We present a new test of non-randomness that tests both the lower and the upper critical limit of aχ2-statistic. While checking the upper critical value has been employed by other tests, we argue that also the lower critical value should be examined for non-randomness. To this end, we prepare a binary sequence where all possible bit strings of a certain length occurs the same number of times and demonstrate that such sequences pass a well-known suite of tests for non-randomness. We show that such sequences can be compressed, and therefore are somewhat predictable and thus not fully random. The presented test can detect such non-randomness, and its novelty rests on analysing fixed-length bit string frequencies that lie closer to the a priori probabilities than could be expected by chance 

Lithium niobate (LN) is a ferroelectric crystal offering a broad transparency spectrum, together with excellent electro-optic and nonlinear optical properties. Thanks to them, LN is setting the standard for quantum optics and telecommunications in critical applications such as ultrafast modulation and frequency conversion. The development of a reliable nanophotonic platform in LN can be expected to effectively leverage all such appealing functionalities in compact and integrated formats and provide important and complementary functionalities to current silicon-photonics platforms.

This thesis encompasses systematic and consistent efforts with the goal to achieve the key building blocks for a comprehensive integrated nanophotonic platform in LN. It involves work on the technology side, sustained and complemented by modelling and experiments, ultimately leading to the demonstration of a few novel devices.

Ultrahigh field confinement in nanophotonic waveguides is accompanied by the appearance of non-negligible longitudinal components in the guided optical fields. By fabricating high-quality LN nanopillars and analyzing with theory and experiments their second harmonic generation (SHG) response, we provide evidence for the existence of longitudinal field components and demonstrate the possibility to reshape the SHG polar emission properties of these submicrometric waveguides by fine-tuning the nanopillar size.

This thesis also presents a different technological approach, allowing the fabrication of photonic wires as small as 250 nm with lengths up to 1 cm on LN-on-insulator (LNOI), suitable for upscaling to photonic integrated circuit (PIC) architectures. By optimizing the fabrication process, the propagation losses of single-mode waveguides at telecom wavelengths on this platform were brought down from 76 to 1.13 dB/cm. Fine-pitch waveguide structuring was also successfully achieved, enabling LNOI-to-fiber grating couplers and waveguide Bragg gratings, the latter featuring record extinction ratios in LNOI (45 dB), comparable to the state of the art in silicon.

The thesis involves also theoretical work on the design of photonic wires where the interplay between LN and waveguide birefringence is used to achieve polarization-insensitive operation for the fundamental guided modes.

Finally, two demonstrators are provided for novel and emerging applications of LN to the life sciences, using LNOI surface-patterned templates for enhanced Raman spectroscopy and LN templates for controlled neuron growth and manipulation in microfluidic environments, respectively.

We demonstrate narrowband integrated filters with 0.23 mm-long phase-shifted Bragg gratings in corrugated single-mode thin-film LiNbO3 photonic wires, achieving quality factors of 1.24x10(4) and extinction ratios up to 24 dB at telecom wavelengths.

We design, fabricate and characterize sidewall corrugated Bragg gratings in a high confinement integrated optics lithium niobate platform, comprising submicrometric photonic wires, tapers and grating couplers to interface off-chip standard telecom optical fibers. We analyze the grating performance as band-rejection filter for TE-polarized signals in the telecom C-band, considering both rectangular and sinusoidal sidewall profiles, and demonstrate record extinction ratios as high as 27 dB and rejection bandwidths as narrow as 3 nm. The results show the potential for an efficient integration of novel photonic functionalities into low-footprint LiNbO3 nonlinear and electro-optical waveguide devices.

Nd3+-sensitized upconversion nanoparticles (UCNPs) can be excited by both 980 and 808 nm light, which is regarded as a particularly advantageous property of these particles. In this work, we demonstrate that the nanoparticles can exhibit significantly different response when excited at these two excitation wavelengths, showing dependence on the intensity of the excitation light and the way it is distributed in time. Specifically, with 808 nm excitation saturation in the emitted luminescence is more readily reached with increasing excitation intensities than upon 980 nm excitation. This is accompanied by delayed upconversion luminescence (UCL) kinetics and weaker UCL intensities. The different luminescence response at 808 and 980 nm excitation reported in this work is relevant in a manifold of applications using UCNPs as labels and sensors. This could also open new possibilities for multi-wavelength excitable UCNPs for upconversion color display and in laser-scanning microscopy providing selective readouts and sub-sectioning of samples.

Precisely positioned and scalable single-photon emitters (SPEs) are highly desirable for applications in quantum technology. This Perspective discusses single-photon-emitting atomistic defects in monolayers of MoS2 that can be generated by focused He-ion irradiation with few nanometers positioning accuracy. We present the optical properties of the emitters and the possibilities to implement them into photonic and optoelectronic devices. We showcase the advantages of the presented emitters with respect to atomistic positioning, scalability, long (microsecond) lifetime, and a homogeneous emission energy within ensembles of the emitters. Moreover, we demonstrate that the emitters are stable in energy on a timescale exceeding several weeks and that temperature cycling narrows the ensembles' emission energy distribution.

Photonic entanglement swapping, the procedure of entangling photons without any direct interaction, is a fundamental test of quantum mechanics and an essential resource to the realization of quantum networks. Probabilistic sources of nonclassical light were used for seminal demonstration of entanglement swapping, but applications in quantum technologies demand push-button operation requiring single quantum emitters. This, however, turned out to be an extraordinary challenge due to the stringent prerequisites on the efficiency and purity of the generation of entangled states. Here we show a proof-of-concept demonstration of all-photonic entanglement swapping with pairs of polarization-entangled photons generated on demand by a GaAs quantum dot without spectral and temporal filtering. Moreover, we develop a theoretical model that quantitatively reproduces the experimental data and provides insights on the critical figures of merit for the performance of the swapping operation. Our theoretical analysis also indicates how to improve stateof-the-art entangled-photon sources to meet the requirements needed for implementation of quantum dots in long-distance quantum communication protocols.

