# Harnessing Unconventional and Multiple Parametric Couplings for Superconducting Quantum Information

Lanes, Olivia (2020) Harnessing Unconventional and Multiple Parametric Couplings for Superconducting Quantum Information. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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## Abstract

Josephson-junction based parametric amplifiers have become a ubiquitous component in superconducting quantum machines. Although parametric amplifiers regularly achieve near-quantum limited performance, they have many limitations, including low saturation power, lack of directionality, and narrow bandwidth. The primary aim of this thesis is to attack these problems by using multiparametric drives. We will discuss an assortment of multiparametric pumping schemes, and in particular, present an amplifying scheme that is created by applying imbalanced, simultaneous, strong gain and conversion pump tones in a Josephson Parametric Converter. This mode of amplification features broadband gain in transmission that is 10X the bandwidth of a typical, single-pumped JPC amplifier and is matched in reflection up to -15 dB, making it only one scattering parameter away from the ideal quantum-limited amplifier. Since this amplifier is matched in reflection, we also explore the possibility of being able to chain these amplifiers to enhance the saturation power and work towards a fully directional amplifier.

In addition, we discuss superconducting, thin-film van der Waals materials for use in superconducting circuits. We began by studying the nature of the contact made between 3D bulk aluminum and these 2D flakes, and discovered we could create truly superconducting contact at their interface. Next, we created a superconducting SQUID from two of these atypical junctions, and studied its quantum interference pattern. We were able to measure critical currents of 10-100's of $\mu$A, and also found that the effective area of both the junctions and the superconducting loop itself is much larger than their physical size due to the geometry of the flake. In addition, we studied the kinetic inductance of these flakes by placing them in NbTiN superconducting resonators, and found that the kinetic inductance we were measuring is around 2 orders of magnitude higher than what was predicted by theory.

The thesis paves the way for using nontraditional elements and pumping schemes in superconducting circuits to create a new generation of devices for use in superconducting quantum information processes. In the future, hopefully, these fabrication techniques and experimental discoveries will bring the field closer to a fault tolerant, universal quantum computer.

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## Details

Item Type: University of Pittsburgh ETD
Status: Unpublished
Creators/Authors:
Lanes, Oliviaotl1@pitt.eduotl1
ETD Committee:
Committee ChairHatridge, Michaelhatridge@pitt.edu
Committee MemberHunt, Benjaminbmhunt@andrew.cmu.edu
Committee MemberLevy, Jeremyjlevy@pitt.edu
Committee MemberPekker, Davidpekkerd@pitt.edu
Date: 16 September 2020
Date Type: Publication
Defense Date: 12 June 2020
Approval Date: 16 September 2020
Submission Date: 23 June 2020
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 191
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Physics
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Superconducting qubits
Date Deposited: 16 Sep 2020 14:26