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Colloquia This Term

ics Colloquium
Friday, August 25, 2017
3:30 PM
Physics Building, Room 204

"Available"
ics Special Physics Forum for Faculty, Students, and Staff


Friday, September 1, 2017
3:30 PM
Physics Building, Room 203
Note special room.
Physics Forum
ics Colloquium
Friday, September 8, 2017
3:30 PM
Physics Building, Room 204
Tianran Chen [Host: Seunghun Lee]
UVA-Physics
"Origin of Long Lifetime of Band-Edge Charge Carriers in Organic-Inorganic Lead Iodide Perovskites"
ABSTRACT:

Long carrier lifetime is what makes hybrid organic-inorganic perovskites high performance photovoltaic materials. Several microscopic mechanisms behind the unusually long carrier lifetime have been proposed, such as formation of large polarons, Rashba effect, ferroelectric domains, and photon recycling. Here, we show that the screening of band-edge charge carriers by rotation of organic cation molecules can be a major contribution to the prolonged carrier lifetime. Our results reveal that the band-edge carrier lifetime increases when the system enters from a phase with lower rotational entropy to another phase with higher entropy. These results imply that the recombination of the photo-excited electrons and holes is suppressed by the screening, leading to the formation of polarons and thereby extending the lifetime. Thus, searching for organic-inorganic perovskites with high rotational entropy over a wide range of temperature may be a key to achieve superior solar cell performance.

ics Colloquium
Friday, September 15, 2017
3:30 PM
Physics Building, Room 204
Cass Sackett [Host: Joe Poon]
UVA-Physics
"Tune-out wavelength spectroscopy: a new technique to characterize atomic structure"
 
 Slideshow (PDF)
ABSTRACT:

When you shine a laser on an atom, the electric field of the light induces a dipole moment, resulting in an energy shift. The dipole can be either parallel or anti-parallel to the field, depending on the frequency of the light. This corresponds to negative or positive energies. At certain frequencies, however, the induced dipole is zero. The corresponding light wavelength is called a tune-out wavelength. The location of the various tune-out wavelengths depend on the electronic wave function in the atom, particularly the dipole matrix elements . So by measuring the tune-out wavelength, the dipole matrix elements can be determined more accurately than by conventional techniques. This is useful because the dipole matrix elements are also used to relate precision atomic experiments like parity violation to fundamental particle properties like the weak mixing angle. We have developed a new technique for measuring  tune-out wavelengths, which should improve our knowledge of many matrix elements by an order of magnitude or more. We hope that this will support new generations of precision atomic measurements.

SLIDESHOW:
ics Special Colloquium and Hoxton Lecture


Thursday, September 21, 2017
7:00 PM
Chemistry Building, Room 402
Note special date.
Note special time.
Note special room.
Nergis Mavalvala
M.I.T.
"The Warped Universe: the one hundred year quest to discover Einstein’s gravitational waves"
ABSTRACT:

In 2016, scientists announced the first ever detection of gravitational waves from colliding black holes, launching a new era of gravitational wave astrophysics. Gravitational waves were predicted by Einstein a hundred years earlier. I will describe the science, technology, and human story behind these discoveries that provide a window into some of the most violent and warped events in the Universe.

 

ics Colloquium
Friday, September 22, 2017
3:30 PM
Physics Building, Room 204
Nergis Mavalvala [Host: Cass Sackett]
M.I.T.
"Future directions in gravitational-wave detection"
ABSTRACT:

The Laser Interferometer Gravitational-wave Observatory (LIGO) detected gravitational waves for the first time in 2015. Since then there have been a couple more detections of binary black hole mergers. I will discuss the instruments that made these discoveries, the science so far, and plans for future improvements and upgrades to LIGO. 

VIDEO:
ics Colloquium
Friday, September 29, 2017
3:30 PM
Physics Building, Room 204
Xiaochao Zheng [Host: Joe Poon]
UVA-Physics
"Peeling the Atomic Onion"
ABSTRACT:

The word "atom" (a-tomos) originates from ancient Greek philosophers, who argued that objects can be eventually divided into discrete, small particles, beyond which matter is no longer cuttable.  Our search for the answer to "What the matter is made of" has gone a long way, from the first experimental evidence of atoms in the 1800's, to Rutherford's alpha scattering on gold foils, to modern day's linear accelerators looking into the atomic nucleus. We now understand that matter is made of quarks and leptons, currently named elementary particles (objects of no size) that form the foundation of the Standard Model of Particle Physics. However, if we look back at this journey, one may wish to oppose the view of the ancient Greeks and argue that quarks and leptons cannot be the end of the story, that our quest for peeling the atomic onion may be a timeless journey.

