Abstract

We investigate the dewetting of a disordered melt of diblock copolymer from an ordered residual wetting layer. In contrast to simple liquids where the wetting layer has a fixed thickness and the droplets exhibit a single unique contact angle with the substrate, we find that structured liquids of diblock copolymer exhibit a discrete series of wetting layer thicknesses each producing a different contact angle. These quantized contact angles arise because the substrate and air surfaces each induce a gradient of lamellar order in the wetting layer. The interaction between the two surface profiles creates an effective interface potential that oscillates with film thickness, thus, producing a sequence of local minimums. The wetting layer thicknesses and corresponding contact angles are a direct measure of the positions and depths of these minimums Self-consistent field theory is shown to provide qualitative agreement with the experiment.

Abstract

We propose a practical scheme to use photons from causally disconnected cosmic sources to set the detectors in an experimental test of Bells inequality. In current experiments, with settings determined by quantum random number generators, only a small amount of correlation between detector settings and local hidden variables, established less than a millisecond before each experiment, would suffice to mimic the predictions of quantum mechanics. By setting the detectors using pairs of quasars or patches of the cosmic microwave background, observed violations of Bells inequality would require any such coordination to have existed for billions of yearsan improvement of 20 orders of magnitude.

Abstract

It has recently been shown that dark-matter annihilation to bottom quarks provides a good fit to the Galactic Center gamma-ray excess identified in the Fermi-LAT data. In the favored dark-matter mass range \( m \sim \) 30–40 GeV, achieving the best-fit annihilation rate \( \sigma v \sim 5 \times 10^{-26} \, \mathrm{cm^3 s^{-1}} \) with perturbative couplings requires a sub-TeV mediator particle that interacts with both dark matter and bottom quarks. In this paper, we consider the minimal viable scenarios in which a Standard Model singlet mediates s-channel interactions only between dark matter and bottom quarks, focusing on axial-vector, vector, and pseudoscalar couplings. Using simulations that include on-shell mediator production, we show that existing sbottom searches currently offer the strongest sensitivity over a large region of the favored parameter space explaining the gamma-ray excess, particularly for axial-vector interactions. The 13 TeV LHC will be even more sensitive; however, it may not be sufficient to fully cover the favored parameter space, and the pseudoscalar scenario will remain unconstrained by these searches. We also find that direct- detection constraints, induced through loops of bottom quarks, complement collider bounds to disfavor the vector-current interaction when the mediator is heavier than twice the dark-matter mass. We also present some simple models that generate pseudoscalar-mediated annihilation predominantly to bottom quarks.

Abstract

We show that the existence of new, light gauge interactions coupled to Standard Model (SM) neutrinos gives rise to an abundance of sterile neutrinos through the sterile neutrinos’ mixing with the SM. Specifically, in the mass range of MeV–GeV and coupling of \( g' \sim 10^{-6} \)–\( 10^{-3} \), the decay of this new vector boson in the early Universe produces a sufficient quantity of sterile neutrinos to account for the observed dark matter abundance. Interestingly, this can be achieved within a natural extension of the SM gauge group, such as a gauged \( L_{\mu} \) − \( L_{\tau} \) number, without any tree-level coupling between the new vector boson and the sterile neutrino states. Such new leptonic interactions might also be at the origin of the well-known discrepancy associated with the anomalous magnetic moment of the muon.

Abstract

We experimentally study the ghost critical field (GCF), a magnetic field scale for the suppression of superconducting fluctuations, using Hall effect and magnetoresistance measurements on a disordered superconducting thin film near its transition temperature \( T_c \). We observe an increase in the Hall effect with a maximum in field that tracks the upper critical field below \( T_c \), vanishes near \( T_c \), and returns to higher fields above \( T_c \). Such a maximum has been observed in studies of the Nernst effect and identified as the GCF. Magnetoresistance measurements near Tc indicate quenching of superconducting fluctuations, agree with established theoretical descriptions, and allow us to extract the GCF and other parameters. Above \( T_c \), the Hall peak field is quantitatively distinct from the GCF, and we contrast this finding with ongoing studies of the Nernst effect and superconducting fluctuations in unconventional and thin-film superconductors.

Abstract

We present a microfabricated surface-electrode ion trap with a pair of integrated waveguides that generate a standing microwave field resonant with the 171Yb+ hyperfine qubit. The waveguides are engineered to position the wave antinode near the center of the trap, resulting in maximum field amplitude and uniformity along the trap axis. By calibrating the relative amplitudes and phases of the waveguide currents, we can control the polarization of the microwave field to reduce off-resonant coupling to undesired Zeeman sublevels. We demonstrate single-qubit π-rotations as fast as 1 μs with less than 6% variation in Rabi frequency over an 800 μm microwave interaction region. Fully compensating pulse sequences further improve the uniformity of X-gates across this interaction region.

