Events at Physics |
Events on 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
- Speaker: Joonseok Hur, University of Colorado Boulder
- 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