Home Graduate Center CUNYfirst Bb MyQC Queens College

Colloquia

Sign up to receive notifications about colloquia:
“ If I were again beginning my studies, I would follow the advice of Plato and start with mathematics. ”
- Galileo Galilei
iCal feed feed Help icon
iCalendar (*.ics extension) is a popular file format used to distribute calendar information between different applications over the internet.

Once you click the iCal feed link with the right button, copy the link URL and paste it into any calendar app that takes iCal feeds (Google Calendar, Outlook, etc).

Left click on a single event downloads the *.ics file with selected event, but it will not allow calendar apps to update automatically their calendar with other or upcoming events.

How to use feed with:
Google Calendar
Microsoft Outlook
Mozilla Thunderbird
Physics Conference Room, SB B326
Coffee starts at 12:00 PM and talk starts at 12:15 PM
25
Jul '18
Sylvain Gigan  -  Wednesday, July 25, 2018
Optical wave propagation in complex media: from pulse shaping to an invariance of the path length
Sorbonne Université Kastler-Brossel Laboratory, Collège de France
ABSTRACT: Scattering of light in heterogeneous media, for instance the skin or a glass of milk, is usually considered an inevitable perturbation or even a nuisance. Through repeated scattering and interferences, this phenomenon seemingly destroys both the spatial and the phase information of any laser illumination. At the spatial level, it gives rise to the well-known “speckle” interference patterns. At the temporal (or spectral) level, a short pulse entering a scattering medium will see its length greatly extended due to the multiplicity of possible path length light can take before exiting the medium. From an operative point of view, scattering greatly limits the possibility to image or manipulate an object with light through or in a scattering medium. Multiple scattering is nonetheless an invaluable field of research for experimentalists and theoreticians alike, at the crossing of optics, condensed matter physics, statistical physics, chaos, to name just a few. 

