Fall 2026 Colloquium Schedule

Colloquia are Wednesdays at 4:00 p.m. in the JILA Auditorium.

Coffee, tea and cookies will be available in G1B31 (across from G1B20) from 3:30 - 3:50 p.m.

August 26 — Einstein-Podolsky-Rosen experiment with two Bose-Einstein condensates

  • Presenter: Philipp Treutlein, University of Basel, Switzerland
  • Host: Ana Maria Rey
  • Abstract: In 1935, Einstein, Podolsky, and Rosen (EPR) conceived a Gedankenexperiment that has become a cornerstone of quantum physics and continues to challenge our understanding of reality and locality. While the EPR paradox has been demonstrated with small quantum systems, its realization with massive many-particle systems remains a key challenge, as such systems are closely linked to local realism in our everyday experience and may serve as probes of the quantum-to-classical transition. 
    I will report an EPR experiment with two spatially separated Bose-Einstein condensates, each containing about 700 rubidium atoms [1]. Entanglement between the condensates results in strong correlations of their collective spins, enabling the first observation of the EPR paradox with spatially separated, massive many-particle systems. Our results show that the conflict between quantum mechanics and local realism persists even for systems comprising more than a thousand massive particles. From a technological perspective, our system constitutes an array of entangled atomic sensors that allows us to implement novel protocols for multiparameter quantum metrology [2].
  • [1] P. Colciaghi et al., Phys. Rev. X 13, 021031 (2023).
    [2] Y. Li et al., Science 391, 374 (2026).

September 2

  • Presenter: Dana Anderson, University of Colorado Boulder, Infleqtion
  • Host: Ana Maria Rey
  • Abstract: 

September 9

  • Presenter: Keith Ulmer, University of Colorado Boulder
  • Host: Tobin Munsat
  • Abstract: 

September 16 — Dense Associative Memory: physical systems for novel AI architectures

  • Presenter: Dmitry Krotov
  • Host: Andrew Lucas
  • Abstract: Dense Associative Memories are recurrent neural networks with fixed-point attractor states that are described by an energy function. In contrast to conventional Hopfield Networks, which were popular in the 1980s, Dense Associative Memories have a very large information storage capacity, making them appealing tools for many problems in AI. In this talk, I will provide an intuitive understanding and mathematical framework for this class of models and give examples of problems in AI that can be tackled using these new ideas. Specifically, I will explore the relationship between Dense Associative Memories and transformers. I will present a neural network called the Energy Transformer, which unifies energy-based modeling, associative memories, and transformers in a single architecture. I will demonstrate how Energy Transformers can be used for challenging tasks in image processing, solve partial differential equations, and serve as computational modules for energy-based language modeling. I will also discuss an exciting possibility of mapping these models onto analog hardware accelerators, which could enable much more energy-efficient inference compared with GPUs.

September 23

  • Presenter: Philip Stark, University of California Berkeley
  • Host: Michael Ritzwoller
  • Abstract: 

September 30

  • Presenter: Karl Krushelnik, University of Michigan
  • Host: Michael Litos
  • Abstract: 

October 7 — Electrons behaving badly: metallic properties at high magnetic fields in wide band-gap insulators

  • Presenter: John Singleton, National High Magnetic Field Laboratory, Los Alamos National Laboratory
  • Host: Minhyea Lee
  • Abstract: From an early age, we are taught that metals are good conductors of electricity and heat but that insulators are not. At High School we learn that metals contain vast numbers of charged electrons that are free to move and carry heat and current, whereas insulators do not. At University, we find out that electrons are fermions, and perhaps comprehend Fermi-Dirac statistics, leading to the well-known definition that “a metal is a solid with a Fermi surface”. The Fermi surface is the constant-energy surface which at zero temperature separates the occupied electron states from the empty in momentum space; if we know the size and shape of a metal’s Fermi surface, we understand how its free electrons behave and hence can account for almost all of its electrical, thermal and magnetic properties. Over the past decade, this comforting picture has been upset by experiments on various materials at high magnetic fields and low temperatures. Though these substances are electrical insulators, they exhibit the de Haasvan Alphen effect - an oscillatory phenomenon in magnetic field that is taken as smoking-gun evidence for a Fermi surface; i.e., it is usually seen only in metals.
    After a brief review of the above phenomena, I shall concentrate on measurements of the Kagomelattice Mott insulator YCu3(OH)6Br2[Br1−y(OH)y] (YCOB) in magnetic fields of up to 75 T. Our pulsed-field magnetization experiments strongly suggest that YCOB is a quantum spin liquid. In such a system, antiferromagnetic order is suppressed by geometrical frustration and quantum fluctuations. Under these conditions, spin–charge separation of electrons can produce charge-neutral spinons, fermions that possess spin but no charge. Using ultrasensitive torque magnetometry, de Haas-van Alphen oscillations are observed, giving strong evidence for both the spinons and their companion particles, bosonic chargons; the latter cause the coupling of the applied magnetic field to the charge-neutral spinons. Further constraints are placed on the spinon Fermi surface using high-field susceptometry, capacitance and thermal experiments on YCOB single crystals. A theoretical model of spinon band structure that includes Dirac nodes near a 1/9 magnetization plateau produces quantitative predictions consistent with the observed oscillations. Finally, I shall review very recent measurements on other spin-liquid candidates such as Y-kapellasite, that point to the oscillations as possible universal behaviour in such insulators. 
  • Biography: John Singleton is a condensed-matter physicist and electrical engineer at the National High Magnetic Field Laboratory Pulsed-Field Facility (PFF), visiting professor at Oxford University and fellow of both the American Physical Society and the Institute of Physics. He has authored or co-authored over 500 papers in scientific journals, along with a popular undergraduate text book. The first member of his family to go to university, he was educated at Oxford University (BA, MA, D.Phil.); his D.Phil. involved semiconductor research at the industrial company GEC. Before coming to the PFF, he worked at the University of Nijmegen High-Field Magnet Laboratory, and was the equivalent of a full professor at Oxford University, where he founded a large research group that continues to this day. Other interests include unusual antennas (involving radio waves emitted by accelerated polarization currents that travel faster than the speed of light, mimicking some astronomical objects), playing the pipe organ, theology, caving (led the expedition that first bottomed the then seventh deepest cave in the world), youth work, mountains, free-range chickens and bread making.

October 14

  • Presenter: 
  • Host: 
  • Abstract: 

October 21

  • Presenter: Dennis Perepelitsa, University of Colorado Boulder
  • Host: Tobin Munsat
  • Abstract: 

October 28

  • Presenter: Harold Hwang, Stanford University
  • Host: Dan Dessau
  • Abstract: 

November 4

  • Presenter: Matina Gkioulidou, Johns Hopkins University
  • Host: Mihaly Horanyi
  • Abstract: 

November 11

  • Presenter: Lois Pollack, Cornell University
  • Host: Loren Hough
  • Abstract: 

November 18

  • Presenter: John Fasullo, NCAR
  • Host: Ivy Tan
  • Abstract: 

No Colloquium November 25 — Fall Break

December 2

  • Presenter: Nick Huggett, University of Illinois Chicago
  • Host: Allan Franklin
  • Abstract: 

For more information about colloquia this semester, contact: Mike Litos