Events List for the Academic Year
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Monday, January 18, 2021 | 3:00 pm - 4:00 pm
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2021-01-18T15:00:00
2021-01-18T16:00:00
Gravity, entropy, and cosmology: in search of clarity
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I discuss the statistical mechanics of gravitating systems and in particular its cosmological implications, and argue that many conventional views on this subject in the foundations of statistical mechanics embody significant confusion; I attempt to provide a clearer and more accurate account. In particular, I observe that (i) the role of gravity in entropy calculations must be distinguished from the entropy of gravity, that (ii) although gravitational collapse is entropy-increasing, this is not usually because the collapsing matter itself increases in entropy, and that (iii) the Second Law of thermodynamics does not owe its validity to the statistical mechanics of gravitational collapse.
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Monday, January 18, 2021 | 12:00 pm - 1:00 pm
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2021-01-18T12:00:00
2021-01-18T13:00:00
Superconducting instability in a doped Mott insulator: Exact results
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Because the cuprate superconductors are doped Mott insulators, it would be advantageous to solve even a toy model that exhibits both Mottness and superconductivity. In this talk, I consider the Hatsugai-Kohmoto model, an exactly solvable system that is a prototypical Mott insulator above a critical interaction strength at half filling. Upon doping or reducing the interaction strength, our exact calculations show that the system becomes a non-Fermi liquid metal with a superconducting instability. In the presence of a weak pairing interaction, the instability produces a thermal transition to a superconducting phase, which is distinct from the BCS state, as evidenced by a gap-to-transition temperature ratio exceeding the universal BCS limit. The elementary excitations of this superconductor are not Bogoliubov quasiparticles but rather superpositions of doublons and holons, composite excitations signaling that the superconducting ground state of the doped Mott insulator inherits the non-Fermi liquid character of the normal state. An unexpected feature of this model is that it exhibits a superconductivity-induced transfer of spectral weight from high to low energies as seen in the cuprates as well as a suppression of the superfluid density relative to that in BCS theory. Finally, I discuss the relation between the Hatsugai-Kohmoto model and the Hubbard model, showing a class of intermediate models that are exactly solvable and may elucidate the mechanism of the pseudogap.
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https://ubc.zoom.us/j/63241480784?pwd=dE4yOHNlaUpLWEQrVHBTNjV0ZEFpZz09 Passcode: 535921
Event Time:
Thursday, January 14, 2021 | 4:00 pm - 5:00 pm
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2021-01-14T16:00:00
2021-01-14T17:00:00
Our Boldest Effort to Answer our Oldest Question: The Breakthrough Listen Search for Intelligent Life Beyond Earth
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Some 500 years ago, a growing awareness of cracks in the Ptolemaic model led to the Copernican revolution - a paradigm shift in our understanding in which we came to realize that the Earth was not the center of our cosmos, but rather just one of several bodies in orbit about the Sun. Centuries later, watershed discoveries brought us awareness of the structure of our galaxy, innumerable galaxies beyond our own, the cosmological evolution of the universe and the rich physics that tie them together. Just 10 years ago brought another humbling realization - planets, including planets like our own Earth, are abundant throughout our galaxy, and indeed planetary systems are the rule rather than the exception. Today we look towards a vista of yet further discovery, one that may answer our oldest and most profound question about the universe: Are we alone?
Of the many ways we now search for life beyond Earth, only the search for extraterrestrial intelligence (SETI) holds the promise of identifying communicative and technologically capable beings like ourselves. Here I will describe the latest developments in the the search for technosignatures, the remotely detectable manifestations of technologically-capable life. Among the most exciting developments is the Breakthrough Listen Initiative - a ten-year 100M USD global research program that constitutes the most comprehensive, intensive and sensitive search for extraterrestrial intelligence in history. Together with our international partners we are marshaling the world’s foremost observational astronomy resources to conduct state-of-the-art searches for a wide range of technosignatures, spanning the electromagnetic spectrum and leveraging the most powerful and cutting-edge data analysis techniques available.
