Events at Physics |
Events During the Week of September 14th through September 21st, 2025
Monday, September 15th, 2025
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Plasma physics, results, and learnings from the first year of WHAM’s operation
- Time: 12:00 pm - 1:00 pm
- Place: 2241 Chamberlin Hall
- Speaker: Jay Anderson, UW Madison
- Abstract: WHAM has just completed its first year of operation, becoming the first fusion experiment to combine high-temperature-superconducting coils with MW-scale plasma heating systems in confining a relatively small (a ~ 15 cm, L = 2 m) plasma. Applying 17 T on the plasma in the mirror throat (a world record in magnetic confinement fusion research) presents a broad 4 T contour in the plasma to enable fundamental ECH at 110 GHz with access to high density operation. Indeed, WHAM’s achieved operational space spans central electron density between 2x10^17 and 2x10^20 per m3, bookended by an intense hot electron regime at low density and a fully collisional gas-dynamic regime at high density. WHAM’s physics missions focus on an intermediate density regime dominated by hot ions (via neutral beam injection) where particle confinement is governed by ion-ion pitch angle scattering and increases rapidly with average energy. The axisymmetric mirror is unstable to MHD interchange, and the tradeoff to its simple geometry and engineering advantages is requirement of additional actuators to ensure MHD stabilization. WHAM has partially reproduced the spectacularly successful vortex confinement technique via imposed ExB rotation and has achieved modest perpendicular beta of nearly 10% and ion energies up to 1 keV. Ongoing work aims to reduce charge exchange and radiated power losses, investigate alternate stabilization techniques, determine optimal mirror ratio, and continue to press upwards in ion energy via addition of rf heating. WHAM’s construction was funded by ARPA-E and ongoing research is supported by Realta Fusion.
- Host: Cary Forest
- Theory Seminar (High Energy/Cosmology)
- Astrophysical Probes of Complex Dark Sectors
- Time: 1:00 pm - 2:30 pm
- Place: Chamberlin 5280
- Speaker: Caleb Gemmell, UW-Madison
- Abstract: Complex dark sectors are models where a 'sector' of new particles with intra-sector interactions are used to extend the Standard Model. Motivated by theoretical considerations such as the Hierarchy Problem, these models generically also provide dark matter candidates. In this talk I will cover a range of astrophysical probes from the indirect detection of dark matter to using cosmological simulations to study sub-galactic structure, and outline how these methods are sensitive to the novel interactions and signatures that become possible in new dark confining sectors, or models of atomic dark matter. Event recording:
- Host: Joshua Fonster
Tuesday, September 16th, 2025
- No events scheduled
Wednesday, September 17th, 2025
- Department Meeting
- Time: 12:15 pm - 1:15 pm
- Place: B343 Sterling
- Speaker: Kevin Black, UW-Madison
- Closed meeting to discuss personnel matters—pursuant to Section 19.85(1)(c) of the Wisconsin Open Meetings Law Closed to all but tenured faculty
- Host: Kevin Black
Thursday, September 18th, 2025
- Astronomy Colloquium
- Show & Tell
- Time: 3:30 pm - 4:30 pm
- Place: 4421 Sterling Hall
- Abstract: The first two colloquia on September 11th and September 18th will be our annual department orientation (also known as the “show and tell”). During these sessions, everyone will have 1.5 minutes to introduce themselves and provide a brief overview of their work. This is a great chance to get to know the diversity of research within our department, the faces behind the names, and everyone’s favorite hobbies and interests.
We invite undergrads doing research, grad students, postdocs, scientists, and faculty members to participate. - Host: Nicholas Stone
Friday, September 19th, 2025
- Atomic Physics Seminar
- Spin-Squeezed Atomic Clock with Precision Beyond the Standard Quantum Limit at the 10⁻¹⁸ Level
- Time: 10:00 am - 11:00 am
- Place: 5280 Chamberlin Hall
- Speaker: Joonseok Hur, Colorado University
- Abstract: Optical atomic clocks (OACs), utilizing optical transitions in atoms as a timebase, have achieved unprecedented precision and accuracy in scientific measurement, offering new frontiers in metrology and fundamental physics.
The precision of state-of-the-art OACs has reached the standard quantum limit (SQL), the fundamental bound set by quantum projection noise in measurements on uncorrelated atoms. While increasing atom numbers can statistically suppress this noise, it also introduces unwanted atomic interactions that compromise clock accuracy. Engineered entanglement between atoms can overcome the SQL, and atomic clocks with spin-squeezed states have demonstrated improved precision with various platforms. However, quantum advantage in entanglement-enhanced clocks, surpassing the best precision of conventional OACs, has yet to be achieved.
In this talk, I will present our spin-squeezed optical lattice clock that achieves precision beyond the SQL at the 10⁻¹⁸ level, representing a significant step toward quantum advantage in optical clocks. We squeezed the collective projection noise of 30,000 atoms by 7.1(1.0) dB using quantum nondemolition measurements mediated by strong atom-cavity coupling. Improved motional control preserves clock-state coherence, resulting in a 5.1(1.0) dB metrological enhancement. A synchronous comparison between two independent spin-squeezed clock ensembles demonstrates a 2.0(2) dB improvement beyond the SQL, reaching a fractional instability of 1.1×10⁻¹⁸.
This work marks a milestone toward quantum-enhanced timekeeping and provides a promising platform to explore the interplay between gravity and quantum entanglement.
- Host: Josiah Sinclair
- Physics Department Colloquium
- Waves of Topological Origin in the Fluid Earth System and Beyond
- Time: 3:30 pm - 6:00 pm
- Place: Chamberlin 2241
- Speaker: Brad Marston, Brown University
- Abstract: Symmetries and topology are central to our understanding of physical systems. Topology, for instance, explains the precise quantization of the Hall effect and the protection of surface states in topological insulators against scattering from disorder or bumps. However discrete symmetries and topology have not, until recently, contributed much to our understanding of the fluid dynamics of oceans and atmospheres. In this talk I show that, as a consequence of the rotation of the Earth that breaks time reversal symmetry, equatorial Kelvin and Yanai waves emerge as topologically protected edge modes. The non-trivial topology of the bulk Poincaré waves is revealed through their winding number in frequency - wavevector space. Bulk-interface correspondence then guarantees the existence of the two equatorial waves. I discuss our recent direct detection of the winding number in observations of Earth’s stratosphere. Thus the oceans and atmosphere of Earth naturally share basic physics with topological insulators. As equatorially trapped Kelvin waves in the Pacific ocean are an important component of El Niño Southern Oscillation, the largest climate oscillation on time scales of a few years, topology plays a surprising role in Earth’s climate system. We also predict that waves of topological origin will arise in magnetized plasmas. I will describe experiments that we are conducting at UCLA’s Basic Plasma Science Facility (BaPSF). The waves may also arise in the solar system and beyond.
- Host: Alex Levchenko