CM Seminar, Avraham Klein, Hebrew University of Jerusalem, "Vortex core deformation in weakly coupled superfluids"
Nov 30, 2015 · 1:15 p.m.– 2:30 p.m. · PCTS Seminar Room
Quantum vortices in weakly coupled superfluids have a large healing length, so that many particles reside within the vortex core. They are characterized by topologically protected singular points, which in principal should keep their core structure rigid. I will describe how, in practice, the point singularity of a vortex deforms into a line singularity, in proportion with the Magnus force experienced by the vortex. The vortex structure is described by weak solutions of the Gross-Pitaevskii equation, similar to shock waves in hydrodynamics. I will discuss how the core deformation significantly affects many aspects of vortex dynamics.
High Energy Theory IAS - Maurizio Pierini, CERN, “Signs of Hope: A Few LHC Run I Results to Watch for Run II”
Nov 30, 2015 · 2:30 p.m.– 3:30 p.m. · Bloomberg Lecture Hall - Institute for Advanced Study
During the first LHC long shutdown, the CMS collaboration finalised the study of the 8TeV data collected in 2012. Within the impressive amount of results produced, a few searches for new physics show a tension with the prediction from the Standard Model. While the significance is still too small to allow any conclusion, some of these excesses could reveal the first footprint of new processes at the TeV scale. I will discuss a few of these excesses, and give a perspective of the expectation for Run II.
Nov 30, 2015 · 4:00 p.m.– 5:30 p.m. · Jadwin 303
The modern S-matrix program has seen immense progress constructing scattering amplitudes in gauge and gravity theories without the aid of a Lagrangian, instead using only physical principles like Lorentz invariance and factorization. In this talk, I discuss how a similar approach is sufficient to construct effective field theories (EFTs), yielding a ``periodic table'' of scalar EFTs labelled by two numbers. We derive these EFTs--Lagrangians, symmetries, and all--from an ansatz of all possible S-matrices consistent with Lorentz invariance, factorization, and a certain infrared property, obtaining well-known examples like the chiral Lagrangian, Dirac-Born-Infeld theory, and the Galileon. We the show how tree amplitudes in these EFTs are constructible via on-shell recursion relations. With these methods one can prove stringent no-go theorems on the space of EFTs and, in principle, even discover new ones.
Dec 3, 2015 · 8:00 p.m.–10:30 p.m. · McDonnell A02
"Dark Energy and Cosmic Sound"
Sound waves propagating through the plasma of the Universe only 400,000 years after the Big Bang now offer some of our most precise measures of the composition and history of the Universe. In the last decade, we have been able to detect the fossil imprint of these sound waves using maps of the distribution of galaxies from the Sloan Digital Sky Survey. I will give an overview of the cosmological role of the sound waves and our observational program then describe what the results tell us about the shape of the Universe and the evolution of dark energy.
Dec 4, 2015 · 12:00 p.m.– 1:30 p.m. · PCTS Seminar Room
Dec 4, 2015 · 1:45 p.m.– 3:00 p.m. · Bloomberg Lecture Hall - Institute for Advanced Study
Dec 7, 2015 · 1:15 p.m.– 2:30 p.m. · McDonnell A01
Edges of gapped topological states may host gapless edge modes that cannot be realized as stand-alone systems. Examples include quantum Hall edge states, surface states of topological insulators and super-conductors, etc. In my talk I will examine situations in which these edge states form fractionalized phases of their own. Examples to be discussed include non-abelian defects in edges of abelian quantum Hall states, Haldane-type phases formed by these defects, and topologically ordered states on surfaces of weak topological insulators.
