Seminars And Colloquia This Week

ics Special Colloquium


Monday, February 19, 2018
3:30 PM
Physics Building, Room 204
Note special date.
Wade Hsu [Host: Bob Jones]
Yale University
"New Frontiers of Electromagnetic Phenomena at the Nanoscale"
ABSTRACT:

Optics and photonics today enjoy unprecedented freedom. The ability to synthesize arbitrary light fields (through wavefront shaping) and the ability to design structures at the subwavelength scale (through nanofabrication) enable us to realize phenomena that could only be imagined in the past. In this talk, I will present several experiments and related theory that demonstrate exciting new phenomena which were previously inaccessible. A) Conventional textbook wisdom is that waves cannot be perfectly confined within the continuum spectrum of an open systems. Exceptions called “bound states in the continuum” were hypothesized by von Neumann and Wigner [1] but not realized. I will describe the first realization of such unusual states [2] and their manifestation as polarization vortices protected by topologically conserved “charges” [3]. B) Our ability to control radiation also enables the realization of non-Hermitian phenomena with no counterpart in closed systems. I will show how non-Hermiticity generates unique topologies in photonic band structures and lead to enhanced lightmatter interactions [4,5]. C) Strong disorder in naturally occurring light-scattering media allows us to study mesoscopic physics in a new arena. I will describe the control of optical transport via wavefront shaping, and how the long-range correlations between multiply scattered photons enable us to simultaneously control orders of magnitudes more degrees of freedom than previously thought possible [6,7].

 

[1] C. W. Hsu*, B. Zhen* et al., Nature Reviews Materials 1, 16048 (2016).

[2] C. W. Hsu*, B. Zhen* et al., Nature 499, 188 (2013).

[3] B. Zhen*, C. W. Hsu* et al., Phys. Rev. Lett. 113, 257401 (2014).

[4] B. Zhen*, C. W. Hsu* et al., Nature 525, 354 (2015).

[5] H. Zhou et al., Science, eaap9859 (2018).

[6] C. W. Hsu et al., Phys. Rev. Lett. 115, 223901 (2015).

[7] C. W. Hsu et al., Nature Physics 13, 497 (2017).

ics Nuclear
Tuesday, February 20, 2018
3:30 PM
Physics Building, Room 204

"Available"
ics Joint HEP-Nuclear Seminar


Wednesday, February 21, 2018
3:30 PM
Physics Building, Room 204
Dmitri Denisov [Host: Bob Hirosky]
Fermilab
"Particle Colliders: Past, Present and Future "
ABSTRACT:

Developments of the particle colliders over last 50 years have seen tremendous progress in both the energy of the collisions and the intensity of the colliding beams. In order to reach even higher collision energy many fundamental inventions in the colliders design have been achieved. Progress to even higher energies was strongly stimulated by physics interests in studying smaller and smaller distances and in creation of heavier and heavier elementary particles. Experiments at colliders required major breakthroughs in the particle detection methods in order to discover new particles such as c and t quarks, gluons, tau lepton, W, Z and Higgs bosons which completed currently expected set of elementary particles. Options for even higher energy colliders will be discussed, including their design parameters, acceleration principles as well as construction challenges. Such colliders are the only way to understand Nature at even smaller distances and create particles with higher masses than we can reach today.

 

ics Special Colloquium


Friday, February 23, 2018
3:30 PM
Physics Building, Room 204
Brian DeSalvo [Host: Bob Jones]
University of Chicago
"Quantum Mixology: Creating Novel Interacting Bose-Fermi Mixtures with Cs and Li"
ABSTRACT:

A gas of atoms cooled to sufficiently low temperature will form either a Bose-Einstein condensate (BEC) or a degenerate Fermi gas (DFG) depending on the quantum statistics of the constituent particles. But what happens when you combine a BEC and a DFG in an optical trap and add a healthy dose of interspecies interactions? Mean-field theory predicts three possible outcomes: a miscible mixture for weak interactions, complete demixing for strong repulsive interactions, or a spectacular collapse due to the loss of mechanical stability for strong attractive interactions. In this talk, I will discuss our efforts to answer this question experimentally in the specific case where the bosons are much heavier than the fermions. To this end, we have created the first quantum degenerate mixture of bosonic 133Cs and fermionic 6Li and used an interspecies Feshbach resonance to tune the interactions between the bosons and fermions. For attractive interspecies interactions, we find two surprising results. First,  we show that a degenerate Fermi gas of Li can be trapped by a Cs BEC, even in the absence of external potentials. Second, for strong attractive interactions where collapse is predicted, we observe no such instability. I will discuss the mechanisms at play to explain these results and comment on current and future studies delving deeper into these unexpected regimes.

 

 

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