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Colloquia This Term

ics Colloquium
Friday, January 19, 2018
3:30 PM
Physics Building, Room 204
David Meyer [Host: Olivier Pfister]
University of California at San Diego
"Constraints on multiparticle entanglement"
ABSTRACT:

States of a multiparticle quantum system are useful for quantum information processing when they are entangled, i.e., not product states relative to the tensor product decomposition of the Hilbert space corresponding to the particles.  Arbitrary entanglements between parts of a quantum system are not possible, however; they must satisfy certain “monogamy” constraints which limit how much multiple different subsystems can be entangled with one another.  The standard monogamy constraints can be generalized in several ways:  in this talk we’ll tighten some, generalize others to higher dimensional tensor factors, and derive inequalities satisfied by symmetric sets of entanglement measures.  Along the way we’ll contrast the quantum results with corresponding statements about classical random variables. 

https://math.ucsd.edu/people/profiles/david-meyer/

ics Special Colloquium


Tuesday, January 23, 2018
3:30 PM
Physics Building, Room 204
Note special date.
Jennifer Cano [Host: Israel Klich ]
Princeton University
"Topological Quantum Chemistry"
ABSTRACT:

The past decade's apparent success in predicting and experimentally discovering distinct classes of topological insulators (TIs) and semimetals masks a fundamental shortcoming: out of 200,000 stoichiometric compounds extant in material databases, only several hundred of them are topologically nontrivial. Are TIs that esoteric, or does this reflect a fundamental problem with the current piecemeal approach to finding them? To address this, we propose a new and complete electronic band theory that highlights the link between topology and local chemical bonding, and combines this with the conventional band theory of electrons. We classify the possible band structures for all 230 crystal symmetry groups that arise from local atomic orbitals, and show which are topologically nontrivial. We show how our topological band theory sheds new light on known TIs, and demonstrate the power of our method to predict new TIs.

ics Special Colloquium


Friday, January 26, 2018
3:30 PM
Physics Building, Room 204
Sho Yaida [Host: Israel Klich ]
Duke University
"Imprints of complex landscapes on glassy materials"
ABSTRACT:

Amorphous solids are omnipresent in everyday life, from window glasses to plastics to piles of sand. Yet our understanding of their properties lags far behind that of their crystalline counterparts. Recent advances are rapidly changing the way in which we understand these materials. This talk overviews two such advances: (i) the algorithmic developments that link dramatic slowdown of glass-forming liquids to growing amorphous order, and (ii) the discovery of the critical replica-symmetry-breaking transition within solid glasses. Taken together, these results reinforce the overriding role of rugged free-energy landscapes in controlling glassiness.

ics Special Colloquium


Friday, February 2, 2018
3:30 PM
Physics Building, Room 204
Yuxuan Wang [Host: Israel Klich ]
UIUC
"Topological Superconductivity From Electronic Interactions"
ABSTRACT:

Topological superconductors exhibit exotic Majorana modes at the boundaries and vortices, and can provide important applications in quantum computing. In addition to usual path of “engineering” topological superconductivity with heterostructure of conventional superconductors, we show that intrinsic topological superconductivity can also be naturally realized through electron-electron interactions. Specifically, we analyze the topological superconducting state that emerges near the onset of an inversion-breaking electronic order. Other than topological superconductivity, we show that the system has an enhanced U(1)xU(1) symmetry as well as a rich phase diagram. We address the relevance of our results with recent experiments in Cd2Ce2O7 and half-Heusler superconductors. We argue that important progress can be made at the intersection of topological superconductivity and unconventional superconductivity.

ics Special Colloquium


Monday, February 5, 2018
3:30 PM
Physics Building, Room 204
Note special date.
Peter Maurer [Host: Bob Jones]
Stanford University
"Quantum sensing in a new single-molecule regime"
ABSTRACT:

Quantum optics has had a profound impact on precision measurements, and recently enabled probing various physical quantities, such as magnetic fields and temperature, with nanoscale spatial resolution. Such advancements in ‘quantum sensing’ have brought the elusive dream of performing nuclear magnetic resonance spectroscopy (NMR) on individual biomolecules closer to reality. In my talk, I will discuss the development and application of novel quantum metrological technologies to study biological systems at a single-molecule level. I will start with a general introduction to quantum sensing, with a focus on the measurement of magnetic fields at a nanoscale. I will then show how we utilize such sensing techniques to control the temperature profile in living systems with subcellular resolution. Finally, I will provide an outlook on how quantum sensing and single-molecule biophysics can be utilized to perform NMR spectroscopy with unprecedented sensitivity, possibly down to the level of individual biomolecules.

