Colloquia will begin at 4 p.m. in room 1412 of the John S. Toll Physics Building. Refreshments are served there at 3:30 p.m.

For further information, please contact the Physics Department at This email address is being protected from spambots. You need JavaScript enabled to view it..

## February 1
| ## John Mather, NASA and UMDHosted by Drew Baden ## Progress towards Opening the Infrared Treasure Chest with JWSTThe long-awaited James Webb Space Telescope was launched on Dec. 25, 2021 and is well along in its trip to L2. With its 6.5 m deployable primary mirror, and cameras and spectrometers covering 0.6 to 28 µm, it promises extraordinary improvements in observing capabilities. Webb will be able to observe the first objects that formed after the Big Bang, the growth of galaxies, the formation of stars and planetary systems, individual exoplanets through coronography and transit spectroscopy, and all objects in the Solar System from Mars on out. It could observe a 1 cm^{2} bumblebee at the Earth-Moon distance, in reflected sunlight and thermal emission. I will show the mission status, and review the observatory capabilities and planned observing program. The Webb is a joint project of NASA with the European and Canadian space agencies. I will also note the possibilities for the next generation of ground-based telescopes with adaptive optics, including orbiting laser guide stars and an orbiting starshade for direct observation of exoplanets. |

## February 8 | ## Alicia Kollár, UMD
## Circuit QED LatticesThe field of circuit QED has emerged as a rich platform for both quantum computation and quantum simulation. Lattices of coplanar waveguide (CPW) resonators realize artificial photonic materials in the tight-binding limit. Combined with strong qubit-photon interactions, these systems can be used to study dynamical phase transitions, many-body phenomena, and spin models in driven-dissipative systems. I will show that waveguide resonators permit the creation of unique devices which host photons in curved spaces, gapped at bands, and novel forms of qubit-qubit interaction. I will show that graph theory is the natural language for describing these microwave photonic systems and that combining this mathematical tool box with the physics of lattice systems sheds light both on the kinds of devices that are achievable in circuit QED as well as open questions in pure and applied mathematics. |

## February 15Online | ## Sara Walker, Arizona State UniversityHosted by the Graduate Student Colloquium Committee ## Life is What?!Currently, no general theory exists that explains what life is. While many definitions for life do exist, these are primarily descriptive, not predictive, and they have so far proved insufficient to explain the origins of life, or to provide rigorous constraints on what properties we might expect all examples of life to share (e.g., in our search for life in alien environments). In this talk I discuss new approaches to understanding what universal principles might explain the nature of life and elucidate the mechanisms of its origins, focusing on recent work in our group elucidating regularities and law-like behavior of biochemical networks on Earth from the scale of individual organisms to the planetary scale.To be held via Zoom: https://umd.zoom.us/j/97470621369?pwd=S2V1bmxNeStNTnJmT3JiY1g3TTUvdz09 Meeting ID: 974 7062 1369 |

## February 22 | ## Monika Schleier-Smith, Stanford UniversityHosted by Alicia Kollár ## Atoms and Photons: Quantum Technology meets Fundamental PhysicsThe power of quantum information lies in its capacity to be non-local, encoded in correlations among entangled particles. Yet our ability to produce, understand, and exploit such correlations is hampered by the fact that the interactions between particles are ordinarily local. To circumvent this limitation in the laboratory, we let distant atoms “talk” to each other with the aid of photons that act as messengers. By tailoring the frequency spectrum of an optical control field, we program the spin-spin couplings in an array of atomic ensembles, thereby accessing frustrated interaction graphs and exotic geometries and topologies. Such advances in optical control of interactions open new opportunities in areas ranging from quantum technologies to fundamental physics. I will touch on implications for quantum optimization algorithms, quantum-enhanced sensing, and simulating quantum gravity. |

