Events
Astrophysics and Cosmology Seminar
Shot noise in galaxy clustering: halo model approach and its cosmological implications
Mr. Dimitry Ginzburg
Technion
Wed, 11 Dec 2019, 11:10
Sacta-Rashi Building for Physics (54), room 207
Abstract: Shot noise is an important ingredient to any measurement or theoretical modeling of discrete tracers of the large scale structure. Recent work has shown that the shot noise in the halo power spectrum becomes increasingly sub-Poissonian at high mass. Interestingly, while the halo model predicts a shot noise power spectrum in qualitative agreement with the data, it leads to an unphysical white noise in the cross halo-matter and matter power spectrum. We show that absorbing all the halo model sources of shot noise into the halo fluctuation field leads to meaningful predictions for the shot noise contributions to halo clustering statistics and remove the unphysical white noise from the cross halo-matter statistics. We show a new class of consistency relations for discrete tracers, which appear to be satisfied by our reformulation of the halo model. We test our theoretical predictions against measurements of halo shot noise bispectra extracted from numerical simulations. Our m
odel reproduces qualitatively the observed sub-Poissonian noise, although it underestimates the magnitude of this effect. Also, we calculate the effect of the uncertainty in the model for the shot noise on parameters which become important on large scales - parameters which appear in red shift surveys due to projection effects and the primordial non-Gaussianity. We use Fisher analysis to compare the systematic error due to the use of a wrong model in those parameters to their statistical errors and we calculate the effect of marginalization over all shot noise values. We compare the measurement significance of those parameters when various numbers of bins is used and we show the optimal division into mass bins when only two bins are considered.
Condensed Matter Theory Seminar
Dynamics and escape of active particles in a harmonic trap
Dan Wexler
Ben Gurion University
Wed, 11 Dec 2019, 13:30
Sacta-Rashi Building for Physics (54), room 207
Abstract: The dynamics of active particles are of interest at many levels and is the focus of theoretical and experimental research. There have been many attempts to describe the dynamics of particles affected by random active forces in terms of an effective temperature. This kind of description is tempting due to the similarities (or lack thereof) with systems in or near thermal equilibrium. However, the generality and validity of the effective temperature is not yet fully understood. I will present expressions derived for the effective temperature due to the potential and kinetic energies, their ability to predict escape times from a harmonic trap and alternative expressions where effective temperatures are a poor indicator of the escape time. I will also show some evidence for the validity of these effective temperatures for non-harmonic dynamics, as well as their limitations in describing different active force implementations.
Quantum optics seminar
Quantum control of nanomechanical oscillators
Dr. Itay Shomroni
Laboratoire De Photonique Et De Mesure Quantique, Lausanne, Switzerland
Wed, 11 Dec 2019, 15:00
Sacta-Rashi Building for Physics (54), room 207
Abstract: Within the emerging field of Quantum Optomechanics, it has become possible in
recent years to establish a quantum interface between light and the motion of an
engineered mechanical oscillator, and to observe such effects as motional
sideband asymmetry, radiation pressure shot noise, and ponderomotive squeezing.
These achievements are now being extended towards applications and fundamental
research. The possibility to manipulate motion at the quantum level opens new
avenues such as sensing technologies with unprecedented sensitivities, encoding
quantum information in ultrahigh-quality nanomechanical systems, and engineering
macroscopic quantum states for testing of fundamental quantum physics. I will
describe my recent work with optomechanical photonic crystals, demonstrating
quantum measurement techniques that evade quantum backaction noise [1,2] and laser
cooling of macrosopic mechanical motion down to a record level of 92% ground state
occupation [4]. I will show how to extend these results with related methods that
generate mechanical squeezed states, to realize sensing of force and displacement
beyond the standard quantum limit. In addition I will describe my recent theoretical
proposal for generating superposition (cat) states in a macroscopic oscillator [5], that
directly builds upon these techniques.
