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<p>Dipole-dipole interactions are ubiquitous fundamental physical phenomena that govern physical effects such as Casimir Forces, van der Waals forces, collective Lamb shifts, cooperative decay, and resonance energy transfer. These interactions are associated with real and virtual photon exchange between the interacting emitters. Such interactions are crucial in realizing quantum memories, novel super-radiant light sources, and light-harvesting devices. Owing to this, the control and modification of dipole-dipole interactions have been a longstanding theme. The electromagnetic environment plays a crucial role in enhancing the range and strength of the interactions. This work focuses on modifying the nanophotonic environment near interacting emitters to enhance dipole-dipole interactions instead of spontaneous emission. To this end, we focus on engineering the nanophotonic environment to enhance the strength and range of dipole-dipole interactions between an ensemble of emitters. We explore ordered and disordered nanophotonic structures. We experimentally demonstrate long-range dipole-dipole interactions mediated by surface lattice resonances in a periodic plasmonic nanoparticle lattice. Further, the modified electromagnetic environment reduces the apparent dimensionality of the interacting system compared to non-resonant in-homogeneous and homogeneous environments. We also develop a spectral domain inverse design technique for the accelerated discovery of disordered metamaterials with unique spectral features. </p> <p>Further, we explore the novel regimes of light localization at near-zero-index in such disordered media. The disordered near-zero-index medium reveals enhanced localization and near-field chirality. This work paves the way to engineer the electromagnetic nanophotonic environment to realize enhanced long-range dipole-dipole interactions.</p>

<p dir="ltr">This thesis is about the exciting discovery of a new kind of single photon emitter that<br>is suspected to occur at the interface of silicon nitride SixNy and silicon dioxide SiO2 after<br>being rapidly annealed. Since SixNy is one of the most developed platforms for integrated<br>photonics the discovery of a native emitter in this platform opened up the possibility for<br>seamless integration of these single photon emitters with photonic circuitry for the first<br>time. This seamless integration was demonstrated as is shown in Chapter 3 by creating the<br>emitters and then patterning the SixNy layer into a waveguide. This work demonstrated for<br>the first time the coupling of such single photon emitters with on-chip integrated photonics.<br>However, the integration approach demonstrated was based on the stochastic integration of<br>emitters which limits the efficiency of the devices and the possible types of devices that can<br>be designed. This is why the next stage of research focused on the development of a site-<br>controlled process for creating these single photon emitters. Remarkably, it was found that<br>if the SixNy and SiO2 are nanostructured into nanopillars and then annealed then a single<br>photon emitter forms over 65% of the time within the nanopillar! Due to the lithography<br>defined nature of this process for creating the single photon emitters the first multi-mask<br>integration process was also developed and demonstrated. This fabrication process was used<br>to demonstrate the integration of several thousand single photon emitters with complex<br>integrated photonic structures such as topology optimized couplers. These developments<br>has generated a great deal of excitement due to the inherent scalability of the approach and<br>it’s obvious applications for the development of very large scale integrated (VLSI) on-chip<br>quantum photonic systems.</p>

[ES] La optomecánica de cavidades se ocupa de la interacción entre la luz y la materia a través del efecto de presión de radiación cuando las ondas ópticas y mecánicas implicadas están confinadas en una cavidad. En estos sistemas optomecánicos, la interacción entre fotones y fonones da lugar a multitud de fenómenos en función de las condiciones en las que se excita el sistema. En particular, se pueden obtener dos regímenes distintos en los que se puede, o bien absorber fonones (denominado como enfriamiento de la cavidad), o bien éstos se pueden amplificar (régimen conocido como calentamiento de la cavidad). El primer régimen puede usarse, por ejemplo, para reducir la ocupación térmica del sistema y se usa comúnmente para aplicaciones relativas al procesado de información cuántica. Sin embargo, la amplificación de fonones, que puede ser desarrollada a temperatura ambiente, ha permitido conseguir alcanzar incluso las condiciones necesarias para obtener láseres de fonones, lo cual permite poder usar esta característica como elemento de referencia en aplicaciones