We experimentally demonstrate time-frequency entangled photons with comb-like spectra via both bulk optical crystals and on-chip microring resonators and explore their characterization in both time and frequency domain using quantum state manipulation techniques. Our characterization of these quantum frequency combs involves the use of unbalanced Mach-Zehnder interferometers and electro-optic modulators for manipulation in time- and frequency-domain, respectively. By creating indistinguishable superposition states using these techniques, we are able to interfere states from various time- and frequency-bins, consequently proving time- and frequency-bin en-tanglement. Furthermore, our time-domain manipulations reveal pair-wise continuous time-energy entanglement that spans multiple frequency bins, while our utilization of electro-optic modulators to verify high-dimensional frequency-bin entanglement constitutes the proof of this phenomenon for a spontaneous four-wave mixing pro-cess. By doing so, we show the potential of these quantum frequency combs for high-dimensional quantum computing with frequency-encoded quantum states, as well as fully secure quantum communications via quantum key distribution by per-forming a nonlocal dispersion cancellation experiment. To show the potential of our entangled photons source for encoding quantum information in the frequency domain, we carry out a frequency-domain Hong-Ou-Mandel interference experiment by implementing a frequency beam splitter. Lastly, we use the high-dimensionality of our time-frequency entangled source in both time and frequency domain to implement deterministic high-dimensional controlled quantum gates, with the quantum information encoded in both the time and frequency degrees of freedom of a single photon. This novel demonstration of deterministic high-dimensional quantum gates paves the way for scalable optical quantum computation, as quantum circuits can be implemented with fewer resources and high success probability using this scheme.<div><br></div><div> </div>

<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>

[pt] A internet quântica atrai a atenção de muitos pesquisadores e empresas. O elemento essencial para realizá-la é o emaranhamento. A distribuição do emaranhamento permite a transmissão de qubits sem realmente enviá-los pelo canal quântico. Portanto, a fonte que produz esses estados emaranhados deve fazê-lo de forma confiável e com taxa competitiva à de comunicação clássica. Este trabalho apresenta uma ferramenta de simulação para a fonte de pares de fótons emaranhados mais comum, o EPPS baseado em SPDC. Além disso, usando filtros, emulamos o efeito do SPDC dentro de uma cavidade. Otimizando os parâmetros da fonte, obtivemos um ganho de 6dB na taxa de chaves secretas em comparação com um processo SPDC simples. / [en] The quantum internet has dragged the attention of many researchers and companies. The essential element to accomplish it is entanglement. Distributing entanglement allows the transmission of qubits without really sending them through the quantum channel. Therefore, the source that produces these entangled states shall do it reliably and with a competitive rate to classical communication. This work presents a simulation tool for the most common entangled photon pair source, the SPDC-based EPPS. Furthermore, using filters, we can emulate the effect of cavity-enhanced SPDC. Optimizing the parameters of the source, we achieved a 6dB gain on the Secret Key Rate compared to a simple SPDC process.

<p dir="ltr">Quantum information science and technology has been at the forefront of science and technology since MIT mathematician Peter Shor discovered a quantum algorithm to factor large numbers in 1994. Advancement in quantum theory also advances practical technological applications. Quantum technology can be applied both in civilian society and the military field from encryption, artificial intelligence, sensing, to communications. This multi-purpose applicability, therefore, has the potential to alter international security as scientifically advanced nation-states vie for quantum supremacy. This research examines the applications of quantum science and how these applications can potentially impact international security. Because nation-states fund and support quantum science research, sources of method will include academic journals and online resources as well as government reports. Practical applications of quantum technology, including quantum computing, quantum sensing, and quantum communication, will constitute the primary scope of this research.</p>

The recent advancement of superconducting nano devices has allowed for making a Superconducting Nanowire Single Photon Detector (SNSPD), whose extraordinary features have strongly motivated the research community to exploit it in many practical applications. In this thesis, an experimental setup for testing the SNSPD has been established. It contains an in-house packaging that meets the requirements of RF/microwave and optoelectronic characterizations. The quantum efficiency and detection efficiency measurements have confirmed that our approach is satisfactory. The dark count performance has reached the anticipated level. The factors affecting rise and fall times of the photoresponses are addressed. Based on the successful setup, the characterizations including dc, small signal ac measurements have been undertaken. The measurements are aimed at quantitatively investigating Cooper pair density in the superconducting nanowire. The experimental method involves a two-step, small signal S-parameter measurement either in the presence or absence of optical powers. The subsequent measurements by varying the temperature and dc bias current have achieved remarkable understanding on the physical properties of SNSPD nanowires. Then, the electrically induced nonlinearity is studied via the large signal RF and Microwave measurements. The experiments are a set of one-tone and two-tone measurements, in which either the RF driving power is varied at a fixed frequency, or vice versa. Two major nonlinear microwave circuit analysis methods, i.e. time-domain transient and hybrid-domain harmonic balance analysis, are employed. The simulation result reveals the optimized conditions of reaching the desired nonlinearity. Finally, we have successfully measured the optoelectronic mixing products in an electrically pumped optoelectronic mixer, which has identical structures as that of the SNSPD. The experiments confirm that this mixer is not only sensitive to the classical light intensities, but also to that of the single photon level. Meanwhile, the quantum conversion matrices is derived to interpret the quantum optoelectronic mixing effects.