Efficient all-photonic quantum teleportation requires fast and deterministic sources of highly indistinguishable and entangled photons. Solid-state-based quantum emitters-notably semiconductor quantum dots-are a promising candidate for the role. However, despite the remarkable progress in nanofabrication, proof-of-concept demonstrations of quantum teleportation have highlighted that imperfections of the emitter still place a major roadblock in the way of applications. Here, rather than focusing on source optimization strategies, we deal with imperfections and study different teleportation protocols with the goal of identifying the one with maximal teleportation fidelity. Using a quantum dot with sub-par values of entanglement and photon indistinguishability, we show that the average teleportation fidelity can be raised from below the classical limit to 0.842(14), adopting a polarization-selective Bell state measurement and moderate spectral filtering. Our results, which are backed by a theoretical model that quantitatively explains the experimental findings, loosen the very stringent requirements set on the ideal entangled-photon source and highlight that imperfect quantum dots can still have a say in teleportation-based quantum communication architectures.

Quantum technologies are poised to move the foundational principles of quantum physics to the forefront of applications. This roadmap identifies some of the key challenges and provides insights on material innovations underlying a range of exciting quantum technology frontiers. Over the past decades, hardware platforms enabling different quantum technologies have reached varying levels of maturity. This has allowed for first proof-of-principle demonstrations of quantum supremacy, for example quantum computers surpassing their classical counterparts, quantum communication with reliable security guaranteed by laws of quantum mechanics, and quantum sensors uniting the advantages of high sensitivity, high spatial resolution, and small footprints. In all cases, however, advancing these technologies to the next level of applications in relevant environments requires further development and innovations in the underlying materials. From a wealth of hardware platforms, we select representative and promising material systems in currently investigated quantum technologies. These include both the inherent quantum bit systems and materials playing supportive or enabling roles, and cover trapped ions, neutral atom arrays, rare earth ion systems, donors in silicon, color centers and defects in wide-band gap materials, two-dimensional materials and superconducting materials for single-photon detectors. Advancing these materials frontiers will require innovations from a diverse community of scientific expertise, and hence this roadmap will be of interest to a broad spectrum of disciplines.

Through density functional theory (DFT), we investigate the electronic and transport properties of zigzag phosphorene nanoribbons (ZPNRs) and armchair phosphorene nanoribbons (APNRs) passivated with only H or O, or both H and O with different arrangements, systematically. According to the calculated cohesive energies, all structures are stable. Also, the simulation results reveal a semiconductor-to-metal transition in zigzag groups, but all the APNRs are semiconductors. We see the direct-to-indirect energy bandgap transition in armchair groups, while all the semiconductors of zigzag groups have a direct energy bandgap. We also study the effect of external transverse electric field on electronic properties. The applying electric field changes the energy bandgap leading to a semiconductor-to-metal transition at a certain electric field. In addition, the direct-to-indirect bandgap transition and vice versa occurs for some samples. Moreover, edge passivation has a significant effect on transport properties. The breakdown voltage of the devices changes from 0 to 1.94 eV, and we observe negative differential resistance (NDR) for some devices. The results indicate that passivated phosphorene nanoribbons are possible, and their properties can effectively be tuned by the arrangement, type of edge atoms, and external electric field, which make these structures a promising candidate for feasible nanodevices.

Melt quenching technique is used to prepare the glasses composition (KF-CaO-B2O3) with different concentration of manganese oxide in the range of 0.1-0.4 wt %. Nature of the fabricated glasses is confirmed by X-ray diffraction analysis. All calculated stability factors from differential thermal analysis increases with increasing the content of MnO. Infrared spectral analysis provided the information that those glass samples exhibited some symmetrical as well as asymmetrical bands belong to the borate group. The absorption results show a shifting in the absorption band, which is corresponding to the exchange of Mn2+ into the Mn3+ ions. Electron paramagnetic resonance results are shown two signals, which is characterized by Mn2+ and Mn3+. The variation in the intensity of these signals is discovered an improvement into glass stability with increased MnO content. The dielectric analyses is presented with different parameters with the variation of frequency from 103 Hz to 105 Hz and temperature 20 ?-400 ?.

Fluorescence methods offer extraordinary sensitivity and specificity, and are extensively used in the life sciences. In recent years, super resolution fluorescence imaging techniques have developed strongly, uniquely combining ~10 nm sub diffraction resolution and specific labeling with high efficiency. This thesis explores this potential, with a major focus on Stimulated Emission Depletion, STED, microscopy, applications thereof, image analyses and simulation studies. An additional theme in this thesis is development and use of single molecule fluorescence correlation spectroscopy, FCS, and related techniques, as tools to study dynamic processes at the molecular level. In paper I the proteins cytochrome-bo3 and ATP-synthase are studied with fluorescence cross-correlation spectroscopy, FCCS. These two proteins are a part of the energy conversion process in E. coli, converting ADP into ATP. We found that an increased interaction between these proteins, detected by FCCS, correlates with an increase in the ATP production. In paper II an FCS-based imaging method is developed, capable to determine absolute sizes of objects, smaller than the resolution limit of the microscope used. Combined with STED, this may open for studies of membrane nano-domains, such as those investigated by simulations in paper VII. In paper III and paper IV super resolution STED imaging was applied on Streptococcus Pneumoniae, revealing information about function and distribution of proteins involved in the defense mechanism of the bacteria, as well as their role in bacterial meningitis. In paper V, we used STED imaging to investigate protein distributions in platelets. We then found that the adhesion protein P-selectin changes its distribution pattern in platelets incubated with tumor cells, and with machine learning algorithms and classical image analysis of the STED images it is possible to automatically distinguish such platelets from platelets activated by other means. This could provide a strategy for minimally invasive diagnostics of early cancer development, and deeper understanding of the role of platelets in cancer development. Finally, this thesis presents Monte-Carlo simulations of biological processes and their monitoring by FCS. In paper VI, a combination of FCCS and simulations was applied to resolve the interactions between a transcription factor (p53) and an oncoprotein (MDM2) inside live cells. In paper VII, the feasibility of FCS techniques for studying nano-domains in membranes is investigated purely by simulations, identifying the conditions under which such nano-domains would be possible to detect by FCS. In paper VIII, proton exchange dynamics at biological membranes were simulated in a model, verifying experimental FCS data and identifying fundamental mechanisms by which membranes mediate proton exchange on a local (~10nm) scale.

