Le déploiement de réseaux de communication quantique représente un défi auquel cette thèse apporte des solutions originales. Deux dispositifs très performants sont construits uniquement autour de composants standards de l'optique intégrée et des télécommunications optiques. Le premier correspond à un schéma de synchronisation tout optique sur longue distance à très haute cadence et de précision inégalée pour la communication sécurisée par cryptographie quantique. Le montage expérimental repose sur une configuration de relais quantique mettant en œuvre deux sources indépendantes de paires de photons intriqués dont il faut synchroniser les temps d'émissions. L’idée principale s’appuie sur l’utilisation d’un unique laser télécom picoseconde cadencé à 2.5 GHz afin de générer l’horloge et de pouvoir la distribuer efficacement aux deux sources. Nous démontrons la synchronisation de notre lien relais pour une distance effective séparant les sources de plus de 100 km. Le second dispositif correspond quant à lui à la réalisation d'une expérience de compression à une longueur d'onde des télécommunications réalisée, pour la première fois, de manière entièrement guidée. La lumière comprimée étant une ressource fondamentale dans bon nombre de protocoles d'information quantique, la réalisation de systèmes expérimentaux facilement reconfigurables et compatibles avec les réseaux télécoms fibrés existants représente une étape cruciale en vue du déploiement de dispositifs de communication quantique en régime de variables continues. Enfin, un traitement quantique des effets de gigue temporelle dans les détecteurs de photons 0N/0FF est proposé. Malgré l'importance des systèmes de détection dans les technologies quantiques photoniques émergentes, aucune modélisation quantique de leurs effets de gigue temporelle n'avait été, à notre connaissance, développé jusqu'à présent. / This thesis presents solutions to the challenges of developing quantum communication networks. Two powerful experimental devices have been set up relying only on standard telecom and integrated optical components. The first device corresponds to an all-optical synchronization scheme allowing, with an unprecedented accuracy, quantum key distribution at a high rate over long distances. The experimental scheme relies on two independent entangled photon pair sources that have to be synchronized in their emission time. Our approach is based on using a 2.5 GHz picosecond telecom laser as a master clock to efficiently synchronize the different sources. We demonstrate the synchronization for an effective distance of 100 km between sources. With our second device, we perform a squeezing experiment at telecom wavelengths and this for the first time in a fully guided-wave approach. Squeezed light being a fundamental resource for several quantum information protocols, developing plug-and-play experimental devices that are compatible with already existing telecom fiber networks is of first interest in the perspective of future quantum networks. Finally, we propose a quantum description of timing jitter effects in 0N/0FF detectors. Despite the importance of detection systems in emerging photonic quantum technologies, no quantum description of their timing jitter effects has been proposed so far.

Rare-earth ions in crystalline hosts have been identified as attractive media for quantum optical applications where record-high coherence times, quantum storage efficiency in solids, and quantum storage bandwidth have been demonstrated. Among rare-earth ions, Erbium uniquely possesses optical transitions at 1.5 micrometer region, making it suitable for integration with fiber telecommunication and silicon photonics. However, the intra-4f optical transitions are parity forbidden for rare-earth ions. Although, transitions are observed due to the interaction of the 4f valence electrons' energy levels with crystal fields or the lattice vibrations, the photon emission rate is prolonged for these ions. For example, Er³⁺ excited state lifetime for 1530nm transition is around 10 ms, which is about a million times longer than the excited state lifetime of alkali atoms like cesium and rubidium. There have been some recent works showing enhanced emission rate of erbium ions by about 10³ times by building a nano-photonic cavity to reach high Purcell factors. Our alternative approach to solving this problem is to use an ensemble of ions instead of a single ion to induce collective interactions in a suitable platform. In one experiment, we fabricated a SiN micro-ring resonator and implanted 10⁴ isotopically pure ¹⁶⁸Er ions in narrow segments located precisely in solids. The segments are typically separated by 0.962nm corresponding to multiples of the wavelength of Er emission at 1520nm. And we showed that when the lattice of ions is commensurate with the wavelength of the light, the scattering loss caused by the other ions is reduced. We have demonstrated for the first time that how designing atomic geometries in a solid-state photonic system can reduce the radiative loss due to spontaneous emission of ions into other photonic channels. This phenomenon is analogous to the Borrmann effect seen in x-ray transmissions of crystals at the Bragg angle of incidence. We have also shown how the interference between the optical cavity mode and atomic Bragg mode generates Fano-type resonance features. We performed these measurements using erbium ions in the SiN host. The limitations such as low coherence time and large inhomogeneous broadening in this platform prohibit observing cooperative and quantum behavior. To improve the optical property of erbium ions and study other cooperative effects, we engineered an effective ion array in an Er-doped Yttrium Orthosilicate crystal which can exhibit higher coherence time and narrower inhomogeneous broadening compared to SiN. So, we used the spectral hole burning technique to make an atomic grating in randomly distributed Er ions inside YSO. Two counter-propagating pump pulses created a standing wave inside the crystal, which enabled the creation of spectral holes only near the antinode locations. At the same time, atoms near nodes remain in the ground state. Such atomic population grating behaved like an atomic array. We have seen coherent backscattering up to 20% of the incident probe from this atomic grating resembling a mirror. To increase the reflection efficiency, we tried to increase the ion concentration in the YSO crystal. But, at high concentrations, the dipole-dipole interaction increases the broadening and decoherence rates of the ions. To increase the optical density without increasing the ion concentration, we fabricated long waveguides in SiN and LiNbO₃ with rare-earth ions implanted inside.As a future direction, we are trying to increase the reflection efficiency from the atomic grating to the point where we can see atomic mirror-assisted light trapping. We are also trying to see long-range co-operative behavior from rare-earth ion-doped crystals and rare-earth ions implanted inside long waveguides. This can open possibilities of new quantum photonic device engineering for applications in scalable and multiplexed quantum networks.

