Graduate Program Events

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

Monday, August 21st, 2023

Faculty contract year begins
Abstract: *Note: actual end time may vary.* URL:
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Tuesday, August 22nd, 2023

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Wednesday, August 23rd, 2023

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Thursday, August 24th, 2023

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

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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Saturday, August 26th, 2023

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Sunday, August 27th, 2023

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