Fluctuations, dissipation and the dynamical Casimir effect

Vacuum fluctuations provide a fundamental source of dissipation for systems coupled to quantum fields by radiation pressure. In the dynamical Casimir effect, accelerating neutral bodies in free space give rise to the emission of real photons while experiencing a damping force which plays the role of a radiation reaction force. Analog models where non-stationary conditions for the electromagnetic field simulate the presence of moving plates are currently under experimental investigation. A dissipative force might also appear in the case of uniform relative motion between two bodies, thus leading to a new kind of friction mechanism without mechanical contact. In this paper, we review recent advances on the dynamical Casimir and non-contact friction effects, highlighting their common physical origin.Comment: 39 pages, 4 figures. Review paper to appear in Lecture Notes in Physics, Volume on Casimir Physics, edited by Diego Dalvit, Peter Milonni, David Roberts, and Felipe da Rosa. Minor changes, a reference adde

Harnessing Spatial Intensity Fluctuations for Optical Imaging and Sensing

Properties of light such as amplitude and phase, temporal and spatial coherence, polarization, etc. are abundantly used for sensing and imaging. Regardless of the passive or active nature of the sensing method, optical intensity fluctuations are always present! While these fluctuations are usually regarded as noise, there are situations where one can harness the intensity fluctuations to enhance certain attributes of the sensing procedure. In this thesis, we developed different sensing methodologies that use statistical properties of optical fluctuations for gauging specific information. We examine this concept in the context of three different aspects of computational optical imaging and sensing. First, we study imposing specific statistical properties to the probing field to image or characterize certain properties of an object through a statistical analysis of the spatially integrated scattered intensity. This offers unique capabilities for imaging and sensing techniques operating in highly perturbed environments and low-light conditions. Next, we examine optical sensing in the presence of strong perturbations that preclude any controllable field modification. We demonstrate that inherent properties of diffused coherent fields and fluctuations of integrated intensity can be used to track objects hidden behind obscurants. Finally, we address situations where, due to coherent noise, image accuracy is severely degraded by intensity fluctuations. By taking advantage of the spatial coherence properties of optical fields, we show that this limitation can be effectively mitigated and that a significant improvement in the signal-to-noise ratio can be achieved even in one single-shot measurement. The findings included in this dissertation illustrate different circumstances where optical fluctuations can affect the efficacy of computational optical imaging and sensing. A broad range of applications, including biomedical imaging and remote sensing, could benefit from the new approaches to suppress, enhance, and exploit optical fluctuations, which are described in this dissertation

Nitrogen-Vacancy Centers in Diamond for Nanoscale Magnetic Resonance Imaging Applications

The nitrogen-vacancy (NV) center is a point defect in diamond with unique properties for use in ultra-sensitive, high-resolution magnetometry. One of the most interesting and challenging applications is nanoscale magnetic resonance imaging (nano-MRI). While many review papers have covered other NV centers in diamond applications, there is no survey targeting the specific development of nano-MRI devices based on NV centers in diamond. Several different nano-MRI methods based on NV centers have been proposed with the goal of improving the spatial and temporal resolution, but without any coordinated effort. After summarizing the main NV magnetic imaging methods, this review presents a survey of the latest advances in NV center nano-MRI

Light localization in biological media

Light in natural and biological media is known as freely diffusing. When light undergoes multiple scattering through inhomogeneous dielectric biomacromolecules, interference is ignored. If scattered waves return to their origin points along the time-reversed paths for constructive interference, outgoing waves can be forbidden, occasionally being on-resonance or off-resonance with Anderson localized modes. However, such a phenomenon in optics requires high-refractive-index contrasts, which intrinsically do not exist in organic molecules (e.g. proteins, lipids, carbohydrates, and nucleic acids). Here we predict and show experimentally that the long-standing perception of diffusive nature of light in biological media is broken by an exquisite distribution of silk protein structures produced from Bombyx mori (silkworm) and layered aragonite structures produced from Haliotis fulgens (abalone). We demonstrate how optical transmission quantities (e.g. light flux in transmission channels) are analyzed satisfying critical values of the Anderson localization transition. We find that the size of modes is smaller than specimen sizes and that the statistics of modes, decomposed from excitation at the gain-loss equilibrium, clearly differentiates silk and nacre from diffusive structures sharing the microscopic morphological similarity. This explains how the dimension, the size, and the distribution of disordered biological nanostructures result in enhanced light-matter interactions, in spite of low refractive index contrasts of constituent materials. As wave localization is universal, the presented results of electromagnetic waves will allow us to extend insight into electronic and mechanical waves in biological systems. Importantly, such optical resonances are extremely sensitive to subtle nanoscale perturbations, and thus can be implemented to biosensing platforms