In this study, we systematically investigate the decay characteristics of upconversion luminescence (UCL) under anti-Stokes excitation through numerical simulations based on rate-equation models. We find that a UCL decay profile generally involves contributions from the sensitizer's excited-state lifetime, energy transfer and cross-relaxation processes. It should thus be regarded as the overall temporal response of the whole upconversion system to the excitation function rather than the intrinsic lifetime of the luminescence emitting state. Only under certain conditions, such as when the effective lifetime of the sensitizer's excited state is significantly shorter than that of the UCL emitting state and of the absence of cross-relaxation processes involving the emitting energy level, the UCL decay time approaches the intrinsic lifetime of the emitting state. Subsequently, Stokes excitation is generally preferred in order to accurately quantify the intrinsic lifetime of the emitting state. However, possible cross-relaxation between doped ions at high doping levels can complicate the decay characteristics of the luminescence and even make the Stokes-excitation approach fail. A strong cross-relaxation process can also account for the power dependence of the decay characteristics of UCL.

Background Increasing evidence suggests that platelets play a central role in cancer progression, with altered storage and selective release from platelets of specific tumor-promoting proteins as a major mechanism. Fluorescence-based super-resolution microscopy (SRM) can resolve nanoscale spatial distribution patterns of such proteins, and how they are altered in platelets upon different activations. Analysing such alterations by SRM thus represents a promising, minimally invasive strategy for platelet-based diagnosis and monitoring of cancer progression. However, broader applicability beyond specialized research labs will require objective, more automated imaging procedures. Moreover, for statistically significant analyses many SRM platelet images are needed, of several different platelet proteins. Such proteins, showing alterations in their distributions upon cancer progression additionally need to be identified. Results A fast, streamlined and objective procedure for SRM platelet image acquisition, analysis and classification was developed to overcome these limitations. By stimulated emission depletion SRM we imaged nanoscale patterns of six different platelet proteins; four different SNAREs (soluble N-ethylmaleimide factor attachment protein receptors) mediating protein secretion by membrane fusion of storage granules, and two angiogenesis regulating proteins, representing cargo proteins within these granules coupled to tumor progression. By a streamlined procedure, we recorded about 100 SRM images of platelets, for each of these six proteins, and for five different categories of platelets; incubated with cancer cells (MCF-7, MDA-MB-231, EFO-21), non-cancer cells (MCF-10A), or no cells at all. From these images, structural similarity and protein cluster parameters were determined, and probability functions of these parameters were generated for the different platelet categories. By comparing these probability functions between the categories, we could identify nanoscale alterations in the protein distributions, allowing us to classify the platelets into their correct categories, if they were co-incubated with cancer cells, non-cancer cells, or no cells at all. Conclusions The fast, streamlined and objective acquisition and analysis procedure established in this work confirms the role of SNAREs and angiogenesis-regulating proteins in platelet-mediated cancer progression, provides additional fundamental knowledge on the interplay between tumor cells and platelets, and represent an important step towards using tumor-platelet interactions and redistribution of nanoscale protein patterns in platelets as a basis for cancer diagnostics.

Protein contents in platelets are frequently changed upon tumor development and metastasis. However, how cancer cells can influence protein-selective redistribution and release within platelets, thereby promoting tumor development, remains largely elusive. With fluorescence-based super-resolution stimulated emission depletion (STED) imaging we reveal how specific proteins, implicated in tumor progression and metastasis, re-distribute within platelets, when subject to soluble activators (thrombin, adenosine diphosphate and thromboxane A2), and when incubated with cancer (MCF-7, MDA-MB-231, EFO21) or non-cancer cells (184A1, MCF10A). Upon cancer cell incubation, the cell-adhesion protein P-selectin was found to re-distribute into circular nano-structures, consistent with accumulation into the membrane of protein-storing alpha-granules within the platelets. These changes were to a significantly lesser extent, if at all, found in platelets incubated with normal cells, or in platelets subject to soluble platelet activators. From these patterns, we developed a classification procedure, whereby platelets exposed to cancer cells, to non-cancer cells, soluble activators, as well as non-activated platelets all could be identified in an automatic, objective manner. We demonstrate that STED imaging, in contrast to electron and confocal microscopy, has the necessary spatial resolution and labelling efficiency to identify protein distribution patterns in platelets and can resolve how they specifically change upon different activations. Combined with image analyses of specific protein distribution patterns within the platelets, STED imaging can thus have a role in future platelet-based cancer diagnostics and therapeutic monitoring. The presented approach can also bring further clarity into fundamental mechanisms for cancer cell-platelet interactions, and into non-contact cell-to-cell interactions in general.

Protein contents in platelets are frequently changed upon tumor development and metastasis. However, how cancer cells can influence protein-selective redistribution and release within platelets, thereby promoting tumor development, remains largely elusive. With fluorescence-based super-resolution stimulated emission depletion (STED) imaging we reveal how specific proteins, implicated in tumor progression and metastasis, re-distribute within platelets, when subject to soluble activators (thrombin, adenosine-diphosphate and thromboxaneA2), and when incubated with cancer (MCF-7, MDA-MB-231, EFO21) or non-cancer cells (184A1, MCF10A). Upon cancer cell incubation, the cell-adhesion protein P-selectin was found to re-distribute into circular nano-structures, consistent with accumulation into the membrane of protein-storing alpha-granules within the platelets. These changes were to a significantly lesser extent, if at all, found in platelets incubated with normal cells, or in platelets subject to soluble platelet activators. From these patterns, we developed a classification procedure, whereby platelets exposed to cancer cells, to non-cancer cells, soluble activators as well as non-activated platelets all could be identified in an automatic, objective manner. We demonstrate that STED imaging, in contrast to electron and confocal microscopy, has the necessary spatial resolution and labelling efficiency to identify protein distribution patterns in platelets and can resolve how they specifically change upon different activations. Combined with image analyses of specific protein distribution patterns within the platelets, STED imaging can thus have a role in future platelet-based cancer diagnostics and therapeutic monitoring. The presented approach can also bring further clarity into fundamental mechanisms for cancer cell-platelet interactions, and into non-contact cell-to-cell interactions in general. 