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Thursday, January 14, 2021 | 10:00 am - 11:00 am
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2021-01-14T10:00:00
2021-01-14T11:00:00
CM Seminar - Hidden magnetoelectric multipoles in multiferroics and superconductors
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Zoom link: https://ubc.zoom.us/j/64183011430?pwd=U2lFNXEwSmlBRWVBdTR5OG1ZdlVSZz09
Meeting ID: 641 8301 1430
Passcode: 113399
Most magnetic materials, phenomena and devices are well described in terms of magnetic dipoles of either spin or orbital origin. There is mounting evidence, however, that higher-than-dipolar order multipoles both exist (often in hiding) and lead to intriguing magnetic behaviors. In this talk I will discuss the relevance of the so-called magnetoelectric multipoles, which form the next-order term, after the magnetic dipole, in the multipolar expansion of the magnetization density in a magnetic field. First I will describe how magnetoelectric multipoles underlie multiferroic behavior and in particular how they determine the magnetic response to applied electric fields. Then I will discuss signatures of hidden magnetoelectric multipolar order, how it can be unearthed using density functional theory calculations and possibilities for its direct measurement. Finally, I will suggest that such magnetoelectric hidden order occurs in the high-Tc cuprate materials, where it might be relevant for the superconducting behavior, providing a link between multiferroism and exotic superconductivity.
Nicola Spaldin is the Professor of Materials Theory at ETH Zurich. She is best known for her developement of the class of materials known as multiferroics, which combine simultaneous ferromagnetism and ferroelectricity. She is a passionate science educator, coordinator of the curriculum development project "The Materials Scientist 2030, Who is She?", and holder of the ETH Golden Owl Award for excellence in teaching. When not trying to make a room-temperature superconductor, she can be found playing her clarinet, or skiing or climbing in the Alps.
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Wednesday, January 13, 2021 | 11:00 am - 12:00 pm
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2021-01-13T11:00:00
2021-01-13T12:00:00
A Spheroidal Harmonic Picture for GWs from Binary Black Holes
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Central to gravitational wave detection and the inference of source parameters is the representation of gravitational radiation in terms of multipole moments. By construction, these functions of time or frequency allow the radiation's angular dependence to be given by spin weighted harmonic functions. This leaves the radiation itself to be represented as a sum over harmonic functions, whereby each term is weighted by a different multipole moment. The choice of representation, namely the choice of which harmonic functions to use, is not unique. Only the radiation's spin weight must be respected. And while there are multiple appropriate spin weighted functions, only one set of harmonic functions corresponds to the physical system's natural modes. In this talk I will discuss recent and ongoing work regarding a new set of functions that are naturally suited to the modes of astrophysical gravitationally radiating systems. I will outline the mathematical nature of these functions, and comment on their potential use in gravitational wave theory and data analysis.
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Monday, January 11, 2021 | 3:00 pm - 4:00 pm
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2021-01-11T15:00:00
2021-01-11T16:00:00
Cosmos and Canvas: Using Data Visualization to Explore and Communicate Your Science
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Data visualizations that resonate with human perception strongly enhance discovery-based science. Examples include perception-based colour mappings through to bold colour images from telescopes that act as extraordinary ambassadors for astronomers. But are these astronomy images snapshots documenting physical reality or are they artistically digitized space-scapes? To answer this, the lecture illustrates how original black and white astronomy data are converted into the colour images gracing magazines and websites. It also describes how graphics are "read" by the eye-brain system and how a scientist can harness a powerful visual grammar, including colour contrast and composition, to explore data and communicate results with greater clarity to both their colleagues and the non-expert public. Often the attempt by scientists to represent their discoveries all but drowns out the voice of visual literacy. Yet sometimes in this battle, between the cultures of science and visual art, both sides win. This struggle will be presented from the perspective of a research astronomer who has created numerous images for NASA and also trained as a visual artist.
