Events
Physics Colloquium
The quantum Carnot engine and its quantum signature
Prof. Ronnie Kosloff
Institute Of Chemistry The Hebrew University, Jerusalem
Tue, 19 Nov 2019, 15:30
Ilse Katz Institute for Nanoscale Science & Technology (51), room 015
Abstract: Quantum thermodynamics follows the tradition of learning by example. The Carnot cycle would
be a primary candidate. The attempts to model the four stroke quantum Carnot cycle failed due
to the difficulty to model the isothermal branches, where the working medium is driven while in
contact to the thermal bath. Motivated by this issue we derived a time dependent Non Adiabatic
Master Equation (NAME) with a fixed driving protocol. This master equation is consistent with
thermodynamic principles. We then were able to generalize to protocols with small acceleration
with respect to the fixed fast protocols. This approach was con firmed experimentally in a driven
Ytterbium ion in a Paul trap. Using this construction we are able to find shortcuts to an isothermal
transformation. Unlike unitary transformations the map changes entropy. After this journey, we
are able close a Carnot like cycle in finite time and explore its performance. In the limit of short
cycle times we are able to locate a quantum region of operation. Once the global coherence is
eliminated the engines cannot operate. The nonadiabatic drive forces us to reconsider the quantum
thermodynamical definition of heat and work.
Astrophysics and Cosmology Seminar
A discovery and surprising properties of the white dwarf radio pulsar in AR Scorpii
Dr. Nazar Ikhsanov
Pulkovo Observatory, St. Petersburg, Russia
Wed, 20 Nov 2019, 11:10
Sacta-Rashi Building for Physics (54), room 207
Abstract: AR Scorpii is a 3.56h orbital period binary system composed of a M5V red dwarf and a white
dwarf which rotates with the period of 117s and manifests itself as a spin-powered radio pulsar.
The rapid spin-down of the white dwarf indicates that its surface magnetic field exceeds 150 MG
and prevents the surrounding material from penetrating to within its Roche lobe. Since the
cooling age of the white dwarf significantly exceeds its spin-down timescale the system could
not be formed in its current state. On the other hand, an attempt to model the origin of the system
in terms of accretion-driven spin-up scenario also encounters difficulties. Using currently
adopted disk accretion scenario one finds that a white dwarf with the surface field of 150 MG
could be spun-up to a period of 117s only if the mass accretion rate onto the white dwarf were in
excess of the Eddington limit. Otherwise, the centrifugal barrier at the Alfven radius would
prevent material from reaching the surface of the white dwarf well before its spin period reaches
the currently observed value. This may indicate that either the surface magnetic field of the white
dwarf during a previous spin-up epoch was buried by the accreted material or/and the inner
radius of the accretion disk was significantly smaller than the conventional Alfven radius. In my
talk I discuss both of these possibilities and show that similar corrections to the accretion
scenario may help to model the origin of the fast rotating white dwarf in AE Aquarii.
Astrophysics and Cosmology Seminar
The Multiphase Circum- and Intergalactic Media at the Nexus Between Galaxy Formation and Cosmology
Dr. Nir Mandelker
Yale
Wed, 20 Nov 2019, 12:10
Sacta-Rashi Building for Physics (54), room 207
Abstract: Galaxies are not closed boxes. Rather, it has become clear in recent years that it is the flow of gas into and out of galaxies that shapes their evolution. Cycles of gas accretion, star-formation, galactic outflows and reaccretion, intimately link galaxies to the circumgalactic medium (CGM, gas outside galaxies but within dark matter halos) and the intergalactic medium (IGM, gas outside dark matter halos). While the diffuse gas in these regions has traditionally been very difficult to study, recent advances in both observations and numerical simulations are now providing a wealth of information on the gas around galaxies, revealing complex, multiphase and multiscale structure. I will describe my ongoing efforts to study the phase-structure of the C/IGM by combining novel cosmological magnetohydrodynamic moving-mesh simulations that I modified to overcome difficulties in resolving the diffuse gas in these regions, with analytic modeling and idealized numerical experiments that address detailed questions about physical processes affecting multiphase gas in the C/IGM. I will present two main results from these studies. I will first show how non-linear thermal instabilities cause hot gas to "shatter" into small-scale clouds of cool and dense gas. I will then present a model for the interaction of cold accretion streams with the ambient hot CGM by considering the Kelvin-Helmholtz Instability in a dense, supersonic, self-gravitating, and radiatively cooling cylinder. These have helped us to understand how the C/IGM are shaped by a complex interplay of hydrodynamical, thermal, and gravitational instabilities which we are beginning to put together in a coherent framework.