We investigate the properties of the field emitted through parametric down-conversion (PDC) in a nonlinear photonics crystal (NPC) with a hexagonal poling pattern, both from a theoretical point of view and with an experiment performed at the University of Insubria. Considering the high gain regime of PDC, we demonstrate the existence of concurrent PDC processes mediated by two noncollinear poling vectors which are coherently coupled and reciprocally stimulated. We find that these non-standard 3-mode and 4-mode interaction processes undergo a substantial enhancement of the parametric gain with respect to the usual 2-mode PDC, and give rise to hot spots order of magnitudes brighter than standard 2-mode fluorescence which have been observed in the source far field. We performed a complete characterization of the source spectral-angular emission, finding a very good agreement between the experiment and the theoretical predictions.

We characterized the performance of abiased superconducting nanowire to detect X-ray photons. The device, made of a 10 nm thin NbTiN film and fabricated on a dielectric substrate (SiO2, Nb3O5) detected 1000 times larger signal than anticipated from direct X-ray absorption. We attributed this effect to X-ray induced generation of secondary particles in the substrate. The enhancement corresponds to an increase in the flux by the factor of 3.6, relative to a state-of-the-art commercial X-ray silicon drift detector. The detector exhibited 8.25 ns temporal recovery time and 82 ps timing resolution, measured using optical photons. Our results emphasize the importance of the substrate in superconducting X-ray single photon detectors.

Nanocrystalline InP quantum dots (QDs) hold promise for heavy-metal-free optoelectronic applications due to their bright and size tunable emission in the visible range. Photochemical stability and high photoluminescence (PL) quantum yield are obtained by a diversity of epitaxial shells around the InP core. To understand and optimize the emission line shapes, the exciton fine structure of InP core/shell QD systems needs be investigated. Here, we study the exciton fine structure of InP/ZnSe core/shell QDs with core diameters ranging from 2.9 to 3.6 nm (PL peak from 2.3 to 1.95 eV at 4 K). PL decay measurements as a function of temperature in the 10 mK to 300 K range show that the lowest exciton fine structure state is a dark state, from which radiative recombination is assisted by coupling to confined acoustic phonons with energies ranging from 4 to 7 meV, depending on the core diameter. Circularly polarized fluorescence line-narrowing (FLN) spectroscopy at 4 K under high magnetic fields (up to 30 T) demonstrates that radiative recombination from the dark F = +/- 2 state involves acoustic and optical phonons, from both the InP core and the ZnSe shell. Our data indicate that the highest intensity FLN peak is an acoustic phonon replica rather than a zero-phonon line, implying that the energy separation observed between the F = +/- 1 state and the highest intensity peak in the FLN spectra (6 to 16 meV, depending on the InP core size) is larger than the splitting between the dark and bright fine structure exciton states.

At the core of quantum photonic information processing and sensing, two major building pillars are single-photon emitters and single-photon detectors. In this review, we systematically summarize the working theory, material platform, fabrication process, and game-changing applications enabled by state-of-the-art quantum dots in nanowire emitters and superconducting nanowire single-photon detectors. Such nanowire-based quantum hardware offers promising properties for modern quantum optics experiments. We highlight several burgeoning quantum photonics applications using nanowires and discuss development trends of integrated quantum photonics. Also, we propose quantum information processing and sensing experiments for the quantum optics community, and future interdisciplinary applications.

Shortly after their inception, superconducting nanowire single-photon detectors (SNSPDs) became the leading quantum light detection technology. With the capability of detecting single-photons with near-unity efficiency, high time resolution, low dark count rate, and fast recovery time, SNSPDs outperform conventional single-photon detection techniques. However, detecting lower energy single photons (<0.8 eV) with high efficiency and low timing jitter has remained a challenge. To achieve unity internal efficiency at mid-infrared wavelengths, previous works used amorphous superconducting materials with low energy gaps at the expense of reduced time resolution (close to a nanosecond), and by operating them in complex milliKelvin (mK) dilution refrigerators. In this work, we provide an alternative approach with SNSPDs fabricated from 5 to 9.5 nm thick NbTiN superconducting films and devices operated in conventional Gifford-McMahon cryocoolers. By optimizing the superconducting film deposition process, film thickness, and nanowire design, our fiber-coupled devices achieved >70% system detection efficiency (SDE) at 2 mu m and sub-15 ps timing jitter. Furthermore, detectors from the same batch demonstrated unity internal detection efficiency at 3 mu m and 80% internal efficiency at 4 mu m, paving the road for an efficient mid-infrared single-photon detection technology with unparalleled time resolution and without mK cooling requirements. We also systematically studied the dark count rates (DCRs) of our detectors coupled to different types of mid-infrared optical fibers and blackbody radiation filters. This offers insight into the trade-off between bandwidth and DCRs for mid-infrared SNSPDs. To conclude, this paper significantly extends the working wavelength range for SNSPDs made from polycrystalline NbTiN to 1.5-4 mu m, and we expect quantum optics experiments and applications in the mid-infrared range to benefit from this far-reaching technology. Published by Chinese Laser Press under the terms of the Creative Commons Attribution 4.0 License.

In the past decade, superconducting nanowire single-photon detectors (SNSPDs) have gradually become an indispensable part of any demanding quantum optics experiment. Until now, most SNSPDs have been coupled to single-mode fibers. SNSPDs coupled to multimode fibers have shown promising efficiencies but have yet to achieve high time resolution. For a number of applications ranging from quantum nano-photonics to bio-optics, high efficiency and high time resolution are desired at the same time. In this paper, we demonstrate the role of polarization on the efficiency of multimode-fiber-coupled detectors and fabricated high-performance 20 mu m, 25 mu m, and 50 mu m diameter detectors targeted for visible, near-infrared, and telecom wavelengths. A custom-built setup was used to simulate realistic experiments with randomized modes in the fiber. We achieved over 80% system efficiency and <20 ps timing jitter for 20 mu m SNSPDs. Also, we realized 70% system efficiency and <20 ps timing jitter for 50 mu m SNSPDs. The high-efficiency multimode-fiber-coupled SNSPDs with unparalleled time resolution will benefit various quantum optics experiments and applications in the future.

