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Events During the Week of July 14th through July 21st, 2024

Monday, July 15th, 2024

No events scheduled

Tuesday, July 16th, 2024

Thesis Defense
Suppressing Drift-Wave-Driven Turbulence with Magnetic Field Shaping
Time: 9:00 am - 11:00 am
Place: 106 Engineering Research Building;
Speaker: Joseph Duff, Physics PhD Graduate Student
Abstract: The effect of triangularity and sign of geodesic curvature $\mathcal{K}^x$ on ion-temperature-gradient (ITG)-driven turbulence was investigated, covering both extreme positive and negative triangularities. Triangularity had a substantial impact on linear and nonlinear physics, and reversing $\mathcal{K}^x$ significantly impacted turbulence saturation. Negative triangularity reduced peak linear growth rates and broadened the growth rate spectrum as a function of radial wavenumber $k_x$. Positive triangularity increased peak growth rates that shifted to finite $k_x$ and narrowed the growth rate spectrum. Reversing the sign of $\mathcal{K}^x$ slightly lowered linear growth rates, except for $\delta=0.85$, where the growth rates decreased significantly. The effect of triangularity on linear instability properties at low perpendicular wavenumbers can be explained through its impact on magnetic polarization and curvature. The nonlinear heat flux was weakly dependent on triangularity for $-0.5\le\delta\le0$, increasing significantly with extreme $\delta$, regardless of sign. When $\mathcal{K}^x$ was reversed, the heat flux decreased, became weakly dependent on triangularity for $\abs{\delta}\le0.5$, and decreased significantly at extreme triangularity, regardless of sign. Zonal modes play an important role in nonlinear saturation for the configurations studied, and artificially suppressing zonal modes increased the nonlinear heat flux by a factor of at least two and a half, with negative triangularities having a larger increase. When $\mathcal{K}^x$ was reversed, so did the trend of heat flux ratios with triangularity. Proxies for zonal-flow damping and drive suggest that zonal flows are enhanced with increasing positive $\delta$ in both $\mathcal{K}^x$ scenarios. Conventional quasilinear models did not capture the nonlinear heat flux trends, but, by using a reduced three-field fluid model for ITGs, the effect of unstable modes coupling to stable modes via zonal modes was added to the quasilinear model. This three-wave-interaction corrected quasilinear model was only able to capture the nonlinear trends in triangularity when $\mathcal{K}^x$ was reversed. The failure of the modified quasilinear model to estimate the nonlinear trend for the physical equilibria was likely due to the nonlinear heat flux spectra extending into scales where the fluid model is not valid. Optimizations resulted in two three-dimensionally-shaped magnetic configurations with suppressed trapped-electron-mode (TEM)-driven turbulence. Initial equilibria had flux surface shapes with a helically rotating negative triangularity (NT) and positive triangularity (PT). The optimization targeted quasihelical symmetry and the available energy of trapped particles. In electron-temperature-gradient-driven scenarios, the most unstable linear modes of the TEM-optimized configurations were inconsistent with TEMs, and the nonlinear simulations showed no significant fluctuations at ion scales. When a density gradient was present, the most unstable modes at low $k_y$ were toroidal universal inabilities (UIs) in the NT case and slab UIs in the PT geometry. Nonlinear simulations showed that UIs drove substantial heat flux in the NT and PT configurations. Increasing the ratio of plasma pressure to magnetic pressure to $\beta=4\times10^{-3}$ significantly reduced linear instability at low $k_y$, halved the nonlinear heat flux for the NT case, and almost completely suppressed the turbulence in the PT configuration.
Host: Chris Hegna
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Wisconsin Quantum Institute
Quantum Coffee Hour
Time: 3:00 pm - 4:00 pm
Place: Rm.5294, Chamberlin Hall
Abstract: Please join us for the WQI Quantum Coffee today at 3PM in the Physics Faculty Lounge (Rm.5294 in Chamberlin Hall). This series, which takes place approximately every other Tuesday, aims to foster a casual and collaborative atmosphere where faculty, post-docs, students, and anyone with an interest in quantum information sciences can come together. There will be coffee and treats.
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R. G. Herb Condensed Matter Seminar
Ultrafast quantum simulation and quantum computing with ultracold atom arrays at quantum speed limit
Time: 4:00 pm - 5:00 pm
Place: 5310 Chamberlin Hall
Speaker: Kenji Ohmori, Institute for Molecular Science (IMS), National Institutes of Natural Sciences, Japan
Abstract: Many-body correlations drive a variety of important quantum phenomena and quantum machines including superconductivity and magnetism in condensed matter as well as quantum computers. Understanding and controlling quantum many-body correlations is thus one of the central goals of modern science and technology. My research group has recently pioneered a novel pathway towards this goal with nearby ultracold atoms excited with an ultrashort laser pulse to a Rydberg state far beyond the Rydberg blockade regime [1-7]. We first applied our ultrafast coherent control with attosecond precision [2,3] to a random ensemble of those Rydberg atoms in an optical dipole trap, and successfully observed and controlled their strongly correlated electron dynamics on a sub-nanosecond timescale [1]. This new approach is now applied to arbitrary atom arrays assembled with optical lattices or optical tweezers that develop into a pathbreaking platform for quantum simulation and quantum computing on an ultrafast timescale [4-7]. In this ultrafast quantum computing, as schematically shown in Fig. 1, we have recently succeeded in executing a controlled-Z gate, a conditional two-qubit gate essential for quantum computing, in only 6.5 nanoseconds at quantum speed limit, where the gate speed is solely determined by the interaction strength between two qubits [5]. This is, faster than any other two-qubit gates with cold-atom hardware by two orders of magnitude. It is also two orders of magnitude faster than the noise from the external environment and operating lasers, whose timescale is in general 1 microsecond or slower, and thus can be safely isolated from the noise. Moreover, this two-qubit gate is faster than the fast two-qubit gate demonstrated recently by “Google AI Quantum” with superconducting qubits [8]. References [1] N. Takei et al., Nature Commun. 7, 13449 (2016). Highlighted by Science 354, 1388 (2016); IOP (2016). [2] H. Katsuki et al., Acc. Chem. Res. 51, 1174 (2018). [3] C. Liu et al., Phys. Rev. Lett. 121, 173201 (2018). [4] M. Mizoguchi et al., Phys. Rev. Lett. 124, 253201 (2020). [5] Y. Chew et al., Nature Photonics 16, 724 (2022). (Front Cover Highlight) [6] V. Bharti et al., Phys. Rev. Lett. 131, 123201 (2023). [7] V. Bharti et al., arXiv:2311.15575 (2023). [8] B. Foxen et al., Phys. Rev. Lett. 125, 120504 (2020).
Host: Robert McDermott
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Wednesday, July 17th, 2024

Summer Recess
Time: 12:30 pm - 1:00 pm
Place: Bascom Hill outside Birge
Speaker: Sharon Kahn
Abstract: Come take a break and play from 12:30-1 on Bascom Hill (outside of Birge)! Some of us will be walking up, leaving from the courtyard between Chamberlin and Sterling ~12:25 – feel free to walk with us!

Cornhole, ladder toss, frisbee, juice boxes. . . .
Hope you’ll join us!
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Thursday, July 18th, 2024

No events scheduled

Friday, July 19th, 2024

No events scheduled