Events List for the Academic Year

Event Time: Monday, February 8, 2021 | 3:00 pm - 4:00 pm
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Add to Calendar 2021-02-08T15:00:00 2021-02-08T16:00:00 A lower density universe? - Measuring imprints of large scale structure on the CMB Event Information: Large-scale structures (LSS) can leave various imprints on the cosmic microwave background(CMB). Two main features come from the spatial and temporal perturbations of the CMB photon trajectory due to LSS: weak lensing and the integrated Sachs-Wolfe effect. I will give a summary of our paper "Galaxy clustering in Legacy Survey and its imprint on the CMB" (arXiv: 2010.00466), where we use the DESI Legacy Imaging Survey to extract cosmological information from the above effects in the redshift range 0<z<0.8. The Legacy Survey, covering about a third of the sky area and containing tens of millions of galaxies, is excellent for the purpose of cross-correlation studies, although a difficulty is to obtain a robust redshift distribution for those galaxies given the very limited photometric bands. In this study, we use our own method to find competitive photometric redshifts using colour information and construct galaxy density maps in four tomographic redshift slices. These maps are cross-correlated in angular space with the Planck 2018 lensing convergence and temperature maps. By comparing our measurements with theoretical predictions from the standard Lambda-CDM model assuming Planck 2018 cosmology, we find that interestingly the lensing amplitude is lower than expected, consistent with other weak lensing results. This may add to the existing tension in the Omega_m-sigma_8 parameter space. Event Location: Connect via zoom
Event Time: Monday, February 8, 2021 | 12:00 pm - 1:00 pm
Event Location:
https://ubc.zoom.us/j/69495792445?pwd=RURFQmt1S3UwSE1FYk9YQUFweWxUZz09 Passcode: 764070
Add to Calendar 2021-02-08T12:00:00 2021-02-08T13:00:00 Topological quantum matter: beyond band-insulators Event Information: Building quantum technology, from electronic devices to quantum computers, requires achieving precision control over the quantum correlations and entanglement of many particles. Since the probability of microscopic defects or control errors grows with system size, there appears to be a fundamental tension between scaling quantum technology and maintaining this precision control.  In contrast, gapped (insulating) matter at ultra low-temperatures exhibit strikingly robust macroscopic quantum properties, tied to global topological invariants of the systems ground-state wave-function. These topological properties are stabilized by collective many-body effects, and become increasingly insensitive to microscopic imperfections as sample dimensions are scaled up. In this talk, I will explore progress down two avenues for discovering new types of quantum topology in i) semi-metallic materials without a gap, and ii) in the dynamics of “qubit” systems driven far from thermal equilibrium. Event Location: https://ubc.zoom.us/j/69495792445?pwd=RURFQmt1S3UwSE1FYk9YQUFweWxUZz09 Passcode: 764070
Event Time: Thursday, February 4, 2021 | 4:00 pm - 5:00 pm
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Add to Calendar 2021-02-04T16:00:00 2021-02-04T17:00:00 The Chiral Puzzle of Life Event Information: Understanding the origin of life surely qualifies as one of the deepest and most perplexing questions facing humankind. While we have not yet reached a consensus on the definition of life, biological homochirality seems to be part of the definition as a necessary step for life's emergence. The unraveling of its origin require interdisciplinary research, by exploring each of fundamental physics, modern chemistry, astrophysics and biology. In this talk, We will focus on the origin of biological homochirality in the context of astrophysics and particle physics. The weak force, one of the fundamental forces operating in nature, is parity-violating, and has been implicated in biological homochirality since over half a century. Cosmic rays, high energy particles coming from outer space, induce showers of billions of secondary particles when they interact with atoms in the atmosphere. On Earth, at ground level, most of our cosmic radiation dose comes from polarized muons formed in a decay involving the weak force. We will show how the spin-polarization is transmitted in cosmic showers in different environments, how it can induce a chiral preference in the early biological life forms and we will discuss the implications for the search of life in other worlds. Event Location: Connect via zoom
Event Time: Thursday, February 4, 2021 | 10:00 am - 11:00 am