The aromatic amino acids tryptophan, tyrosine, and phenylalanine have been extensively used for different label-free protein studies. These investigations extract information on protein conformations and interactions from the emitted fluorescence's intensity, wavelength, and/or polarization. Like most fluorescent organic compounds, these amino acids also undergo transitions into dark meta-stable states, including triplet and photo-radical states. These transitions are notably sensitive to the surrounding environment, offering an additional set of parameters that reflect the protein's interactions, folding states, and immediate surroundings.

Transient State (TRAST) monitoring has been developed to quantify fluorophore transition dynamics by recording the average fluorescence intensity in response to a modulated excitation. In this work, we performed TRAST experiments to investigate tyrosine autofluorescence and used it to detect conformational changes in calmodulin, a calcium-binding protein containing two tyrosine residues. A photophysical model for tyrosine was established, and it was revealed how tyrosine's dark state transitions changed with excitation intensity, solvent pH, and redox conditions. The TRAST experiments demonstrated that tyrosine's dark state transitions could serve as valuable information sources for label-free analyses of protein conformations and interactions.

NbTiN has a high critical temperature (Tc) of up to 17 K, making it a great candidate for superconducting nanowire single-photon detectors (SNSPDs) and other applications requiring a bias current close to the depairing current. However, superconducting inhomogeneities are often observed in superconducting thin films, and superconducting inhomogeneities can influence the vortex nucleation barrier and furthermore affect the critical current Ic of a superconducting wire. Superconducting inhomogeneities can also result in stochastic variations in the critical current between identical devices, and therefore, it is crucial to have a detailed understanding of inhomogeneities in SNSPDs in order to improve device efficiency. In this study, we utilized scanning tunneling microscopy/spectroscopy (STM/STS) to investigate the inhomogeneity of superconducting properties in meandered NbTiN nanowires, which are commonly used in SNSPDs. Our findings show that variations in the superconducting gap are strongly correlated with the film thickness. By using time-dependent Ginzburg-Landau simulations and statistical modeling, we explored the implications of the reduction in the critical current and its sample-to-sample variations. Our study suggests that the thickness of NbTiN plays a critical role in achieving homogeneity in superconducting properties.

We experimentally demonstrate the superconducting nanowire single-photon detectors integrated with current reservoirs that function as low-noise pre-amplifiers to increase the signal-to-noise ratio of detectors' outputs.

Photonic integration technologies are key to scale-up superconducting quantum computers. Here, we identify suitable classical optical links to control and read out the qubits in cryostats and resolve the power dissipation issue of superconducting computing platforms. Recent results and future solutions are shown.

We demonstrate superconducting nanowire single-photon detectors (SNSPDs) based on a fractal design of the nanowires to reduce the polarization sensitivity of detection efficiency. We patterned niobium titanium nitride thin films into Peano curves with a linewidth of 100 nm and integrated the nanowires with optical microcavities to enhance their optical absorption. At a base temperature of 2.6 K, the fractal SNSPD exhibited a polarization-maximum device efficiency of 67% and a polarization-minimum device efficiency of 61% at a wavelength of 1550 nm. Therefore, the polarization sensitivity, defined as their ratio, was 1.1, lower than the polarization sensitivity of the SNSPDs in the meander design. The reduced polarization sensitivity of the detector could be maintained for higher-order spatial modes in multimode optical fibers and could tolerate misalignment between the optical mode and the detector. This fractal design is applicable to both amorphous and polycrystalline materials that are commonly used for making SNSPDs.

We develop a general model, based on a (2+1)D unidirectional pulse propagation equation, for describing broadband noncollinear parametric interactions in two-dimensional quadratic lattices. We apply it to the analysis of twin-beam optical parametric generation in hexagonally poled LiTaO&#60;inf>3&#60;/inf>, gaining further insights into experimental observations.

Comprehensive understanding of the electrochemical activity of single nanoparticles (NPs) is in critical need for opening new avenues in the broad field of electrochemistry. Published reports on single-NP electrocatalysts typically include complicated and difficult methods of synthesis and characterization; moreover, these methods usually fail to provide a reliable way to measure the activities of individual NPs within larger ensembles of particles, i.e., in real-life nanocatalyst systems. In the present work, we synthesized from the gas phase Pd NPs that act as nanoportals for electron transfer within surface-oxidized Mg thin films. The physical synthesis method provided excellent control over the deposition density and, hence, enabled the design of a system where each individual open nanoportal forms an independent active single-NP electrode (SNPE). Being uncoupled from one another, these SNPEs contribute separately toward the total electrocatalytic activity while simultaneously providing a measure of their average, individual activities. We were thus able to fabricate a stable, steady-state electrode for the electrochemical oxygen evolution reaction (OER) and to study the activity and stability of the SNPEs over a period of 20 days; the former depended on the size of the NPs, while the latter depended on the SNPEs' resistance to aerial oxidation. The remarkable stability of the ensemble catalysts under OER conditions proves that this concept can be used for further studies on the activities of different single NPs in numerous real-life systems.

Nonlinear optics (NLO) plays a major role in the modern world: nonlinear optical phenomena have been observed in a wavelength range going from the deep infrared to the extreme ultraviolet, to THz radiation. The optical nonlinearities can be found in crystals, amorphous materials, polymers, liquid crystals, liquids, organic materials, and even gases and plasmas. Nowadays, NLO is relevant for applications in quantum optics, quantum computing, ultra-cold atom physics, plasma physics, and particle accelerators. The work presented in the thesis is limited only to the semiconductors that have a second-order optical nonlinearity and includes two phenomena that use second-order nonlinearity: second-harmonic generation (SHG) and spontaneous parametric down-conversion (SPDC). Among the many options available, the investigation presented concerns gallium phosphide (GaP) and gallium indium phosphide (Ga_0.51In_0.49P), two semiconductors of the group III-V with the ¯43m crystal symmetry.

However, some of the results found can be generalized for other materials with ¯43m crystal symmetry.

