The Welsh Lectures in Physics

2018 H.L. Welsh Lectures in Physics
An annual physics event since 1975!

The Welsh Lectures in Physics have been held annually since 1975 in honour of H.L. Welsh, a distinguished former faculty member in the Physics Department. They are the major public event in the life of the Department of Physics and are intended to celebrate discoveries in physics and their wider impact. They are intended to be broadly accessible to an audience drawn from across the university, other academic institutions and the interested public.

The Speakers for 2018

Prof. Ana Maria Rey

University of Colorado

Ana María Rey is a Fellow of JILA, a NIST Fellow, and a Professor Adjoint at the Department of Physics at the University of Colorado Boulder. She received a B.S. from Universidad de los Andes, in Bogota Colombia, and a Ph.D. from the University of Maryland. Between 2005 and 2008, she was a postdoctoral fellow at the Harvard Smithsonian Center for Astrophysics in Cambridge (U.S.), after which she joined the faculty at JILA and UC Boulder. Rey has wide research interests in atomic, molecular, and optical systems, and is the author of over 120 research articles. She has been the recipient of numerous awards, including the DAMOP Thesis Prize (2005), the Fundacion Alejandro Angel Escobar Physical and Natural Sciences Prize (2007), the Great Minds in STEM - Most Promising Scientist Award (2013), a MacArthur Foundation Fellowship (2013), the Presidential Early Career Award for Scientists and Engineers (2013), the Maria Goeppert Mayer Award of the American Physical Society (2014), and the Alexander Cruickshank Award in Atomic Physics (2017). Rey is a Fellow of the American Physical Society.

Prof. Seamus Davis

Cornell University

J.C. Seamus Davis is the J.G. White Distinguished Professor of Physical Sciences at Cornell University; he is also the SUPA Distinguished Research Professor of Physics at St. Andrews University, Scotland, and a senior physicist at Brookhaven National Laboratory in Upton, New York. He received his B. Sc. from University College Cork, National University of Ireland and his Ph. D. from University of California, Berkeley. He was a faculty member at Berkeley until his move to Cornell in 2003. Between 2009 and 2014 he was the Director of the Center for Emergent Superconductivity, an Energy Frontier Research Center of the U.S. Department of Energy. Davis has been the recipient of the Outstanding Performance Award of the Lawrence Berkeley National Laboratory (2001), the Science and Technology Award of Brookhaven National Laboratory (2013), the Fritz London Memorial Prize (2005), the H. Kamerlingh-Onnes Memorial Prize (2009). He also received an Honorary Doctorate from National University of Ireland (2014), and the Medal of Science from the Science Foundation Ireland (2016). Davis is a fellow of the Institute of Physics (U.K.), the American Physical Society (U.S.), and a member of the U.S. National Academy of Sciences.

Public Talks

The Department of Physics invites faculty, students and the public to our 44nd annual celebration of physics.


MAY 3, 2018


Earth Sciences Centre
5 Bancroft Avenue
Auditorium (ES 1050)


1:30 p.m.

Prof. Seamus Davis (Cornell University)

"Visualizing Quantum Matter"

Everything around us, everything each of us has ever experienced, and virtually everything underpinning our technological society and economy is governed by quantum mechanics. Yet this most fundamental physical theory of nature often feels as if it is a set of somewhat eerie and counterintuitive ideas of no direct relevance to our lives. Why is this? One reason is that we cannot perceive the strangeness (and astonishing beauty) of the quantum mechanical phenomena all around us by using our own senses. But with the recent emergence of a Second Quantum Revolution, visualization of quantum matter is becoming ever more necessary for its science and technology to advance.
I will describe the recent development of techniques that allow us to image electronic quantum matter directly at the atomic scale. We will visually explore the previously unseen and very beautiful forms of quantum matter making up Composite Quantum Particles in heavy-fermion compounds, Electronic Liquid Crystals in correlated metals, topological surface states of the Quantum Anomalous Hall Effect, and macroscopic quantum state of a Cooper-Pair Condensate. I will discuss the implications of the capability to visualize quantum matter, for fundamental physics research and also for advanced materials and new technologies.

3:00 p.m.

Coffe Break

3:30 p.m.

Prof. Ana Maria Rey (University of Colorado)

"Quantum clocks: the greatest rulers of time"

The best clock in the world has no hands, no pendulum, no face or digital display. It is made of ultra-cold Strontium atoms trapped in crystals of light. The clock is so precise that, had it begun ticking when Earth formed billions of years ago, it would not yet have gained or lost a second. These ultraprecise atomic clocks not only can serve as the state-of-the-art timekeepers, but also they could help us unveil the mysteries of the quantum world, which is ruled by the bizarre concept of entanglement or “spooky action at a distance”. In fact, the new generation of atomic clocks are paving the ground for the construction of quantum computers with computational powers beyond that of any imaginable classical machine. A quantum computer should be able solve otherwise intractable problems, with far-reaching applications to cryptology, material design and fundamental physical sciences. Can we make the clock even better? Regardless of their impressive precision and accuracy, current atomic clocks still operate with independent atoms which are fundamentally fuzzy. Interestingly, this fuzziness could be reduced if we entangle them. So atomic clocks are a win-win business, not only the current generation of clocks will help us to better understand the quantum world, but the gained understanding will in turn allow us to build the most incredible quantum rulers of time in the future.

