Events at Physics

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Events During the Week of August 20th through August 27th, 2023

Monday, August 21st, 2023

Academic Calendar
Faculty contract year begins
Abstract: *Note: actual end time may vary.* URL:
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Physics Department Colloquium
Design and Testing of a Laser Thermal Propulsion Facility
Time: 11:00 am - 12:00 pm
Place: B343 Sterling Hall
Speaker: Siera Riel , REU student, McGill University
Abstract: New developments in laser physics have recently steered the discussion on alternative propulsion towards directed energy methods. In recent years, phase-locked fiber optic lasers have been extensively studied and appear to be promising methods of spacecraft propulsion for inter-planetary and eventually interstellar missions. In comparison to CO2 lasers considered in the 1970s-80s, the modularity and 1-µm operating wavelengths of fiber optic lasers allow their effective range to be extended by two orders of magnitude. They can be locked on reflectors onboard a spacecraft and redirected to sustain an on-board plasma core within a hydrogen heating chamber, theoretically reaching specific impulse values of approximately 3000 s. The application of these modular arrays to laser-thermal propulsion (LTP) for short-term Mars missions thus provides an adequate platform to explore its utility in interstellar missions. This experiment aims to develop a multi-purpose testing facility to investigate the thrust and thermal efficiency of an LTP system, as well as the effect of gas seeding on these characteristics. Zoom Meeting ID: 935 7095 9934 Passcode: 747340
Host: Alex Squitieri
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Tuesday, August 22nd, 2023

Council Meeting
Time: 3:00 pm - 4:00 pm
Place: 2314 Chamberlin
Speaker: Mark Eriksson, UW-Madison
Host: Mark Eriksson
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Network in Neutrinos, Nuclear Astrophysics, and Symmetries (N3AS) Seminar
The imprint of their explosions: Using supernova remnants to understand stellar death
Time: 6:00 pm
Place: Please note the unusual time...Join Zoom Meeting Meeting ID: 912 3071 4547
Speaker: Katie Auchettl , University of Melbourne, Australia
Abstract: One of the most uncertain aspects related to our understanding of the end points of stellar evolution is the link between the progenitor star and the nature of the supernova explosion that the progenitor will undergo. Even though hundreds of supernovae are discovered each year by optical surveys, these sources are usually too distant to resolve the ejecta and immediate surrounding of the exploded star. However, due to their long lifetimes and close proximity, supernova remnants which are the long lived structures that result from the supernova explosion of either a white dwarf or a massive star, provide us with a unique opportunity to study supernova explosion and dynamics up close and in detail. In this talk, I will highlight some recent advances that have been made in the understanding of supernovae and their progenitors using multi-wavelength studies of supernova remnants.
Host: A. Baha Balantekin
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Wednesday, August 23rd, 2023

Department Meeting
Time: 12:15 pm - 1:00 pm
Place: B343 Sterling Hall
Speaker: Mark Eriksson, UW-Madison
agenda to come a day or so before the meeting.
Host: Mark Eriksson
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Theory Seminar (High Energy/Cosmology)
Practical Dirac-Majorana Confusion Theorem: Issues and Applicability
Time: 2:30 pm - 3:30 pm
Place: Chamberlin 5280
Speaker: C S Kim, Yonsei U.
Abstract: We inspect the model-independent study of practical Dirac Majorana confusion theorem (pDMCT) -- a wide spread belief that the difference between Dirac and Majorana neutrinos via any kinematical observable would be practically impossible to determine because of the difference only being proportional to the square of neutrino mass -- in context of processes that have at least a neutrino antineutrino pair in their final state. We scrutinize the domain of applicability of pDMCT and also highlight those aspects that are often misunderstood. We try to clarify some of the frequently used concepts that are used to assert pDMCT as a generic feature irrespective of the process, or observable, such as the existence of any analytic continuity between Dirac and Majorana neutrinos in the limit mass(neutrino) -> 0. In summary, we illustrate that pDMCT is not any fundamental property of neutrinos, instead, it is a phenomenological feature of neutrino non-observation, depending on models and processes.
Host: George Wojcik
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Thursday, August 24th, 2023

