Operating in a deep underground facility improves the locking of gradiometric fluxonium qubits at the sweet spots

• URL: http://arxiv.org/abs/2201.09779v1
• Date: Mon, 24 Jan 2022 16:16:17 GMT
• Title: Operating in a deep underground facility improves the locking of gradiometric fluxonium qubits at the sweet spots
• Authors: Daria Gusenkova, Francesco Valenti, Martin Spiecker, Simon G\"unzler, Patrick Paluch, Dennis Rieger, Larisa-Milena Piora\c{s}-\c{T}imbolma\c{s}, Liviu P. Z\^arbo, Nicola Casali, Ivan Colantoni, Angelo Cruciani, Stefano Pirro, Laura Cardani, Alexandru Petrescu, Wolfgang Wernsdorfer, Patrick Winkel, Ioan M. Pop
• Abstract summary: The gradiometric fluxonium shows two orders of magnitude suppression of sensitivity to homogeneous magnetic fields. We observe unexpectedly short fluxon lifetimes of a few hours, which cannot be explained by thermal or quantum phase slips.
• Score: 40.52930634139674
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: We demonstrate flux-bias locking and operation of a gradiometric fluxonium artificial atom using two symmetric granular aluminum (grAl) loops to implement the superinductor. The gradiometric fluxonium shows two orders of magnitude suppression of sensitivity to homogeneous magnetic fields, which can be an asset for hybrid quantum systems requiring strong magnetic field biasing. By cooling down the device in an external magnetic field while crossing the metal-to-superconductor transition, the gradiometric fluxonium can be locked either at $0$ or $\Phi_0/2$ effective flux bias, corresponding to an even or odd number of trapped fluxons, respectively. At mK temperatures, the fluxon parity prepared during initialization survives to magnetic field bias exceeding $100 \,\Phi_0$. However, even for states biased in the vicinity of $1 \,\Phi_0$, we observe unexpectedly short fluxon lifetimes of a few hours, which cannot be explained by thermal or quantum phase slips. When operating in a deep-underground cryostat of the Gran Sasso laboratory, the fluxon lifetimes increase to days, indicating that ionizing events activate phase slips in the grAl superinductor.

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