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Add to Calendar 2021-02-04T10:00:00 2021-02-04T11:00:00 CM Seminar - The puzzling superconducting order parameter of Sr2RuO4 Event Information: https://ubc.zoom.us/j/64183011430?pwd=U2lFNXEwSmlBRWVBdTR5OG1ZdlVSZz09Meeting ID: 641 8301 1430Passcode: 113399 Strontium ruthenate has long been thought to host a spin-triplet chiral p-wave superconducting state. However, the singlet-like response observed in recent spin-susceptibility measurements casts serious doubts on this pairing state. Together with the evidence for broken time-reversal symmetry and a jump in the shear modulus c66 at the superconducting transition temperature, the newly available experiments point towards an even-parity chiral superconductor. Here, we show how the orbital degree of freedom can encode the two-component nature of this order parameter, allowing for a local orbital-antisymmetric spin-triplet state that is favored by strong Hund’s coupling. We find that this exotic state can be energetically stable once a complete, realistic three-dimensional model is considered. We highlight how the concept of superconducting fitness was used in order to guide our search in parameter space and to discuss how momentum-dependent spin-orbit coupling terms are key. Event Location: Zoom link in description
Event Time: Wednesday, February 3, 2021 | 11:00 am - 12:00 pm
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Add to Calendar 2021-02-03T11:00:00 2021-02-03T12:00:00 Testing General Relativity with the Second LIGO-Virgo Catalog Event Information: The LIGO and Virgo gravitational wave detectors carried out the first half of their third observing run from April through October, 2019. During this period, they collected 39 new detections of compact binary coalescences, which were compiled in the second LIGO-Virgo catalog (GWTC-2). These and previously detected signals contain invaluable information about the nature of black holes and the properties of spacetime more generally. In this talk, I will summarize results along this front. This includes updated constraints on deviations from the predictions of general relativity for the generation and propagation of gravitational waves, searches for echos, and probes of the behavior of ringing black holes. I will close by outlining future prospects for testing Einstein’s theory with gravitational waves. Event Location: Connect via Zoom
Event Time: Monday, February 1, 2021 | 3:00 pm - 4:00 pm
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Add to Calendar 2021-02-01T15:00:00 2021-02-01T16:00:00 Europa’s Potentially Habitable Interior: Layered and Asymmetric Magnetic Induction Event Information: This lecture will describe recent research evaluating the magnetic induction characteristics of model Europa oceans (Vance et al. 2020). I will highlight how this work relates to efforts to understand the habitability of Europa and other icy ocean worlds. I will also provide an overview of NASA's planned Europa Clipper mission, set to conduct multiple flybys of Europa toward the end of the decade. Event Location: Connect via zoom
Event Time: Monday, February 1, 2021 | 12:00 pm - 1:00 pm
Event Location:
https://ubc.zoom.us/j/62870796359?pwd=SkNWNnB4SW5mOWpEUUxCVE1pcWorUT09 Passcode: 581018
Add to Calendar 2021-02-01T12:00:00 2021-02-01T13:00:00 Magnetic Textures in Quantum Materials: from Topology to Magnonics Event Information: Quantum materials are rapidly emerging as the basis for possible novel computation devices. However, fully understanding the interplay between magnetic and electronic excitations are preventing us from realizing their full potential. In my talk I will show how realizing the microscopic magnetic textures in quantum materials is crucial to the understanding of transport phenomena on the macro scale. I will demonstrate this with two examples from two different types of materials. First, I will show how scanning nanoSQUID-on-tip magnetic imaging of magnetically doped topological insulators reveal the underlying fragility of the Quantum Anomalous Hall effect at elevated temperatures. Then, I will show how with a combination of transport, magnetization, and magnetic imaging of the Weyl semimetal Co3Sn2S2, we find that the dynamics of domain walls are responsible for the anomalous transport behavior in the material. These observations show that better understanding of the microscopic magnetism in these systems reveal new phenomena and deepen our understanding of the interplay between magnetic textures and electronic properties. Event Location: https://ubc.zoom.us/j/62870796359?pwd=SkNWNnB4SW5mOWpEUUxCVE1pcWorUT09 Passcode: 581018