Graduate Program Event
Thesis Defense
Defect Identification using Kelvin Probe Force Microscopy and Optimization of Long Single-Channel One-dimensional Quantum Wires
Time: 4:00 pm - 5:30 pm
Place: 5310 Chamberlin
Speaker: Leah Tom, Department of Physics Graduate Student
Abstract: The advent of quantum computing has been hailed as the next industrial revolution because of its promise to solve problems that are beyond the reach of classical computers. In order to harness the potential of quantum computing, it is important to protect fragile qubit states from environmental disturbances. This requires designing microelectronics with a greater degree of control over their fabrication. This thesis describes two projects, the first of which addresses the need for an enhanced understanding of defects in quantum dot qubit systems, and the second of which develops long single-channel one-dimensional quantum wires for topological qubits.

Charge fluctuators in Atomic Layer Deposited (ALD) aluminum oxide represent a major source of charge noise in quantum dot qubit devices. To mitigate this charge noise, the defects that adversely affect qubit operations need to be identified so that they can eventually be eliminated from the gate oxide. The spatial distribution of the defects in the gate oxide needs to be determined to correlate the defects with the charge noise measured.

Towards this end, Kelvin Probe Force Microscopy (KPFM) measurements are performed on a layer of ALD aluminum oxide grown atop bulk silicon. KPFM measures local variations in the work function that reveal a high density of charged defects in the aluminum oxide layer. Sweeping the AFM tip-to-sample bias induces charging and discharging events near the surface, allowing us to probe the defects' different charge states. With the aid of electrostatic simulations, the charging and discharging energies are extracted as a function of the voltage bias. The sign and magnitude of a charge state can also be determined from KPFM measurements. This thesis presents a method for identifying point defect distributions down to individual defects in a sample of high defect density.

This thesis also proposes a split gate design for creating long and uniform 1D quantum wires in low disorder systems that will be used for topological quantum computation using Majorana Zero Modes. This gate design is predicted to increase the length of a channel in a single conducting mode to 60-75% of lithographic gate length for a range of quantum wire lengths. This thesis also discusses how the split gate design prevents the formation of quantum dots in the channel and how to improve the channel’s adiabaticity.
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Friday, August 25th, 2023

Graduate Program Event
Final Thesis Defense
Rydberg Physics in a Cryogenic System for Hybrid Quantum Interfaces
Time: 10:00 am - 11:30 am
Place: B343 Sterling
Speaker: Juan Camilo Bohorquez, Department of Physics Graduate Student
Abstract: Rydberg atoms coupled to microwave cavities are promising experimental platforms for the development of hybrid atom-superconducting quantum computing systems, and the quantum transduction of microwave quantum information into the telecom band. Experimental efforts to couple Rydberg atoms to two-dimensional microwave resonators face significant challenges due to electric field noise near the cavity surfaces, and the large dc polarizability of Rydberg states, which scales as $\ds \sim a_0^3 n^7$.

In this work we present experimental results in reducing the dc polarizability of Rydberg states by a factor of 7, using an off-resonant microwave dressing field. These experimental results are compared to a model for the dressed atom system. We also present analytical and numerical models for the excitation of Cesium atoms to Rydberg states via a quadrupole-dipole excitation scheme with reduced sensitivity to Doppler shifts, a significant source of noise in entangling gates requiring ground-Rydberg coherence for high fidelity operation. These models are used to engineer an experimental effort which demonstrates the first Rydberg Rabi oscillations using this scheme. Finally, we present a path forward for the Rydberg atom-microwave cavity coupling effort, using a bulk microwave cavity which requires atoms be placed further from surfaces, reducing the effects of dc electric field noise.
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Academic Calendar
Graduate School Summer 2023: Master&#39;s degree deadline
Time: 4:00 pm - 5:00 pm
Abstract: CONTACT: 262-2433,
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Saturday, August 26th, 2023

No events scheduled

Sunday, August 27th, 2023

Academic Calendar
Graduate School Summer 2023: Doctoral degree deadline
Time: 11:55 pm - 12:55 am
Abstract: CONTACT: 262-2433,
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