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Thursday, January 7, 2021 | 4:00 pm - 5:00 pm
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2021-01-07T16:00:00
2021-01-07T17:00:00
The Jazz of Physics: The Link Between Music and The Structure of the Universe
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In this talk Alexander revisits the interconnection between music and the evolution of astrophysics and the laws of motion. He explores new ways that music, in particular jazz music, mirrors modern physics, such as quantum mechanics, general relativity, and the physics of the early universe. Finally, he discusses ways that innovations in physics have been and can be inspired from the "improvisational logic" exemplified in Jazz performance and practice.
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Thursday, January 7, 2021 | 10:00 am - 11:00 am
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2021-01-07T10:00:00
2021-01-07T11:00:00
CM Seminar - Superconductivity in infinite layer nickelates
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https://ubc.zoom.us/j/64183011430?pwd=U2lFNXEwSmlBRWVBdTR5OG1ZdlVSZz09
Meeting ID: 641 8301 1430
Passcode: 113399
Since their discovery, superconductivity in cuprates has motivated the search for materials with analogous electronic or atomic structure. We have used soft chemistry approaches to synthesize superconducting infinite layer nickelate thin films from their perovskite precursor phase, using topotactic reactions. We will present the synthesis and transport properties of the nickelates, observation of a doping-dependent superconducting dome in (Nd,Sr)NiO2, and our current understanding of the electronic structure.
Bio: Harold Y. Hwang is a Professor of Applied Physics and Photon Science (SLAC) at Stanford University, and the Director of the Stanford Institute for Materials and Energy Sciences. He received a B.S. in Physics, B.S. and M.S. in Electrical Engineering from MIT (1993), and a Ph.D. in Physics from Princeton University (1997). He was formerly a Member of Technical Staff at Bell Labs (1996-2003) and Professor at the University of Tokyo (2003-2010). His current research focuses on correlated electrons and emergent phenomena at artificial interfaces and in confined systems; atomic-scale synthesis of heterostructures of quantum materials; low-dimensional superconductivity; oxide heterostructures for energy applications; and novel devices based on interface states. Recognitions include the MRS Outstanding Young Investigator Award (2005), the IBM Japan Science Prize (Physics, 2008), Fellowship in the American Physical Society (2011), the Ho-Am Prize (Science, 2013), and the Europhysics Prize (2014, with Jochen Mannhart and Jean
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Thursday, December 17, 2020 | 4:00 pm - 5:30 pm
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2020-12-17T16:00:00
2020-12-17T17:30:00
The Physics of Santa
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Join members of the Department of Physics & Astronomy to celebrate the festive season by remotely gathering to hear answers to the following questions:
What makes the reindeer able to fly? What technology allows the elves to make all those toys? Does Santa use the principles of relativity and quantum mechanics to deliver all the gifts in a single night?
In the spirit of the holidays, come dressed in your favourite festive hat or outfit (from your own family tradition, whatever you celebrate) - or make an appropriate background - and we'll share the gallery view of the audience!
This event is expected to be at a level appropriate for the general public and high school students who have an interest in physics and astronomy.
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Thursday, December 17, 2020 | 2:00 pm - 3:00 pm
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2020-12-17T14:00:00
2020-12-17T15:00:00
CM Seminar - Twist angle control of moiré superlattice properties
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https://ubc.zoom.us/j/65784122083?pwd=U09vVXJMRzNLaTY3bmVXNEFJZ1k3UT09
Meeting code: 657 8412 2083
Passcode: 113399
Abstract: In van der Waals bilayers, the strict requirement of lattice matching at the interface is lifted. The periodic changes in atomic alignment lead to the formation of an in-plane superlattice, known as the moiré superlattice. The twist angle controls the size of the moiré supercells and acts as a unique knob to control the material properties. While many electronic phases (e.g. superconductivity and orbital magnetism) have been discovered at low temperatures, other aspects of such moiré crystals remain to be explored. In this talk, I will discuss how atomic reconstructions of the moiré pattern change with the twist angle and how one can probe it using simple Raman spectroscopy. Other excited state properties such as exciton lifetime and diffusion are also drastically modified with a subtle change in the twist angle.