relativas al procesado de señales de radiofrecuencia (RF). En esta tesis se aborda el confinamiento simultáneo y la interacción de fotones y fonones en estructuras periódicas y en guías no suspendidas desarrolladas en sistemas CMOS compatibles basados en tecnología de silicio. A través del estudio experimental de estas estructuras periódicas, hemos demostrado que las cavidades optomecánicas pueden actuar como elementos clave en el dominio de la fotónica de microondas, donde todo el procesado de la información puede ser realizado en el dominio óptico a través de la manipulación de fonones en este sistema. En particular, mostramos que un solo oscilador optomecánico puede actuar tanto como un oscilador local y un mezclador de RF, y éste puede operar como un conversor de frecuencias de señales de cadenas de datos reales. Para mejorar esta funcionalidad, también se demuestra que es posible obtener tanto peines de frecuencias ópticos así como múltiples modos mecánicos confinados, aumentando así su rendimiento. Por otro lado, con el objetivo de poder solventar las posibles limitaciones de estos sistemas, en esta tesis también se exploran diferentes configuraciones que permiten la interacción acusto-óptica simultánea en la misma estructura. Específicamente, se analiza la interacción optomecánica en discos de alto índice que soportan estados cuasi-ligados en el continuo así como una propuesta de guías no suspendidas que soportan altas ganancias de Brillouin. Este último estudio debería permitir el desarrollo de sistemas optomecánicos no suspendidos donde el problema de la pérdida de fonones hacia el sustrato se resuelva, hecho que permitiría enormemente simplificar la fabricación de estos sistemas optomecánicos en chips de silicio así como su uso en múltiples aplicaciones. / [CA] L'optomecànica de cavitats s'ocupa de la interacció entre la llum i la matèria a través de l'efecte de pressió de radiació quan les ones òptiques i mecàniques implicades estan confinades en una cavitat. En aquests sistemes optomecànics, la interacció entre fotons i fonons dona lloc a multitud de fenòmens en funció de les condicions de les condicions en les quals s'excita el sistema. En particular, es poden obtindre dos règims diferents en els quals es pot, o bé, absorbir fonons (denominat com a refredament de la cavitat), o bé, es poden amplificar (règim conegut com a calfament de la cavitat). El primer règim pot usar-se, per exemple, per a reduir l'ocupació tèrmica del sistema i s'usa comunament per a aplicacions relatives al processament d'informació quàntica. No obstant això, l'amplificació de fonons, que pot ser desenvolupada a temperatura ambient, ha permés aconseguir fins i tot les condicions necessàries per a obtindre làsers de fonons, la qual cosa permet poder usar aquesta característica com a element de referència en aplicacions relatives al processament de senyals de radiofreqüència (RF). En aquesta tesi s'aborda el confinament simultani i la interacció de fotons i fonons en estructures periòdiques i en guies no suspeses en sistemes CMOS compatibles basats en tecnologia de silici. A través de l'estudi experimental d'aquestes estructures periòdiques, hem demostrat que les cavitats optomecàniques poden actuar com a elements clau en el domini de la fotònica de microones, on tot el processament de la informació pot ser realitzat en el domini òptic a través de la manipulació de fonons en aquest sistema. En particular, vam mostrar que només un oscil·lador optomecànic pot actuar tant com un oscil·lador local i un mesclador de RF, i aquest pot operar com un convertidor de freqüències de senyals de cadenes de dades reals. Per a millorar aquesta funcionalitat, també es demostra que és possible obtindre tant tren de freqüències òptics així com múltiples modes mecànics confinats, augmentant així el seu rendiment. D'altra banda, amb l'objectiu de poder solucionar les possibles limitacions d'aquests sistemes, en aquesta tesi també s'exploren diferents configuracions que permeten la interacció acusto-òptica simultània en la mateixa estructura. Específicament, s'analitza la interacció optomecànica en discos d'alt índex que suporten estats quasi-lligats en el continu així com una proposta de guies no suspeses que suporten altes ganancies de Brillouin. Aquest últim estudi hauria de permetre el desenvolupament de sistemes optomecànics no suspesos on el problema de la pèrdua de fonons cap al substrat es resolga, fet que permetria enormement simplificar la fabricació d'aquests sistema optomecànics en xips de silici així com el seu ús en diverses aplicacions. / [EN] Cavity optomechanics deals with the interaction of light and matter through the radiation pressure effect, when the involved optical and mechanical waves are confined in a cavity. In optomechanical systems, photon and phonon interaction give rise to a plethora of phenomena as a function of the driving conditions of the