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Thesis Defense

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Events During the Week of November 17th through November 23rd, 2024

Monday, November 18th, 2024

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
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Tuesday, November 19th, 2024

No events scheduled

Wednesday, November 20th, 2024

No events scheduled

Thursday, November 21st, 2024

No events scheduled

Friday, November 22nd, 2024

Pulsed-laser calibration of thermal microcalorimeters for X-ray astronomy
Time: 9:00 am - 11:00 am
Place: 6242 Chamberlin Hall or
Speaker: Avirup Roy, Physics PhD Graduate Student
Abstract: The performance of single photon microcalorimeters for high-resolution X-ray spectroscopy has improved to the point that it can be limited by our ability to calibrate these detectors. X-ray fluorescent lines have been the usual standard for calibrations, but they have intrinsic widths much broader than the current detector resolution. Since microcalorimeters respond to total energy deposited as heat, we have investigated the idea that five hundred 3 eV photons from an ultraviolet laser delivered in a pulse much shorter than the thermal integration time of detectors should look the same as a single 1500 eV X-ray photon. We have illuminated devices that have 290 μm square gold absorbers, superconducting transition-edge sensor (TES) thermometers, and about 1 eV FWHM resolution with ∼ 100 ns pulses from an ultraviolet laser. This produces combs of lines with 3 eV spacing and negligible intrinsic width that can be distinguished to at least 1700 eV. The accuracy of the line energies is limited only by our knowledge of the laser wavelength. Simultaneous illumination with oxygen and aluminum K fluorescent lines shows that the response to an X-ray photon is indistinguishable from the response to a burst of UV photons with the same total energy to better than 0.4 eV at 1500 eV. This performance is more than adequate for our current sounding rocket instrument. We discuss the path forward to possibly demonstrating the 0.1 eV at 10 keV standard that would be desirable for instruments on major space missions.
Host: Dan McCammon
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