Practical effects in the preparation of cluster states using weak non-linearities

We discuss experimental effects in the implementation of a recent scheme for performing bus mediated entangling operations between qubits. Here a bus mode, a strong coherent state, successively undergoes weak Kerr-type non-linear interactions with qubits. A quadrature measurement on the bus then projects the qubits into an entangled state. This approach has the benefit that entangling gates are non-destructive, may be performed non-locally, and there is no need for efficient single photon detection. In this paper we examine practical issues affecting its experimental implementation. In particular, we analyze the effects of post-selection errors, qubit loss, bus loss, mismatched coupling rates and mode-mismatch. We derive error models for these effects and relate them to realistic fault-tolerant thresholds, providing insight into realistic experimental requirements.Comment: 8 pages, 5 figure

From Quantum Optics to Quantum Technologies

Quantum optics is the study of the intrinsically quantum properties of light. During the second part of the 20th century experimental and theoretical progress developed together; nowadays quantum optics provides a testbed of many fundamental aspects of quantum mechanics such as coherence and quantum entanglement. Quantum optics helped trigger, both directly and indirectly, the birth of quantum technologies, whose aim is to harness non-classical quantum effects in applications from quantum key distribution to quantum computing. Quantum light remains at the heart of many of the most promising and potentially transformative quantum technologies. In this review, we celebrate the work of Sir Peter Knight and present an overview of the development of quantum optics and its impact on quantum technologies research. We describe the core theoretical tools developed to express and study the quantum properties of light, the key experimental approaches used to control, manipulate and measure such properties and their application in quantum simulation, and quantum computing.Comment: 20 pages, 3 figures, Accepted, Prog. Quant. Ele

Electroweak Measurements of Neutron Densities in CREX and PREX at JLab, USA

Measurement of the parity-violating electron scattering asymmetry is an established technique at Jefferson Lab and provides a new opportunity to measure the weak charge distribution and hence pin down the neutron radius in nuclei in a relatively clean and model-independent way. This is because the Z boson of the weak interaction couples primarily to neutrons. We will describe the PREX and CREX experiments on ${}^{208}$Pb and ${}^{48}$Ca respectively; these are both doubly-magic nuclei whose first excited state can be discriminated by the high resolution spectrometers at JLab. The heavier lead nucleus, with a neutron excess, provides an interpretation of the neutron skin thickness in terms of properties of bulk neutron matter. For the lighter ${}^{48}$Ca nucleus, which is also rich in neutrons, microscopic nuclear theory calculations are feasible and are sensitive to poorly constrained 3-neutron forces.Comment: A contribution to the upcoming EPJA Special Volume on Nuclear Symmetry Energ

Accelerating Permutation Testing in Voxel-wise Analysis through Subspace Tracking: A new plugin for SnPM

Permutation testing is a non-parametric method for obtaining the max null distribution used to compute corrected $p$-values that provide strong control of false positives. In neuroimaging, however, the computational burden of running such an algorithm can be significant. We find that by viewing the permutation testing procedure as the construction of a very large permutation testing matrix, $T$, one can exploit structural properties derived from the data and the test statistics to reduce the runtime under certain conditions. In particular, we see that $T$ is low-rank plus a low-variance residual. This makes $T$ a good candidate for low-rank matrix completion, where only a very small number of entries of $T$ ($\sim0.35\%$ of all entries in our experiments) have to be computed to obtain a good estimate. Based on this observation, we present RapidPT, an algorithm that efficiently recovers the max null distribution commonly obtained through regular permutation testing in voxel-wise analysis. We present an extensive validation on a synthetic dataset and four varying sized datasets against two baselines: Statistical NonParametric Mapping (SnPM13) and a standard permutation testing implementation (referred as NaivePT). We find that RapidPT achieves its best runtime performance on medium sized datasets ($50 \leq n \leq 200$), with speedups of 1.5x - 38x (vs. SnPM13) and 20x-1000x (vs. NaivePT). For larger datasets ($n \geq 200$) RapidPT outperforms NaivePT (6x - 200x) on all datasets, and provides large speedups over SnPM13 when more than 10000 permutations (2x - 15x) are needed. The implementation is a standalone toolbox and also integrated within SnPM13, able to leverage multi-core architectures when available.Comment: 36 pages, 16 figure