In the thesis, the fabrication of GaP nanowaveguides with dimensions from 0.03 μm and an aspect ratio above 20 using focused ion beam (FIB) milling is discussed. The problem of the formation of gallium droplets on the surface is solved by using a pulsed laser to oxidize the excess surface gallium locally on the FIB-milled nanowaveguides. SHG is used to evaluate the optical quality of the fabricated GaP nanowaveguides. Additionally, a theoretical and experimental way to enhance SHG in nanowaveguides is introduced. This process uses the overlap of interacting fields defined by the fundamental mode of the pump and the second-order mode of the SHG, which is enhanced by the longitudinal component of the nonlinear polarization density. Through this method, it was possible to obtain a maximum efficiency of 10⁻⁴, which corresponds to 50 W⁻¹cm⁻². The method can be generalized for any material with a ¯43m crystal symmetry. Furthermore, SHG is used to characterize the nonlinear properties of a nanostructure exposed for a long time to a CW laser at 405 nm to reduce the photoluminescence (PL) of Ga_0.51In_0.49P. The PL was reduced by -34 dB without causing any damage to the nanostructures or modifying the nonlinear properties. The fabrication process for obtaining the nanowaveguide is interesting as well, since the fabricated waveguide in Ga_0.51In_0.49P, whose sizes are 200 nm thick, 11 μm wide and 1.5 mm long, was transferred on silicon dioxide (SiO₂). This type of nanowaveguide is interesting for SPDC, since it satisfies the long interaction length necessary for an efficient SPDC. Finally, a configuration consisting of illuminating the top surface of a nanowaveguide with a pump beam to generate signal and idler by SPDC is presented. These fabricated nanostructures open a way to the generation of counter-propagating idler and signal with orthogonal polarization. By using a different cut of the crystal, i.e. [110], it makes possible to obtain degenerate wavelength generation, and in certain conditions to obtain polarization-entangled photons or squeezed states.

GaP multilayer slab waveguides were fabricated by FIB milling. Limited transmission properties of the nanostructures, due to appreciable residuals of gallium, were recovered by fspulsed laser exposure. The waveguides were assessed by SHG technique. 

In this paper, a configuration consisting in a pump propagating in an orthogonal direction with respect to the surface of a nanowaveguide is studied. It is possible to show that the generation by spontaneous parametric down-conversion of a signal and an idler photons inside the nanowaveguide is strongly dependent on the waveguide thickness, because the high refractive index of the waveguide core creates also an optical cavity for the pump field. Furthermore, it was evaluated the best condition for photon-pair generation in case of a nanowaveguide in gallium indium phosphide, which has a −43m symmetry.For the same waveguide geometry, but orientation parallel to the [110] plane, it is possible to use spontaneous parametric down-conversion to generate counter-propagating photon-pair with the same polarization. When the efficiency of the generated photon-pairs in TM0 and TE0 modes is the same, then it is possible to obtain polarization entangled photons, by using this configuration. Furthermore, by adding a mirror at one of the end of the waveguide, the system can be used to produce a squeezed-state.

Gallium indium phosphide (Ga0.51In0.49P), lattice matched to gallium arsenide, shows remarkable second-order nonlinear properties, as well as strong photoluminescence due to its direct band gap. By measuring the second-harmonic generation from the GaInP microwaveguide (0.2 x 11 x 1300 μm) before and after stimulating intrinsic photobleaching, we demonstrate that the photoluminescence could be strongly suppressed (-34 dB), leaving the nonlinear properties unchanged, making it suitable for low-noise applications.

Nanostructured GaInP shows remarkable second-order nonlinear properties. By measuring the second harmonic generation before and after stimulating intrinsic photobleaching, we observed suppressed photoluminescence and unchanged nonlinear properties, making it suitable for low-noise applications. 

Cuprous oxide ([Formula: see text]) has recently emerged as a promising material in solid-state quantum technology, specifically for its excitonic Rydberg states characterized by large principal quantum numbers (n). The significant wavefunction size of these highly-excited states (proportional to [Formula: see text]) enables strong long-range dipole-dipole (proportional to [Formula: see text]) and van der Waals interactions (proportional to [Formula: see text]). Currently, the highest-lying Rydberg states are found in naturally occurring [Formula: see text]. However, for technological applications, the ability to grow high-quality synthetic samples is essential. The fabrication of thin-film [Formula: see text] samples is of particular interest as they hold potential for observing extreme single-photon nonlinearities through the Rydberg blockade. Nevertheless, due to the susceptibility of high-lying states to charged impurities, growing synthetic samples of sufficient quality poses a substantial challenge. This study successfully demonstrates the CMOS-compatible synthesis of a [Formula: see text] thin film on a transparent substrate that showcases Rydberg excitons up to [Formula: see text] which is readily suitable for photonic device fabrications. These findings mark a significant advancement towards the realization of scalable and on-chip integrable Rydberg quantum technologies.

Fluorescence methods have developed very strongly in the last decade, allowing single- molecule detection sensitivity, high specificity, high time- and spatial resolution, as well as high readout speeds. Together, this makes fluorescencea very central readout modality for biomolecular and cellular studies. The photophysics of the fluorescence emitters, fluorophores, used is of central importance or the performance. Here, the photostability and brightness ofthe fluorophores, but also their blinking properties set the limits of the performance. Fluorophore blinking, arising from photo-induced, non-fluorescent transient states of fluorophores, can however also be taken advantage of cellular and biomolecular studies. Blinking is a prerequisite for essentially allso-called fluorescence-based super-resolution techniques. Moreover, blinkingis often sensitive to micro-environmental parameters such as pH, oxygen concentrations,redox conditions and viscosity. This follows from the fact that the underlying, non-luminescent, dark transient states typically have 10³ to 10⁶ longer lifetimes than the fluorescent excited states of the fluorophores, thereby giving fluorescent molecules in the dark states more time to interactwith their surrounding in biological environment. It can thus be utilized as an alternative readout parameter to provide useful information on molecules and cells and their environments, beyond what can be monitored by traditional fluorescence methods. This thesis takes as one starting point the transient state (TRAST) spectroscopy technique, designed to monitor such long-lived, dark transient states, including triplet, photo-oxidation, photo-reduction and photo-isomerized states of fluorophores, by measuring how the time-averaged fluorescence signal detected in the sample is changed upon systematically varying the excitation modulation.

