Colloquia

Click on the following link to attend the online colloquium:
https://web.phys.virginia.edu/Private/Covid-19/colloquium.asp

Friday, February 12, 2021
2:00 PM
Online, Room via Zoom
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"Complexity of magnetic patterns and self-induced spin-glass state"


Prof. Mikhail Katsnelson , Radboud University of Nijmegen, The Netherlands,
[Host: Dima Pesin]
ABSTRACT:

The origin of complexity remains one of the most important and, at the same time, the most controversial scientific problems. Earlier attempts were based on theory of dynamical systems but did not lead to a satisfactory solution of the problem. I believe that a deeper understanding is possible based on a recent development of statistical physics, combining it with relevant ideas from evolutionary biology and machine learning.

Using patterns in magnetic materials as the main example, I discuss some general problems such as (a) a formal definition of pattern complexity [1]; (b) self-induced spin glassiness due to competing interactions as a way to interpret chaotic patterns [2]; (c) multi-well states intermediate between glasses and ordinary ordered states and their relevance for the problem of long-term memory in complicated systems [3]; and (d) complexity of frustrated quantum spin systems [4]. I will also review a very recent experimental observation of self-induced spin-glass state in elemental neodymium [5].

[1] A. A. Bagrov, I. A. Iakovlev, A. A. Iliasov, M. I. Katsnelson, and V. V. Mazurenko, Multi-scale structural complexity of natural patterns, PNAS 117, 30241 (2020).
[2] A. Principi and M. I. Katsnelson, Spin glasses in ferromagnetic thin films, Phys. Rev. B 93, 054410 (2016); Self-induced glassiness and pattern formation in spin systems due to long-range interactions, Phys. Rev. Lett. 117, 137201 (2016).
[3] A. Kolmus, M. I. Katsnelson, A. A. Khajetoorians, and H. J. Kappen, Atom-by-atom construction of attractors in a tunable finite size spin array, New J. Phys. 22, 023038 (2020).
[4] T. Westerhout, N. Astrakhantsev, K. S. Tikhonov, M. I. Katsnelson, and A. A. Bagrov, Generalization properties of neural network approximations to frustrated magnet ground states, Nature Commun. 11, 1 (2020).
[5] U. Kamber et al, Self-induced spin glass state in elemental and crystalline neodymium, Science 368, eaay6757 (2020).
VIDEO:
Click on the following link to attend the online colloquium:
https://web.phys.virginia.edu/Private/Covid-19/colloquium.asp

Friday, February 5, 2021
3:30 PM
Physics Building, Room via Zoom
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"A fermionic triangular-lattice quantum gas microscope "


Peter Schauss , University of Virginia - Physics Dept.
[Host: Bob Jones]
ABSTRACT:

Geometrically frustrated many-body systems show many interesting emerging phenomena, ranging from kinetic frustration to exotic spin ordering and chiral spin liquid phases. Ultracold atom systems offer great tunability and flexibility to realize such systems in a wide parameter range of interactions, densities, and spin-imbalance.

In this talk, I will present our recent results on site-resolved imaging of ultracold fermionic lithium atoms on a triangular optical lattice.

Degenerate Fermi gases with about one tenth of the Fermi temperature have been realized within a crossed dipole trap and successfully loaded into a two-dimensional triangular optical lattice. To characterize this lattice, we observed Kapitza-Dirac scattering using a molecular Bose-Einstein condensate. Collecting the emitted photons during Raman sideband cooling in the triangular lattice using a high-resolution microscope objective enabled the high-fidelity imaging of individual fermionic atoms in the lattice with single-site resolution.

The next step will be the realization of a triangular lattice Hubbard model by implementing an additional optical lattice to increase interactions.

This novel experimental platform will allow us to study spin and density correlations in the triangular Hubbard model to explore signatures of frustration and spin-hole bound states and may lead to a direct observation of non-vanishing chiral correlations.

VIDEO:
Click on the following link to attend the online colloquium:
https://web.phys.virginia.edu/Private/Covid-19/colloquium.asp

Friday, October 23, 2020
3:30 PM
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"Bosonic Quantum Information Processing with Superconducting Circuits"


Professor Liang Jiang , Pritzker School of Molecular Engineering, University of Chicago
[Host: Olivier Pfister]
ABSTRACT:

Bosonic modes are widely used for quantum communication and information processing. Recent developments in superconducting circuits enable us to control bosonic microwave cavity modes and implement arbitrary operations allowed by quantum mechanics, such as quantum error correction against excitation loss errors. We investigate different bosonic encoding and error correction protocols, and provide a perspective on using bosonic quantum error correction for various applications.