<p>Rare-earth ions (REIs) in solids are attractive optical centers due to their stable optical transitions and long lifetimes. Miniaturizing solid-state devices incorporated with REIs as quantum centers can play a key role in the implementation of future multiplexed quantum optical networks. Among the solid-state host materials for REIs, the Dissertation specifically studies silicon nitride (SiN) and crystalline lithium niobate (LN) materials. </p> <p><br></p> <p>SiN and Si are a CMOS-compatible material, and leveraging the well-developed technologies from the microelectronics industry is important for practical purposes because the cost of fabrication can be significantly reduced. Also, a recent study showed that the inhomogeneous broadening of Er-doped crystalline Si can be as low as 1GHz. Moreover, low-loss waveguide and high Q resonators were reported, making it a promising host for strong light-atom interactions. </p> <p><br></p> <p>On the other hand, LN is a promising host material for REIs due to its unique piezoelectric, electro-optic, nonlinear, and acousto-optic properties. Until recently, direct etching of LN has not been realized. But recently developed lithium niobate on insulator (LNOI) platform and direct LN etching techniques made it possible to fabricate low loss and strong confinement waveguides. Furthermore, LN has been used for quantum light storage and on-chip photon generation and wavelength conversion. Motivated by these recent advances and the interesting properties of LN, the Dissertation investigates thin-film crystalline LN. </p> <p><br></p> <p>In this dissertation, the methods and processes of fabricating long waveguides and ring resonators in 1)silicon nitride and 2)lithium niobate are introduced and the study of optical characterizations of Yb3+ ions in two different solid-state host materials are presented, specifically including photoluminescence (PL) spectroscopy, lifetime measurement, absorption and other characterization of light-atom interactions. </p> <p><br></p> <p>Furthermore, a study of Tm3+ ion arrays in thin-film LN is presented, specifically including the PL lifetime comparison between the periodically ordered sample and the randomly ordered sample and the scattering/reflection measurement from periodic ion arrays, both indicating the early evidence of cooperative effects of arrays in solids. Also, the theory of collective emission from atomic arrays is presented. Finally, I propose future plans to improve the fabrication process in these materials and possible future research directions based on the Dissertation.</p>

Nous présentons deux expériences de plasmonique quantique, c’est-à-dire des expériencesd’optique quantique ayant pour support des plasmons de surface. Dans la première expérience, nous montrons la dualité onde-corpuscule d’un plasmon de surface unique (1) en utilisant la démarche de l’article de Philippe Grangier, Gérard Roger et Alain Aspect (2) sur les interférences à un photon unique. Dans la deuxième expérience, nous mettons en évidence les propriétés d’intrication entre un photon et un plasmon de surface. Nous produisons des photons intriqués en polarisation et les séparons spatialement. / We present two quantum plasmonics experiments, namely quantum optics on surface plasmons. In the first experiment, we show the wave-particle duality of a single surface plasmon along the same lines as the single-photon interferences experiment of Philippe Grangier, Gérard Roger and Alain Aspect (2). In the second experiment, we bring out between a photon and a surface plasmon. We generate paires of polarization entangled photons and separate the pair photons spatially. A former photon is send to a semi-plasmonic Mach-Zehnder interferometer whose first beam splitter is a polarization beam splitter whose output are converted to plasmons and on a plasmonic beamsplitter.