## March 8 | ## Aida El-Khadra, University of Illinois Urbana-ChampaignHosted by Zohreh Davoudi ## The Dance of the MuonMore than eighty years after the muon was first discovered, it is still a source of mystery. Indeed, several experiments are underway or planned that use muons as a window to search for new physics — a central goal of the high energy physics community. In an exciting development, last year's announcement by the Fermilab experiment of it's first measurement result sharpens the long-standing tension between experiment and theory for the muon’s magnetic moment to 4.2 standard deviations. The Fermilab experiment's measurement uncertainty will continue to improve, with the ultimate goal of reducing it by a factor of four. In addition, a planned experiment in Japan will provide a completely independent measurement of this quantity. After a brief tour of its history, I will discuss the ongoing interplay between theory and experiment that is essential for unlocking the discovery potential of this effort. |

## March 29 | ## Nicole Yunger Halpern, QuICS, IPST and NISTHosted by Steve Rolston ## Quantum Steampunk: Quantum information meets thermodynamicsThermodynamics has shed light on engines, efficiency, and time’s arrow since the Industrial Revolution. But the steam engines that powered the Industrial Revolution were large and classical. Much of today’s technology and experiments are small-scale, quantum, far from equilibrium, and processing information. Nineteenth-century thermodynamics requires updating for the 21st century. Guidance has come from the mathematical toolkit of quantum information theory. Applying quantum information theory to thermodynamics sheds light on fundamental questions (e.g., how does entanglement spread during quantum thermalization? How can we distinguish quantum heat from quantum work?) and practicalities (e.g., nanoscale engines and the thermodynamic value of quantum coherences). I will overview how quantum information theory is being used to modernize thermodynamics for quantum-information-processing technologies. I call this combination quantum steampunk, after the steampunk genre of literature, art, and cinema that juxtaposes futuristic technologies with 19th-centurysettings. |

## April 5 | ## Vidya Madhavan, University of Illinois Urbana-ChampaignHosted by Johnpierre Paglione## Helical tunneling of Dirac FermionsA well-known result from quantum mechanics is that when normal electrons scatter from a potential barrier, the probability of tunneling is suppressed with both barrier height and width. In a surprising result, Oskar Klein showed in 1929 that relativistic Dirac fermions can show completely unexpected tunneling behavior. For example, an electron encountering a barrier may be perfectly transmitted even for an infinitely tall barrier. Topological insulators hosting boundary modes with Dirac dispersion are ideal candidates to demonstrate the unique tunneling properties of relativistic fermions. However, such experiments have been difficult to carry out due to a combination of materials issues and geometric constraints. In this work we use nanowires of a special correlated topological insulator (SmB6) mounted on the tip of a scanning tunneling microscope to demonstrate a tunneling process called `helical tunneling’ where the tunneling Dirac fermions are spin-polarized even in the absence of broken time-reversal symmetry. Our calculations show that the spin-polarization must reverse sign when traveling in the opposite direction, which we confirm in our experiments. Our findings show that the topological surface states in SmB6 nanowires are conduits for robust spin polarized currents and demonstrate another unexpected tunneling property of relativistic Dirac electrons. |

## April 12
| ## TBA |

## April 19 | ## John Carlstrom, University of ChicagoHosted by Drew Baden |

## April 26 | ## Postponed: Jogesh Pati, Stanford University |

## May 3 | ## Postponed: Cora Dvorkin, Harvard University |

## May 10 | ## Jeff Newman, University of PittsburghHosted by Drew Baden## DESI and Beyond: Exploring the Universe with Spectroscopic SurveysOver the past two decades, large spectroscopic surveys have measured the redshifts of millions of individual galaxies and quasars, allowing us to map the three-dimensional distribution of matter in the Universe. These experiments help to constrain the nature of dark energy by measuring the baryonic acoustic oscillation (BAO) distance scale, test for deviations from general relativity by measuring redshift-space distortions in the observed clustering of galaxies, and place limits on neutrino masses via the strength of clustering signals. In this talk, I will primarily focus on the plans for and status of the ongoing Dark Energy Spectroscopic Instrument (DESI) survey. DESI is the first of the next-generation, "Stage IV" dark energy experiments to begin operations. I will also summarize key results from the recently-completed Sloan Digital Sky Survey-4 eBOSS survey, which has helped to prototype methods now being used for DESI. Finally, I will briefly describe ideas for new telescopes and instruments that would enable surveys an order of magnitude larger than what is possible now, as well as how such surveys would help us to understand our universe. |