Event Time: Friday, January 29, 2021 | 1:00 pm - 3:00 pm
Event Location:
via Zoom
Add to Calendar 2021-01-29T13:00:00 2021-01-29T15:00:00 Departmental Doctoral Oral Examination (Thesis Title: “The Space Weather of Ultracool Dwarfs”) Event Information: Abstract: Empirical trends in stellar X-ray and radio luminosities suggest that very low mass stars and brown dwarfs should not produce significant radio emission. Defying these expectations, strong non-thermal emission has been observed in a few UCDs in the 1-10 GHz range, often attributed to global aurorae. At higher radio frequencies, flux due to global aurorae becomes unphysical, and is instead attributed to gyrosynchrotron radiation. In my Ph.D. work I used observations in this frequency range (30-100 GHz) to infer the presence of gyrosynchrotron radiation from ultracool dwarfs in three stars, and to place upper limits on the radio flux on three other stars that were not detected. Prior to this work, only one ultracool dwarf had been detected at such high radio frequencies. My results suggest that gyrosynchrotron radiation from radio active ultracool dwarfs may be more common than previously assumed, indicating a threat to the atmospheric stability of surrounding planets. Another key component of my thesis has been an extensive radio study of the ultracool dwarf TRAPPIST-1. The TRAPPIST-1 system is notable for its system of seven terrestrial planets, at least three of which orbit within the habitable zone. I put upper limits on the quiescent radio emission from the star at 44 and 97.5 GHz using the VLA and ALMA, and monitored the long-term 3 GHz emission from the star over 50 hours to search for variability. I used these results to constrain the possible gyrosynchrotron radiation from the star, as well as the resulting space weather impacts on surrounding planets. My results from the TRAPPIST-1 studies suggest that while the TRAPPIST-1 planets are not regularly exposed to high populations of energetic particles due to stellar activity, supporting the case for planetary habitability. Event Location: via Zoom
Event Time: Thursday, January 28, 2021 | 4:00 pm - 5:00 pm
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Add to Calendar 2021-01-28T16:00:00 2021-01-28T17:00:00 Towards Quantum Computation With Superconducting Circuits Event Information: By exploiting effects such as quantum superpositions and entanglement, quantum computers could solve problems that are intractable on standard, classical, computers. While building a full-scale quantum computer capable of rivalling today's supercomputers remains a challenge, the last few years have seen tremendous improvements in our ability to build small superconducting quantum processors and run simple algorithms on these processors. In this talk, I will review some of the basic concepts that could allow quantum computers to outperform their classical counterparts. With an emphasis on superconducting quantum processors, I will also discuss recent developments of the field and outline some of the challenges that lie ahead. Event Location: Connect via zoom
Event Time: Thursday, January 28, 2021 | 10:00 am - 11:00 am
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Add to Calendar 2021-01-28T10:00:00 2021-01-28T11:00:00 CM Seminar - Z3-vestigial nematic order due to superconducting fluctuations in the doped topological insulator Event Information: https://ubc.zoom.us/j/64183011430?pwd=U2lFNXEwSmlBRWVBdTR5OG1ZdlVSZz09 Meeting ID: 641 8301 1430Passcode: 113399 Abstract: A state of matter with a multi-component order parameter can give rise to vestigial order. In the vestigial phase, the primary order is only partially melted, leaving a remaining symmetry breaking behind, an effect driven by strong classical or quantum fluctuations. Vestigial states due to primary spin and charge-density-wave order have been discussed in the context of iron-based and cuprate materials. Here we discuss  a partially melted superconductor in which pairing fluctuations condense at a separate phase transition and form a nematic state with broken Z_3, i.e.  three-state Potts-model symmetry. This state was recently confirmed in measurements of the doped topological insulator Nb_xBi_2Se_3 and Cu_xBi_2Se_3. Event Location: Zoom link in description
Event Time: Wednesday, January 27, 2021 | 12:00 pm - 1:00 pm
Event Location:
https://ubc.zoom.us/j/65104619882?pwd=UE80WkY4RXdEMFMxU2VCbEFwaXhjdz09 Passcode: 428347