Multiple scattering is a highly complex but nonetheless deterministic process: it is therefore reversible, in the absence of absorption. Speckle is coherent, and can be coherently controlled. By « shaping » or « adapting » the incident light, it is in principle possible to control the propagation and overcome the scattering process. I will show our recent results on achieving a complete pulse control (spatial and temporal) by means of wavefront shaping. I will also show the experimental demonstration of a peculiar property of light in disorder, namely that the mean path length is independent of the disorder strength. 
31
Aug '18
Silas Hoffman  -  Friday, August 31, 2018
ABSTRACT: Spin superfluids enable long-distance spin transport through classical ferromagnets by developing topologically protected defects in the magnetic texture. For small spins, in which the magnetization takes quantized values, the topological protection suffers from strong quantum fluctuations. We study the remanence of spin superfluidity inherited from the classical magnet by considering the two-terminal spin transport through a finite spin-1/2 ferromagnetic chain with planar exchange. In the absence of anisotropy in the exchange or an applied magnetic field, the spectrum is gapless. There exist zero-energy domain-wall modes that rotate within the plane of the exchange interaction and are the analogue of the topological defects found in classical magnets. If the system is ordered by an exchange anisotropy, the spectrum is gapped and there exist zero-energy modes localized to the ends of the ferromagnetic chain which are guaranteed by topological properties of the bulk spectrum. We find zero-energy domain-walls, polarized perpendicular to the anisotropy, incident on an ordered chain are reflected as domain-walls polarized in the opposite direction. Furthermore, a domain-wall polarized within the plane of the exchange can be ballistically transmitted through the same magnetic chain of a resonant length. This resonant length depends linearly on the applied magnetic field so that, for a fixed length of chain, the transmission of domain-walls can be tuned by the magnetic field.
17
Sep '18
Misha Sumetsky  -  Monday, September 17, 2018
Localization of light in an optical microcapillary induced by a droplet
Aston University, Institute of Photonic Technologies
ABSTRACT: We show experimentally and theoretically that whispering gallery modes in a silica microcapillary can be fully localized (rather than perturbed) by evanescent coupling to a water droplet and, thus, form a high-quality-factor microresonator. The spectra of this resonator, measured with a microfiber translated along the capillary, present a hierarchy of resonances that allow us to determine the size of the droplet and variation of its length due to the evaporation. The discovered phenomenon of complete localization of light in liquid-filled optical microcapillaries suggests a new type of microfluidic photonic device as well as an ultraprecise method for microfluidic characterization.
24
Sep '18
Alex Krasnok  -  Monday, September 24, 2018
Novel aspects of light scattering
Advance Science Research Center and Graduate Center, CUNY
ABSTRACT: Scattering of electromagnetic waves lies in the heart of the most experimental techniques in radiophysics, visible and X-ray optics that allow us to investigate the micro- and nanoworld. Recently, a wide spectrum of exceptional scattering effects attainable in carefully engineered structures have been predicted and demonstrated. In my talk, I will present our recent results on novel aspects of light scattering including coherent virtual absorption, coherently enhanced WPT, and strong coupling regime in excitonic systems.
15
Oct '18
Larry Liebovitch  -  Monday, October 15, 2018
22
Oct '18
Miriam Rafailovich  -  Monday, October 22, 2018
5
Nov '18
Andrea Alù  -  Monday, November 5, 2018
New frontiers for light control and manipulation using metamaterials
Advanced Science Research Center and Graduate Center, CUNY
ABSTRACT: Metamaterials are artificial materials with properties well beyond what offered by nature, providing unprecedented opportunities to tailor and enhance the interaction between waves with materials. In this talk, I discuss our recent research activity in electromagnetics, nano-optics and acoustics, showing how suitably tailored meta-atoms and arrangements of them open exciting venues to manipulate and control waves in unprecedented ways. I will discuss our recent theoretical and experimental results, including metamaterials for scattering suppression, metasurfaces to control wave propagation and radiation, large nonreciprocity without magnetic bias, giant nonlinearities in properly tailored metamaterials and metasurfaces, and active metamaterials. Physical insights into these exotic phenomena, new devices based on these concepts, and their impact on technology will be discussed during the talk.
12
Nov '18
Nikodem Poplawski  -  Monday, November 12, 2018
ABSTRACT: The conservation law for the total (orbital plus spin) angular momentum of a Dirac particle in the presence of gravity requires that spacetime is not only curved, but also has a nonzero torsion. The coupling between the spin and torsion in the Einstein–Cartan theory of gravity generates gravitational repulsion at extremely high densities, which prevents a singularity in a black hole and may create there a new, closed, baby universe undergoing one or more nonsingular bounces. We show that quantum particle production caused by an extremely high curvature near a bounce creates enormous amounts of matter and can generate a finite period of inflation. Our scenario has only one parameter, does not depend significantly on the initial conditions, does not involve hypothetical scalar fields, avoids eternal inflation, and predicts plateau-like inflation that is supported by the Planck observations of the cosmic microwave background. This scenario suggests that our Universe may have originated from a black hole existing in another universe.
26
Nov '18
Ivan Corwin  -  Monday, November 26, 2018
A drunk walk in a drunk world
Columbia University
ABSTRACT: We will consider the effect of a space-time random environment of jumping probabilities on a collection of independent random walkers. Surprisingly, the extreme value behavior for these walkers is governed by the Kardar-Parisi-Zhang universality class which arises in random growth models and random matrix theory. No background of any of these subjects will be assumed.
3
Dec '18
Demetrios Christodoulides  -  Monday, December 3, 2018
Thermodynamics of nonlinear multimode fibers
University of Central Florida, CREOL
10
Dec '18
Eleana Makri  -  Monday, December 10, 2018
ABSTRACT: Photonic limiters are protection devices which transmit electromagnetic radiation at low-level incident intensity while blocking high-intensity electromagnetic signals. Passive limiters typically block excessive radiation by means of absorption, which can often cause their destruction due to overheating. We propose the design of a reflective limiter based on resonant transmission through a defect localized mode. The benefit of this design is that it offers protection by reflecting the excessive radiation instead of absorbing it, which reduces overheating problems and results in a device with an extended dynamic range. In this talk, I will present implementations of this idea in band-gap systems in (i) the infrared domain, based on multilayer photonic crystals, and (ii) the microwave domain, based on chiral or CT symmetric coupled resonator waveguide arrays.