Events During the Week of August 3rd through August 10th, 2025
Monday, August 4th, 2025
- Thesis Defense
- Scaling Technologies for Si/SiGe Spin Qubits
- Time: 10:00 am - 12:00 pm
- Place: 5310 Chamberlin
- Speaker: Michael Wolfe, Physics PhD Graduate Student
- Abstract: In my talk, I will present several experiments that address scalability challenges ahead for Si/SiGe quantum processors. Silicon qubits are uniquely positioned among quantum computing platforms due to their exceptionally small feature sizes and compatibility with the mature semiconductor industry infrastructure. However, the path to large-scale quantum computation capable of transformative societal impact is fraught with challenges. Chief among these are achieving device uniformity, establishing scalable connectivity to control electronics, enabling rapid initialization compatible with error correction, and maintaining qubit control at elevated temperatures. This thesis first addresses device uniformity by demonstrating a novel technique to control density of charge traps in the Si/SiGe heterostructure. Next, connectivity is explored with an on-chip cryogenic multiplexer which exponentially reduces the number of chip-to-fridge readout connections. Finally, experiments a on Intel Tunnel falls device are presented: (1) a new technique to quickly initialize spin qubits out of a latched state, and (2) a novel readout method that opens the door for high-temperature control of Si/SiGe qubits. Put together, these advances move Si/SiGe quantum dot qubits closer towards large-scale quantum computation.
- Host: Mark Eriksson
Tuesday, August 5th, 2025
- No events scheduled
Wednesday, August 6th, 2025
- Social Gathering
- Summer Recess
- Time: 12:30 pm - 1:00 pm
- Place: Bascom Hall in front of Birge Hall
- Speaker: Everyone is welcome
- Abstract: If the weather is nice, we'll meet on Bascom Hill (in front of Birge Hall). Feel free to bring your lunch. We will borrow cornhole and ladder toss from the L&S Dean's Office and play outside for 30 minutes. Some of us will probably walk up together, meeting in the courtyard between Chamberlin and Sterling ~12:25. Feel free to walk with us! No need to sign up. Just come join us!
- Host: Sharon Kahn
Thursday, August 7th, 2025
- Thesis Defense
- Utilizing the Quadrupole Transition for Cooling and Imaging of Cs Atoms
- Time: 2:00 pm - 4:00 pm
- Place: 5310 Chamberlin
- Speaker: Jacob Scott, Physics PhD Graduate Student
- Abstract: Neutral atom quantum computing platforms depend on precise control and measurement of atomic qubits to realize high-fidelity operations at scale. This thesis presents a set of experimental and engineering contributions that address critical requirements on laser systems and light–atom interactions for advancing quantum control of cesium atoms.
It details the development of low-noise electronic feedback systems for laser frequency locking and magnetic field stabilization, engineered to support stable and low-noise experimental operation. It further introduces the design, implementation, and noise characterization of narrow-linewidth laser systems driving Rydberg-level transitions, which underpin high-fidelity two-qubit gates via the Rydberg blockade mechanism.
The work also establishes the electric quadrupole transition in cesium as a powerful tool for state-selective, background-free quantum state readout, achieving a classification fidelity of 0.9993 and an atom survival probability of 0.995. Additionally, it demonstrates that laser cooling on this transition effectively reduces post-optical pumping atom temperatures to 5.4 uK.
Collectively, these results advance the frontier of robust, high-performance control in cesium-based quantum computing and significantly expand the capabilities of neutral atom architectures. - Host: Mark Saffman
Friday, August 8th, 2025
- Thesis Defense
- Characterization of Tearing Mode Dynamics with the Radial Interferometer-Polarimeter on DIII-D
- Time: 10:00 am - 12:00 pm
- Place: B343 Sterling or https://uwmadison.zoom.us/j/94014298365?pwd=6dvdDdkZDykib5djQPCEDDhwEMftfA.1
- Speaker: Rachel Myers, Physics PhD Graduate Student
- Abstract: The Faraday-effect Radial Interferometer-Polarimeter (RIP) diagnostic on DIII-D measures line-integrated magnetohydrodynamic fluctuations, such as tearing modes, at all radii, including modes not detected with external sensing coils. RIP results are compared to a synthetic line-integrated eigenfunction, corresponding to the mode amplitude on coils, using the linear code TJ. Even modes are finite on RIP, where the cylindrical approximation shows them vanishing. It is confirmed that RIP measures odd sidebands generated by linear coupling to toroidicity, which scales with inverse aspect ratio, and shaping. Experimentally measured shaping effects on RIP and tearing stability in inner-wall limited plasmas, which have more shape flexibility, are presented. Stability is calculated with DCON, which relies on equilibrium reconstructions with kineticEFIT. Modes grow as they approach the ideal-wall stability limit, which is near the classical tearing limit. These low-safety factor plasmas were dominated by sawteeth, which did not trigger tearing modes as expected. Tearing modes were driven as the plasma approached the ideal-wall limit, as opposed to the triggered, pressure-driven neoclassical tearing modes found in higher-performance plasmas. Even modes were less attenuated than previously measured because low safety factor induces a strong, detectable odd sideband to the even mode. RIP amplitudes varied over time due to nonlinear effects. RIP also experimentally confirms nonlinear coupling between edge harmonic oscillation (EHO) components in quiescent H-mode (QH-mode), previously predicted by nonlinear MHD simulations. We observe with RIP, but not sensing coils, nonlinear coupling of the EHO to core-resonant tearing modes, which interrupts the EHO and prevents access to long-lived QH-mode. This is concerning because QH-mode has an H-mode pedestal without edge localized modes (ELMs), which is attractive for ITER or a fusion reactor. Bicoherence values above 99% significance reveal that the first three EHO components are coupled throughout the QH phase, reflecting the cascade that sustains the EHO. In a case where QH-mode ceases and ELMy H-mode arises, we detect with RIP, but not with the coils, an intermittently returning EHO nonlinearly coupled to two core-resonant tearing modes. Coupling to tearing modes has caused the coupling between EHO components to vanish. The EHO becomes intermittent, while ELMs persist.
- Host: John Sarff/Brett Chapman
Saturday, August 9th, 2025
- No events scheduled
Sunday, August 10th, 2025
- Academic Calendar
- 8-week summer session ends
- Abstract: *Note: actual end time may vary.*