Gradient Field Transduction of Nanomechanical Resonators

Das Forschungsgebiet nanomechanischer Systeme betrachtet die Bewegung von Strukturen, deren Länge in mindestens einer Richtung deutlich unter einem Mikrometer liegt. Meist werden dabei Auslenkungen untersucht, die in der Nähe einer mechanischen Resonanz angetrieben werden. Das wissenschaftliche Interesse an solchen Strukturen hat mehrere Gründe: aufgrund der kleinen Masse und oftmals geringen Dämpfung (d.h. hohe Güte) reagieren solche nanomechanischen Systeme sehr empfindlich auf Änderungen ihrer Umgebung oder ihrer eigenen Eigenschaften wie etwa ihrer Masse. Die große Vielfalt der nanomechanischen Systeme erlaubt die Kopplung an verschiedenste physikalische Größen wie (Umgebungs-)Druck, Licht, elektrische/magnitische Felder. Dies ermöglicht, die Wechselwirkung selbst zu untersuchen oder entsprechende Änderungen empfindlich zu detektieren. Im Rahmen der vorliegenden Arbeit wurde die Resonator Bewegung von doppelseitig eingespannten Balken untersucht; diese wurden mit konventioneller Mikrofabrikation aus verspanntem Silizium-Nitrid gefertigt. Die große Zugspannung in den Balken führt zu einer hohen mechanischen Stabilität und ebenso zu hohen mechanischen Güten. Ein Teil der Arbeit befasste sich mit der Entwicklung neuer Detektions- und Antriebsmechanismen. Unter Ausnutzung der Polarisierbarkeit des Resonators wurde ein lokaler Antrieb realisiert, der sich durch besondere Einfachkeit auszeichnet. Ebenso wurden Fortschritte in der optischen Detektion erzielt. Ein Photodetektor konnte innerhalb einer optischen Wellenlänge Abstand zum Resonator plaziert werden; dies ermöglicht die lokale Detektion seiner Bewegung. Hochempfindliche Messungen nutzen oft optische Resonanzen; bisherige Umsetzungen basieren auf Reflexionen und sind daher auf Objekte beschränkt, die größer als die verwendete Wellenlänge sind. In einer Zusammenarbeit mit Prof. Kippenberge konnte diese Beschränkung umgangen werden, indem geführtes Licht in einem Mikro-Toroiden verwendet wurde. Weiter wurde in der Arbeit die resonante Bewegung selbst untersucht. Im Bereich hoher Amplituden zeigt die rücktreibende Kraft nichtlineares Verhalten. Das sich dadurch ergebende bistabile Verhalten des Resonators wurde mit Hilfe von kurzen, resonanten Pulsen untersucht; schnelles Schalten wurde erreicht. Die mechanische Dämpfung der Siliziumnitrid Resonatoren wurde untersucht. Die hohen Güten von Systemen unter Zugspannung konnte erklärt werden durch die sich ergebende erhöhte gespeicherte elastische Energie; im Gegensatz zu einem veränderten Dämpfungsverhalten

Dynamics of Spin and Charge of Color Centers in Diamond under Cryogenic Conditions

Individual quantum systems in semiconductors are currently the most sought-after platform for applications in quantum science. Most notably, the nitrogen-vacancy (NV) center in diamond features a defect deep within the electronic bandgap, making it amenable for precise manipulation to help pave the way to perform fundamental quantum physics experimentation. The NV center also offers long coherence times and versatile spin-dependent fluorescent properties, making it an ideal candidate for a nanoscale magnetometer. Furthermore, multi-color excitation offers deterministic charge state manipulation. While ambient operation has been key to their appeal, bringing NVs to cryogenic conditions opens new opportunities for alternate forms of control schemes and phenomena. This dissertation discusses experimental work and the theoretical analysis of surface dynamics on NV-based AFM probes in proximity to a superconductor. A brief introduction on the experimental infrastructure is reviewed. Time-resolved experiments on the NV’s single electron spin are analyzed to lend insight into the interdependence between magnetic and electric field noise sources affecting the surface of a diamond. This thesis also examines the use of the NV’s cryogenic optical transitions in single crystal diamond for sub-diffraction charge control to implement long-term, multiplexed, and rewritable data storage. Lastly, experimentations on the NV’s spin-dependent optical transitions as a means of detection sensitivity enhancement are investigated, with the goal to ultimately revert to applications in the context of nanoscale metrology

Learning as a Nonlinear Line of Attraction for Pattern Association, Classification and Recognition

Development of a mathematical model for learning a nonlinear line of attraction is presented in this dissertation, in contrast to the conventional recurrent neural network model in which the memory is stored in an attractive fixed point at discrete location in state space. A nonlinear line of attraction is the encapsulation of attractive fixed points scattered in state space as an attractive nonlinear line, describing patterns with similar characteristics as a family of patterns. It is usually of prime imperative to guarantee the convergence of the dynamics of the recurrent network for associative learning and recall. We propose to alter this picture. That is, if the brain remembers by converging to the state representing familiar patterns, it should also diverge from such states when presented by an unknown encoded representation of a visual image. The conception of the dynamics of the nonlinear line attractor network to operate between stable and unstable states is the second contribution in this dissertation research. These criteria can be used to circumvent the plasticity-stability dilemma by using the unstable state as an indicator to create a new line for an unfamiliar pattern. This novel learning strategy utilizes stability (convergence) and instability (divergence) criteria of the designed dynamics to induce self-organizing behavior. The self-organizing behavior of the nonlinear line attractor model can manifest complex dynamics in an unsupervised manner. The third contribution of this dissertation is the introduction of the concept of manifold of color perception. The fourth contribution of this dissertation is the development of a nonlinear dimensionality reduction technique by embedding a set of related observations into a low-dimensional space utilizing the result attained by the learned memory matrices of the nonlinear line attractor network. Development of a system for affective states computation is also presented in this dissertation. This system is capable of extracting the user\u27s mental state in real time using a low cost computer. It is successfully interfaced with an advanced learning environment for human-computer interaction