Ce travail porte sur le développement d'outils pour l'ingénierie quantique d'états non-classiques de la lumière. Trois axes différents sont étudiés qui, combinés ensembles, permettent d'obtenir un protocole efficace et polyvalent pour la génération d'états quantiques Ces états sont générés en tirant profit des avantages distincts des deux descriptions possibles de la lumière grâce à l'utilisation conjointe des variables discrètes et continues.Le premier axe repose sur la réalisation de superpositions arbitraires d’états de Fock à zéro et deux photons à partir de deux états à un photon indiscernables. Cette expérience permet, entre autre, de créer des superpositions d'états cohérents appelés états chats de Schrödinger optiques. Afin d'augmenter l'amplitude des états produits, une itération du procédé est possible.Pour pouvoir rendre possible cette itération, nous augmentons dans un premier temps le taux de production de notre ressource de base: le photon unique. Pour cela, nous installons deux cavités optiques synchrones qui permettent d'accroître la puissance crête des impulsions du laser, exaltant ainsi les effets non-linéaires à l'origine de la production des photons.Le dernier axe, consiste à réduire les problèmes liés à la création probabiliste des photons. Pour cela, une mémoire quantique a été implémentée, permettant de stocker puis d'extraire un photon sur demande. Le stockage d’états contenant un et deux photons a été réalisé. Ce dispositif permettra à terme, en synchronisant l'état stocké avec l'arrivée d'un autre photon, de créer des états chats à l'intérieur même de la cavité. / This work is focused on the development of tools for quantum state engineering of non-classical state of light. Three different directions are studied, which when combined, lead to efficient and versatile protocols towards the generation of quantum states. Those states are produced by taking advantage of both descriptions of the light: the discrete and continuous variables of the light.The first direction consists in the réalisation of arbitrary superpositions of zero and two-photon Fock states with two indistinguishable single-photon states. This protocol permits, among others, to create superpositions of coherent states called Schrödinger cat states. An iteration of the protocol could allow the growth of the amplitude of the state.To realize such iteration, we increase the production rate of our basic resource, namely, the single photon.To do so, we implement two synchronous cavities allowing the increase of the peak power of the laser pulses, which ultimately enhanced the non-linear effect at the origin of the photon creation.The last direction aims to solve the problems related to the probabilistic nature of the photon creation. In order to store and extract the single photons on demand, a quantum memory is implemented. The storage of single and two-photon states has been experimentally realized. This setup could allow in the near future, by synchronizing the state stored in the cavity with the income of another photon, to create a cat state inside the cavity itself.

Les évolutions récentes de la cryptographie quantique ont permis de proposer sur le marché des appareils de distribution quantique de clé secrète (QKD). Ceci est obtenu en utilisant soit des variables discrètes et des compteurs de photons (DV), soit des variables continues et des systèmes de détection cohérente (CV). Les avancées technologiques s'orientent maintenant vers la réalisation de dispositifs plus petits, moins chers, et plus commodes à utiliser.L'objectif de cette thèse est de mettre en oeuvre un protocole CV-QKD sur un circuit optique intégré en silicium, en utilisant une modulation Gaussienne d'états cohérents. Deux approches sont utilisées: dans la première l'émetteur Alice et le récepteur Bob sont sur le même circuit photonique (chip) pour une validation de principe, et dans la deuxième ils sont séparés.Les valeurs mesurées des paramètres de la communication permettent d'échanger une clé secrète. / During recent years there have been significant developments in quantum cryptography, bringing quantum key distribution (QKD) devices on the market. This can be done by using either discrete variables (DV) and photon counting, or continuous variables (CV) and coherent detection. Current technological evolutions are now aiming at developing smaller, cheaper and more user-friendly devices.This work focuses on the implementation of CV-QKD using silicon photonics techniques, which provide a high degree of integration. This is exploited to build an on-chip realization of a cryptographic protocol, using Gaussian modulation of coherent states. Two different approaches have been used, first by physically implementing the sender (Alice) and the receiver (Bob) on the same chip for validation purposes, and then by having them onto two separate chips. The measured communication parameters give the possibility to extract a secret key