VIDEO:
Click on the following link to attend the online colloquium:
https://web.phys.virginia.edu/Private/Covid-19/colloquium.asp

Friday, October 2, 2020
3:30 PM
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"Isolated Superfluid Liquid Helium Drops in a Magneto-Gravitational Trap"


Dr. Charles Brown II , University of California, Berkeley
[Host: Bellave Shivaram]
ABSTRACT:

The unique properties of superfluid 4He (low mechanical stiffness, zero viscosity, high structural and chemical purity and extremely low optical loss) may allow the direct pursuit of optomechanics with quantum mechanical oscillators. We have constructed an optomechanical system consisting entirely of a magnetically levitated drop of superfluid 4He in vacuum. Levitation removes a source of loss associated with physically clamped oscillators. and allows the drop to efficiently cool itself via evaporation. The drop’s optical whispering gallery modes (WGMs) and its surface vibrations couple to each other via the usual optomechanical interactions. We demonstrate the stable magnetic levitation of superfluid 4He drops in vacuum, and present measurements of the drops' evaporation rates, temperatures, optical modes and surface vibrations. We found optical modes with finesse ≈40 (limited by the drop's size). We found surface vibrations with decay rates 1 Hz (in rough agreement with theory). Lastly, we found that the drops reach a temperature T≈330 mK, and that a single drop can be trapped indefinitely.

VIDEO:
Click on the following link to attend the online colloquium:
https://web.phys.virginia.edu/Private/Covid-19/colloquium.asp

Friday, September 25, 2020
3:30 PM
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"Finding Needles in an Avalanche of Haystacks: The New Precision Timing Detector for CMS "


Chris Neu , University of Virginia - Department of Physics
[Host: Bob Jones]
ABSTRACT:

The full potential of the Large Hadron Collider will ultimately be realized through the running period that will take collider operations into the late 2030s. The so-called High Luminosity era of the LHC (HL-LHC), planned to begin in 2027, will see up to a 5-fold increase in the nominal brightness of the LHC beams, which will consequently allow experiments to collect a data set of proton-proton collisions approximately 20 times larger than what has been collected so far in high-energy LHC running. This significant increase in data sample will be a boon for the physics program of the LHC experiments, furthering searches for ultra-rare phenomena and refining precision measurements of known processes. At the CMS experiment, a suite of novel upgrades will be deployed that will enable the experiment to cope with the onslaught of collisions in the high luminosity environment and fully capitalize on the opportunities presented in the HL-LHC era. In this talk I will focus on the MIP Timing Detector (MTD), a device capable of measuring the time-of-arrival for minimum-ionizing particles (MIPs) produced within CMS with a resolution of 30 picoseconds. This entirely new detector system will be built in part at UVA before being shipped to CERN and integrated with the CMS experiment. I will describe the principle of operation of the MTD, the current status of the project and UVA's role in the construction of the device. I will also discuss the expected impact the MTD will have on several high-profile physics signatures that are prime targets in the HL-LHC era and, in particular, the power of using timing information in the reconstruction of exotic long-lived particle decays. 

VIDEO:
Click on the following link to attend the online colloquium:
https://web.phys.virginia.edu/Private/Covid-19/colloquium.asp

Friday, September 18, 2020
3:30 PM
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"Multiscale modeling of metal-insulator transition in correlated electron systems"


Gia-Wei Chern , University of Virginia - Department of Physics
[Host: Bob Jones]
ABSTRACT:

In this talk, I will present our recent efforts on dynamical simulations of correlated electron systems. I will first discuss new quantum molecular dynamics (QMD) methods based on advanced many-body techniques, such as Gutzwiller/slave-boson and dynamical mean-field theory, that are capable of modeling strong electron correlation phenomena. We apply our new QMD to simulate the correlation-induced Mott transition in a metallic liquid, and the nucleation-and-growth of Mott droplets in Hubbard-type models. I will also discuss the implementation of the ab initio Gutzwiller MD for simulating hydrogen liquids under high pressure. To overcome the obstacle of huge computational complexity in such large-scale simulations, I will discuss how simulation efficiency can be significantly improved with the aid of modern machine learning methods. In particular, deep-learning neural-network holds the potential of achieving large-scale quantum-accuracy simulation of correlated systems without the electrons.

VIDEO:
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https://virginia.zoom.us/j/99745389785

Meeting ID: 997 4538 9785 Passcode: 540373


Friday, September 4, 2020
3:30 PM
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"Programmable Quantum Simulation with Superconducting Qubits and Microwave Photons "


Professor Steven M. Girvin , Department of Physics and Yale Quantum Institute Yale University
[Host: Olivier Pfister and Israel Klich]
ABSTRACT:

‘Circuit QED’ is the quantum theory of superconducting qubits strongly interacting with microwave photons in electrical circuits. It is the leading solid-state architecture in the race to develop large-scale fault-tolerant quantum computers, and is the only technology that has demonstrated quantum error correction that actually extends the lifetime of quantum information. 