Dec 7, 2015 · 2:30 p.m.– 3:30 p.m. · Jadwin A07
Special Condensed Matter Physics Seminar - Stefan Putz, TU Wien - "Circuit Cavity QED with Collective Spin States"
Dec 10, 2015 · 1:15 p.m.– 2:30 p.m. · PCTS Seminar Room
In this talk I will present recent progress in examining collective spin phenomena’s such as cavity protection, spectral hole burning and amplitude bi-stability in a hybrid solid state system consisting of a superconducting microwave cavity strongly coupled to an ensemble of electron spins in nitrogen-vacancy centers in diamond. I will show how the total de-coherence rate scales with the collective enhanced coupling strength in a broadened spin ensemble coupled to a single mode cavity, known as “cavity protection” effect. Furthermore, I will explain how the coherence times can be improved beyond the natural limit given by the cavity protection effect, by spectral-hole burning techniques. Long lived coherence is shown by examining Rabi oscillations with high visibility. The observed total decay rates are significantly reduced, a factor of forty compared to the spin ensemble line width and over a factor of three compared to the pure cavity dissipation rate. This verifies that a "new" class of states, dark states, can be employed for the coherent exchange of excitation's between the cavity and spin ensemble. This is the first step towards a solid-state microwave frequency comb realised by engineering multiple long-lived dark states. I will also show how this system is a versatile tool in studying strong non-linear effects such as collective amplitude bi-stability in a macroscopic spin ensemble coupled to a single mode cavity. This engineered hybrid system approach opens up the possibility for truly long lived quantum memories and solid-state microwave frequency combs but also a new route to cavity QED experiments with dense interacting ensembles where exotic quantum transport phenomena can be studied.
Putz, S. et al. Protecting a spin ensemble against de-coherence in the strong-coupling regime of cavity QED. Nature Physics 10, 720–724 (2014).
Amsüss, R. et al. Cavity QED with Magnetically Coupled Collective Spin States. Phys. Rev. Lett. 107, 060502 (2011).
Hamilton Colloquium Series: Steven Tobias, University of Leeds (UK), "Order from Chaos: From the Solar Cycle to the Jets on Jupiter"
Dec 10, 2015 · 4:30 p.m.– 6:00 p.m. · Jadwin A10
The eleven year solar activity cycle is a remarkable example of regular behavior emerging from an extremely turbulent system. The jets on Jupiter sit unmoving on a sea of turbulent eddies. Astrophysical phenomena often display organization on spatial and temporal scales much larger than the turbulent processes that drive them. An outstanding problem of astrophysics (and indeed other branches of nonlinear physics) is how to describe the statistics of systematic behavior emerging from the underlying chaos, given that Direct Numerical Simulation of these objects is simply impossible. Here, I shall introduce these fascinating phenomena and describe how methods from non-equilibrium statistical mechanics and many body quantum systems may be developed to give some insight into their behavior.
Dec 11, 2015 · 12:00 p.m.– 1:30 p.m. · PCTS Seminar Room
Dec 11, 2015 · 1:45 p.m.– 3:00 p.m. · PCTS Seminar Room
Biophysics Seminar - Eleni Katifori, U. Penn "Emerging hierarchies in biological distribution networks'
Dec 14, 2015 · 12:00 p.m.– 1:00 p.m. · Joseph Henry Room
Biological transport webs, such as the blood circulatory system in the brain and other animal organs, or the slime mold Physarum polycephalum, are frequently dominated by dense sets of nested cycles. The architecture of these networks, as defined by the topology and edge weights, determines how efficiently the networks perform their function. In this talk we present some general models regarding the emergence and extraction of hierarchical nestedness in biological transport networks. In particular, we discuss how a hierarchically organized vascular system is optimal under conditions of variable, time-dependent flow, but also how it emerges naturally from a set of simple local feedback rules. To characterize the topology of these weighted cycle-rich network architectures, we develop an algorithmic framework that analyzes how the cycles are nested. Finally, using this algorithmic framework and an extensive dataset of more than 180 leaves and leaflets, we show how the hierarchical organization of the nested architecture is in fact a distinct phenotypic trait, akin to a fingerprint, that characterizes the vascular systems of plants and can be used to assist species identification from leaf fragments.
Dec 14, 2015 · 2:30 p.m.– 3:30 p.m. · Bloomberg Lecture Hall - Institute for Advanced Study
Dec 15, 2015 · 4:00 p.m.– 5:30 p.m. · Jadwin 303
Dec 15, 2015 · 4:00 p.m.– 5:30 p.m. · Jadwin 303
Jan 19, 2016 · 4:00 p.m.– 5:30 p.m. · Jadwin 303
Jan 22, 2016 · 1:45 p.m.– 3:00 p.m. · Bloomberg Hall of Physics Library - Institute for Advanced Study
Mar 1, 2016 · 4:30 p.m.– 5:30 p.m. · Jadwin 343
Apr 19, 2016 · 4:00 p.m.– 5:30 p.m. · Jadwin 303