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This thesis probes the usefulness of non-classical correlations within imperfect continuous variable decoherent quantum systems. Although a consistent function and practical usefulness of these correlations is largely unknown, it is important to examine their characteristics in more realistic dissipative systems, to gain further insight into any possible advantageous behaviour. A bipartite separable discordant state under the action of controlled loss on one subsystem was considered. Under these conditions the Gaussian quantum discord not only proved to be robust against loss, but actually improves as loss is intensified. Harmful imperfections which reduce the achievable level of discord can be counteracted by this controlled loss. Through a purification an explanation of this effect was sought by considering system-environment correlations, and found that a flow of system-environment correlations increases the quantumness of the state. Entanglement recovery possibilities were discussed and revealed the importance of hidden quantum correlations along bi-partitions across the discordant state and a classically prepared "demodulating" system, acting in such a way as to partially cancel the entanglement preventing noise. Entanglement distribution by separable states was studied by a similar framework, in an attempt to explain the emergence of quantum entanglement by a specific flow of correlations in the globally pure system. Discord appears to play a less fundamental role compared to the qubit version of the protocol. The strengthening of non-classical correlations can be attributed to a flow of classical and quantum correlations. This work proves that discord can be created in unique ways and, in select circumstances, can act to counteract harmful imperfections in the apparatus. Due to this advantageous behaviour discord indeed may ultimately aid in more applicable "real world" applications, which are by definition decoherent.

<p dir="ltr">This work is the first report of optically addressable spin qubits in a semi-1D material, Boron Nitride Nanotubes (BNNTs). We perform the characterization of these spin defects and utilize their properties to do omnidirectional magnetic field sensing. We transfer these BNNTs with spin defects onto an AFM cantilever and perform scanning probe magnetometry of a 2D Nickel pattern on a gold waveguide. </p>

La dissertation explore différentes applications des fibres optiques en ingénierie quantique. Deux thématiques sont développées :d'une part l'utilisation des fibres optiques monomodales en silice pour l'implémentation d'algorithmes et de protocoles de communication quantiques et d'autre part l'utilisation de la non-linéarité de ces fibres pour réaliser des sources de paires de photons corrélés. L'étude est à la fois théorique et expérimentale./ The dissertation explores various uses of optical fibers for quantum engineering. Two topics are developed :first the use of single-mode silica fibers for implementing quantum algorithms and communication protocols, second the use of these fibers for generating correlated photon-pairs. / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished

In this thesis, we investigate the quantum mechanical interaction of light with matter in the form of a gas of ultracold atoms: the atomic ensemble. We present a theoretical analysis of two problems, which involve the interaction of quantized electromagnetic fields (called signal and idler) with the atomic ensemble (i) cascade two-photon emission in an atomic ladder configuration, and (ii) photon frequency conversion in an atomic diamond configuration. The motivation of these studies comes from potential applications in long-distance quantum communication where it is desirable to generate quantum correlations between telecommunication wavelength light fields and ground level atomic coherences. In the two systems of interest, the light field produced in the upper arm of an atomic Rb level scheme is chosen to lie in the telecom window. The other field, resonant on a ground level transition, is in the near-infrared region of the spectrum. Telecom light is useful as it minimizes losses in the optical fiber transmission links of any two long-distance quantum communication device. We develop a theory of correlated signal-idler pair correlation. The analysis is complicated by the possible generation of multiple excitations in the atomic ensemble. An analytical treatment is given in the limit of a single excitation assuming adiabatic laser excitations. The analysis predicts superradiant timescales in the idler emission in agreement with experimental observation. To relax the restriction of a single excitation, we develop a different theory of cascade emission, which is solved by numerical simulation of classical stochastic differential equation using the theory of open quantum systems. The simulations are in good qualitative agreement with the analytical theory of superradiant timescales. We further analyze the feasibility of this two-photn source to realize the DLCZ protocol of the quantum repeater communication system. We provide a quantum theory of near-infrared to telecom wavelength conversion in the diamond configuration. The system provides a crucial part of a quantum-repeater memory element, which enables a "stored" near-infrared photon to be converted to a telecom wavelength for transmission without the destruction of light-atom quantum correlation. We calculate the theoretical conversion efficiency, analyzing the role of optical depth of the ensemble, pulse length, and quantum fluctuations on the process.