Bio: Xiaoqin Elaine Li received her B.S degree from Beijing Normal University in 1997 and Ph.D. in physics in 2003 from the University of Michigan. She was a postdoc fellow at JILA, Colorado from 2003-2006. She started as an assistant professor at UT-Austin in 2007 and was promoted to full professor in 2018. Prof. Li has received several awards including the Presidential Early Career Award for Scientists and Engineers in the U. S. and a Sloan Fellowship. She was a Humboldt research fellow at the Technical University of Berlin between 2013-2015. She is a fellow of the American Physics Society. During the pandemic, she started a guided summer reading program on the popular science book “Physics for Future Presidents” for high school students.
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Event Time:
Monday, December 14, 2020 | 3:00 pm - 4:00 pm
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2020-12-14T15:00:00
2020-12-14T16:00:00
The search for biomarkers in the solar system and beyond
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We will review past and current efforts to search for biosignatures in the Solar System and in exoplanets. The recent claim of detection of phosphine, its implications for life on Venus, and the subsequent reactions are summarized. We will also discuss the assumptions inherent in current strategies in the search for extraterrestrial life.
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Thursday, December 10, 2020 | 4:00 pm - 5:00 pm
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2020-12-10T16:00:00
2020-12-10T17:00:00
Dark Matter: A Cosmological Perspective
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While it is considered to be one of the most promising hints of new physics beyond the Standard Model, dark matter is as-yet known only through its gravitational influence on astronomical and cosmological observables. I will discuss our current best evidence for dark matter's existence as well as the constraints that astrophysical probes can place on its properties, while highlighting some tantalizing anomalies that could indicate non-gravitational dark matter interactions. Future observations, along with synergies between astrophysical and experimental searches, have the potential to illuminate dark matter's fundamental nature and its influence on the evolution of matter in the cosmos from the first stars and galaxies to today.
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Thursday, December 10, 2020 | 2:00 pm - 3:00 pm
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https://ubc.zoom.us/j/65784122083?pwd=U09vVXJMRzNLaTY3bmVXNEFJZ1k3UT09
Meeting code: 657 8412 2083
Passcode: 113399
Meeting code: 657 8412 2083
Passcode: 113399
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2020-12-10T14:00:00
2020-12-10T15:00:00
CM Seminar - Induced Superconductivity in the Fractional Quantum Hall Edge in Graphene Heterostructures
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https://ubc.zoom.us/j/65784122083?pwd=U09vVXJMRzNLaTY3bmVXNEFJZ1k3UT09
Meeting code: 657 8412 2083
Passcode: 113399
Abstract: Topological superconductors represent a phase of matter whose properties cannot be smoothly changed from one phase to another, a robustness which renders them suitable for quantum computing. The past decade has witnessed substantial progress towards a qubit based on Majorana modes, non-Abelian excitations whose exchange—braiding—produces topologically protected logic operations. However, because braiding Majoranas cannot provide a universal quantum gate set, Majorana qubits are computationally limited. This drawback can be overcome by parafermions, a novel set of non-Abelian modes whose array supports universal topological quantum computation. The primary route to synthesize parafermions involves inducing superconductivity in the fractional quantum Hall (fqH) edge. In this presentation we use high- quality van der Waals devices, coupled to narrow superconducting NbN, in which superconductivity and robust fqH coexist. We find crossed Andreev reflection (CAR) across the superconductor separating two counterpropagating fqH edges which demonstrates their superconducting pairing. The CAR probability of the integer edges is insensitive to magnetic field, temperature, or filling, providing evidence for spin-orbit coupling which enables the pairing of the otherwise spin-polarized edges. FqH edges, however, may show a higher CAR probability varying with temperature, an observation contrasting with that in integer edges. Control experiments show that CAR vanishes at high temperature and excitation as expected from the finite superconducting and fqH energy gaps. These results demonstrate all the required ingredients for parafermions, laying the groundwork for their experimental research in condensed matter.
