Events on Monday, November 18th, 2024
- Thesis Defense
- Quantum Computing with Superconductor-Semiconductor Hybrid Systems
- Time: 10:00 am - 12:00 pm
- Place: B343, Sterling Hall;
- Speaker: Benjamin Harpt, Physics PhD Graduate Student
- Abstract: Quantum computers offer the potential to solve problems beyond the reach of classical computers by harnessing fundamentally different physics. Today, researchers worldwide are racing to develop quantum computers that are both controllable and scalable, utilizing a wide range of hardware approaches to encode quantum information. Superconducting circuits and semiconductor quantum dots are, individually, two of the leading qubit platforms for building solid-state quantum processors; combining the strengths of both materials in hybrid devices opens up new possibilities for quantum computing architectures. This dissertation explores key aspects of superconductor-semiconductor hybrid systems for quantum computing, and is structured in three parts. Part I presents an in-depth overview of silicon quantum-dot qubits, with a focus on experiments investigating crosstalk between exchange-only spin qubits. Part II addresses the integration of these qubits with superconducting resonators for readout and long-range entanglement. Using a quantum-dot device coupled to a vertically integrated resonator, we demonstrate an unconventional electron-photon interaction mechanism and show how it can be utilized for qubit readout and spectroscopy. Finally, Part III examines superconductor-semiconductor hybrid junctions and their qubit applications, detailing the development of superconducting alloys tailored for germanium-based hybrid devices. Together, these findings advance our understanding and introduce new techniques for developing hybrid quantum technologies.
- Host: Mark Eriksson
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Drift-cyclotron loss cone instability in 3D kinetic-ion simulations of WHAM
- Time: 12:05 pm - 1:00 pm
- Place: 1610 Engineering Hall
- Speaker: Aaron Tran, University of Wisconsin-Madison
- Abstract: WHAM's "peak-performance" beam-ion plasma may induce drift-cyclotron loss-cone (DCLC) instability: a coupled ion Bernstein / drift wave excited by the plasma’s radial density gradient and loss-cone velocity distribution. We present 3D plasma simulations, using kinetic ions and isothermal fluid electrons, of various WHAM configurations with sloshing (45 deg. pitch angle) beam-ion distributions from the collisional Fokker-Planck code CQL3D-m as an initial condition. Edge-localized electrostatic waves grow and saturate in ~1–10 μs with ω ~ 1–2× the ion cyclotron frequency. Wave properties can be explained by linear theory of DCLC in a planar slab. DCLC scattering fills the loss cone, so particle confinement is set by axial free streaming (aka "gas dynamic" confinement). Adding cool (~1 keV) ions to the plasma edge improves confinement by ~2–5×. I will also briefly comment on (i) other ways to stabilize DCLC, (ii) how DCLC fits into a broader landscape of instabilities in mirrors, and (iii) the effect of externally-driven shear flows.