I will discuss the frontier research in electron scattering at the GeV energy level. I will focus on parity violation in electron scattering off the proton and the neutron and the extraction of neutral-weak effective couplings between electrons and quarks, and show how such high precision measurements are now helping us venturing further into the study of subatomic structure. 

ics Colloquium
Friday, October 6, 2017
3:30 PM
Physics Building, Room 204
Kent Paschke [Host: Joe Poon]
UVA-Physics
"Looking for New Physics with the Weak Interaction in Electron Scattering: Recent Results from Qweak and Future Perspectives"
ABSTRACT:

The measurement of the violation of parity symmetry in electron scattering has proven to be a powerful technique for exploring nuclear matter and searching for new fundamental forces. In the Standard Model of particle physics, parity violation can only occur through the weak interaction. Precision measurements of this symmetry breaking can test the completeness of this description of the weak force at low energies. I will describe the result of one such measurement - the recently completed Qweak experiment - along with the experimental challenges and triumphs.  Future measurements in the field of parity-violating electron scattering will also be reviewed, including other Standard Model tests and experiments using the weak force to determine the size of a heavy atomic nucleus.

ics Colloquium
Friday, October 13, 2017
3:30 PM
Physics Building, Room 204
Prem Kumar [Host: Olivier Pfister]
Northwestern University
"All-optical Switching for Photonic Quantum Networks"
ABSTRACT:

Quantum internet of the future will require device functionalities that implicitly respect the fundamental facts such as quantum information cannot be copied, and cannot be measured precisely. A quantum repeater, for example,—analog of an optical amplifier that enabled global reach of the ubiquitous Internet connectivity we enjoy today—is yet to be demonstrated, although recent years have seen tremendous progress. Many other device functionalities—switches, routers, format converters, etc.—would also be needed that do not unnecessarily disturb or corrupt the quantum information as it flows from one node of the internet to another. In recent years, my group has engineered an all-optical quantum switch that fulfills many of the requirements for distributing quantum information in a networked environment. In this talk, I will present our motivation, design, construction, characterization, and utilization of such a switch in near-term networked quantum applications.

ics Colloquium
Friday, October 20, 2017
3:30 PM
Physics Building, Room 204
Simonetta Liuti [Host: Joe Poon]
UVA-Physics
"Tomography of the Atomic Nucleus"
ABSTRACT:

The history of our exploration of subatomic matter has witnessed a major breakthrough with every new probe being introduced. In the 1950’s Hofstadter and collaborators using elastic electron scattering measured for the first time the electromagnetic form factors of nucleons and nuclei and provided the first information on the nuclear spatial charge and magnetization distributions. In the late 1960’s and early 70’s, Friedman, Kendall and Taylor using Deep Inelastic Scattering of electrons off the nucleon, discovered its underlying quark structure displayed in their longitudinal momentum distributions. 

I will discuss probes at the next frontier that will allow us to access dynamically correlated distributions in both momentum and coordinate space -- the Wigner distributions -- at the femtoscale. Deeply Virtual Compton Scattering, namely a high energy lepton scattering off a nucleon target producing a high energy real photon and a small angle recoil proton, is one of such probes. I will explain how a detailed mapping of the quarks and gluons in the nucleon and nucleus in phase space, or a phase-space tomography, besides providing for the first time images of quarks and gluons spatial distributions, is essential for understanding the so far elusive nucleon mass and spin decompositions in terms of its quark and gluon components. 

ics Colloquium
Friday, October 27, 2017
3:30 PM
Physics Building, Room 204
Avi Pe'er [Host: OSA/SPIE Student Chapter]
Bar Ilan University
"Lifting the Bandwidth Limit of Optical Homodyne Measurement - A Key for Broadband Quantum Information"
ABSTRACT:

Homodyne measurement is a corner-stone of quantum optics. It measures the fundamental variables of quantum electrodynamics - the quadratures of light, which represent the cosine-wave and sine-wave components of an optical field. The quadratures constitute the quantum optical analog of position and momentum in mechanics and obey quantum uncertainty, indicating the inherent inability to measure both simultaneously. The homodyne process, which extracts a chosen quadrature amplitude by correlating the optical field against an external quadrature reference (local-oscillator, LO), forms the backbone of coherent detection in physics and engineering, and plays a central role in quantum information processing. Homodyne can reveal non-classical phenomena, such as squeezing of the quadrature uncertainty; It is used in tomography to fully characterize quantum states of light; Homodyne detection can generate non-classical states, provide local measurements for teleportation and serve as a major detector for quantum key distribution (QKD) and quantum computing. Yet, standard homodyne suffers from a severe bandwidth limitation. While the bandwidth of optical states can easily span many THz, standard homodyne detection is inherently limited to the electrically accessible, MHz to GHz range, leaving a dramatic gap between the relevant optical phenomena and the measurement capability. This gap impedes effective utilization of the huge bandwidth resource of optical states and the potential enhancement of the information throughput \emph{by several orders of magnitude} with parallel processing in quantum computation, QKD and other applications of quantum squeezed light. Here we demonstrate a fully parallel optical homodyne measurement across an arbitrary optical bandwidth, effectively lifting the bandwidth limitation completely. Using optical parametric amplification, which amplifies one quadrature while attenuating the other, we measure two-mode quadrature squeezing of 1.7dB below the vacuum level simultaneously across a bandwidth of 55THz using a single LO - the pump. This broadband parametric homodyne measurement opens a wide window for parallel processing of quantum information.

