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From quantum transport in semiconducting nanowires to hybrid semiconducting-superconducting qubits

Zarassi, Azarin (2021) From quantum transport in semiconducting nanowires to hybrid semiconducting-superconducting qubits. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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A practical quantum computer demands a physical quantum bit (qubit) that is scalable, has a well-defined initial state, and brings together coherence with reliable control and read-out. A compelling idea is to put together a locally protected Majorana qubit with a superconducting qubit. The superconducting qubit is used to read out the Majorana states while the Majorana qubit may act as a quantum memory. This thesis presents a series of studies on quantum transport in semiconducting nanowires coupled to superconductors to investigate various platforms for realizing Majorana. These studies are followed by microwave measurements on superconducting circuits compatible with semiconducting-superconducting heterostructures.
We first evaluate the potential of Ge/Si core/shell nanowires by achieving induced superconductivity as well as estimating spin-orbit coupling. Next we explore the transport mediated by Andreev bound states formed in InSb nanowire quantum. A subgap negative differential conductance is investigated together with the coalescing Andreev resonances at zero bias relevant for the correct interpretation of Majorana experiments done on the same structures. We conclude our studies of semiconducting nanowires by exploring tunnel junctions in Sn-InSb nanowires that are prepared by in-situ shadowing using nearby nanowires and flakes. Tin shells are found to induce a hard superconducting gap persisting up to high magnetic fields. We observe the two-electron charging effect from a small superconducting island of Sn-InSb. This effect is attributed to charge parity stability, which makes this nanowire system an intriguing candidate for superconducting and topological quantum circuits.
These Sn-InSb junctions are then used as the nonlinear element in a transmon qubit design where we observe a dispersive coupling between this nanowire Josephson junction and a superconducting resonator. We also present our progress towards building a magnetic field resilient superconducting circuit that allows integration with semiconducting and topological structures.
In the last chapter, InSb semiconducting nanowires are utilized as shadow masks prior to superconductor deposition on an InAs quantum well. We study Josephson current properties in Josephson junctions made from these nanowire shadows. Our results point to highly transparent junctions that can be developed further for hybrid superconductor-semiconductor qubit systems.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Zarassi, Azarinazarin.zarassi@gmail.comazz2@pitt.edu0000-0003-3111-4468
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairFrolov, Sergey
Committee MemberHatridge, Michael
Committee MemberPekker, David
Committee MemberBezanson, Rachel
Committee MemberLeu, Paul
Date: 20 January 2021
Date Type: Publication
Defense Date: 6 August 2020
Approval Date: 20 January 2021
Submission Date: 21 July 2020
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 205
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: Quantum transport. Semiconducting naonwires. Superconductivity. Superconducting quantum circuits.
Date Deposited: 20 Jan 2021 19:22
Last Modified: 20 Jan 2021 19:22


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