system. Relative to that, two distinctive regimes can be obtained which enable either the absorption of phonons (cavity cooling) or their amplification (cavity heating). The first regime can be used to reduce the thermal occupancy of the system and it is commonly used for quantum processing information applications. However, the amplification of phonons, which can be performed at room temperature, has enabled to even reach phonon lasing conditions, a feature that could be used as a reference element for RF processing applications. In this thesis, we address the simultaneous confinement and interaction of photons and phonons in periodic structures and unreleased waveguides on CMOS-compatible silicon-based technology. Throughout the experimental study of those periodic structures, we demonstrate that optomechanical cavities can perform as key blocks in the microwave photonics domain where all the information processing can be performed in the optical domain through phonon manipulation. In particular, we show that a single optomechanical oscillator can perform as both a local oscillator and an RF mixer, and it can operate as a frequency-converted of real data stream signals. To improve its performance, it is also demonstrated that optical frequency combs can be obtained by means of this system and multiple mechanical mode confinement can also be achieved, thus improving the functionality of the system. On the other hand, in order to fulfill the possible limitations of those systems, we explore different configurations enabling the simultaneous acousto-optic interaction together into the same structure. Especially, optomechanical interaction in high-index disks supporting quasi-bound states in the continuum is addressed, as well as a proposal of unreleased waveguides supporting strong Brillouin gains is also reported. The last one should lead to unreleased optomechanical interacting systems where the issue of phonon leakage into the substrate is solved, which could enormously simplify the fabrication of optomechanical systems in silicon chips as well as their practical use in multiple applications. / This work has been carried out under the framework of the H2020 FET-Open EU project PHENOMEN. This Thesis was also supported by the Programa de Ayudas de Investigación y Desarrollo (PAID-01-16) de la Universitat Politècnica de València / Mercadé Morales, L. (2021). Phonons Manipulation in Silicon Chips Using Cavity Optomechanics [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/171461

<p><br></p><p dir="ltr">Over the past decade, optical frequency combs have spurred significant advancements in both classical ultrafast optics and quantum optics. My research contributes to these two fields, catering to applications in precision metrology and optical networking. In the domain of quantum optics, the study delves into biphoton frequency combs with time-energy entanglement, employing novel electro-optic modulation schemes to enhance sensitivity and enable precise measurements of temporal correlations. Additionally, Bell states, a crucial class of entangled quantum bases, are generated in the frequency domain, showcasing their utility in delay metrology and quantum cryptographic protocols. </p><p dir="ltr">In the realm of classical optical frequency combs, this work explores dynamic steering of pulsed optical beams, holding promise for applications in imaging and remote sensing. The concept of time-efficient dynamic beam steering using a spatial array of optical frequency combs is elucidated and experimentally demonstrated through the utilization of a high-resolution spectral disperser, specifically a virtually imaged phased array (VIPA). Furthermore, integrated photonic designs featuring wavelength-selective switches and spectral dispersers are proposed to enable a versatile on-chip implementation of the beam steering approach. In sum, this research leverages the capabilities of classical and quantum optical frequency combs, with implications for emerging applications such as distributed sensing, quantum networking, and light detection and ranging (LIDAR).</p>

<p dir="ltr">Quantum-enhanced approaches enable high-resolution imaging and sensing with signal-to-noise ratios beyond classical limits. However, operating in the quantum regime is highly susceptible to environmental influences and experimental conditions. Implementing these techniques necessitates highly controlled environments or intricate preparation methods, which can restrict their practical applications. This thesis explores the practical applications of quantum sensing, focusing on thermal sensing with bright quantum sources in biological and electronic contexts. Additionally, I discuss the development of a multimode source for quantum imaging applications and an on-chip atomic interface for scalable light-atom interactions. I built all the experimental setups from the beginning; a microscope setup for nanodiamond-based thermal sensing inside living cells, a four-wave mixing setup using a Rb cell for thermal imaging of microelectronics and multimode source, and a vacuum chamber for on-chip atomic interface.