In this talk, I will present an elementary introduction to the basic concepts underlying superconducting quantum processors. Their ability to control and make quantum non-demolition (QND) measurements of individual microwave photons is a powerful resource for quantum computation, communication and simulation.   I will illustrate these capabilities with recent experiments on a programmable quantum simulator that uses efficient boson sampling of microwave photons to predict the Franck-Condon vibrational spectra of various small tri-atomic molecules.  Finally, I will briefly explore possible future directions for simulation of quantum many-body problems involving interacting bosons.

 

VIDEO:
Special Colloquium


Monday, February 24, 2020
3:30 PM
Physics Building, Room 203
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"Integrated x(2) photonics"


Professor Hong Tang , Department of Electrical Engineering, Yale University
[Host: UVA Student Chapter of OSA/SPIE]
ABSTRACT:

The ability to generate and manipulate photons with high efficiency and coherence is of critical importance for both fundamental quantum optics studies and practical device applications. However mainstream integrated photonic platforms such as those based on silicon and silicon nitride lack the preferred cubic c(2) nonlinearity, which limits active photon control functionalities. In this talk, I will present integrated photonics based on aluminum nitride (AlN) and lithium niobite (LN), whose non-centrosymmetric crystal structures give rise to the strong second-order optical nonlinearity. Together with their low optical loss, the integrated AlN and LN photonics can provide enhanced c(2) photon-photon interactions to achieve high fidelity photon control, including on-chip parametric down-conversion, coherent light conversion, spectral-temporal shaping, and microwave-to-optical frequency conversions.

 

 

Special Colloquium


Wednesday, February 19, 2020
3:30 PM
Physics Building, Room 204
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"Deconfinement on Axion Domain Walls"


Mohamed Anber , Lewis & Clark College
[Host: Peter Arnold]
ABSTRACT:

The general lore, according to effective field theory, is that one ignores the high energy degrees of freedom when studying low energy phenomena. For example, we usually do not need to know quantum chromodynamics (QCD) (the strong nuclear force) in order to study fluid mechanics! However, the existence of 't Hooft anomalies (subtle phases in the partition function) may signal non-trivial intertwining between the high and low energy scales. This assertion can be seen in axion physics; axion is a hypothetical particle that may play important roles in solving a few puzzles in the Universe.  After a brief introduction to QCD and axions, I show how this intertwining takes place on axion domain walls (DW). To this end, I first discuss a new class of 't Hooft anomalies that was recently identified, and then use the anomalies to argue that quarks are deconfined (liberated) on axion DW. This newly discovered phenomenon implies that non-trivial interplay between different scales happens on the walls. Further, I confirm this picture by performing explicit calculations in a toy model, which is argued to be continuously connected to the full-fledged QCD.

Special Colloquium


Wednesday, February 12, 2020
3:30 PM
Physics Building, Room 204
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"New connections between Quantum Field Theory and String Theory"


Christoph Uhlemann , University of Michigan
[Host: Peter Arnold]
ABSTRACT:

Quantum field theory is a universal language in theoretical physics, which provides the foundation for the Standard Model of elementary particles, underlies the physics of the early universe, and describes a wealth of interesting phenomena in condensed matter. But despite its great successes, fully understanding this important framework is still very much a work in progress. Many insights, especially into theories with strong interactions, have been obtained using mathematical tools from string theory, and this has reshaped our understanding of what quantum field theory is. In this talk I will discuss new connections between quantum field theory and string theory that provide access to a remarkable class of theories that would not have been believed to exist based on conventional lore.

Special Colloquium


Wednesday, February 5, 2020
3:30 PM
Physics Building, Room 204
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"Neutrinos - Harbingers of New Physics"


Julian Heeck , University of California, Irvine
[Host: Peter Arnold]
ABSTRACT:

Neutrinos are the most elusive known elementary particles; they fly through all of us in vast numbers but are extremely difficult to detect. Immense progress has been made in analyzing their properties over the last decades, culminating in the surprising discovery of neutrino flavor oscillations. These neutrino oscillations imply that neutrinos have tiny but nonzero masses, which provides strong evidence for physics beyond the Standard Model of particle physics. With the increasing precision in neutrino measurements it has even become possible to use neutrinos as a tool to probe for further new physics, e.g. by studying how neutrinos scatter off electrons. In addition, neutrinos could prove uniquely helpful in the search for dark matter and provide complementary information to standard indirect detection signatures.

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