The Magnus expansion and the in-medium similarity renormalization group

We present an improved variant of the in-medium similarity renormalization group (IM-SRG) based on the Magnus expansion. In the new formulation, one solves flow equations for the anti-hermitian operator that, upon exponentiation, yields the unitary transformation of the IM-SRG. The resulting flow equations can be solved using a first-order Euler method without any loss of accuracy, resulting in substantial memory savings and modest computational speedups. Since one obtains the unitary transformation directly, the transformation of additional operators beyond the Hamiltonian can be accomplished with little additional cost, in sharp contrast to the standard formulation of the IM-SRG. Ground state calculations of the homogeneous electron gas (HEG) and $^{16}$O nucleus are used as test beds to illustrate the efficacy of the Magnus expansion.Comment: 12 pages, 9 figures; fixed typos and added a referenc

White lies in hand : are other-oriented lies modified by hand gestures : possibly not

Previous studies have shown that the hand-over-heart gesture is related to being more honest as opposed to using self-centred dishonesty. We assumed that the hand-over-heart gesture would also relate to other-oriented dishonesty, though the latter differs highly from self-centred lying. In Study 1 (N = 83), we showed that performing a hand-over-heart gesture diminished the tendency to use other-oriented white lies and that the fingers crossed behind one’s back gesture was not related to higher dishonesty. We then pre-registered and conducted Study 2 (N = 88), which was designed following higher methodological standards than Study 1. Contrary, to the findings of Study 1, we found that using the hand-over-heart gesture did not result in refraining from using other-oriented white lies. We discuss the findings of this failed replication indicating the importance of strict methodological guidelines in conducting research and also reflect on relatively small effect sizes related to some findings in embodied cognition

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 spectroscopy with the in-medium similarity renormalization group

"The in-medium similarity renormalization group (IMSRG) is an ab initio many-body method which features soft polynomial scaling with system size and a Hermitian framework to create Hamiltonians tailored for use with low-level approximations such as Hartree-Fock (HF) theory or the random phase approximation (RPA). The flexibility that comes with these characteristics has made the IMSRG a mainstay in contemporary nuclear structure theory. However, spectroscopy with IMSRG calculations has been limited to scalar observables in nuclei accessible with shell model machinery, where the IMSRG is used to construct effective valence-space interactions. In this thesis, we present two novel developments which have greatly extended the IMSRG's capability to perform spectroscopic calculations. First is the introduction of the equations-of-motion IMSRG (EOM-IMSRG), which uses an approximate, but systematically improvable diagonalization scheme in conjunction with the IMSRG to produce spectra and wave functions. The method does not suffer the model-space limitations of the shell model, but sacrifices some accuracy due to the approximate diagonalization. We benchmark this new method with the well established equations-of-motion coupled cluster and full configuration interaction methods, where we demonstrate that the method is indeed viable for closed-shell systems, encouraging expansion to open shells using a multireference formalism. We also introduce a perturbative framework to add systematic corrections to the EOM-IMSRG, showing results for closed shell nuclei and quantum dots. The second development is a generalized effective operator formalism for the IMSRG, capable of consistently evolving non-scalar operators relevant for electroweak transitions and moments. This general framework is applicable to both the EOM-IMSRG and the valence-space IMSRG approaches. We benchmark electromagnetic transition strengths and moments using both of these methods, also comparing with the quasi-exact no-core shell model and experiment when available. We demonstrate that consistent renormalization of observables is critical for precise computations with the IMSRG. We find that our methods perform well for transitions that are strongly single particle in nature, but for collective transitions involving many particles, we note that work remains to properly incorporate these effects in the IMSRG."--Pages ii-iii.(Ph. D.)--Michigan State University. Physics, 2017Includes bibliographical references (pages 160-171

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

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

From the heart: hand over heart as an embodiment of honesty

Motor movements increase the accessibility of the thought content and processes with which they typically co-occur. In two studies, we demonstrate that putting a hand on one’s heart is associated with honesty, both perceived in others and shown in one’s own behavior. Target persons photographed when performing this gesture appeared more trustworthy than the same targets photographed with both hands down (Study 1). Participants who put their hand on their hearts were more willing to admit their lack of knowledge (Study 2), compared to when they performed a neutral gesture. These findings replicate and extend the notion that bodily experience related to abstract concepts of honesty can influence both perceptions of others, and one’s own actions

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