In the twentieth century, the founding fathers of quantum mechanics explored the implications of their theory by designing gedanken experiments. In recent years, continuous improvement of the experimental manipulation of individual quantum systems has opened the way to exciting research, both on blackboards and in laboratories, and even towards field experiments. The manipulation of individual quantum systems is the basis for quantum information processing: when an information content is associated with transformations and measurements of quantum systems, it offers a new paradigm, full of potentialities, to information theory. This leads to quantum random number generation, quantum computing, quantum communication, including quantum teleportation and quantum cryptography, etc. One of the promises of quantum information is the realization of a quantum internet: quantum communication links would allow to share quantum states between the nodes (quantum computers) of the network.<p><p>Our work lies in the context of experimental quantum optics in optical fibers at telecommunication wavelengths, in view of quantum communication applications. More particularly, we study photon pairs entangled in their energy-time degree of freedom. The traditional approach to manipulate energy-time entangled photons is based on the notion of time bin: quantum information is encoded in the relative phase between distinct spatio-temporal paths, which interfere via Mach-Zehnder interferometers. The aim of our work is to demonstrate an alternative approach to manipulate energy-time entangled photons in optical fibers at telecommunication wavelengths. We investigate and implement an original method for their manipulation by building on proven techniques for their production, transmission and detection (namely nonlinear waveguides, optical fibers and single-photon detectors, respectively). The photon pairs produced by a parametric down-conversion source are sent through independent electro-optic phase modulators, which act as high-dimensional frequency beam splitters, transforming the photonic states in the frequency domain. We then use frequency filters to discriminate the photons' frequencies. Such experimental methods, whose classical origin can be traced back to coherent communication, have been previously used with attenuated coherent states as approximations of single photons.<p><p>In the present work, we aim to show that frequency-bin entanglement provides an interesting alternative platform for quantum communication. Our main experimental results towards this goal are the obtaining of high-visibility two-photon interference patterns allowing Bell inequality violations. Our method provides decisive advantages: high dimensionality, use of standard optical and optoelectronic components, inherent stability and robustness, no need for active stabilization in laboratory conditions, visibilities comparable to the highest obtained using other degrees of freedom, etc. It has however a few drawbacks, mainly high losses and the somewhat complexity of the radio-frequency system which is not standard in quantum optics. Exploiting the high dimensionality is also challenging. Overall, our method allows the implementation of traditional and original quantum optics experiments with interesting perspectives for quantum information and communication. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

This thesis is an attempt at studying quantum coherence effects coupled via plasmons. After introducing the quantum coherence in atomic systems in Chapter 1, we utilize it in Chapter 2 to demonstrate a new technique of detection of motion of single atoms or irons inside an optical cavity. By taking into account the interaction of coherences with surface plasmonic waves excited in metal nanoparticles, we provide a theoretical model along with experimental data in Chapter 3 to describe the modification of Raman spectra near metal nanoparticles. We show in chapter 4 that starting from two emitters, coupled via a plasmonic field, the symmetry breaking occurs, making detectable the simultaneous existence of the fast super-radiance and the slow sub-radiance emission of dye fluorescence near a plasmonic surface. In Chapter 5, we study the photon statistics of a group of emitters coupled via plasmons and by the use of quantum regression theorem, we provide a theoretical model to fully investigate the dependence of photon bunching and anti-bunching effects to the interaction between atoms, fields and surrounding mediums.

<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>

<p>Developing a hybrid platform that combines nanophotonic circuits and atomic physic may provide new chip-scale devices for quantum application or versatile tools for exploring photon-mediated long-range quantum systems. However, this challenging project demands the excellent integration of cold atom trapping and manipulation technology with cutting-edge nanophotonics circuit design and fabrication. In this thesis project, we aim to develop a novel suspended membrane platform that serves as a quantum interface between laser-cooled, trapped atoms in an ultrahigh vacuum and the photons guided in the nanophotonic circuits based on high-quality silicon nitride microring resonators fabricated on a transparent membrane substrate. </p> <p><br></p> <p>The proposed platform meets the stringent performance requirements imposed by nanofabrication and optical physics in an ultra-high vacuum. These include a high yield rate for mm-scale suspended dielectric photonic devices, minimization of the surface roughness to achieve ultrahigh-optical quality, complete control of optical loss/in-coupling rate to achieve critical photon coupling to a microring resonator, and high-efficiency waveguide optical input/output coupler in an ultrahigh vacuum environment. This platform is compatible with laser-cooled and trapped cold atoms. The experimental demonstration of trapping and imaging single atoms on a photonic resonator circuit using optical tweezers has been demonstrated. Our circuit design can potentially reach a record-high cooperativity parameter C$>$500 for single atom-photon coupling, which is of high importance in realizing a coherent quantum nonlinear optical platform and holds great promise as an on-chip atom-cavity QED platform.</p>

<p><br></p><p dir="ltr">Achieving high optical resolution imaging is one of the most important goals in the history of optics. However, due to finite aperture sizes, a diffraction limit is imposed on optical imaging. Therefore, the Rayleigh limit, which describes the minimum separation at which two point sources are resolvable, has served as a critical limit in optical resolution. Many methods have been studied to break the limit and succeed in resolving nearby sources below the Rayleigh criterion but only beyond a certain distance. Furthermore, it has been demonstrated that quantum-inspired optics techniques maintain consistent variance in estimating the separation of point sources even at low separations, but only with prior information like a known number of sources and equal brightness. Therefore, achieving the ultimate optical resolution remains an open question. This thesis will conclusively address this challenge considering real-world scenarios, i.e., no prior information or controlled lab environment as well as low signal-to-noise ratio (SNR), turbulence, and other practical challenges.</p><p><br></p><p dir="ltr">In information theory, the estimation variance of a random parameter can be quantified using the inverse of Fisher information. By maximizing the Fisher information, one can minimize the variance in estimation. In my thesis, we have shown that the measurement can be accelerated without sacrificing optical resolution using the adaptive mode so that quantum Fisher information per detected photon is maximized. The notable attribute that sets it apart from other quantum-inspired methods is that it does not require any prior information, making it more feasible for practical application. We have further shown that the space domain awareness (SDA) challenge can be effectively handled with the aforementioned approach with a very limited photon budget and even in the presence of turbulence. Toward solving the challenges, we designed a photon statistics-based direct imaging method that can also serve as a baseline method for quantum optics. In my thesis, atmospheric turbulence is also deeply explored and the effect is mitigated using reinforcement learning.</p><p><br></p>