<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>

No description available.

<p dir="ltr">As the design of computer chips heavily relies on computer simulations, it is envisioned that numerical modeling will play an increasingly important role in the development of unconventional computing technologies. This thesis studies the computational frameworks related to the development of unconventional computing, including probabilistic computing and quantum computing. The capability of probabilistic computing in solving NP-complete number theory problems is demonstrated. Generalized Helmholtz decomposition is shown as a theoretical basis for quantization of electromagnetic fields via numerical mode decomposition. A 2D demonstration of numerical quantization with finite difference method is presented. A computational framework amenable to integral equation solver is proposed to investigate the scattering effect on momentum-entangled photons from spontaneous parametric downconversion. A generic model to investigate field-matter interaction with nonlinearity is presented.</p>

<p dir="ltr">Following the development of laser technology in the 1960s, radiation pressure was soon employed to manipulate particles by Arthur Ashkin in the 1970s. Since then, levitated optomechanics has been widely studied across physics, engineering, chemistry, and biology. In this dissertation, we first experimentally demonstrate GHz rotation and sensing with an optically levitated nanodumbbell near a surface. Then, we propose achieving optical refrigeration below liquid nitrogen temperature using near-field Purcell enhancement.</p><p dir="ltr">The first part of this dissertation focuses on fast rotation and sensing with a non-spherical silica nanoparticle levitated near a surface. Specifically, we optically levitate a nanodumbbell at 430 nm away from a surface in high vacuum and drive it to rotate at 1.6 GHz. This corresponds to a relative linear velocity of 1.4 km/s between the tip of the nanodumbbell and the surface at sub-micrometer separation. The near-surface rotating nanodumbbell demonstrates a superior torque sensitivity of (5.0 +/- 1.1 ) x 10^-26 Nm at room temperature. Our numerical simulation shows that such an ultra-sensitive nanodumbbell levitated near nanostructures can be used to detect fundamental physics, such as Casimir torque and non-Newtonian gravity. </p><p dir="ltr">In the latter part of this dissertation, we propose that optical refrigeration of solid with anti-Stokes fluorescence can be enhanced by Purcell effect. The spontaneous emission rate of high-energy photons is Purcell enhanced by coupling with a near-field cavity. The enhanced emission shifts the mean emission wavelength and enables optical refrigeration with high-absorption cooling laser. We estimate a minimum achievable temperature of 38 K with a Yb³⁺:YLiF₄ nanocrystal near a cavity using our proposed Purcell enhanced optical refrigeration method. This method can be applied to other rare-earth ion doped materials and enable applications that require solid-state cooling below liquid nitrogen temperature.</p>

<p>One of the fundamental predictions of quantum mechanics is the occurrence of random fluctuations which can induce a measurable force between neutral objects, known as the Casimir effect. Casimir effect has attracted a lot of interest in both theoretical and practical work since the first prediction in 1948 because it is the most accessible evidence of quantum electromagnetic fluctuations in vacuum. Besides, it has prospective applications for nanotechnology and for studying fundamental physical theories beyond the standard model. In this dissertation, we report the experimental and theoretical progress towards realizing Casimir-based devices and long sought-after vacuum friction. </p> <p><br></p> <p>First, we propose and experimentally realize the first Casimir diode system that can regulate energy transfer along one direction through quantum vacuum fluctuations. This is the first experimental demonstration of non-reciprocal energy transfer by Casimir effects. We develop a dual-cantilever vacuum system which can be used to measure the Casimir force at separations from 50 nm to 1000 nm.  Parametric coupling scheme is applied to the system to couple two cantilevers with different resonant frequencies by Casimir interaction. By controlling the system near the exceptional point, we are able to break the time reversal symmetry and observe the non-reciprocal energy transfer. </p> <p><br></p> <p>The description of the Casimir diode system is followed by an experimental demonstration of the Casimir transistor system where we achieve the first measurement of Casimir interaction between three macroscopic objects. Three cantilevers can be coupled through quantum vacuum fluctuations by the parametric coupling scheme. Moreover, we have realized the first three-terminal Casimir transistor system that can switch and amplify quantum vacuum mediated energy transfer. These two Casimir-based devices will have potential applications in sensing and information processing.  </p> <p><br></p> <p>Subsequently, the first observation of Casimir mediated non-contact friction is demonstrated experimentally. When two parallel surfaces are moving with a relative velocity, they will experience quantum vacuum friction force which tries to slow down the relative motion because of quantum vacuum fluctuations. The quantum vacuum friction comes from the exchange of virtual photons between two moving bodies.  We have designed a novel method to detect the Casimir force mediated non-contact friction force between two harmonic oscillators. The non-contact friction comes from the interaction of virtual photons and phonons. We have experimentally detected the effect of non-contact friction and successfully measured the friction force at different velocities. </p> <p><br></p> <p>In the latter part of this thesis, two theoretical proposals about detecting the Casimir torque and rotational quantum vacuum friction torque by a levitated optomechanical system are discussed. The optically levitated nanoparticle system is a good candidate for precision measurements because it can achieve an ultrahigh mechanical quality factor due to the well isolation from the thermal environment. The calculation of the Casimir torque on a levitated nanorod near a birefringent plate is demonstrated. The calculation of the rotational quantum vacuum friction torque on a rotating nanosphere near a plate is also presented. By comparing these small torques to the sensitivity of our levitation system, we show that it is feasible to detect the Casimir torque and the rotational quantum vacuum friction torque under realistic conditions in the near future. </p> <p><br></p>