The major focus of the present thesis work is to further extent the use of long-lived dark transient states of fluorescence emitters in solution, lipid membranes and live cells. For this different TRAST modalities were adapted and developed, and then demonstrated as useful characterization methods. First, we showed how the relaxed brightness requirements of TRAST made it possible to characterize the photo-physical properties of the high triplet yield carboxy-fluorescein dye and its brominated derivatives (paper I). By widefield TRAST measurements, we demonstrated its capability to sense heavy atom effect of bromine and iodide atoms, and how they affected the triplet and long-lived photo-oxidation states and their transitions rates. Next, we developed and demonstrated a concept based on TRAST method and its ability to distinguish fluorophores with different blinking properties as a way to perform fluorescence-based barcoding and multiplexing. This concept, demonstrated by exploiting the by TRAST well distinguishable photophysical transitions of two fluorescent dyes, which emit in the same spectral range, was demonstrated in paper II. In the same work, we also developed a TRAST modality for microfluidic measurements of molecules and lipid vesicles, on which the bar-coding concept could be demonstrated on-the-fly, as the molecules and vesicles passed through the microfluidic channel. Furthermore, with TRAST implemented in camera-based wide-field microscopy, multicolor barcoded images of cells with high spatial resolution could be further investigated for the first time due to the specific blinking dynamics of these labels. The last two papers of this thesis describe further extensions of the TRAST concept, and the monitoring of fluorescence blinking to live cell studies. In paper III, TRAST in a widefield microscopy setting was employed in combination with FCS to study the folding of dye-labelled RNA strands into G-quadruplex structures in solution and live cells using photo-isomerization kinetics of cyanine dye as a readout parameter. Here, we took advantage of the high sensitivity of cyanine dye photoisomerization, to viscosity and steric constraints,and the resulting blinking of the cyanines, to monitor conformation changes of RNAs in live cells. Finally, in paper IV, we demonstrated how it by TRAST imaging, taking advantage of the photo-induced dark states of a mitochondrial localization fluorophore (n-Nonyl Acridine Orange, NAO), is possible to give this localization probe environmental sensing properties as well.

To sum up, the experimental findings and papers included in this thesis show that fluorescence blinking represent a rich source of information for biomolecular and cellular studies. By the TRAST technique, and the variants further adapted and developed in this work, it is shown that it possible tocapture this rich source of complementary information in a broad range of samples. The work in this thesis suggest that further combination of classical fluorescence readouts and a continued development of different TRAST modalities will open yet new windows and provide insights into molecular interaction studies in biological research.

Photo-induced dark transient states of fluorophores can pose a problem in fluorescence spectroscopy. However, their typically long lifetimes also make them highly environment sensitive, suggesting fluorophores with prominent dark-state formation yields to be used as microenvironmental sensors in bio-molecular spectroscopy and imaging. In this work, we analyzed the singlet-triplet transitions of fluorescein and three synthesized carboxy-fluorescein derivatives, with one, two or four bromines linked to the anthracence backbone. Using transient state (TRAST) spectroscopy, we found a prominent internal heavy atom (IHA) enhancement of the intersystem crossing (ISC) rates upon bromination, inferred by density functional theory calculations to take place via a higher triplet state, followed by relaxation to the lowest triplet state. A corresponding external heavy atom (EHA) enhancement was found upon adding potassium iodide (KI). Notably, increased KI concentrations still resulted in lowered triplet state buildup in the brominated fluorophores, due to relatively lower enhancements in ISC, than in the triplet decay. Together with an antioxidative effect on the fluorophores, adding KI thus generated a fluorescence enhancement of the brominated fluorophores. By TRAST measurements, analyzing the average fluorescence intensity of fluorescent molecules subject to a systematically varied excitation modulation, dark state transitions within very high triplet yield (>90%) fluorophores can be directly analyzed under biologically relevant conditions. These measurements, not possible by other techniques such as fluorescence correlation spectroscopy, opens for bio-sensing applications based on high triplet yield fluorophores, and for characterization of high triplet yield photodynamic therapy agents, and how they are influenced by IHA and EHA effects.

Deep learning methods are of utmost importance in the field of nanotechnology due to their practical applications provide insights into an optimal design of nanomaterials with multi-characteristics. In the context of present research, we propose fully connected deep neural network (DNN) classifiers which have the capability to classify light transmission from polymer nanocomposite films made up of polystyrene (PS) latex particles and multi-walled carbon nanotubes (MWCNTs). For this purpose, collected spectroscopic data were first divided into three classes based on transmitted light intensity, mass fraction of MWCNT nanofillers, annealing temperature, and particle diameter of PS latexes. Bayesian optimizer has then been implemented for each proposed DNN classifier and the most optimal hyperparameters such as activation functions and hidden layer sizes, which provide the best classification accuracy, were acquired through trial-and-error method. Accuracy, cross-entropy loss, precision, recall and F1-score metrics together with confusion matrix and area under curve computed for receiver operating characteristic (ROC) curves have been extensively employed to assess the performance of proposed DNN classifiers. The highest accuracy, precision, recall and F1-score metrics can be achieved for both training and testing data sets when two hidden layer sizes are set to 30 and 20, respectively and sigmoid functions are used in those of hidden layer units. Computational results have indicated that DNNs can be exploited to classify optical transparency of film samples even with a limited amount of experimental data. 

The present study addresses a comparative performance assessment of multivariate regression (MVR) and well-optimized feed-forward, generalized regression and radial basis function neural network models which aimed to predict transmitted light intensity (I-tr) of carbon nanotube (CNT)-loaded polymer nanocomposite films by employing a large set of spectroscopic data collected from photon transmission measurements. To assess prediction performance of each developed model, universally accepted statistical error indices, regression, residual and Taylor diagram analyses were performed. As a novel performance evaluation criterion, 2D kernel density mapping was applied to predicted and experimental I-tr data to visually map out where the correlations are stronger and which data points can be more precisely estimated using the studied models. Employing MVR analysis, empirical equation of I-tr was acquired as a function of only four input elements due to sparseness and repetitive nature of the remaining input variables. Relative importance of each input variable was calculated separately through implementing Garson's algorithm for the best ANN model and mass fraction of CNT nanofillers was found as the most significant input variable. Using interconnection weights and bias values obtained for feed-forward neural network (FFNN) model, a neural predictive formula was derived to model I-tr. in terms of all input variables. 2D kernel density maps computed for each ANN model have shown that correlations between measured data and ANN predicted values are stronger for a specific I-tr range between 0% and 18%. To measure the stability of the ANN models, as a final analysis, 5-fold cross-validation method was applied to whole measurement data and 5 different iterations were additionally performed on each ANN model for 5 different training and test data splits. Statistical results found from 5-fold cross-validation analysis have reaffirmed that FFNN model exhibited outperformed prediction ability over all other ANN models and all FFNN predicted It,. values agreed well with experimental I-tr data. Taken all computational results together, one can adapt our proposed FFNN model and neural predictive formula to predict I-tr of polymer nanocomposite films, which can be made from different polymers and nanofillers, by considering specific data range as presented in this study with statistical details.