</p><p dir="ltr">Quantum sensing can be realized using atomic spins or optical photons possessing quantum information. Among these, color centers inside diamonds stand out as robust quantum spin defects (effective atomic spins), maintaining their quantum properties even in ambient conditions. In this thesis, I studied the role of an ensemble of color centers inside nanodiamonds as a probe of temperature in a living cell. Our approach involves incubating nanodiamonds in endothelial culture cells to achieve sub-kelvin sensitivity in temperature measurement. The results reveal a temperature error of 0.38 K and a sensitivity of 3.46 K/sqrt(Hz)<i> </i>after 83 seconds of measurement. Furthermore, I discuss the constraints of nanodiamond temperature sensing in living cells, propose strategies to surmount these limitations, and explore potential applications arising from such measurements.</p><p dir="ltr">Another ubiquitous quantum probe is light with quantum properties. Photons, the particles of light, can carry quantum correlations and have minimal interactions with each other and, to some extent, the environment. This capability theoretically allows for quantum-enhanced imaging or sensing of sample’s properties. In this thesis, I report on the demonstration of quantum-enhanced temperature sensing in microelectronics using bright quantum optical signals. I discuss the first demonstration of quantum thermal imaging used to identify hot spots and analyze heat transport in electronic systems.</p><p dir="ltr">To achieve this, we employed lock-in detection of thermoreflectivity, enabling us to measure temperature changes in a micro-wire induced by an electric current with an accuracy better than 0.04 degrees, averaged over 0.1 seconds. Our results demonstrate a nearly 50 % improvement in accuracy compared to using classical light at the same power, marking the first demonstration of below-shot-noise thermoreflectivity sensing. We applied this imaging technique to both aluminum and niobium-based circuits, achieving a thermal resolution of 42 mK during imaging. We scanned a 48 × 48 μm<i> </i>area with 3-4 dB squeezing compared to classical measurements. Based on these results, we infer possibility of generating a 256×256 pixel image with a temperature sensitivity of 42 mK within 10 minutes. This quantum thermoreflective imaging technique offers a more accurate method for detecting electronic hot spots and assessing heat distribution, and it may provide insights into the fundamental properties of electronic materials and superconductors.</p><p dir="ltr">In transitioning from single-mode to multimode quantum imaging, I conducted further research on techniques aimed at generating multimode quantum light. This involved an in-depth analysis of the correlation characteristics essential for utilizing quantum light sources in imaging applications. To achieve the desired multimode correlation regime, I developed a system centered on warm Rubidium vapor with nonlinear gain and feedback processes. The dynamics of optical nonlinearity in the presence of gain and feedback can lead to complexity, even chaos, in certain scenarios. Instabilities in temporal, spectral, spatial, or polarization aspects of optical fields may arise from chaotic responses within an optical <i>x</i>(2) or <i>x</i>(3) nonlinear medium positioned between two cavity mirrors or preceding a single feedback mirror. However, the complex mode dynamics, high-order correlations, and transitions to instability in such systems remain insufficiently understood.</p><p dir="ltr">In this study, we focused on a <i>x</i>(3) medium featuring an amplified four-wave mixing process, investigating noise and correlations among multiple optical modes. While individual modes displayed intensity fluctuations, we observed a reduction in relative intensity noise approaching the standard quantum limit, constrained by the camera speed. Remarkably, we recorded a relative noise reduction exceeding 20 dB and detected fourth-order intensity correlations among four spatial modes. Moreover, this process demonstrated the capability to generate over 100 distinct correlated quadruple modes.</p><p dir="ltr">In addition to conducting multimode analysis to develop a scalable imaging system, I have explored methodologies aimed at miniaturizing light-atom interactions on a chip for the scalable generation of quantum correlations. While warm atomic vapors have been utilized for generating or storing quantum correlations, they are plagued by challenges such as inhomogeneous broadening and low coherence time. Enhancing control over the velocity, location, and density of atomic gases could significantly improve light-atom interaction. Although laser cooling is a common technique for cooling and trapping atoms in a vacuum, its implementation in large-scale systems poses substantial challenges. As an alternative, I focused on developing an on-chip system integrated with atomic vapor controlled by surface acoustic waves (SAWs).