Refs:
[1] Shomroni et al., Phys. Rev. X 9, 041022 (2019)
[2] Shomroni et al., Nat. Commun. 10, 2086 (2019)
[3] Qiu*, Shomroni* et al., Phys. Rev. A 100, 053852 (2019)
[4] Qiu*, Shomroni* et al., arXiv:1903.10242
[5] Shomroni et al., arXiv:1909.10624
Biological and soft-matter physics
Nurturing Nature for Nanotechnology
Dr. Michael Zwolak
National Institute Of Standards And Technology
Thu, 12 Dec 2019, 12:00
Sacta-Rashi Building for Physics (54), room 207
Abstract: It has long been a dream to design molecular devices and machines. We are not, though, very good at it, but Nature is. From the complex machinery of the ribosome to the integration of information, sensing, and actuation in cells, biological systems conduct the most exquisite nanofabrication and molecular operation that we know of. Our best methods so far for creating nanoscale objects mimic and exploit biological systems – top-down lithographic techniques notwithstanding. DNA nanotechnology, in particular, makes information – the sequence of bases – into structures by taking advantage of the specificity of Watson-Crick pairing. An appropriate chosen sequence of DNA, or sequences of many pieces of DNA, will self-assemble into different shapes and patterns, and can even generate structures that move and respond to different stimuli. This assembly process, though, is not fool proof; it does not always give us what we want. To do as biology does (whether chemical, e.g., ribosomal, or structural), we better develop the tools to measure, model, and understand biomolecular assembly. I will present theoretical principles of biomolecular nanostructure design, as well as experimental results to test these principles in the context of DNA origami. In other words, I will discuss how we can better nurture Nature to give us novel structures and devices, from sensors to machines to drug delivery systems.
Condensed Matter Seminar
Crystalline symmetry in topological materials
Dr. Raquel Queiroz
Weizmann Institute Of Science
Mon, 16 Dec 2019, 11:30
Sacta-Rashi Building for Physics (54), room 207
Abstract: In this talk I will show how we can extract information encoded in the crystalline symmetry representations of solid state systems in order to understand how topological bands can be formed. In particular I will show in two examples how we can explore the sub- and super-group structures of symmetry representations to characterize and engineer topological phases. First, we will understand the unreasonable prevalence of topological phenomena in bismuth and related compounds; and second we will see how spatial defects can make a topologically trivial system host novel embedded topological phases. General consequences and extensions of this approach will be discussed.
Particles and Fields Seminar
Inverse Magnetic Catalysis in Holographic QCD
Matti Jarvinen
Tel Aviv University
Mon, 16 Dec 2019, 14:00
Sacta-Rashi Building for Physics (54), room 207
Abstract: Typically one expects that the chiral condensate increases with magnetic field in QCD and other field theories. This phenomenon is called "magnetic catalysis". Therefore it came as a surprise when lattice simulations found the opposite behavior near the chiral and deconfinement transition temperatures of QCD. After a brief introduction to holography at finite magnetic field, I demonstrate that this "inverse magnetic catalysis" is found in a bottom-up holographic model, which includes the backreaction of the flavors to the glue dynamics. The model agrees well with lattice results for the condensate and related observables. It also predicts the extent of inverse catalysis at finite chemical potential, where no lattice data is currently available. A detailed analysis of the effect suggests that it arises due to the anisotropy caused by the magnetic field rather than the magnetic field directly.
Physics Colloquium
TBA
Prof. Gregory Fiete
The University Of Texas At Austin
Tue, 17 Dec 2019, 15:30
Ilse Katz Institute for Nanoscale Science & Technology (51), room 015
Abstract:
Biological and soft-matter physics
Random interactions and high-dimensionality in ecology
Prof. Guy Bunin
Department Of Physics, Technion-Israel Institute Of Technology
Thu, 19 Dec 2019, 12:00
Sacta-Rashi Building for Physics (54), room 207
Abstract: Natural ecosystems exhibit astounding richness. This suggests that we treat them as many-variable interacting systems, but is there evidence to support this perspective? I will discuss possible footprints of high-dimensionality, including phase-transitions, and “thermodynamic” variables which determine the system’s large-scale behavior. We show that the latter are found in a wide range of accepted models in the field. Then, I’ll present a theory for how interactions organize to allow many species to coexist. Data from plant-competition experiments confirms the theoretical predictions, providing evidence for high-dimensionality in that ecosystem.
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