Events - Weekly
|Sunday, March 10|
|Monday, March 11|
Henrik Flyvbjerg (Danish Technical University) "Optimal estimation of diffusion coefficients from noisy single-particle trajectories"
Einstein argued in 1905 that the mean squared displacement of a microscopic particle suspended in a fluid at rest is proportional to time with the constant of proportionality giving the particle's
diffusion coefficient. Since then, diffusion coefficients have been determined from particle trajectories by fitting a straight line to the observed mean squared displacement. This procedure is accurate,but not precise in any of its incarnations, yet dominates practise.
We present a simpler, optimal, and unbiased estimator of diffusion coefficients of freely diffusing particles in homogeneous media. It takes time-lapse recorded single-particle trajectories as input,
is vastly superior to estimates based on the mean squared displacement as function of time, and is superior to Maximum Likelihood estimation for short trajectories. We extend this estimator to taught fluctuating substrates in a manner that removes the false contribution from substrate motion to the measured diffusion coefficient.
As a pertinent practical illustration of its power, this estimator reveals a two-state kinetics in the diffusion of hOGG1 protein on flow-stretched
DNA, a fluctuating substrate. This kinetics is found in data that previously were analyzed with the mean squared displacement, which revealed only simple diffusion.
Joseph Henry Room · 12:00 p.m.– 1:00 p.m.
High Energy Theory Seminar - IAS - Dieter Luest, Max-Planck-Institute for Physics, Munich - “Closed Strings and Non-Commutative/Non-Associative Ge
In this talk I discuss that non-commutative and non-associative geometry emerges for closed stringsmoving in non-geometric backgrounds. The origin of closed string non-commutativity (non-associativity)is due to new closed string boundary conditions in the presence of non-geometric background fields. We will also discusssome aspects of closed string CFT in non-geometric target spaces.
Bloomberg Lecture Hall · 2:30 p.m.– 4:00 p.m.
|Tuesday, March 12|
High Energy Theory Seminar Informal - IAS - Seok Kim, Seoul National University - “M5-brane Indices from 5d Gauge Theories”
I will talk about the index which counts BPS local operators ofthe 6d (2,0) theory, calculated from gauge theories on the 5-sphere.
Bloomberg Lecture Hall · 1:30 p.m.– 3:00 p.m.
|Wednesday, March 13|
Special Condensed Matter Seminar-Roman Lutchyn, Microsoft Sta. Q, UC, SB - Majorana zero-energy modes in semiconductor/superconductor heterostructures
The exploration of topological phases of matter is one of the main challenges in condensed matter physics. Among the exciting recent developments in this direction are the discoveries of new phases of matter with many intriguing properties, such as topological insulators and superconductors. In this talk, I will focus on topological superconductors, and will discuss how one can engineer non-trivial superconductivity in the laboratory at the interface of an s-wave superconductor and a conventional semiconductor with a strong spin-orbit interaction. I will show that such topological state emerging at the interface hosts quasi-particles (Majoranas) that obey unconventional exchange statistics. Their exotic properties can be exploited for implementing fault-tolerant topological quantum computation schemes that are inherently decoherence-free. I will conclude my talk by reviewing recent experimental efforts in realizing and detecting Majorana zero-energy modes in one-dimensional nanowires.
Jadwin A06 · 1:15 p.m.– 2:30 p.m.
|Thursday, March 14|
PCTS/Condensed Matter Seminar - Salvatore R. Manmana, Goettingen University - Far-from-Equilibrium Quantum Magnetism with Ultracold Polar Molecules
Recent theory has indicated how to emulate tunable models of quantum magnetism with ultracold polar molecules.
Here we show that present molecule optical lattice experiments can accomplish three crucial goals for quantum emulation, despite currently being well below unit filling and not quantum degenerate. The first is to verify and benchmark the models proposed to describe these systems. The second is to prepare correlated and possibly useful states in well-understood regimes.
The third is to explore many-body physics inaccessible to existing theoretical techniques. Our proposal relies on a nonequilibrium protocol that can be viewed either as Ramsey spectroscopy or an interaction quench. The proposal uses only routine experimental tools available in any ultracold molecule experiment. To obtain a global understanding of the behavior, we treat short times pertubatively, develop analytic techniques to treat the Ising interaction limit, and apply a time-dependent density matrix renormalization group to disordered systems with long range interactions.
[PRL 110, 075301 (2013)]
Jadwin A09 · 1:15 p.m.– 2:30 p.m.
Hamilton Colloquium Series - William Young, Scripps Institution of Oceanography, UC, San Diego - "Two Dimensional Turbulence"
In the first part of this talk I will review basic results about two-dimensional turbulence emphasizing the absence of a dissipative anomaly in D=2, and the energy-conserving long-time behavior of solutions of the inviscid equations of motion. Arguments dating back to Onsager predict the formation of an en-semble of vortices separated by potential flow. Close encounters between like-signed vortices lead to irreversible merger into larger vortices. A simple scal-ing argument predicts relations between different quantities, such as the de-cay of the vortex density and the expansion in radius of a typical vortex. In the second part of the talk I will turn to forced two-dimensional turbulence and the problem of vortex condensation into the gravest mode of a finite box. I will show that for most forcing functions the amplitude of the condensate in the inviscid limit is independent of viscosity. This non-singular inviscid limit is compatible with the energy power integral because the flow adjusts so that the work done on the two-dimensional fluid by a prescribed force is linearly proportional to viscosity in the inviscid limit.
Jadwin A10 · 4:30 p.m.– 5:30 p.m.
|Friday, March 15|
Special Condensed Matter Seminar - Ville Lahtinen - Condensate-induced transitions and critical spin chains
We show that the framework of condensate-induced transitions between two-dimensional topological phases can be used to relate one-dimensional spin models at their critical points. To illustrate this, we show that two well-known spin chains, namely the XY chain and the transverse field Ising chain with only next-nearest-neighbor interactions, differ at their critical points only by a non-local boundary term and can be related via an exact mapping. The boundary term constrains the set of possible boundary conditions of the transverse field Ising chain, reducing the number of primary fields in the conformal field theory that describes its critical behavior. We argue that the reduction of the field content is equivalent to the confinement of a set of primary fields, in precise analogy to the confinement of quasiparticles resulting from a condensation of a boson in a topological phase. To provide evidence for the generality of the framework we apply it to the XY chain with only next-nearest-neighbor interactions. In the presence of a confining boundary term, this XY chain can be mapped to a spin chain with the u(1)_2 ×u(1)_2 critical behavior predicted by the condensation framework.
Jadwin A06 · 1:15 p.m.– 2:30 p.m.
HET Seminar - IAS - Yuji Tachikawa, Kavli Institute for the Physcs & Mathematics of the Universe - “Yet Another Dual Description for N=1 SQCD”
Description: N=1 supersymmetric SU(2) gauge theory with 4 flavors has not only the usual Seiberg dual description, but also the Intriligator-Pouliot dual as an Sp(1) gauge theory, and yet another one found by Csaki, Schmaltz, Skiba and Terning (CSST). We show that the dual description of CSST can be generalized to SU(N) gauge theory with 2N flavors, by using non-Lagrangian theories. This talk is based on a collaboration with A. Gadde, K. Maruyoshi and W. Yan.
Bloomberg Lecture Hall · 1:30 p.m.– 3:00 p.m.
|Saturday, March 16|