This thesis contains several theoretical studies on optomechanical systems, i.e. physical devices where mechanical degrees of freedom are coupled with optical cavity modes. This optomechanical interaction, mediated by radiation pressure, can be exploited for cooling and controlling mechanical resonators in a quantum regime. The goal of this thesis is to propose several new ideas for preparing meso- scopic mechanical systems (of the order of 10^15 atoms) into highly non-classical states. In particular we have shown new methods for preparing optomechani-cal pure states, squeezed states and entangled states. At the same time, proce-dures for experimentally detecting these quantum effects have been proposed. In particular, a quantitative measure of non classicality has been defined in terms of the negativity of phase space quasi-distributions. An operational al- gorithm for experimentally estimating the non-classicality of quantum states has been proposed and successfully applied in a quantum optics experiment. The research has been performed with relatively advanced mathematical tools related to differential equations with periodic coefficients, classical and quantum Bochner’s theorems and semidefinite programming. Nevertheless the physics of the problems and the experimental feasibility of the results have been the main priorities. / Die vorliegende Arbeit besteht aus verschiedenen theoretischen Untersuchungen von optomechanischen Systemen, das heißt physikalische Bauteile bei denen mechanische Freiheitsgrade mit Lichtmoden in optischen Kavitäten gekoppelt sind. Diese optimechanischen Wechselwirkungen, die über den Strahlungsdruck vermittelt werden, lassen sich zur Kühlung und Kontrolle von mechanischen Resonatoren im Quantenregime verwenden. Das Ziel dieser Arbeit ist es, verschiedene neue Ideen für Methoden vorzuschlagen, mit denen sich mesoskopische mechanische Systeme (bestehend aus etwa 10^15 Atomen) in sehr nicht-klassischen Zuständen präparieren lassen. Außerdem werden Techniken beschrieben, mit denen sich diese Quateneffekte experimentell beobachten lassen. Insbesondere wird ein quantitatives Maß für Nichtklassizität auf der Basis von Quasiwahrscheinlichkeitsverteilungen im Phasenraum definiert und ein operationeller Algorithmus zu dessen experimenteller Beschrieben, der bereits erfolgreich in einem quantenoptischen Experiment eingesetzt wurde.

[pt] Nas últimas décadas, interações entre luz e matéria provaram ser uma ferramenta versátil para medir e controlar sistemas mecânicos, encontrando aplicações desde detecção de forças até resfriamento ao estado fundamental de nanoesferas. Nesta dissertação, nós apresentamos algumas das ferramentas teóricas necessárias para descrever interferômetros, pinças ópticas e cavidades ópticas, constituintes fundamentais da caixa de ferramentas optomecânica. No regime clássico, estudamos o campo eletromagnético circulante em interferômetros lineares e mostramos como encontrar o campo resultante transmitido, apresentando exemplos de cavidades ópticas com um número arbitrário de elementos dispersivos. Nós também estudamos as forças de pressão de radiação que feixes ópticos podem imprimir em partículas dielétricas e mostramos como o aprisionamento óptico 3D é possível em focos claros e escuros. A potencial aplicação para captura de organismos vivos é estudada. No regime quântico, nós estudamos como o campo ressonante de cavidades ópticas pode interagir de forma dispersiva com diferentes sistemas mecânicos, dando origem a uma dinâmica quântica fechada emaranhante. Ao considerar uma nuvem ultra resfriada de átomos interagindo com dois modos ópticos, mostramos o surgimento de emaranhamento óptico que evidencia a natureza não-clássica do conjunto atômico macroscópico. A viabilidade experimental deste experimento com tecnologia atual é estudada. Além disso, nós investigamos o cenário em que uma pinça óptica posiciona uma partícula levitada dentro de uma cavidade óptica de forma que os fótons da pinça espalhados pela partícula possam sobreviver dentro da cavidade. Já foi demonstrado que esta interação, chamada de espalhamento coerente, pode resfriar nanopartículas até números de fônons menores do que um, atingindo profundamente o regime quântico. Nós mostramos que esta interação também pode gerar emaranhamento mecânico entre muitas partículas levitadas, mesmo em um ambiente a temperatura de 300K. Um resumo sobre sistemas de variáveis contínuas e a caixa de ferramentas numérica customizada usada ao longo deste trabalho são apresentados. / [en] Over the last decades, light-matter interactions have proven to be a versatile tool to measure and control mechanical systems, finding application from force sensing to ground state cooling of nanospheres. In this dissertation, we present some of the theoretical tools that describe interferometers, optical tweezers and optical cavities, fundamental constituents of the optomechanical toolbox. In the classical regime, we study the circulating electromagnetic field within linear interferometers and show how one can find the resulting transmitted field, presenting examples of optical cavities with an arbitrary number of dispersive elements. Moreover, we also study the radiation-pressure forces that optical beams can imprint on dielectric particles and show how 3D optical trapping is possible in both bright and dark focuses. Potential application to trapping of living organisms is studied. In the quantum regime, we study how the resonant field of optical cavities can dispersivelly interact with different mechanical systems, giving rise to an entangling closed quantum dynamics. When considering an ultracold cloud of atoms interacting with two optical modes, we show the emergence of optical entanglement which evidences the nonclassical nature of the macroscopic atomic ensemble. The experimental feasibility of this experiment with current technology is studied. Furthermore, we investigate the scenario where a finely tuned optical tweezer places a trapped particle inside an optical cavity such that the tweezer s scattered photons can survive inside the cavity. This so-called coherent scattering interaction has been shown to cool nanoparticles to phonon numbers lower than one deep into the quantum regime. We show that it also can generate mechanical entanglement between many levitated particles even in a room temperature environment. An overview on continuous variable systems and the custom numerical toolbox used throughout this work are presented.

<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>

<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>