 

ics Special Colloquium


Wednesday, February 7, 2018
3:30 PM
Physics Building, Room 204
Note special date.
Norbert Linke [Host: Bob Jones]
Joint Quantum Institute, University of Maryland, and NIST
"A programmable quantum computer based on trapped ions"
ABSTRACT:

Quantum computers can solve certain problems more efficiently than any classical computer. Trapped ions are a promising candidate for realizing such a system. We present a modular quantum computing architecture comprised of a chain of 171Yb+ ions with individual Raman beam addressing and individual readout [1]. We use the transverse modes of motion in the chain to produce entangling gates between any qubit pair. This creates a fully connected system which can be configured to run any sequence of single- and two-qubit gates, making it in effect an arbitrarily programmable quantum computer that does not suffer any swap-gate overhead [2].
Recent results from different quantum algorithms on five and seven ions will be presented [3,4], including a quantum error detection protocol that fault-tolerantly encodes a logical qubit [5]. I will also discuss current work and ideas to scale up this architecture.

[1] S. Debnath et al., Nature 563:63 (2016).
[2] NML et al., PNAS 114 13:3305 (2017).
[3] C. Figgatt et al., Nat. Communs. 8, 1918 (2017).
[4] NML et al., arXiv:1712.08581 (2017)
[5] NML et al., Sci. Adv. 3, 10 (2017).


 

ics Special Colloquium


Thursday, February 8, 2018
3:30 PM
Physics Building, Room 204
Note special date.
Thomas Scaffidi [Host: Israel Klich]
University of California, Berkeley
"Electron hydrodynamics in solid-state physics"
ABSTRACT:

Wolfgang Pauli called solid-state physics "the physics of dirt effects", and this name might appear well-deserved at first sight since transport properties are more often than not set by extrinsic properties, like impurities. In this talk, I will present solid-state systems in which electrons behave hydrodynamically, and for which transport properties are instead set by intrinsic properties, like the viscosity. This new regime of transport opens the way for a “viscous electronics”, and provides a new angle to study how quantum mechanics can constrain and/or enrich hydrodynamics.

ics Joint Colloquium with Physics and Astronomy/NRAO


Friday, February 9, 2018
3:30 PM
Physics Building, Room 203
Note special room.
Alexander Ji [Host: Xiaochao Zheng]
Carnegie Observatories
"A Rare and Prolific r-process Event Preserved in an Ultra-Faint Dwarf Galaxy"
ABSTRACT:

The heaviest elements in the periodic table are synthesized through the rapid neutron-capture process (r-process), but the astrophysical site producing these elements has been a long-standing conundrum. Ultra-faint dwarf galaxies contain a simple fossil record of early chemical enrichment that provide an ideal laboratory to investigate the origin of r-process elements. Previous measurements found very low levels of neutron-capture elements in ultra-faint dwarfs, preferring supernovae as the r-process site. I present high-resolution chemical abundances of nine stars in the recently discovered ultra-faint dwarf Reticulum II, which display extremely enhanced r-process abundances 2-3 orders of magnitude higher than the other ultra-faint dwarfs. Stars with such extreme r-process enhancements are only rarely found in the Milky Way halo. The r-process abundances imply that the neutron-capture material in Reticulum II was synthesized in a single prolific event that is incompatible with r-process yields from ordinary core-collapse supernovae but consistent with a neutron star merger. Together with the recent gravitational wave observations of a neutron star merger and its electromagnetic afterglow, it is now clear that neutron star mergers dominate cosmic production of r-process elements.

ics Colloquium
Monday, February 12, 2018
3:30 PM
Physics Building, Room 204
Note special date.
Gia-Wei Chern
UVA-Department of Physics
"Quantum Molecular Dynamics of Strongly Correlated Electron Materials"
ABSTRACT:

I will present a new formulation of quantum molecular dynamics for strongly correlated materials. Our novel scheme enables the study of the dynamical behavior of atoms and molecules with strong electron correlations. In particular, our scheme is based on the efficient Gutzwiller method that goes beyond the conventional mean-field treatment of the intra-atomic electron repulsion and captures crucial correlation effects such as band narrowing and electron localization. We use Gutzwiller quantum molecular dynamics to investigate the Mott metal-insulator transition in the liquid phase of a single-band metal and uncover intriguing structural and transport properties of the atoms. I will also discuss future plans for large-scale dynamical simulations of strongly correlated systems.

ics Special Colloquium


Friday, February 16, 2018
3:30 PM
Physics Building, Room 204
Haitan Xu [Host: Bob Jones]
Yale University
"Topological and nonreciprocal dynamics in an optomechanical system"
ABSTRACT:

Non-Hermitian systems exhibit rich physical phenomena that open the door to qualitatively new forms of control. In this talk, I will introduce our recent work on topological and nonreciprocal dynamics in a non-Hermitian optomechanical system. Specifically, we realized topological energy transfer between nearly degenerate modes by adiabatically encircling an exceptional point (a singularity of the complex spectrum). We also demonstrated that this energy transfer is non-reciprocal: a given topological operation can only transfer energy in one direction. We have extended the topological and nonreciprocal dynamics to highly non-degenerate modes by exploiting a generic form of nonlinearity, which should allow these effects to be exploited in a very wide range of physical systems. In addition, we realized nonreciprocal dynamics by optomechanical interference.

