Events
Particles and Fields Seminar
Swampland, Wormholes and Global Symmetries
Prof. Arthur Hebecker
University Of Heidelberg
Mon, 30 Nov 2020, 14:00
Zoom
Abstract: I will briefly introduce the general ideas of Landscape and Swampland, focussing in particular on the Weak Gravity Conjecture. The latter has a generalisation to axions and instantons. Wormholes come in as the possible universal realisations of the instantons predicted by the Weak Gravity Conjecture. However, once they are included in the path integral, many interesting conceptual issues such as the "baby universe state" also arise. I will end by discussing recent proposals for a Swampland Global Symmetry Conjecture, which are closely related to wormholes.
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https://us02web.zoom.us/j/84553949396?pwd=dzNaYjNGeHp4Tzg2N0Jycm12SFpydz09
Meeting ID: 845 5394 9396
Passcode: 345123
Physics Colloquium
A long history of black holes
Hagai Netzer
Tel Aviv University
Mon, 30 Nov 2020, 16:00
Zoom: https://us02web.zoom.us/j/88390741064
Abstract: The first black holes were seeded in pre-born galaxies in the early Universe. Active black holes are the lamp-posts of the Universe. Every 50-100 million years they light up for a short period of time, providing a glimpse of their parent galaxies and their environment.
I will present the black hole history of the Universe using recent observations and focusing on the first 1-2 billion years. To each black hole I will assign a measured mass: one of the greatest achievements of modern astronomy which resulted, among other things, in the 2020 Nobel prize in Physics. I will show how black hole activity is related to mergers of galaxies, and to the quenching of star-formation, and argue that such processes control the growth of the largest galaxies of today.
Zoom link: https://us02web.zoom.us/j/88390741064
Condensed Matter Seminar
Collective Dynamics of Coexisting Spin Textures
Dr. Eran Maniv
Berkeley
Tue, 01 Dec 2020, 18:00
Zoom
Abstract: **** Please note the change of time/date ****
Advances in controlling electron correlations in transition metal dichalcogenides have opened a new frontier of many-body physics in two dimensions. A field where these materials have yet to make a deep impact is antiferromagnetic spintronics—a relatively new research direction promising technologies with fast switching times, insensitivity to magnetic perturbations and reduced cross-talk. The theory behind the electrical switching of antiferromagnets is premised on the existence of a well-defined broken symmetry state that can be rotated to encode information. A spin glass is in many ways the antithesis of this state, characterized by an ergodic landscape of nearly degenerate magnetic configurations, freezing into its final distribution in a manner that is seemingly bereft of information.
In this talk, I will show that the coexistence of spin glass and antiferromagnetic order allows a novel mechanism to facilitate the switching of the intercalated transition metal dichalcogenide Fe1/3±δNbS2, which is rooted in the electrically stimulated collective winding of the spin glass. We find that remarkably low current densities of the order of 104 A/cm−2 can reorient the magnetic order in a single pulse activation. The local texture of the spin glass opens an anisotropic channel of interaction that can be used to rotate the equilibrium spin-orientation of the antiferromagnetic state. Moreover, I will present the first experimental observation of the predicted spin glass collective modes, known as Halperin-Saslow spin waves. The use of a spin glass’ collective dynamics to electrically manipulate antiferromagnetic spin textures has never been applied before, opening the field of antiferromagnetic spintronics to many more material platforms with complex magnetic textures.
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https://us02web.zoom.us/j/2052110067
Quantum optics seminar
Dressing ultra-cold atoms for circuits, shells and lattices
Prof. Barry M Garraway
University Of Sussex
Wed, 02 Dec 2020, 15:00
ZOOM
Abstract: Zoom link: https://us02web.zoom.us/j/85617462457
Abstract:
In quantum optics, the dressed atom proved to be a useful concept for
Cohen-Tannoudji and Reynaud in the analysis of resonance fluorescence from
an atom back in 1977 [1]. More recently it has been found that by
adiabatically dressing atoms with radio-frequency and microwave radiation
we can produce a variety of different types of spatial trap for ultra-cold
atoms (see reviews in Refs. [2, 3]). In this talk we will see how shell
potentials can be tuned and the results and applications for dressing and
probing RF dressed potentials with microwave pulses.
[1] Dressed-atom description of resonance fluorescence and absorption
spectra of a multi-level atom in an intense laser beam, C Cohen-Tannoudji
and S Reynaud, J. Phys. B 10, 345 (1977).
[2] Topical Review: Recent developments in trapping and manipulation of
atoms with adiabatic potentials, B.M. Garraway and H. Perrin, J. Phys. B
49, 172001 (2016).
[3] Trapping atoms with radio-frequency adiabatic potentials, H. Perrin
and B.M. Garraway, in Advances in Atomic, Molecular and Optical Physics,
vol. 66, pp 181-262 (2017).