Yaakobv Shaked, Yoad Michael, Rafi Vered, Leon Bello, Michael Rosenbluh and Avi Pe'er, Physics Dept. and BINA center for  Nanotechnology, Bar Ilan University, Ramat Gan 5290002, Israel

ics Colloquium
Friday, November 3, 2017
3:30 PM
Physics Building, Room 204
Ted Hodapp [Host: Olivier Pfister]
APS Bridge Program
"APS Bridge Program: Changing the Face of Physics Graduate Education"
ABSTRACT:

In nearly every science, math, and engineering field there is a significant falloff in participation by underrepresented minority (URM) students who fail to make the transition between undergraduate and graduate studies.  The American Physical Society (APS) has realized that a professional society can erase this gap by acting as a national recruiter of URM physics students and connecting these individuals with graduate programs that are eager to a) attract motivated students to their program, b) increase domestic student participation, and c) improve the diversity of their program.  Now in its fifth year the APS has placed enough students into graduate programs nationwide to eliminate this achievement gap.  The program has low costs, is popular among graduate programs, and has inspired other departments to adopt practices that improve graduate admissions and student retention. This presentation will review project activities, present data that demonstrate effectiveness, and discuss future actions.

This material is based upon work supported in part by the National Science Foundation under Grant No. (NSF-1143070).

ics Colloquium
Friday, November 10, 2017
3:30 PM
Physics Building, Room 204
Vladimir Dobrosavljevic [Host: Gia-Wei Chern]
Florida State University
"Bad Metal Behavior and Mott Quantum Criticality"
ABSTRACT:

According to early ideas of Mott and Anderson, the interaction-­â€driven metal-­â€ insulator transition – the Mott transition – remains a sharp T=0 phase transition even in absence of any spin or charge ordering.  Should this phase transition be regarded as a quantum critical point?  To address this question, here we examine the phase diagram and transport properties of the maximally frustrated half-­â€filled Hubbard model, in the framework of dynamical mean-­â€field theory (DMFT).  We identify a “quantum Widom line” (QWL) which defines the center of the corresponding quantum critical region associated with Mott metale insulator transition for this model.  The evolution of resistivity with temperature is then evaluated along trajectories following (parallel to) the QWL, displaying remarkable scaling behavior characteristic of quantum criticality.  Precisely this kind of behavior was found in very recent experiments on organic Mott systems [1,2].  In the case of the doping-driven Mott transition, we show that the mysterious “Bad Metal” behavior (T-linear resistivity around the Mott-Ioffee- Regel limit) coincides with the Quantum Critical region of the Mott transition.

 

[1] Quantum criticality of Mott transition in organic materials, Tetsuya Furukawa, Kazuya Miyagawa, Hiromi Taniguchi, Reizo Kato & Kazushi Kanoda, Nature Physics, 9 Feb.  2015; doi:10.1038/nphys3235.

[2] See also:

http://condensedconcepts.blogspot.com/2015/03/quantum-criticality-near-mott.html

ics Colloquium
Friday, November 17, 2017
3:30 PM
Physics Building, Room 204
Patrick Charbonneau [Host: Marija Vucelja]
Duke University
"Recent Advances on the Glass Problem"
ABSTRACT:

Recent theoretical advances in the mean-field theory of glasses predict the existence, deep in the glass phase, of a novel phase transition, a so-called Gardner transition. This transition signals the emergence of a complex free energy landscape composed of a marginally stable hierarchy of sub-basins. It is also thought to be the onset of the anomalous thermal and transport properties of amorphous systems, and to ultimately lead to the unusual critical behavior at jamming. In this talk, I will present an overview of our recent theoretical and numerical advances in capturing and characterizing this novel materials feature.

ics Colloquium
Friday, December 1, 2017
3:30 PM
Physics Building, Room 204
Xiaoliang Qi [Host: Israel Klich ]
Stanford University
"TBA"
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.]