Condensed Matter Theory Seminar
Differentiating Majorana from Andreev Bound States in a Superconducting Circuit
Mr. Konstantin Yavilberg
Ben Gurion University
Wed, 20 Nov 2019, 13:30
Sacta-Rashi Building for Physics (54), room 207
Abstract: We investigate the low-energy theory of a one-dimensional finite capacitance topological Josephson junction. Charge fluctuations across the junction couple to resonant microwave fields and can be used to probe microscopic excitations such as Majorana and Andreev bound states. This marriage between localized microscopic degrees of freedom and macroscopic dynamics of the superconducting phase, leads to unique spectroscopic patterns which allow us to reveal the presence of Majorana fermions among the low-lying excitations.
Quantum optics seminar
Gas-phase biomolecules: Structural motifs by laser spectroscopies combined with quantum computations
Mr. Itai Kallos
Ben-Gurion University Of The Negev
Wed, 20 Nov 2019, 15:00
Sacta-Rashi Building for Physics (54), room 207
Abstract: Student Seminar (Adviser: Ilana Bar)
A compact laser desorption source for spectroscopic studies of jet-cooled biomolecules, comprising simple parts for sample movement and desorption was designed, assembled and attached to a home-built time-off light mass spectrometer. Samples were prepared by mixing sample particles with graphite and pressing them as a thin layer into a graphite sample bar, positioned in front of a pulsed valve delivering the carrier gas. Continuous linear translation of the sample, in front of a fiber-coupled Nd:YAG laser beam (1064 nm, 10 Hz), led to its desorption, forming a stripe. The desorbed sample and carrier gas were expanded, skimmed, and entrained into the detection chamber. By assessing the relative timings between valve opening, desorption and ionizing lasers, with the optimal conditions for sample preparation, sample bar height, and movement velocity, optimization tests were conducted to improve signal stability and signal-to-noise ratio. The performance of the system was validated by monitoring the resonantly enhanced two-photon ionization and ionization-loss stimulated Raman spectroscopy spectrum of tryptamine and guanine, in the region of the origin band transitions. This spectrum resembled that previously acquired, from heated samples and quantum chemical calculation.
Biological and soft-matter physics
Organizing principles behind two diverse systems: the immune system and the microbiome
Dr. Amir Erez
Princeton University
Thu, 21 Nov 2019, 12:00
Sacta-Rashi Building for Physics (54), room 207
Abstract: Both the immune system and the microbiome - the communities of microbes that live in us - are complex dynamical systems which impact our health and well-being in many ways. However, their huge complexity seemingly poses a barrier towards their understanding, motivating approaches that strip down this complexity to its essential elements. To guide our understanding, we can turn to physics to seek out organizing principles. In this talk, I present several such organizing principles distilled from particular biological contexts, but which apply broadly across different systems. Making use of these principles - including temporal continuity of protein abundance, conservation of chemical elements, and trade-offs in resource allocation – I show how one can develop theory, glean new insight from experimental data, generate hypotheses, and guide experiments. Finally, I will briefly discuss my plans to study immune-microbiome interactions.