[pt] Detectores de fótons únicos baseados em fotodiodos de avalanche (SPADs) são essenciais em aplicações que requerem alta resolução, como comunicações quânticas e metrologia quântica. O efeito da largura de janela de detecção temporal de fótons é pouco explorado, e não há estudos para a faixa de comprimentos de onda de interesse em telecomunicações em torno de: 1550 nm. Neste trabalho, apresenta-se uma proposta para análise de impacto da largura de janela de detecção de um SPAD de InGaAs/InP, realizando uma análise da estatística entre detecções consecutivas e da probabilidade de detecção de 0 ou 1 evento em função da atenuação óptica. Variou-se o número médio de fótons por janela medido pelo SPAD, e os resultados foram avaliados para os valores de 4 ns, 8 ns, 12 ns, 16 ns e 20 ns de largura de janela de detecção, sendo estimada a Incerteza de Medição Expandida para cada ensaio. Os resultados obtidos indicam uma faixa adequada de potência óptica para calibração de um SPAD com eficiência de detecção de 15 porcento e um tempo morto de 1 microssegundo, no intervalo de 10 nW a 0,15 nW. Nesta faixa de potência, os respectivos produtos associados ao efetivo número médio de fótons por janela de detecção correspondem aos valores de 190 x 10-(4) a 0,32 x 10(-4) (para 4 ns) e 140 x 10(-4) a 2,9 x 10(-4) (para 8 ns). Foram obtidos comportamentos lineares para os ajustes das curvas de calibração para larguras de janela de 4 ns e 8 ns. / [en] Single photon detectors based on avalanche photodiodes (SPADs) are essential in applications that require high resolution, such as quantum communications and quantum metrology. The effect of the width of photon detection gate is little explored, and there are no studies for the wavelength range of interest in telecommunications around 1550 nm. In this work, a proposal is presented for analyzing the impact of the detection gate width of an InGaAs/InP SPAD, performing a statistical analysis of consecutive detections and the probability detection of 0 or 1 events depending on the optical attenuation. The average number of photons per gate measured by the SPAD was varied, and the results were evaluated for the values of 4 ns, 8 ns, 12 ns, 16 ns and 20 ns of detection gate widths, and Expanded Measurement Uncertainty was estimated for each test. The results obtained indicate an adequate optical power range for calibrating a SPAD with a detection efficiency of 15 percent and dead – time of 1 microssecond, in the range of 10 nW to 0,15 nW. In this power range, the respective products, which are associated with an effective average number of photons per gate window, correspond to the values of 190 x 10(-4) to 0,32 x 10(-4) (for 4 ns) e 140 x 10(-4) to 2,9 x 10(-4) (for 8 ns). Linear behaviors were obtained for the adjustment of the calibration curves for gate widths of 4 ns and 8 ns.

Indiana University-Purdue University Indianapolis (IUPUI) / In the first part of this thesis, we investigate the propagation of quantum fluctuations in a nonlinear interferometer comprising under conditions of harmonic generation by computer simulations. This investigation assumes idealized conditions such as lossless and uniform nonlinear media, an ideal cavity and ideal photodetectors. After linearizing wave equations for harmonic generation with a coherent state input, we obtain equations for one dimensional spatial propagation of the mean field and quantum fluctuations for initial conditions set by arbitrary interferometer phase. We discover that fluctuations are de-squeezed in the X and Y quadratures as the interferometer phase is tuned. However, we discover that there is are quadratures P-Q obtained by rotating the X-Y quadratures for which squeezing is improved by factors of 10^9. We present a practical idea to implement rotation of X quadrature fluctuations to the Q quadrature by using an ideal empty optical cavity. Signal-to-Noise ratio of the nonlinear interferometer was calculated and compared with that of a linear interferometer with coherent state input. We calculated a maximum performance improvement of a factor of 60 for a normalized propagation length ζ0 = 3 under ideal conditions. In the second part of this thesis, we investigate experimentalarrangements to transfer atomic coherence from light to cesium atoms. We discuss the experimental arrangement to generate coherence under conditions of electromagnetically induced transparency (EIT). We measure a continuous wave EIT width of 7.18 MHz and present results for pulsed arrangements.