The recent advancement of superconducting nano devices has allowed for making a Superconducting Nanowire Single Photon Detector (SNSPD), whose extraordinary features have strongly motivated the research community to exploit it in many practical applications. In this thesis, an experimental setup for testing the SNSPD has been established. It contains an in-house packaging that meets the requirements of RF/microwave and optoelectronic characterizations. The quantum efficiency and detection efficiency measurements have confirmed that our approach is satisfactory. The dark count performance has reached the anticipated level. The factors affecting rise and fall times of the photoresponses are addressed. Based on the successful setup, the characterizations including dc, small signal ac measurements have been undertaken. The measurements are aimed at quantitatively investigating Cooper pair density in the superconducting nanowire. The experimental method involves a two-step, small signal S-parameter measurement either in the presence or absence of optical powers. The subsequent measurements by varying the temperature and dc bias current have achieved remarkable understanding on the physical properties of SNSPD nanowires. Then, the electrically induced nonlinearity is studied via the large signal RF and Microwave measurements. The experiments are a set of one-tone and two-tone measurements, in which either the RF driving power is varied at a fixed frequency, or vice versa. Two major nonlinear microwave circuit analysis methods, i.e. time-domain transient and hybrid-domain harmonic balance analysis, are employed. The simulation result reveals the optimized conditions of reaching the desired nonlinearity. Finally, we have successfully measured the optoelectronic mixing products in an electrically pumped optoelectronic mixer, which has identical structures as that of the SNSPD. The experiments confirm that this mixer is not only sensitive to the classical light intensities, but also to that of the single photon level. Meanwhile, the quantum conversion matrices is derived to interpret the quantum optoelectronic mixing effects.

La téléportation quantique promet d'être centrale à de nombreuses applications du futur tels la cryptographique quantique et l'ordinateur quantique. Comme toute mise en œuvre physique s'accompagne inévitablement d'imperfections expérimentales, on étudie la téléportation dans un contexte où la ressource quantique, c'est-à-dire l'intrication, que l'on consomme est brouillée. Pour ce faire, on introduit en premier lieu le formalisme de l'informatique quantique. En seconde partie, on approche les protocoles de téléportation quantique standard, de téléportation avec relais quantiques et de téléportation multi-ports. Notre analyse de la téléportation standard et de la téléportation multi-ports poursuit trois objectifs principaux. Le premier est de comparer l'emploi d'un canal brouillé pour la téléportation d'un état quantique avec l'utilisation de ce même canal pour l'envoi direct de l'état. On trouve ainsi les conditions pour lesquelles les deux protocoles de transmission sont équivalents. Le second but est d'observer le caractère non-local de l'intrication brouillée en regardant quand et comment Alice peut réduire le bruit chez elle à un bruit exclusivement chez Bob. En troisième, on quantifie par une borne inférieure la qualité d'un canal de téléportation en réduisant l'effet de toute intrication brouillée à celui d'un bruit de Pauli à un seul paramètre. On accomplit cette tâche en effaçant au moment approprié l'information classique superflue et en appliquant la wernerisation. Finalement, on analyse la composition de bruits de Pauli et l'effet du taux d'effacement sur la téléportation avec relais quantiques pour mieux comprendre comment se combinent les effets de l'intrication brouillée dans un réseau de téléportation quantique. La suite logique est d'établir des protocoles plus robustes de téléportation quantique qui prennent en compte l'effet de l'intrication brouillée. / Quantum teleportation will be a centerpiece of practical quantum cryptography and quantum computing in a soon to be future. As no physical implementation is perfect, we study quantum teleportation in the context of impaired quantum resources which we call noisy entanglement. In a first part, we introduce how quantum mechanics is formalized by quantum information theory. In the second part, we study standard quantum teleportation, in both the absence and presence of quantum repeaters, as well as port-based teleportation. Our analysis of standard quantum teleportation and port-based teleportation follows three main directions. The first goal is to compare the use of a noisy channel for teleportation to the one of the same channel for direct transmission. We thus find the conditions under which the two cases are equivalent. Our second objective is to observe the non-local properties of noisy entanglement by finding when and how Alice can blame Bob for her noise. Thirdly, we quantify, in the worst-case scenario, the quality of a teleportation channel by reducing the effect of any noisy entanglement to the one of a one-parameter Pauli channel that can be interpreted as a depolarizing channel in most instances. We achieve this task by erasing unneeded classical information at the appropriate time and by twirling either the entanglement or the teleported state. Finally, we analyze the composition of Pauli noises and the impact of the erasure channel parameter on the protocol of teleportation with quantum repeaters. We thus aim to understand how the effects of noisy entanglement cumulate in a teleportation network. The next logical step is to create robust teleportation schemes that take into account the effects of noisy entanglement.