Add to Calendar 2021-01-27T12:00:00 2021-01-27T13:00:00 Monopolar and dipolar relaxation in classical spin ice Event Information: The quantum spin liquid is a hypothesized state characterized by macroscopic entanglement and fractionalized quasiparticles. While the physical realization of long-range entanglement of spins remains elusive, the phenomenon of spin fractionalization has been exemplified by magnetic monopoles in classical spin ice. In this talk, I will discuss how we experimentally distinguish emergent monopoles from individual spin dipoles through magnetic relaxation dynamics of spin ice Ho2Ti2O7. Combining time-resolved neutron scattering and broad-band magnetometry, we have probed over ten decades of time scales and uncovered a thermal crossover between two distinct relaxation processes. Magnetic relaxation at low temperatures is associated with monopole motion through the spin-ice vacuum, while at elevated temperatures, relaxation occurs through reorientation of spin dipoles. Disorders serve as a tuning parameter of monopole mobility, suggesting a potential controlling method of achieving coherent monopole dynamics in quantum spin ice. Reference Y. Wang et al., Monopolar and dipolar relaxation in spin ice Ho2Ti2O7, arXiv: 2011.06477 (2020) Event Location: https://ubc.zoom.us/j/65104619882?pwd=UE80WkY4RXdEMFMxU2VCbEFwaXhjdz09 Passcode: 428347
Event Time: Wednesday, January 27, 2021 | 11:00 am - 12:00 pm
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Add to Calendar 2021-01-27T11:00:00 2021-01-27T12:00:00 How do you make a binary black hole? Event Information: Since 2015, LIGO and Virgo have detected nearly 50 gravitational waves from merging black holes and neutron stars, ushering in a new era of observational astronomy.  But how are the binary progenitors of these systems actually formed in the first place?     In this talk, I will attempt to answer that question, by describing how massive and old star clusters, such as the globular clusters in the Milky Way, are an ideal site for the production of binary black holes.  I will show how unique features of these dense stellar environments directly influence the gravitational waveforms themselves, and how repeated binary mergers in clusters produce black hole masses that cannot be explained through normal stellar evolutionary processes.  Finally, I will connect these results to the binary black holes detected by LIGO/Virgo, including GW190412 and GW190521, two recently reported gravitational-wave detections with unique masses and spins. Event Location: Connect via Zoom
Event Time: Monday, January 25, 2021 | 3:00 pm - 4:00 pm
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Add to Calendar 2021-01-25T15:00:00 2021-01-25T16:00:00 Cosmic flows crank up the tension in cosmology Event Information: Peculiar velocities - deviations from Hubble expansion - are the only practical probe of the growth of matter density fluctuations on very large scales in the nearby Universe.  I will discuss recent measurements of cosmological parameters based on our approach of predicting peculiar velocities from the density field. This yields interesting results for the rms density fluctuations on 8 Mpc/h scales and their growth rate that may require new physics beyond the standard Lambda Cold Dark Matter model. Event Location: Connect via zoom
Event Time: Monday, January 25, 2021 | 12:00 pm - 1:00 pm
Event Location:
https://ubc.zoom.us/j/66194846742?pwd=STlJSFhUOEZBWUM2OEpkWHB5VEZ0QT09 Passcode: 038461
Add to Calendar 2021-01-25T12:00:00 2021-01-25T13:00:00 Electrical probes of non-Abelian spin liquids Event Information: Recent thermal-conductivity measurements evidence a magnetic-field-induced non-Abelian spin liquid phase in the Kitaev material α-RuCl3. In this talk, I will explain how we leverage fermion condensation to propose a series of measurements for electrically detecting the hallmark chiral Majorana edge states and bulk anyons in the spin-liquid phase -- despite the fact that α-RuCl3 is a good Mott insulator. In particular, I introduce circuits that exploit interfaces between electronic systems and α-RuCl3 to convert physical fermions into emergent fermions, thus enabling analogs of transport and probes of non-Abelian-anyon physics in topological superconductors. I will also explain how we developed an anyon-interferometry framework that incorporates nontrivial energy-partitioning effects. These results illuminate a partial pathway toward using Kitaev materials for topological quantum computation. Event Location: https://ubc.zoom.us/j/66194846742?pwd=STlJSFhUOEZBWUM2OEpkWHB5VEZ0QT09 Passcode: 038461
Event Time: Monday, January 25, 2021 | 11:00 am - 2:00 pm
Event Location:
via Zoom
Add to Calendar 2021-01-25T11:00:00 2021-01-25T14:00:00 Departmental Doctoral Oral Examination (Thesis Title: “Development of a single vacuum ultra-violet photon-sensing solution for nEXO”) Event Information: Event Location: via Zoom