Astrophysics and Cosmology Seminar
Learning Cosmology from the First Stars and Reionization
Dr. Julian Muñoz
Cfa Harvard
Wed, 02 Dec 2020, 15:00
Sacta-Rashi Building for Physics (54), room 207
Abstract: I will describe how to use current and upcoming astrophysical measurements in the redshift range z=4-20 to learn new cosmological information. I will first describe the 21-cm line during the cosmic-dawn era, which saw the formation of the first stars. The radiation from these stars excited neutral hydrogen and allowed it to absorb 21-cm photons from the cosmic microwave background (CMB). I will illustrate how the timing of this signal, which is dictated by the formation of the small minihalos that hosted the first stars, can be used to tightly constrain the small-scale behavior of dark matter, and determine if it's cold, warm, or self interacting. Then, I will explain how the acoustic physics of recombination become imprinted onto the 21-cm fluctuations, resulting in robust velocity-induced acoustic oscillations (VAOs) in the expected signal. These act as a new standard ruler during cosmic dawn, bridging the gap in measurements of the expansion rate of our universe between us and the CMB, which are presently at tension with each other. Finally, I will show how current measurements of UV luminosity functions during reionization can be used to probe primordial non-Gaussianity at smaller scales than accessible by the CMB.
Biological and soft-matter physics
PCR-free sensing of Covid-19, metastatic mRNA biomarkers and towards single-cell proteomics using solid-state nanopore devices
Prof. Amit Meller
Dept. Of Biomedical Engineering, Technion - Israel Institute Of Technology
Thu, 03 Dec 2020, 12:10
ZOOM only - Meeting ID: 841 9016 0947
Abstract: The recent outbreak of the coronavirus disease (COVID-19) reinforced the acute need for extremely sensitive, accurate and point-of-care mRNA quantification sensors worldwide. In the past two decades our lab promoted solid-state nanopores as single-biomolecule sensors. In a nanopore device, an electrical field pulls the electrically charged analyte towards and through a nanometer-scale pore, allowing recognition of the molecule based on its ion-current signature. Here I will present results showing the ability to target mRNA biomarkers with sensitivity superseding the “gold-standard” RT-qPCR. Importantly, we developed and validated a purification-free biochemical assay to sense mRNAs from cell lines and from clinical samples, that allow single molecule multiplexed counting of the target RNAs. We applied our method for the sensing of cancer metastatic biomarkers MACC1 and S100A4 at early stage, and for PCR-free sensing of SARS-CoV-2 RNA molecules from clinical samples. Moving beyond nucleic acids, I will discuss our on-going efforts towards the use of plasmonic nanopore devices for the single protein molecules identification based on partial labelling of only two or three amino acids. This approach involves sophisticated signal analysis from each and every passage of the SDS-denatured protein through the nanopore. According to our simulations the noisy single-molecule signals can be robustly and uniquely associated with specific proteins using a custom deep learning strategy. This opens up a new route for single-cell proteomics of even rare proteins.
References:
(1) Rozevsky, Y.; Gilboa, T.; van Kooten, X. F.; Kobelt, D.; Huttner, D.; Stein, U.; Meller, A. Quantification of mRNA Expression Using Single-Molecule Nanopore Sensing. ACS Nano 2020, 14, 13964–13974.
(2) Zrehen, A.; Ohayon, S.; Huttner, D.; Meller, A. On-Chip Protein Separation with Single-Molecule Resolution. Sci Rep 2020, 10, 15313–12.
(3) Zrehen, A.; Huttner, D.; Meller, A. On-Chip Stretching, Sorting, and Electro-Optical Nanopore Sensing of Ultralong Human Genomic DNA. ACS Nano 2019, 13, 14388–14398.
(4) Spitzberg, J. D.; Zrehen, A.; van Kooten, X. F.; Meller, A. Plasmonic-Nanopore Biosensors for Superior Single-Molecule Detection. Adv. Mater. 2019, 31, e1900422–18.
(5) Ohayon, S.; Girsault, A.; Nasser, M.; Shen-Orr, S.; Meller, A. Simulation of Single-Protein Nanopore Sensing Shows Feasibility for Whole-Proteome Identification. PLoS Comput. Biol. 2019, 15, e1007067–21.
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https://us02web.zoom.us/j/84190160947
Meeting ID: 841 9016 0947
Biological and soft-matter physics
A three-sphere micro-swimmer in a structured fluid
Prof. Shigeyuki Komura
Department Of Chemistry, Tokyo Metropolitan University
Thu, 10 Dec 2020, 12:10
ZOOM only - Meeting ID: 841 9016 0947
Abstract: We discuss the locomotion of a three-sphere microswimmer
in a viscoelastic structured fluid characterized by typical length and time
scales. We derive a general expression to link the average swimming
velocity to the sphere mobilities. In this relationship, a viscous contribution
exists when the time-reversal symmetry is broken, whereas an elastic
contribution is present when the structural symmetry of the microswimmer
is broken. As an example of a structured fluid, we consider a polymer gel,
which is described by a "two-fluid" model. We demonstrate in detail that the
competition between the swimmer size and the polymer mesh size gives
rise to the rich dynamics of a three-sphere microswimmer.
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https://us02web.zoom.us/j/84190160947
Meeting ID: 841 9016 0947
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