Sponsored by the Department of Physics: (416) 978-7135 or or


  • Entanglement dynamics in a trapped ion quantum magnet
    Prof. Ana Maria Rey, University of Colorado
    Fri. May 4, 2018 at 11:00 a.m.
    Koffler House, Room KP 108, 569 Spadina Crescent
    abstract >>


    One of the most important goals of modern quantum sciences is to learn how to control and entangle many-body systems and use them to make powerful and improved quantum devices, materials and technologies. In this talk I will report on our current effort to develop protocols that can quantify the build-up of quantum correlations and storage of quantum information in a planar crystal of trapped ions. Using a pair of lasers, we couple the spins to the vibrational modes (phonons) of the crystal. The phonons mediate tunable-range interactions between the spins which we use to generate entanglement starting from easily prepared uncorrelated states. We can operate in two different regimes. In one regime, phonons do not play an active role in the many-body dynamics and instead are used to mediate spin-spin coupling between ions. In the other regime, phonons actively participate and we use them to simulate the Dicke model an iconic model in quantum optics which describes the coupling of a (large) spin to an oscillator. The Dicke model is known to exhibit rich and interesting phenomena. For instance, it features a quantum critical point, and displays classical chaotic behavior. I will also discuss a new measurement scheme, implemented by using a many-body echo sequence that reverses the Hamiltonian dynamics, which can give experimental access to a type of out-of-time-order correlations (OTOCs) which have caught great deal of interest in the recent years. The reason is that those correlations can measure the “scrambling” of quantum information across the system’s many-body degrees of freedom. Measuring OTOCs in controllable atomic laboratories can not only have a great impact on quantum information processing and quantum enhanced metrology, but also opens a path for future tests of the holographic duality between quantum and gravitational systems.

  • Discovery of the Cooper-Pair Density Wave State of Cuprates:Phenomenology & Consequences
    Prof. Seamus Davis, Cornell University
    Thu. May 4, 2017 at 2:00 p.m.
    Koffler House, Room KP 108, 569 Spadina Crescent
    abstract >>


    Cooper-pairs, if they have finite center-of-mass momentum QP, can form a remarkable state in which the density of pairs modulates periodically in space at wavevector QP. Intense theoretical interest has recently emerged in whether such a ‘pair density wave’ (PDW) state could, due to strong local electron-electron interactions, be another principal state in the phase diagram of underdoped cuprates. The most common model invoked is an eight unit-cell (8a0) periodic modulation of the electron-pair condensate.
    To search for a cuprate PDW at zero field, we invented a nanometer-resolution scanned Josephson tunneling microscopy (SJTM) to image Cooper-pair tunneling from a d-wave superconducting STM tip at millikelvin temperatures to the Cooper-pair condensate of underdoped Bi2Sr2CaCu2O8. The resulting images of the Cooper-pair condensate show clear pair density modulations oriented along the Cu-O bond directions wavevectors QP≈(0.25,0)2π/a0;(0,0.25)2π/a0 [1].

    At very high magnetic fields an exceptional electronic phase supports unexplained quantum oscillations and exhibits an unidentified density wave (DW) state. To search for evidence of the PDW at high fields, we visualize the modulations in the density of electronic states N(r) within the halo surrounding vortex cores. This revealed multiple signatures of a field-induced PDW, including two sets of N(r) modulations occurring at wavevectors QP and 2QP both having predominantly s-symmetry form factors, the amplitude of the latter decaying twice as rapidly as the former. This is in detailed agreement with theory for a field-induced primary PDW that generates secondary CDWs within the vortex halo [2].

    These data indicate that PDW exists in the pseudogap regime of cuprates and, moreover, that the fundamental state generated by increasing magnetic fields from the underdoped cuprate superconducting phase is actually a PDW with approximately eight CuO2 unit-cell periodicity and predominantly d-symmetry form factor. We review the implications from these discoveries for the microscopic theory of the cuprate pseudogap phase.

    [1] Nature 532, 343 (2016)
    [2] arXiv arXiv:1802.04673 & Science (2018)


Prof. Harry L. Welsh

Prof. Harry L. Welsh

Prof. Harry Welsh's distinguished research activity in molecular spectroscopy at the University of Toronto spanned a period of forty years. He pioneered the study of collision-induced infrared absorption and of molecular complexes, and of the infrared and Raman spectra of liquid and solid hydrogen. During his years as chair in the 1960's, Prof. Welsh guided a period of rapid growth of the Department of Physics. The H.L. Welsh Lectures in Physics were begun in 1975 on the occasion of his 65th birthday and have become an annual event.

Past Speakers

  • 2017
    Prof. Nergis Mavalvala (MIT)
    Prof. Leon Balents (University of California, Santa Barbara)
  • 2016
    Dr. Nima Arkani Hamed (Princeton University)
    Dr. Andrea Ghez (University of California, Los Angeles)
  • 2015
    William Bialek (Princeton University)
    Prof. Serge Haroche (Collège de France, Paris)
  • 2014
    Rolf Dieter Heuer (CERN)
    Zhi-Xun Shen (Stanford University)
  • 2013
    Jean-Loup Puget (Institut d'Astrophysique Spatalie, Universite Paris Sud)
    Robert Austin (Princeton University)
  • 2012
    Kerry Emanuel (MIT)
    Roger Bilham (University of Colorado)
  • 2011
    Deborah Jin (JILA and University of Colorado)
  • more past speakers...

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