High-resolution X-ray spectroscopy of Warm-Hot Baryons in Intergalactic Medium

The dissertation focuses on observational research of diffuse, highly ionized intergalactic gas that populates the dark-matter dominated large-scale structure of the Universe. Such intergalactic medium is expected to be the most important reservoir of cosmic baryons, yet studying it observationally is challenging due to its hot temperature (T ~ 10⁵ - 10⁷ K), high ionization states (so that signals are produced mainly in UV/X-ray bands) and low number densities of metal ions. Therefore observational information on the evolution, state and the distribution of the cosmic baryons is currently limited, and our understanding on these matters rely heavily on the information yielded by cosmological, hydrodynamical simulations. The goal of the research included in this work was to improve this situation by producing new, observation--based information on X-ray emitting/absorbing diffuse cosmic structures. The soft X-ray band is especially suitable for studying the diffuse intergalactic medium because it covers the energy range that can trace the most important spectral lines produced by the hot (T ~ 10⁶ K) gas phases. Generally this also means that the X-ray band is sensitive to signals other than those measurable at FUV/EUV -bands, which instead yield information on the cooler gas phases (T ~ 10⁵ K or less). Whereas the focus of the PhD research is on soft X-ray band high energy resolution studies, the X-ray band picture is complemented with relevant information on UV -band/simulations whenever such information is available. Indeed, even small additional observational information obtained at one of these bands can have significant scientific value when considered properly with the relevant data available at the other. The topics of the presented research papers range from mesurements of the intra-cluster/-group medium (ICM/IGM) physical properties to those of the warm-hot intergalactic medium (WHIM). We publish several astrophysically noteworthy measurement results, including the first detections of line emission (OVII) from cooled gas (kT ≲ 0.5 keV) in IGM/ICM environment of individual objects, the first measurement results on asymmetric velocity fields in intra-group medium, and two possible discoveries of multiphase WHIM absorbers, both of which appear be to associated to filamentary galaxy large scale structures. In general, our results seem to draw somewhat more variegated picture on the inter-galactic gas than one might have expected beforehand: our observational studies indicate existence of complex multiphase structures and gas dynamics in ICM/IGM environments, while our WHIM studies imply that multiphase structures are common also in filamentary WHIM. These outcomes were achieved through combination of extensive exploration of archival data and by use of novel type of analysis methods that I developed as a part of the work. The thesis is structured as follows: in the first half of the introductionary section I give a broad picture on the research field and on the open qestions within it, introduce (some of the) newly developed analysis methods that are utilized in the presented papers, and present the current high energy resolition spectrographs (Chapters 1-3). In the latter half of the introductionary section (Chapters 4-6), I discuss the future instruments relevant to our research, the methods availing the physical interpretation of X-ray spectral analysis results, and give short summaries of the included research papers. The introductionary section is followed by the copies of the original research papers.Maailmankaikkeuden suuren mittakaavan rakenne seuraa pimeän aineen jakauman muodostamaa universaalia, kolmiulotteista verkkomaista rakennetta. Tämän rakenteen muodostamat gravitaatiokentät sitovat sisälleen suurimman osan maailmankaikkeuden baryonisesta (ts. tavallisesta) materiasta. Vaikka suuri osa kosmisesta materiasta sijaitseekin tämän nk. kosmisen verkon rakenteissa, aine on erittäin harvaa ja sen lämpötila on hyvin korkea (T ~ 10⁵ – 10⁷ K). Tällaisissa olosuhteissa atomit esiintyvät korkeissa ionisaatiotiloissa, joka rajoittaa niiden havaitsemismahdollisuudet ultravioletti- (UV) ja röntgenalueille. Näilläkin spektrialueilla aineen muodostamien spektrisignaalien alhainen taso toimii tutkimusmahdollisuuksia rajaavana tekijänä, ja aihepiiri on tästä syystä tällä hetkellä huonosti tunnettu. Väitöskirjatutkimus keskittyy maailmankaikkeuden suuren mittakaavan rakenteiden tutkimukseen korkean energiaresoluution röntgenspektridataa hyödyntämällä. Pehmeä röntgenalue soveltuu erinomaisesti diffuusin, galaksien välisen kaasun tutkimukseen sillä tälle spektrialueelle sijoittuu useimmat astrofysikaalisesti merkittävimmät kuuman (T ~ 10⁶ K) plasman synnyttämät spektriviivat. Käytännössä pehmeä röntgenalue soveltuu siten kuumempien kaasufaasien tutkimiseen siinä missä UV -alue soveltuu parhaiten viileämpien (T ≲ 10⁵ K) faasien synnyttämien spektrisignaalien mittaamiseen. Vaikka tämä väitöskirjan sisältämät tutkimukset keskittyvät suurilta osin pehmeän röntgendatan analyysiin, röntgenanalyysin kautta saatua informaatiota on täydennetty yhtäältä UV -alueen spektridatan informaatiolla, sekä toisaalta kosmologisien simulaatioden tuottamalla tiedolla. Nämä informaatiolähteet yhdistämällä voimme päästä merkittävästi tarkempaan käsitykseen tutkittavan kohteen fysikaalisista ominaisuuksista kuin keskittymällä ainoastaan yhteen em. informaatiolähteistä. Osa väitöskirjan sisältämistä tutkimuspapereista keskittyy kosmisen verkon solmukohdissa esiintyvien massiivisten galaksiklustereiden ja -joukkojen sisältämän galaksien välisen plasmakaasun viivaemission ominaisuuksien analysointiin, sekä tämän spektridatan sisältämän informaation tulkitsemiseen. Lisäksi osa papereista keskittyy kosmisen verkkorakenteen “säikeiden” sisältämien baryonien synnyttämien absorptiosignaalien tutkimukseen. Väitöskirjan tutkimusartikkelit sisältävät uusia mittaustuloksia intergalaktisten baryonien jakaumiin sekä niiden fysikaalisiin tiloihin liittyen, edistäen siten omalta osaltaan tavoitettamme ymmärtää maailmankaikkeutta paremmin sen kaikista suurimmassa mittakaavassa