Condensed Matter Seminar
Active Matter: `active thermodynamics’ and the dynamics of biopolymer gels
Dr. Tomer Markovich
Ctbp, Rice University And Damtp, University Of Cambridge
Mon, 25 Nov 2019, 11:30
Sacta-Rashi Building for Physics (54), room 207
Abstract: Active materials are composed of many components that can convert energy from its environment (usually in the form of chemical energy) into directed mechanical motion. Time reversal symmetry is thus locally broken, leading to a variety of novel phenomena such as motility induced phase separation, reversal of the Ostwald process and flocking. Examples of active matter are abundant and range from living matter such as bacteria, actomyosin networks and bird flocks to Janus particles, colloidal rollers and macroscale driven chiral rods. Nevertheless, in many cases experiments on active materials exhibit equilibrium like properties (e.g., sedimentation of bacteria). In the first part of the talk I will try to answer the important question: how do we know a system is `active’? And if it is, can we have generic observables as in equilibrium thermodynamics? Can we measure how far it is from equilibrium? In the second part of the talk I will focus on examples of activity in biopolymer gels, such as the cytoskeleton of living cells. I will show some of the effects of active motors with emphasis on chiral motors. The latter does not have a unique hydrodynamic description, which one can utilize to gain access to the microscopic details of the complex motors using macroscopic measurements. I will also discuss non-motor activity and demonstrate how it can result in contractility, e.g., in the process of cell division.
Biological and soft-matter physics
Theory of microbial genome evolution
Dr. Itamar Sela
National Institutes Of Health, Bethesda
Thu, 28 Nov 2019, 12:00
Sacta-Rashi Building for Physics (54), room 207
Abstract: The rapid accumulation of genome sequences from diverse organisms presents an opportunity and a challenge for theoretical research: is it possible to derive quantitative laws of genome evolution and an underlying theory? Microbes have small genomes with tightly packed protein-coding genes, and the different functional classes of genes (such as information processing, metabolism, or regulation) show distinct scaling exponents with the genome size. The compactness of microbial genomes is traditionally explained by genome streamlining under selection for high replication rate but so far, there has been no general theoretical model to account for the observed universal laws of genome content scaling. We developed a model for microbial genome evolution within the framework of population genetics and tested it against extensive data from multiple genome comparisons. The analyses indicate that the evolution of genome size is not governed by streamlining but rather, reflects the balance between the benefit of additional genes and the intrinsic preference for DNA deletion over acquisition. These results explain the observation that, contrary to the common belief, microbes with large genomes are subject to stronger selection than small genomes. Employing this model to recover the differential scaling of functional gene classes in bacterial genomes allowed us to identify the underlying factors that govern the evolution of the genome content. A key factor that we termed genome plasticity shapes genome evolution and provides a simple mathematical representation of evolvability, a central but elusive concept in evolutionary biology. These findings demonstrate that key aspects of genome evolution can be captured by general population genetics models, and pave the way for further theoretical analyses of fundamental evolutionary mechanisms.
Condensed Matter Seminar
New directions for diffusive processes: defect formation through a nonequilibrium phase transition, open quantum systems and uncertainty relations in mesoscopic systems
Dr. Ohad Shpielberg
College De France
Mon, 02 Dec 2019, 11:30
Sacta-Rashi Building for Physics (54), room 207
Abstract: The macroscopic fluctuation theory gives an efficient hydrodynamic description for classical nonequilibrium diffusive systems. In this talk, we would cover how it can be applied and generalised in three unexplored directions:
a. Towards a theory for open quantum diffusive systems, comparable to the macroscopic fluctuation theory.
b. Defect formation as a system is (slowly) driven in time through a continuous phase transition can be described by a scaling theory - the Kibble-Zurek Mechanism. The macroscopic fluctuation theory allows to explore the exact evolution of defects for a large set of cases. Thus, we are in a position to go beyond the scaling arguments of the Kibble-Zurek Mechanism.
c. The recently discovered thermodynamic uncertainty relations defines a transport efficiency in thermal systems showing that the mean current, current fluctuations and dissipation are intimately linked. Here we will briefly show how this idea can be extended to (athermal) mesoscopic coherent processes.
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