering of arrays of electric Hertzian dipoles (EHDs). It is found that electrically small arrays of two and three EHDs can enhance the backscattering by factors of 6.22 and 22.01, respectively, with respect to the maximum value generated by a single element. In addition, physical realizations of arrays featuring comparable enhancement factors can be straightforwardly designed by using a simple procedure inspired by Yagi-Uda antenna concepts. The practical implementations of such arrays based on copper wires and printed circuit technologies is also addressed.