Robust detection and verification of linear relationships to generate metabolic networks using estimates of technical errors

<p>Abstract</p> <p>Background</p> <p>The size and magnitude of the metabolome, the ratio between individual metabolites and the response of metabolic networks is controlled by multiple cellular factors. A tight control over metabolite ratios will be reflected by a linear relationship of pairs of metabolite due to the flexibility of metabolic pathways. Hence, unbiased detection and validation of linear metabolic variance can be interpreted in terms of biological control. For robust analyses, criteria for rejecting or accepting linearities need to be developed despite technical measurement errors. The entirety of all pair wise linear metabolic relationships then yields insights into the network of cellular regulation.</p> <p>Results</p> <p>The Bayesian law was applied for detecting linearities that are validated by explaining the residues by the degree of technical measurement errors. Test statistics were developed and the algorithm was tested on simulated data using 3–150 samples and 0–100% technical error. Under the null hypothesis of the existence of a linear relationship, type I errors remained below 5% for data sets consisting of more than four samples, whereas the type II error rate quickly raised with increasing technical errors. Conversely, a filter was developed to balance the error rates in the opposite direction. A minimum of 20 biological replicates is recommended if technical errors remain below 20% relative standard deviation and if thresholds for false error rates are acceptable at less than 5%. The algorithm was proven to be robust against outliers, unlike Pearson's correlations.</p> <p>Conclusion</p> <p>The algorithm facilitates finding linear relationships in complex datasets, which is radically different from estimating linearity parameters from given linear relationships. Without filter, it provides high sensitivity and fair specificity. If the filter is activated, high specificity but only fair sensitivity is yielded. Total error rates are more favorable with deactivated filters, and hence, metabolomic networks should be generated without the filter. In addition, Bayesian likelihoods facilitate the detection of multiple linear dependencies between two variables. This property of the algorithm enables its use as a discovery tool and to generate novel hypotheses of the existence of otherwise hidden biological factors.</p