Event Time: Friday, January 22, 2021 | 12:30 pm - 2:30 pm
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via Zoom
Add to Calendar 2021-01-22T12:30:00 2021-01-22T14:30:00 Departmental Doctoral Oral Examination (Thesis Title: “Generalization of the Haldane conjecture to SU(n) chains”) Event Information: Abstract: In this thesis, we study the low energy properties of SU(n) chains in various representations. We are motivated by Haldane's conjecture about antiferromagnets, namely that integer spin chains exhibit a finite energy gap, while half-odd integer spin chains have gapless excitations. Haldane was led to this conclusion by deriving a sigma model description of the antiferromagnet, and this is what we generalize here to SU(n). We find that most representations of SU(n) admit a mapping to a flag manifold sigma model, with target space SU(n)/U(1)^(n-1). These theories are not automatically relativistic, but we show that at low energies, their renormalization group flow leads to Lorentz invariance. We also show explicitly in SU(3) that the theory is asymptotically free, and contains a novel two-form operator that is relevant at low energies. For all n, these sigma models are equipped with n-1 topological angles which depend on the SU(n) representation at each site of the chain. For the rank-p symmetric representations, which generalize the spin representations of the antiferromagnet, these angles are theta_a = 2p*a*\pi/n. Only when gcd(n,p)=1 are all of these angles nontrivial. This observation, together with recent 't Hooft anomaly matching conditions, and various exact results known about SU(n) chains, allow us to formulate the following generalization of Haldane's conjecture to SU(n) chains in the rank-p symmetric representation: When p is coprime with n, a gapless phase occurs at weak coupling; for all other values of p, there is a finite energy gap with ground state degeneracy equal to n/\gcd(n,p). We offer an intuitive explanation of this behaviour in terms of fractional topological excitations. We also predict a similar gapless phase for two-row representations with even n. The topological content of these chains is the same as the symmetric ones, with p now equal to the sum of row lengths of the representation. Finally, we show that the most generic representation of SU(n) will admit a sigma model with both linear and quadratic dispersion; such theories require further understanding before their low energy spectrum can be characterized. Event Location: via Zoom
Event Time: Thursday, January 21, 2021 | 4:00 pm - 5:00 pm
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Add to Calendar 2021-01-21T16:00:00 2021-01-21T17:00:00 Separating wheat from chaff: Big data challenges from the Legacy Survey of Space and Time Event Information: The Legacy Survey of Space and Time (LSST) on the Vera C. Rubin Observatory will generate a data deluge: millions of astronomical transients and variable sources will need to be classified from their light curves. To study the physics of these objects, or to use them as cosmic beacons to measure the acceleration of the universe, requires classifying the objects into different types. This labelling by their optical photometry alone (rather than obtaining a spectrum of the objects signal), has long been a problem of interest in astronomy, and the issue of classification under sparse data is common across different fields in physics.  So the Photometric LSST Astronomical Time-series Classification Challenge (PLAsTiCC) was born. PLAsTiCC brings a wide range of astronomical transient models together, simulated under LSST-like conditions for the first time. The challenge was delivered to the community through the Kaggle data science platform, and was designed to stimulate interest in time-series photometric classification beyond just astronomers, to discover new approaches and methodologies that will advance the LSST science case. I will give an overview of the road to PLAsTiCC, the models and the validation of the data, present the results from PLAsTiCC (and tell you about how you can use this data set if you want to try your hand at data science!), and discuss the science impact of classification on photometric cosmology with Type Ia supernovae. I'll also discuss the Canadian context for participation in the Rubin Observatory. Event Location: Connect via zoom
Event Time: Thursday, January 21, 2021 | 10:00 am - 11:11 am
Event Location:
Zoom link in description