The integration of indistinguishable single photon sources in photonic circuits is a major prerequisite for on-chip quantum applications. Among the various high-quality sources, nanowire quantum dots can be efficiently coupled to optical waveguides because of their preferred emission direction along their growth direction. However, local tuning of the emission properties remains challenging. In this work, we transfer a nanowire quantum dot onto a bulk lithium niobate substrate and show that its emission can be dynamically tuned by acousto-optical coupling with surface acoustic waves. The purity of the single photon source is preserved during the strain modulation. We further demonstrate that the transduction is maintained even with a SiO2 encapsulation layer deposited on top of the nanowire acting as the cladding of a photonic circuit. Based on these experimental findings and numerical simulations, we introduce a device architecture consisting of a nanowire quantum dot efficiently coupled to a thin-film lithium niobate rib waveguide and strain-tunable by surface acoustic waves.

Mitochondrial membranes and their microenviron-ments directly influence and reflect cellular metabolic states but aredifficult to probe on site in live cells. Here, we demonstrate astrategy, showing how the widely used mitochondrial membranelocalizationfluorophore 10-nonyl acridine orange (NAO) can betransformed into a multifunctional probe of membrane micro-environments by monitoring its blinking kinetics. By transient state(TRAST) studies of NAO in small unilamellar vesicles (SUVs),together with computational simulations, we found that NAOexhibits prominent reversible singlet-triplet state transitions andcan act as a light-induced Lewis acid forming a red-emissivedoublet radical. The resulting blinking kinetics are highlyenvironment-sensitive, specifically reflecting local membrane oxy-gen concentrations, redox conditions, membrane charge,fluidity, and lipid compositions. Here, not only cardiolipin concentrationbut also the cardiolipin acyl chain composition was found to strongly influence the NAO blinking kinetics. The blinking kinetics alsoreflect hydroxyl ion-dependent transitions to and from thefluorophore doublet radical, closely coupled to the proton-transfer eventsin the membranes, local pH, and two- and three-dimensional buffering properties on and above the membranes. Following the SUVstudies, we show by TRAST imaging that thefluorescence blinking properties of NAO can be imaged in live cells in a spatiallyresolved manner. Generally, the demonstrated blinking imaging strategy can transform existingfluorophore markers intomultiparametric sensors reflecting conditions of large biological relevance, which are difficult to retrieve by other means. This opensadditional possibilities for fundamental membrane studies in lipid vesicles and live cells

Current prostate cancer risk classifications rely on clinicopathological parameters resulting in uncertainties for prognostication. To improve individual risk stratification, we examined the predictive value of selected proteins with respect to tumor heterogeneity and genomic instability. We assessed the degree of genomic instability in 50 radical prostatectomy specimens by DNA-Image-Cytometry and evaluated protein expression in related 199 tissue-microarray (TMA) cores. Immunohistochemical data of SATB1, SPIN1, TPM4, VIME and TBB5 were correlated with the degree of genomic instability, established clinical risk factors and overall survival. Genomic instability was associated with a GS >= 7 (p = 0.001) and worse overall survival (p = 0.008). A positive SATB1 expression was associated with a GS <= 6 (p = 0.040), genomic stability (p = 0.027), and was a predictor for increased overall survival (p = 0.023). High expression of SPIN1 was also associated with longer overall survival (p = 0.048) and lower preoperative PSA-values (p = 0.047). The combination of SATB1 expression, genomic instability, and GS lead to a novel Prostate Cancer Prediction Score (PCP-Score) which outperforms the current D'Amico et al. stratification for predicting overall survival. Low SATB1 expression, genomic instability and GS >= 7 were identified as markers for poor prognosis. Their combination overcomes current clinical risk stratification regimes.

The low-lying level structure of 59V and 61V was investigated for the first time. The neutron knockout reaction and inelastic proton scattering were applied for 61V while the neutron knock-out reaction provided the data for 59V. Four and five new transitions were determined for 59V and 61V, respectively. Based on the comparison to our shell-model calculations using the Lenzi-Nowacki-Poves-Sieja (LNPS) interaction, three of the observed ?? rays for each isotope could be placed in the level scheme and assigned to the decay of the first 11/2??? and 9/2??? levels. The (p, p') excitation cross sections for 61V were analyzed by the coupled-channels formalism assuming quadrupole plus hexadecapole deformations. Due to the role of the hexadecapole deformation, 61V could not be unambiguously placed on the island of inversion.

We use dispersion engineering to control the signal propagation speed in the feed lines of superconducting single-photon detectors. Using this technique, we demonstrate time-division-multiplexing of two-pixel detectors connected with a slow-RF transmission line, all realized using planar geometry requiring a single lithographic step. Through studying the arrival time of detection events in each pixel vs the fabricated slow-RF coplanar waveguide length, we extract a delay of 1.7 ps per 1 mu m of propagation, corresponding to detection signal speeds of similar to 0.0019c. Our results open an important avenue to explore the rich ideas of dispersion engineering and metamaterials for superconducting detector applications.

Recent developments in chip-based photonic quantum circuits have radically impacted quantum information processing. However, it is challenging for monolithic photonic platforms to meet the stringent demands of most quantum applications. Hybrid platforms combining different photonic technologies in a single functional unit have great potential to overcome the limitations of monolithic photonic circuits. Our Review summarizes the progress of hybrid quantum photonics integration, discusses important design considerations, including optical connectivity and operation conditions, and highlights several successful realizations of key physical resources for building a quantum teleporter. We conclude by discussing the roadmap for realizing future advanced large-scale hybrid devices, beyond the solid-state platform, which hold great potential for quantum information applications.