Event Location:
https://ubc.zoom.us/j/65784122083?pwd=U09vVXJMRzNLaTY3bmVXNEFJZ1k3UT09
Meeting code: 657 8412 2083
Passcode: 113399
Event Time:
Wednesday, December 9, 2020 | 11:00 am - 12:00 pm
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2020-12-09T11:00:00
2020-12-09T12:00:00
Are there any fundamental problems with quantum gravity?
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I plan to informally discuss several issues that have traditionally been raised in various approaches to quantizing gravity. They are invariably related to the concepts that are thought to be fundamental in one of the two theories (quantum and GR) but are (allegedly) at odds with the other one. I will discuss some of the key issues in my talk, such as Bell non-locality and the equivalence principle, only to conclude that they are, in my view, not fundamentally an obstacle. Lack of experiments, on the other hand, is a real obstacle, but, even here, we are closer than ever to being able to test the quantum nature of gravity in the lab. I will describe how.
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Monday, December 7, 2020 | 3:00 pm - 4:00 pm
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2020-12-07T15:00:00
2020-12-07T16:00:00
Cosmology in the machine learning era
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Recent advances in deep learning are triggering a revolution across fields in science. In this talk I will show how these techniques can also benefit cosmology and astrophysics. I will present a new approach whose final goal is to extract every single bit of information from cosmological surveys. I will start showing the large amount of cosmological information that is embedded on small, non-linear, scales; information that cannot be retrieved using the traditional power spectrum. I will then show how neural networks can learn the optimal estimator needed to extract that information. I will discuss the role played by baryonic effects and point out how neural networks can automatically learn to marginalize over them. This approach requires combining machine learning techniques with numerical simulations. Along the talk, I will present the simulations we are using in this program: the Quijote and the CAMELS simulations. These two suites contain thousands of N-body and state-of-the-art (magneto-)hydrodynamic simulations covering a combined volume larger than the entire observable Universe (Quijote) and sampling the largest volume in parameter space for astrophysics models to-date (CAMELS).
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Thursday, December 3, 2020 | 4:00 pm - 5:00 pm
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2020-12-03T16:00:00
2020-12-03T17:00:00
Stacking van der Waals atomic layers: quest for new quantum materials
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Modern electronics heavily rely on the technology to confine electrons in the interface layers of semiconductors. In recent years, scientists discovered that various atomically thin van der Waals (vdW) layered materials can be isolated. In these atomically thin materials, quantum physics allows electrons to move only in an effective 2-dimensional (2D) space. By stacking these 2D quantum materials, one can also create atomic-scale heterostructures with a wide variety of electronic and optical properties. We demonstrate the enhanced electronic and optoelectronic performances in the vdW heterostructures, suggesting that these a few atom thick interfaces may provide a fundamental platform to realize novel physical phenomena. In this talk, we will discuss several research efforts to realize unusual quasiparticle pairing mesoscopic devices based on stacked vdW interfaces between 2-dimensional materials.
