Setting Experimental Bounds on Entangled Two-Photon Absorption Cross Sections

Two-photon absorption (2PA) is widely used in microscopy for deep, sub-cellular imaging. However, the efficiency of 2PA is limited by the properties of both the absorber and the excitation light. Entangled photon pairs produced via spontaneous parametric down-conversion (SPDC) exhibit correlations in energy, time and space that may improve the excitation efficiency relative to a classical laser. The most significant improvement is expected at low photon flux where isolated pairs interact with the absorber. In this regime, the rate of the entangled two-photon absorption (E2PA) process scales linearly with photon flux and the E2PA cross section (&sigma;E). Despite over a decade of publications claiming to measure huge &sigma;E that suggest a quantum advantage exists of up to 10 orders of magnitude, in this thesis I will show strong evidence that &sigma;E are several orders of magnitude lower than previously reported. First, we provide relevant background information on nonlinear and quantum optics. Next, we discuss theoretical descriptions of &sigma;E and review the large body of experimental work in the field. Afterwards, we discuss the four experiments we designed to measure E2PA. In the first and third experiments, we measure SPDC transmittance through samples of twophoton absorbers in room-temperature liquids. In our second experiment, we collect fluorescence from samples excited with SPDC. Despite the high sensitivity of the techniques, we could not resolve a signal in any of the measurements. We set upper bounds on the &sigma;E of eight independent absorbers that are up to five orders of magnitude lower than previously published &sigma;E. The third experiment also served as a classical 2PA (C2PA) measurement system. We made one-to-one comparisons between E2PA and C2PA to bound the quantum advantage. We derived absolute C2PA cross sections that closely agreed with values already reported in literature. In the fourth experiment, we designed a toluene-filled hollow-core-fiber platform for 2PA measurements. We measured C2PA down to 20 nanowatts, and expect to make further improvements. This platform is at least 4-fold more sensitive than a standard cuvette-based technique and thus is ideal for the next generation of E2PA measurements.</p

Nuclear Structure from the In-Medium Similarity Renormalization Group

Efforts to describe nuclear structure and dynamics from first principles have advanced significantly in recent years. Exact methods for light nuclei are now able to include continuum degrees of freedom and treat structure and reactions on the same footing, and multiple approximate, computationally efficient many-body methods have been developed that can be routinely applied for medium-mass nuclei. This has made it possible to confront modern nuclear interactions from Chiral Effective Field Theory, that are rooted in Quantum Chromodynamics with a wealth of experimental data. Here, we discuss one of these efficient new many-body methods, the In-Medium Similarity Renormalization Group (IMSRG), and its applications in modern nuclear structure theory. The IMSRG evolves the nuclear many-body Hamiltonian in second-quantized form through continuous unitary transformations that can be implemented with polynomial computational effort. Through suitably chosen generators, we drive the matrix representation of the Hamiltonian in configuration space to specific shapes, e.g., to implement a decoupling of low- and high-energy scales, or to extract energy eigenvalues for a given nucleus. We present selected results from Multireference IMSRG (MR-IMSRG) calculations of open-shell nuclei, as well as proof-of-principle applications for intrinsically deformed medium-mass nuclei. We discuss the successes and prospects of merging the (MR-)IMSRG with many-body methods ranging from Configuration Interaction to the Density Matrix Renormalization Group, with the goal of achieving an efficient simultaneous description of dynamic and static correlations in atomic nuclei.Comment: Invited contribution presented by H. H. at the 19th International Conference on Recent Progress in Many-Body Theories, June 25-30, 2017, APCTP, Pohang, Korea. Extended version: 30 pages, 14 figure

Registered Replication Report: Dijksterhuis and van Knippenberg (1998)

Dijksterhuis and van Knippenberg (1998) reported that participants primed with a category associated with intelligence ("professor") subsequently performed 13% better on a trivia test than participants primed with a category associated with a lack of intelligence ("soccer hooligans"). In two unpublished replications of this study designed to verify the appropriate testing procedures, Dijksterhuis, van Knippenberg, and Holland observed a smaller difference between conditions (2%-3%) as well as a gender difference: Men showed the effect (9.3% and 7.6%), but women did not (0.3% and -0.3%). The procedure used in those replications served as the basis for this multilab Registered Replication Report. A total of 40 laboratories collected data for this project, and 23 of these laboratories met all inclusion criteria. Here we report the meta-analytic results for those 23 direct replications (total N = 4,493), which tested whether performance on a 30-item general-knowledge trivia task differed between these two priming conditions (results of supplementary analyses of the data from all 40 labs, N = 6,454, are also reported). We observed no overall difference in trivia performance between participants primed with the "professor" category and those primed with the "hooligan" category (0.14%) and no moderation by gender

Testing microscopically derived descriptions of nuclear collectivity : Coulomb excitation of 22Mg

Many-body nuclear theory utilizing microscopic or chiral potentials has developed to the point that collectivity might be studied within a microscopic or ab initio framework without the use of effective charges; for example with the proper evolution of the E2 operator, or alternatively, through the use of an appropriate and manageable subset of particle–hole excitations. We present a precise determination of E2 strength in 22Mg and its mirror 22Ne by Coulomb excitation, allowing for rigorous comparisons with theory. No-core symplectic shell-model calculations were performed and agree with the new B(E2) values while in-medium similarity-renormalization-group calculations consistently underpredict the absolute strength, with the missing strength found to have both isoscalar and isovector components. The discrepancy between two microscopic models demonstrates the sensitivity of E2 strength to the choice of many-body approximation employed

The human penguin project: climate, social integration, and core body temperature

Social thermoregulation theory posits that modern human relationships are pleisiomorphically organized around body temperature regulation. In two studies (N = 1755) designed to test the principles from this theory, we used supervised machine learning to identify social and non-social factors that relate to core body temperature. This data-driven analysis found that complex social integration (CSI), defined as the number of high-contact roles one engages in, is a critical predictor of core body temperature. We further used a cross-validation approach to show that colder climates relate to higher levels of CSI, which in turn relates to higher CBT (when climates get colder). These results suggest that despite modern affordances for regulating body temperature, people still rely on social warmth to buffer their bodies against the cold.info:eu-repo/semantics/publishedVersio

A Multi-Lab Test of the Facial Feedback Hypothesis by the Many Smiles Collaboration

Following theories of emotional embodiment, the facial feedback hypothesis suggests that individuals’ subjective experiences of emotion are influenced by their facial expressions. However, evidence for this hypothesis has been mixed. We thus formed a global adversarial collaboration and carried out a preregistered, multicentre study designed to specify and test the conditions that should most reliably produce facial feedback effects. Data from n = 3,878 participants spanning 19 countries indicated that a facial mimicry and voluntary facial action task could both amplify and initiate feelings of happiness. However, evidence of facial feedback effects was less conclusive when facial feedback was manipulated unobtrusively via a pen-in-mouth task

A multi-lab test of the facial feedback hypothesis by the Many Smiles Collaboration

Following theories of emotional embodiment, the facial feedback hypothesis suggests that individuals' subjective experiences of emotion are influenced by their facial expressions. However, evidence for this hypothesis has been mixed. We thus formed a global adversarial collaboration and carried out a preregistered, multicentre study designed to specify and test the conditions that should most reliably produce facial feedback effects. Data from n = 3,878 participants spanning 19 countries indicated that a facial mimicry and voluntary facial action task could both amplify and initiate feelings of happiness. However, evidence of facial feedback effects was less conclusive when facial feedback was manipulated unobtrusively via a pen-in-mouth task