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Quantum Matter Seminar

Monday, November 15, 2021
4:00pm to 5:00pm
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Online Event
The transmon as a probe of Andreev bound states
Angela Kou, Professor, Physics, University of Illinois Urbana-Champaign,

This seminar will be held remotely. Zoom information https://caltech.zoom.us/j/83422928274

Hybrid superconducting circuits, which integrate non-superconducting elements into a circuit quantum electrodynamics (cQED) architecture expand the possible applications of cQED. In hybrid superconducting circuits, one can investigate the properties of unconventional Josephson junctions with extremely fine energy resolution or perform readout of quantum dots and spin ensembles. In this talk, I will discuss our work using superconducting transmon qubits to investigating Andreev bound states (ABS) in weak-link junctions formed in Al-proximitized InAs nanowires. First, I will describe our experiments using a quantum dot to control the transmission of ABS in the junction of a transmon qubit. We tuned the transmission of the ABS to near-unity and observe suppression of the transmon charge dispersion consistent with a long-predicted scaling law that incorporates two branches of the Josephson potential. Next, I will discuss our work using a transmon to investigate the ground state of a weak-link junction with a quantum dot embedded in it. In such a device, the competition between the charging energy of the dot and superconductivity stabilizes different spin ground states in the junction. I will present our measurements of the phase diagram in this composite system and the quasiparticle poisoning dynamics associated with each phase.

For more information, please contact Tracy Mikuriya by phone at 626-395-8579 or by email at [email protected].