<div>Field-orthogonal temporal mode analysis of optical fields was recently developed to form a new framework of quantum information science. But so far, the exact profiles of the temporal modes are not known, which makes it difficult to achieve mode selection and de-multiplexing. A novel feedback-iteration method which, combined with the stimulated emission method, can give rise to the exact forms of the temporal mode structure of pulse-pumped spontaneous parametric processes both for high gain parametric process, which gives rise to quantum entanglement in continuous variables, and for the low gain case, which produces a two-photon entangled state for discrete variables.</div><div><br></div><div>For the temporal mode analysis in high gain situations, the common treatment of parametric interaction Hamiltonian does not consider the issue of time ordering problem of interaction Hamiltonian and thus leads to the inaccurate conclusion that the mode structure and the temporal mode functions do not change as the gain increases. We use an approach that is usually employed for treating nonlinear interferometers and avoids the time ordering issue. This allows us to derive an evolution equation in differential-integral form. Numerical solutions for high gain situations indicate a gain-dependent mode structure that has its mode distributions changed and mode functions broadened as the gain increases. This will enable us to have a complete picture of the mode structure of parametric processes and produce high quality quantum sources for a variety of applications of quantum technology.</div><div><br></div><div>To verify the feedback-iteration method which measures temporal mode structure directly, we measure the joint spectral density of photon pairs produced with the spontaneous parametric down-conversion process of a pulse-pumped PPKTP crystal. The measurement method is based on a stimulated emission process which significantly improves the measurement time and accuracy compared with old spectrally resolved photon coincidence measurement. With the measured joint spectral density, the amplitude of the temporal modes can be obtained with the mathematical tool of singular value decomposition and compared with those measured directly with the feedback-iteration method.</div><div><br></div><div>Because the parametric amplifier is in essence a linear four-port device, it couples and linearly mixes two inputs before amplifying and sending them to two output ports. We show that for quadrature phase amplitudes, a parametric amplifier can replace beam splitters to play the role of mixer. We apply this idea to a continuous-variable quantum state teleportation scheme in which a parametric amplifier replaces a beam splitter in the Bell measurement. We show that this scheme is loss-tolerant in the Bell measurement process and thus demonstrate the advantage of parametric amplifiers over beam splitter in the applications in quantum measurement.</div>

<p>  </p> <p>Low-dimensional materials (LDMs) are substances that have at least one dimension with thicknesses in the nanometer (nm) scale. They have attracted tremendous research interests in many fields due to their unique properties that are absent in bulk materials. For instance, in quantum optics/photonics, LDMs offer unique advantages for effective light extraction and coupling with photonic/plasmonic structures; in chemistry, the large surface-to-volume ratio of LDMs enables more efficient chemical processes that are useful for numerous applications. In this thesis, several types of LDMs are studied and engineered with the goal to improve their impact in plasmonic and quantum photonic applications. Two-dimensional hexagonal boron nitride (hBN) is receiving increasing attention in quantum optics/photonics as it hosts various types of quantum emitters that are promising for quantum computing, quantum sensing, etc. In the first study, we explore and demonstrate a radiation- and lithography-free route to deterministically create single-photon emitters (SPEs) in hBN by nanoindentation with an atomic force microscopy. The method applies to hBN on flat, chip-compatible silicon-based substrates, and an SPE yield of up to 36% is achieved. This marks an important step toward the deterministic creation and integration of hBN SPEs with photonic and plasmonic devices. In the second study, the recently discovered negatively charged boron vacancy (V_B^-) spin defect in hBN is investigated. V_B^- defects are optically active with spin properties suitable for sensing at extreme scales. To resolve the low brightness issue of V_B^- defects, we couple them with an optimized nano-patch antenna structure and observe emission intensity enhancement that is nearly an order of magnitude higher than previous reports. Our achievements pave the way for the practical integration of V_B^- defects for quantum sensing. Zero-dimensional nanodiamond is another important host material for solid-state SPEs. Specifically, the negatively charged silicon vacancy (SiV) center in nanodiamonds exhibits optical properties that are suitable for quantum information technologies. In the third study, we, for the first time, demonstrate the creation of single SiV centers in nanodiamonds with an average size of ~20 nm using ion implantation. Stable single-photon emission is confirmed at room temperature, with zero-phonon line (ZPL) wavelengths in the range of 730 – 803 nm. This confirms the feasibility of single-photon emitter creation in nanodiamonds with ion implantation, and offers new opportunities to integrate diamond color centers for hybrid quantum photonic systems. Finally, we have also explored using metal-semiconductor hybrid nanoparticles for plasmon-enhanced photocatalysis. A core-shell nanoparticle structure is synthesized, with titanium nitride (TiN) and titanium dioxide (TiO₂) being the core and shell material respectively. It is observed that such core-shell nanoparticles effectively catalyze the generation of single oxygen molecules under 700-nm laser excitation. The main mechanism behind is the hot electron injection from the TiN core to the TiO₂ shell. Considering the chemical inertness and low cost of TiN, TiN@TiO₂ NPs hold great potential as plasmonic photosensitizers for photodynamic therapy and other photocatalytic applications at red-to-near-infrared (NIR) wavelengths.</p>