Add to Calendar 2021-01-21T10:00:00 2021-01-21T11:11:11 CM Seminar - Strongly correlated materials: from topological superconductivity to dark matter detection Event Information: https://ubc.zoom.us/j/64183011430?pwd=U2lFNXEwSmlBRWVBdTR5OG1ZdlVSZz09 Meeting ID: 641 8301 1430 Passcode: 113399 Abstract: Quantum materials containing lanthanide or actinide elements are fascinating because their f electrons may interact with the sea of conduction electrons and give rise to novel emergent phenomena. In addition, the combination of strong electronic correlations and non-trivial topology presents a powerful paradigm with the possibility of unprecedented experimental realizations. In this talk, I will present recent experimental insights into novel strongly correlated materials ranging from topological superconductor candidate UTe2 to narrow-gap semiconductor Eu5In2Sb6. Bio: Priscila Rosa received her PhD in physics in 2013 from the University of Campinas, Brazil. She then joined the University of California at Irvine as a postdoctoral researcher. In 2015, she was awarded a Director’s postdoctoral Fellowship at Los Alamos National Laboratory before becoming a staff scientist in 2016. Her main research interest is the synthesis and characterization of strongly correlated quantum materials that exhibit emergent phenomena, such as unconventional superconductivity, electronic nematicity, complex magnetism, and non-trivial topology. Priscila has coauthored over 90 peer-reviewed articles as well as one patent and two book chapters. At Los Alamos, her research further focuses on the application of extreme conditions (high pressure, high magnetic field, and low temperatures) to tune novel materials towards desired functionality. Event Location: Zoom link in description
Event Time: Wednesday, January 20, 2021 | 12:00 pm - 1:00 pm
Event Location:
https://ubc.zoom.us/j/64320901982?pwd=ZFRVUnNVM0I2ckhYRDJnRlM4MjVBUT09 Passcode: 606472
Add to Calendar 2021-01-20T12:00:00 2021-01-20T13:00:00 Imaging phonon-mediated hydrodynamic flow in WTe2 with cryogenic quantum magnetometry Event Information: Hydrodynamic electron flow, where electrons in a conductor flow collectively - akin to a fluid, is a unique signature of strong electron interactions in a material. This effect has been observed in 2D materials, but observations in bulk materials are intriguing as high-carrier density should screen the interactions. In this talk, I will discuss a recent measurement of hydrodynamic flow in the semimetal WTe2, allowing us to gain insight into the microscopic origin of its electron interactions. We image the spatial profile of the electric current by using a nitrogen-vacancy scanning tip. Using coherent quantum sensing, we obtain magnetic field resolution of ~10nT and spatial resolution of ~100nm. The current pattern we observe differs substantially from the flat profile of a normal metal, and indicates correlated flow through the semimetal. The pattern also shows non-monotonic temperature dependence, with hydrodynamic effects peaking at ~20 K. We compare our results to a model which combines ab initio electron scattering rates and the electronic Boltzmann transport equation. The model shows quantitative agreement with our measurement, allowing us to extract the strength of electron-electron interactions in our material. Furthermore, we conclude that electron interactions are phonon-mediated. This result opens a path for hydrodynamic flow and strong interactions in a variety of new materials. Event Location: https://ubc.zoom.us/j/64320901982?pwd=ZFRVUnNVM0I2ckhYRDJnRlM4MjVBUT09 Passcode: 606472
Event Time: Wednesday, January 20, 2021 | 11:00 am - 12:00 pm
Event Location:
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Add to Calendar 2021-01-20T11:00:00 2021-01-20T12:00:00 Testing the No-Hair Theorem and the Area Theorem with LIGO Event Information: One of the key results of general relativity is that an astrophysical black hole in equilibrium is uniquely described by just two parameters, its mass and spin. This is called the No-Hair Theorem, a result that is not true in alternative theories of gravity. For many years, people have speculated about testing the theorem using gravitational waves from merging black holes. The merger forms a single black hole, which rings down emitting gravitational waves as quasi-normal modes, just like a struck bell. The theorem predicts that the measured mode frequencies and damping times should depend only on the mass and spin of the remnant black hole. For a long time, the consensus has been that this test will require the sensitivity of next-generation detectors. I will show that this consensus is wrong for a surprising reason, and report a test with data from GW150914, the first LIGO gravitational wave detection. An extension of the test confirms Hawking's Area Theorem at the 97% limit. Event Location: Connect via Zoom