Quasiparticle effects in magnetic-field-resilient 3D transmons

• URL: http://arxiv.org/abs/2403.03351v1
• Date: Tue, 5 Mar 2024 22:37:21 GMT
• Title: Quasiparticle effects in magnetic-field-resilient 3D transmons
• Authors: J. Krause, G. Marchegiani, L. M. Janssen, G. Catelani, Yoichi Ando, and C. Dickel
• Abstract summary: We present measurements of the parity-switching time of a field-resilient 3D transmon with in-plane field up to 0.41T. We demonstrate that the superconducting-gap asymmetry plays a crucial role in the observed behavior. We establish that Al-AlO$_x$-Al JJs could be used in architectures for the parity-readout and manipulation of topological qubits.
• Score: 0.0
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Recent research shows that quasiparticle-induced decoherence of superconducting qubits depends on the superconducting-gap asymmetry originating from the different thicknesses of the top and bottom films in Al/AlO$_x$/Al junctions. Magnetic field is a key tuning knob to investigate this dependence as it can change the superconducting gaps in situ. We present measurements of the parity-switching time of a field-resilient 3D transmon with in-plane field up to 0.41T. At low fields, small parity splitting requires qutrit pulse sequences for parity measurements. We measure a non-monotonic evolution of the parity lifetime with in-plane magnetic field, increasing up to 0.2T, followed by a decrease at higher fields. We demonstrate that the superconducting-gap asymmetry plays a crucial role in the observed behavior. At zero field, the qubit frequency is nearly resonant with the superconducting-gap difference, favoring the energy exchange with the quasiparticles and so enhancing the parity-switching rate. With a higher magnetic field, the qubit frequency decreases and gets detuned from the gap difference, causing the initial increase of the parity lifetime, while photon-assisted qubit transitions increase, producing the subsequent decrease at higher fields. Besides giving a deeper insight into the parity-switching mechanism in conventional transmon qubits, we establish that Al-AlO$_x$-Al JJs could be used in architectures for the parity-readout and manipulation of topological qubits based on Majorana zero modes.

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