</p><p dir="ltr">Surface acoustic waves are induced by an RF signal along the surface of a piezoelectric material and have already been proven to be effective for manipulating particles within microfluidic channels. Expanding upon this concept, I investigated the feasibility of employing a similar approach to manipulate atoms near the surface of a photonic circuit. The interaction between SAWs and warm atomic vapor is expected as a mechanism for controlling atomic gases in proximity to photonic chips for quantum applications. Through theoretical analysis spanning molecular dynamics and fluid dynamics regimes, I identified the experimental conditions necessary to observe acoustic wave behavior in atomic vapor. To validate this theory, I constructed an experiment comprising a vacuum chamber housing Rb atoms and a lithium niobate chip featuring interdigital transducers for launching SAWs. However, preliminary experimental results yielded no significant signals from SAW-atom interactions. Subsequent analysis revealed that observing such interactions requires sensitivity and signal-to-noise ratio (SNR) beyond the capabilities of the current setup. Multiple modifications, including increasing buffer gas pressure and mitigating RF cross-talk, are essential for conclusively observing and controlling these interactions.</p>

[pt] Resfriamento é o passo inicial necessário a qualquer experimento optomecânico que tenha como objetivo desbloquear o potencial das pinças ópticas, tanto para a melhoria da sensiblidade a forças em aplicações de sensoreamento quanto para estudos de física quântica fundamental na microescala. O propósito do trabalho descrito nesta dissertação foi o de melhorar a montagem de uma pinça óptica para resfriamento por retroalimentação do movimento translacional de nanopartículas levitadas. Nós implementamos a coleta de luz retroespalhada pela partícula para melhorar a eficiência de detecção do movimento ao longo do eixo óptico. Usando um ambiente de simulação numérica em Python, nós também exploramos o potencial de sistemas optomecânicos como sensores para estados de luz com intensidades muito baixas. / [en] Cooling is the necessary first step for any optomechanical experiment aiming to unleash the full potential of optical tweezers, both in the context of improving force sensitivity in sensor applications and of studying fundamental quantum physics at the microscale. The purpose of the work described in this dissertation was to improve an optical tweezer setup for electrical feedback cooling of the translational motion of levitated nanoparticles. We implement collection of backscattered light from the particle for improved detection efficiency of motion along the optical axis. Using a numerical simulation environment in Python, we also explore the potential of optomechanical systems as sensors for light states with very low intensities.

Depuis l’avènement de la mécanique quantique, l’étude des interactions lumière-matière à l’échelle quantique s’est énormément développée en tant que domaine de recherche. Par exemple, grâce à des prédictions théoriques surprenantes, des interactions d’une force sans précédant ont été démontrées entre de la matière et des radiations terahertz et microonde. Ces résultats correspondent à un régime dit de couplage ultrafort, atteint lorsque l’énergie d’interaction devient comparable aux énergies propres de la lumière et de la matière lorsque celles-ci n’interagissent pas. Dans ce régime, des propriétés intrigantes peuvent subsister telles que la présence de photons même lors qu’aucune énergie n’est fournie au système. Cependant, ces photons ne peuvent, a priori, être émis du système vers l’extérieur de manière à pouvoir être mesurés et par conséquent démontrer ces propriétés.Dans cette thèse, nous avons étudié ces propriétés intrigantes et proposé plusieurs moyens permettant d’y accéder expérimentalement. Nous nous sommes appuyés sur plusieurs plate-formes physiques qui sont de bon candidats pour ces études, et pour chacun de ces systèmes nous avons mis au point un modèle mettant en évidence ces propriétés d’une manière ou d’une autre. De cette façon, nous avons exploré le lien entre le régime de couplage ultrafort et la génération d’états non-classiques de la lumière. En outre, dans une étude plus ouverte nous avons montré que les interactions lumière- matière dans l’une de ces plate-formes peuvent être utilisés pour concevoir des protocols de communication quantique. En plus de montrer un intérêt fondamental, nos résultats s’inscrivent dans une optique de développement d’applications pour les