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Thursday, December 3, 2020 | 2:00 pm - 3:00 pm
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2020-12-03T14:00:00
2020-12-03T15:00:00
CM Seminar - Electronic signatures of the nematic electronic phases of superconducting FeSe1-xSx
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https://ubc.zoom.us/j/65784122083?pwd=U09vVXJMRzNLaTY3bmVXNEFJZ1k3UT09
Meeting code: 657 8412 2083
Passcode: 113399
Title: Electronic signatures of the nematic electronic phases of superconducting FeSe1-xSx
Abstract: Isoelectronic substitution is an ideal tuning parameter to alter electronic states and correlations in iron-based superconductors as this substitution is less affected by the impurity scattering [1-7]. In this talk, I will present the experimental progress made in understanding the nematic electronic states and the nematic criticality of superconducting FeSe1-xSx. A direct signature of the nematic electronic state is in-plane anisotropic distortion of the Fermi surface triggered by orbital ordering effects and electronic interactions that result in multi-band shifts, as detected by angle-dependent photoemission spectroscopy [4-5]. Upon sulphur substitution, the orbital effects, electronic correlations and the Fermi velocities decrease in the tetragonal phase. Quantum oscillations in ultra-high magnetic fields show a complex spectra and the effective masses display non-divergent behaviour at the nematic end point, as opposed to critical spin-fluctuations in other iron pnictides [2,3,7]. The lack of enhanced superconductivity and divergent electronic correlations at the nematic end point in FeSe1-xSx indicate a strong coupling with the lattice.
References
[1] Amalia I. Coldea and Matthew D. Watson, Annual Reviews on Condensed Matter Physics 9, 125 (2018).
[2] A.I. Coldea, et.al, npj Quantum Materials, Nature 4, 2 (2019).
[3] P. Reiss, et al., Nature Physics 16, 89 (2020).
[4] M. D. Watson et al., Phys. Rev. B 92, 121108(R) (2015).
[5] P. Reiss, et al., Phys. Rev. B 96, 121103(R) (2017).
[6]. M. Bristow et al., Phys. Rev. Research 2, 013309 (2020).
[7]. A.I. Coldea, review, arXiv:2009.05523 (2020) https://arxiv.org/abs/2009.05523
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Wednesday, December 2, 2020 | 2:00 pm - 3:00 pm
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2020-12-02T14:00:00
2020-12-02T15:00:00
Quantum interference of “clocks" and Unruh-deWitt detectors
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A major goal of modern physics is to understand and test the regime where quantum mechanics and general relativity both play a role. A promising path towards this goal is to study low-energy but composite quantum particles subject to relativistic effects. The reason is that such particles can model ideal clocks — their internal degrees of freedom measure proper time along the particle’s world line, as well as Unruh-deWitt detectors — when interactions of the internal degrees of freedom with an external quantised field are included. I will discuss what foundational insights into the notions of time, causality and thermalisation are enabled by this approach, specifically looking at the interference effects arising when a quantum clock or an Unruh-deWitt detector follows in superposition different spacetime trajectories.
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Monday, November 30, 2020 | 3:00 pm - 4:00 pm
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2020-11-30T15:00:00
2020-11-30T16:00:00
Computer Simulations and Bayesian Inference in Astrostatistics
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Modern astronomy involves complex data generating mechanisms, complex data collection mechanisms, and complex underlying physics questions, resulting in an abundance of complex statistical challenges. In particular, astronomers may rely on computer simulators to model complex physics, creating a need for statistical methodology that combines these simulators with astrophysical data to perform inference. In this talk I will describe my current work in astrostatistics, which involves developing statistical methods that incorporate physics-based computer simulators, are suited to the particular scientific and data-analytic challenges at hand, and provide uncertainty quantification. Areas of application within astronomy include exoplanet detection, solar physics, stellar evolution, and Mars planetary science, among others.
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Thursday, November 26, 2020 | 4:00 pm - 5:00 pm
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2020-11-26T16:00:00
2020-11-26T17:00:00
Adventures in Amateur Astrophotography
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Amateur astrophotography has undergone a profound transformation over the past twenty years, driven by the advent of digital cameras, along with increasingly affordable large-aperture telescopes. Amateur astronomers today use backyard equipment to produce stunning images that surpass those taken at big observatories only a few decades ago, while some use very modest equipment to produce work of soaring creativity. Some amateurs use their imaging systems to do research, sometimes as part of pro-am collaborations, while arm-chair astronomers process photographic treasures lying untapped in professional archives. In this talk I'll cover some of the many varieties of amateur astrophotography, from the perspective of a theoretical physicist whose personal life was transformed by adventures in this hobby.
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