Nanostructured sonogels

Acoustic cavitation effects in sol-gel liquid processing permits to obtain nanostructured materials, with size-dependent properties. The so-called "hot spots" produce very high temperatures and pressures which act as nanoreactors. Ultrasounds force the dissolution and the reaction stars. The products (alcohol, water and silanol) help to continue the dissolution, being catalyst content, temperature bath and alkyl group length dependent. Popular choices used in the preparation of silica-based gels are tetramethoxysilane (TMOS), Si(OCH3)4 and tetraethoxysilane (TEOS), Si(OC 2H5)4. The resultant "sonogels" are denser gels with finer and homogeneous porosity than those of classic ones. They have a high surface/volume ratio and are built by small particles (1 nm radius) and a high cross-linked network with low -OH surface coverage radicals. In this way a cluster model is presented based on randomly-packed spheres in several hierarchical levels that represent the real sonoaerogel. Organic modified silicates (ORMOSIL) were obtained by supercritical drying in ethanol of the corresponding alcogel producing a hybrid organic/inorganic aerogel. The new material takes the advantages of the organic polymers as flexibility, low density, toughness and formability whereas the inorganic part contributes with surface hardness, modulus strength, transparency and high refractive index. The sonocatalytic method has proven to be adequate to prepare silica matrices for fine and uniform dispersion of CdS and PbS quantum dots (QDs), which show exciton quantum confinement. We present results of characterization of these materials, such as nitrogen physisorption, small angle X-ray/neutrons scattering, electron microscopy, uniaxial compression and nanoindentation. Finally these materials find application as biomaterials for tissue engineering and for CO2 sequestration by means the carbonation reaction.Ministerio de Ciencia y Tecnología MAT2005-158

Synthesis, non-linear optical and electrochemical properties of novel organoimido polyoxometalate derivatives

This thesis concerns the design and synthesis of a new class of earth abundant redox-active, hybrid inorganic-organic chromophores for use in second-order non-linear optics (NLO): organoimido polyoxometalates (POMs). It presents the first experimental measurements of 2nd order NLO (frequency doubling) coefficients (β) (by hyper-Rayleigh scattering, HRS) and the first spectroelectrochemical measurements on such species. Towards the aim of producing practical miniaturized devices, the species characterised include systems functionalised with pyrrole and carbazole donors that can be electropolymerized to form potentially redox switchable, photoactive films. These are the first reported POM-containing electropolymers with a covalently attached POM, and indicate the potential of these materials for straightforward electrodeposition onto optically transparent, conductive surfaces. To investigate the structure-activity relationships of the β response, the series of organoimido-Lindqvist chromophores included organic groups with different electron donors (such as amino, dimethylamino, and diphenylamino functionalities), or acceptors (such as iodo, and nitro), and different π -conjugated bridges. Significant β-values were obtained for derivatives with resonance electron donors, and result from strong ligand-to-polyoxometalate charge transfer transitions. No activity was observed for derivatives with resonance electron acceptors, indicating that the POM can only behave as an acceptor. β values increase steadily as the donor strength increases, and/or the π-conjugation extends, in similar fashion to organic systems. Interestingly, the highest β0-values obtained these derivatives exceed those of any dipolar organic system with comparable donor, π-system and absorption profile, and thus they have much more favourable transparency/non-linearity trade-offs. Resonance Raman and Stark spectroscopy results have confirmed involvement of the POM in the charge transfer transition, which results in unusual dipole moment changes leading to high NLO activity based on the two state model