 

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 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.

 

 

ics Special Colloquium


Thursday, March 1, 2018
3:30 PM
Physics Building, Room 204
Note special date.
Dmytro Pesin [Host: Israel Klich ]
University of Utah
"TBA"
ics Colloquium
Friday, March 2, 2018
3:30 PM
Physics Building, Room 204
Peter Schauss [Host: Bob Jones]
Princeton University
"Quantum gas microscopy of many-body dynamics in Fermi-Hubbard and Ising systems"
ABSTRACT:

The ability to probe and manipulate cold atoms in optical lattices at the atomic level using quantum gas microscopes enables quantitative studies of quantum many-body dynamics. While there are many well-developed theoretical tools to study many-body quantum systems in equilibrium, gaining insight into dynamics is challenging with available techniques. Approximate methods need to be benchmarked, creating an urgent need for measurements in experimental model  systems. In this talk, I will discuss two such measurements. First, I will present a study that probes the relaxation of density modulations in the doped Fermi-Hubbard model. This leads to a hydrodynamic description that allows us to determine the conductivity. We observe bad metallic behavior that we compare to predictions from finite-temperature Lanczos calculations and dynamical mean field theory. Second, I introduce a new platform to study the 2D quantum Ising model. Via optical coupling of atoms in an optical lattice to a low-lying Rydberg state, we observe quench dynamics in the resulting Ising model and prepare states with antiferromagnetic correlations.

ics Special Seminar with Q&A Session


Wednesday, March 14, 2018
3:30 PM
Physics Building, Room 204
Note special date.
Dr. Melissa Henriksen [Host: Joe Poon]
Applied Research Institute
"TBA"
ics Joint Colloquium with Physics and Astronomy/NRAO


Friday, March 16, 2018
3:30 PM
Physics Building, Room 203
Note special room.
TBA [Host: Kent Yagi]
ics Colloquium
Friday, March 23, 2018
3:30 PM
Physics Building, Room 204
William Bialek [Host: Marija Vucelja]
Princeton University
"Statistical mechanics for networks of real neurons"
ABSTRACT:

Thoughts, memories, percepts, and actions all result from the interactions among large numbers of neurons.  Physicists have long hoped that these emergent behaviors could be described using ideas from statistical mechanics.  Recent experimental developments have made it possible to monitor, simultaneously, the electrical activity in hundreds or even thousands of cells.  I will describe surprisingly simple statistical physics models that provide a detailed, quantitative account of these data, and then turn to renormalization group ideas that allow us to search explicitly for some underlying simplicity.  There are signs that real networks are described by non-trivial fixed points, setting the stage for more ambitious theorizing.

http://www.princeton.edu/~wbialek/wbialek.html

ics Colloquium
Friday, March 30, 2018
3:30 PM
Physics Building, Room 204
Adam Kaminski [Host: Utpal Chatterjee]
Iowa State and Aims Lab.
"TBA"
ics Joint Colloquium with Physics and Astronomy/NRAO


Friday, April 6, 2018
3:30 PM
Physics Building, Room 203
Note special room.
Nicolas Yunes [Host: Kent Yagi]
Montana State University
"TBA"
ics Colloquium
Friday, April 13, 2018
3:30 PM
Physics Building, Room 204
James Wynd [Host: OSA/SPIE Student Chapter]
University of Arizona
ics Colloquium
Friday, April 20, 2018
3:30 PM
Physics Building, Room 204
Prof. Jean-Marc Lévy-Leblond (Emeritus) [Host: Olivier Pfister]
"Teaching physics as it is done: A plea for qualitative methods "
ABSTRACT:

It is customary for young physicists, when entering their professional career, to be astonished by the huge difference between physics as it is done and physics as it is taught. The purpose is to show that teaching of physics as it is done is indeed possible and should be encouraged, despite the undeniable existence of didactical, epistemological and institutional obstacles. 

 

ics Colloquium
Thursday, April 26, 2018
3:30 PM
Physics Building, Room 204
Note special date.
Kerry Vahala [Host: OSA/SPIE Student Chapter]
Caltech
"TBA"
ics Colloquium
Friday, April 27, 2018
3:30 PM
Physics Building, Room 204
Andre Luiz De Gouvea [Host: P. Q. Hung]
Colloquia and Special Lectures Committee
Cass Sackett (Chair)
Gordon Cates (Member)
Bob Hirosky (Member)
Bob Jones (Member)
Marija Vucelja (Member)
Nilanga Liyanage (Ex-Officio)

To add a speaker, send an email to cas8m@Virginia.EDU Include the seminar type (e.g. Colloquia), date, name of the speaker, title of talk, and an abstract (if available). [Please send a copy of the email to phys-speakers@Virginia.EDU.]