Events at Physics |
Events on Wednesday, October 21st, 2026
- Preliminary Exam
- Probing Element Specific Ultrafast Carrier and Spin Dynamics in Quantum and Magnetic Materials using X-FAST Instrument
- Time: 11:00 am - 1:00 pm
- Place: Chamberlin 5280
- Speaker: Aakankshya Mishra
- Abstract: Emerging quantum and magnetic materials host strongly coupled electronic, spin, and lattice degrees of freedom that can evolve on femtosecond timescales, making their nonequilibrium behavior important for understanding and ultimately controlling material properties relevant to future information and quantum technologies. This work uses X-ray Femtosecond Absorption Spectroscopy Tabletop (X-FAST), a laboratory-based extreme-ultraviolet (XUV) transient absorption instrument, to investigate these ultrafast processes with element specificity. X-FAST employs high-harmonic generation (HHG) to produce femtosecond XUV pulses that probe element-specific core-to-valence transitions following excitation by an ultrafast optical pump. This preliminary examination will introduce the motivation for studying emerging quantum and magnetic materials, the fundamentals and development of HHG-based tabletop XUV sources, and the experimental methodology and optimization of the X-FAST instrument. The capabilities of X-FAST will be demonstrated through measurements of 2H-MoTe₂ as a benchmark system and through studies of MnPtGa, where element-specific transient absorption provides insight into photoinduced carrier redistribution and its connection to the material’s magnetic electronic structure. In addition, the development and integration of a cryogenic sample environment will extend X-FAST toward temperature-dependent measurements, enabling the separation of electronic, magnetic, and lattice contributions and the investigation of phase-dependent ultrafast dynamics. Finally, future directions will focus on expanding the range of quantum and magnetic materials studied with X-FAST and advancing the instrument toward a versatile platform for probing and understanding nonequilibrium material behavior across ultrafast timescales and variable temperatures.
- Host: Uwe Bergmann
- Theory Seminar (High Energy/Cosmology)
- Entanglement Limits on Coherent Enhancement
- Time: 1:00 pm - 2:30 pm
- Place: Chamberlin 5280
- Speaker: Zach Bogorad, Fermilab
- Abstract: Coherent enhancement is a powerful mechanism for improving the sensitivity of a wide range of detectors, but its practical use is often limited by the difficulty of preparing the required quantum states. In this talk, I will show that this difficulty has a fundamental origin: coherent enhancement is quantitatively constrained by entanglement. I will present general bounds on how the strength of coherent effects can scale with system size, as a function of the single-mode entanglement entropy of the detector. These bounds smoothly interpolate between the incoherent and fully coherent regimes, and apply both to parameter-estimation problems and to scattering processes. I will discuss these results from two complementary perspectives: First, they appear as bounds on the quantum Fisher information of many-body states, which translate directly into limits on parameter sensitivity via the quantum Cramér–Rao bound. Second, they can be interpreted as limits on a class of scattering cross sections, leading to predictions for how minimum detectable interaction strengths scale with target size. Together, these results provide a unified view of coherent enhancement in metrology and scattering experiments, and motivate the development of new techniques for generating entangled detector states.
- Host: Josh Foster