Abstract

In heteroepitaxy, lattice mismatch between the deposited material and the underlying surface strongly affects nucleation and growth processes. The effect of mismatch is well studied in atoms with growth kinetics typically dominated by bond formation with interaction lengths on the order of one lattice spacing. In contrast, less is understood about how mismatch affects crystallization of larger particles, such as globular proteins and nanoparticles, where interparticle interaction energies are often comparable to thermal fluctuations and are short ranged, extending only a fraction of the particle size. Here, using colloidal experiments and simulations, we find particles with short-range attractive interactions form crystals on isotropically strained lattices with spacings significantly larger than the interaction length scale. By measuring the free-energy cost of dimer formation on monolayers of increasing uniaxial strain, we show the underlying mismatched substrate mediates an entropy-driven attractive interaction extending well beyond the interaction length scale. Remarkably, because this interaction arises from thermal fluctuations, lowering temperature causes such substrate- mediated attractive crystals to dissolve. Such counterintuitive results underscore the crucial role of entropy in heteroepitaxy in this technologically important regime. Ultimately, this entropic component of lattice mismatched crystal growth could be used to develop unique methods for heterogeneous nucleation and growth of single crystals for applications ranging from protein crystallization to controlling the assembly of nanoparticles into ordered, functional superstructures. In particular, the construction of substrates with spatially modulated strain profiles would exploit this effect to direct self-assembly, whereby nucleation sites and resulting crystal morphology can be controlled directly through modifications of the substrate.

Abstract

A definition of quantum singularity for the case of static spacetimes has has recently been extended to conformally static spacetimes. Here the theory behind quantum singularities in conformally static spacetimes is reviewed and then applied to a class of spherically symmetric, conformally static spacetimes, including as special cases those studied by Roberts, by Fonarev, and by Husain et al. We use solutions of the generally coupled, massless Klein-Gordon equation as test fields. In this way we find the ranges of metric parameters and coupling coefficients for which classical timelike singularities in these spacetimes are healed quantum mechanically.

Recent Publications

Student authorFaculty author

31.

Mark Ilton, Pawel Stasiak, Mark W. Matsen, and Kari Dalnoki-Veress

Quantized Contact Angles in the Dewetting of a Structured Liquid

Physical Review Letters 112 (2014) 068303.
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32.

Jason Gallicchio, Andrew S. Friedman, and David I. Kaiser

Testing Bell’s Inequality with Cosmic Photons: Closing the Setting-Independence Loophole

Physical Review Letters 112 (2014) 195.
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33.

Eder Izaguirre, Gordan Krnjaic, and Brian Shuve

Bottom-up Approach to the Galactic Center Excess

Physical Review D 90 (2014) 18.
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34.

Brian Shuve and Itay Yavin

Dark Matter Progenitor: Light Vector Boson Decay into Sterile Neutrinos

Physical Review D 89 (2014) 113004.
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35.

Jason Gallicchio and Matthew D Schwartz

Quark and gluon jet substructure

Journal of High Energy Physics 2013 (2013) .
36.

Yang Bai, Hsin-Chia Cheng, Jason Gallicchio, and Jiayin Gu

A toolkit of the stop search via the chargino decay

Journal of High Energy Physics 2013 (2013) .
37.

Nicholas P. Breznay and Aharon Kapitulnik

Observation of the ghost critical field for superconducting fluctuations in a disordered TaN thin film

Physical Review B 88 (2013) 223.
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38.

C. M. Shappert, J. T. Merrill, K. R. Brown, J. M. Amini, C. Volin, Charlie Doret, H. Hayden, C. -S. Pai, K. R. Brown, and A. W. Harter

Spatially uniform single-qubit gate operations with near-field microwaves and composite pulse compensation

New Journal of Physics 15 (2013) 083503.
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39.

John R. Savage, Stefan F. Hopp, Rajesh Ganapathy, Sharon Gerbode, Andreas Heuer, and I. Cohen

Entropy-Driven Crystal Formation on Highly Strained Substrates

Proceedings of the National Academy of Sciences 110 (2013) 9301-9304.
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40.

Thomas Helliwell and D. A. Konkowski

Quantum singularities in spherically symmetric, conformally static spacetimes

Physical Review D 87 (2013) 104041.