technologies quantiques en utilisant différents systèmes expérimentaux disponibles actuellement / Since the advent of quantum mechanics, the study of light-matter interactions at thequantum level has been greatly developed as a research field. For instance, surprisingtheoretical predictions gave rise to experiments with unprecedented interactionstrengths between matter, and terahertz and microwave radiations. These results correspondto the so-called ultrastrong coupling regime, that is reached when the interactionenergy becomes comparable to the typical energies of the light and matter when they arenot interacting. In this regime, intriguing properties can be found such as the presenceof photons even when no energy is given to the system. However, these photons cannot,a priori, be emitted from the system to the outside world in order to be measured andtherefore demonstrate these properties. In this thesis, we studied these intriguing properties and proposed several means toaccess them experimentally. We relied on several physical platforms which are goodcandidates for such studies, and for each one of these systems we devised a model thatcan evidence these properties one way or another. By doing so, we explored the linkbetween the ultrastrong coupling regime and the generation of nonclassical states oflight. Additionally, as an outlook we showed that the light-matter interactions in oneof these platforms could be used to design quantum communication protocols. On topof showing fundamental interest, our results fit in the line of developing applications forquantum technologies using different experimentally available systems.

We investigate two different coupling schemes between a nano-scale mechanical resonator and one-electron atoms. In these schemes, classical electromagnetic radiation mediates a mutual communication between the mechanical resonator and the atoms. In the process it generates atomic coherences, quantum superpositions of excited electronic levels of the atoms. An atomic coherence is highly responsive to subtle variations in the relative frequencies of the levels participating in such superposition state. By exposing the atoms to electromagnetic radiation modulated by the motion of the mechanical resonator, we show how the response of an atomic coherence can, under appropriate conditions, be used to affect on demand the dynamical state of the mechanical resonator. The first scheme realizes a long range interface between a mechanical resonator and an ensemble of three-level atoms. Here, mechanically modulated electromagnetic radiation comes from a laser beam reflected off an oscillating mirror, the mechanical resonator. This light beam drives the transition between an excited level and a hyperfine sublevel of the atoms with a certain detuning. A weaker light beam resonantly couples to the transition between the excited level and another hyperfine sublevel. On full resonance, the atoms evolve into a stationary coherence of the above (non-absorbing) hyperfine sublevels only. The atoms then become transparent to the weaker light beam, in a phenomenon called electromagnetically induced transparency. Off resonance, we find that this transparency is modulated at the mirror frequency with some phase shift, which allows the weaker beam to cause resonant backaction onto the moving mirror. The strength of this backaction is enhanced near atomic resonances and its character can be switched between amplification or damping of mirror vibrations by adjusting the detuning. In contrast, the second scheme accomplishes a closer range interface between a torsion pendulum and guided two level Rydberg atoms. Attaching a point electric dipole to the torsion pendulum allows electromagnetic coupling to two Rydberg levels of a passing atom. This coupling modifies the eigenfrequencies of the Rydberg levels such that they become dependent on the phonon number of the torsion pendulum. Via Ramsey interferometry, we may readout this effect and thus measure the phonon number. We show that, by subjecting several atoms, one by one, to a Ramsey measurement, a quantum non-demolition detection of the phonon number is feasible. Likewise, we show coherent oscillator displacements possible, by driving the atoms with external fields while they interact with the torsion pendulum. We propose a protocol to reconstruct the quantum state of motion of the torsion pendulum, combining these two techniques, Ramsey measurements and oscillator displacements. Our interfaces between a mechanical resonator and atoms provide alternative routes for the control of the state of motion, ultimately quantum mechanical, of a mechanical resonator, in which the latter is not restricted to be part of a cavity. We will thus ease quantum dynamical manipulations of mechanical resonators of sub micron scales, for which an efficient design of cavity opto- and electro-mechanical systems is hard.