[pt] Dois dispositivos de contagem de fótons únicos, sensíveis a comprimentos de onda no infravermelho próximo e médio, são propostos e experimentalmente investigados. Ambos utilizam uma técnica de dois estágios, composta de uma etapa inicial de conversão de freqüências em um cristal não-linear seguida de detecção por um fotodiodo avalanche de silício. Enquanto o primeiro projeto é voltado à detecção de fótons únicos a 1.55 &#956;m para comunicações quânticas via fibra óptica, usando um processo intra-cavidade, o segundo projeto prevê o desenvolvimento de um contador de fótons operando a 4.65 &#956;m para sistemas de espaço livre. Neste caso, um estudo de viabilidade para um sistema prático de criptografia quântica operando em um comprimento de onda no infravermelho médio é realizado. Os resultados mostram que, usando a tecnologia disponível na atualidade, tal sistema pode ser construído, embora sua utilidade se mostre restrita a enlaces possuindo certas condições meteorológicas específicas. / [en] Two single photon counting devices, operating at near- and mid-infrared wavelengths, are introduced and experimentally investigated. Both use a twostage technique, comprised of an initial frequency up-conversion procedure inside a nonlinear crystal followed by a silicon avalanche photodiode. Whereas the first project consists on detection of single photons at 1.55 ìm for fiber-optic-based quantum communications, using a cavity-enhanced procedure, the second project envisions the development of a single-photon counter operating at 4.65 ìm for free-space systems. In this case, a feasibility study for a practical quantum key distribution system operating in a mid-infrared wavelength is performed. The results show that, using present-day technology, such a system can be constructed, albeit its usefulness would be restricted to operation under very specific weather conditions.

[pt] Detectores de fótons únicos baseados em fotodiodo avalanche (SPADs) são elementos essenciais em aplicações que requerem alta sensibilidade, como comunicações quânticas. É proposto um método para caracterização em tempo real da eficiência de detecção e das probabilidades de contagem de escuro e de pós-pulsos em SPADs através da análise da estatística de tempos entre detecções consecutivas utilizando instrumentação simples com o detector sob condições de operação. O método é então aplicado no monitoramento dos detectores utilizados em um sistema de distribuição quântica de chaves, motivado pela falha de segurança que imperfeições apresentadas pela tecnologia atual de detecção podem acarretar. Em especial, os ataques after-gate e time-shif são implementados e analisados. Uma simulação através do método de Monte-Carlo de um detector de fótons únicos composto por uma associação de diversos SPADs ativados serialmente e precedidos por uma chave óptica ativa é apresentada, visando otimizar a performance de detecção com tecnologia atual no tangente à frequência de gatilho. É reportada ainda a interferência estável entre fótons provenientes de fontes laser atenuadas totalmente independentes, cuja visibilidade é monitorada ao longo do tempo para um enlace implementado sobre duas bobinas de 8,5 km com controle ativo de polarização, passo importante para a tecnologia de repetidores quânticos e para o protocolo para distribuição quântica de chaves independente do aparato de medição. Um medidor de estados de Bell é implementado, utilizando-se óptica linear, com a resposta do sistema verificada para diferentes combinações dos estados preparados em duas estações remotas conectadas à estação central de medição através do canal estabilizado. / [en] DetecSingle-photon detectors based on avalanche photodiodes (SPADs) are key elements in ultra-sensitive applications, such as quantum communication. This thesis presents a method for real-time characterization of the overall detection efficiency, afterpulse and dark count probabilities, based on the analysis of the statistics of times between consecutive detections with simple instrumentation under operational condition. The method is employed for monitoring the SPADs on a quantum key distribution system, to prevent security failures due to side-channel attacks caused by current technology loopholes. The after-gate and time-shift attacks are implemented and analyzed. A Monte-Carlo simulation of a serially-activated association of SPADs, preceeded by an active optical switch, is performed for enhancement of the gating frequency performance with detectors based on current technology. The stable interference between photons from two independent faint laser sources is also reported, with visibility stability monitored over time after an optical link composed by two polarization-controlled 8.5-km fiber spools, a key features for quantum repeater and the measurement device independent quantum key distribution protocols. A Bell states analyzer is implemented with linear optics, and its response is verified for different combination of polarization states received from the remote stations through the stabilized channels.