Gate- and flux-tunable sin(2φ) Josephson element with planar-Ge junctions

Axel Leblanc (), Chotivut Tangchingchai, Zahra Sadre Momtaz, Elyjah Kiyooka, Jean-Michel Hartmann, Frédéric Gustavo, Jean-Luc Thomassin, Boris Brun, Vivien Schmitt, Simon Zihlmann, Romain Maurand, Étienne Dumur, Silvano Franceschi () and François Lefloch ()
Additional contact information
Axel Leblanc: Univ. Grenoble Alpes
Chotivut Tangchingchai: Univ. Grenoble Alpes
Zahra Sadre Momtaz: Institut Néel
Elyjah Kiyooka: Univ. Grenoble Alpes
Jean-Michel Hartmann: Univ. Grenoble Alpes
Frédéric Gustavo: Univ. Grenoble Alpes
Jean-Luc Thomassin: Univ. Grenoble Alpes
Boris Brun: Univ. Grenoble Alpes
Vivien Schmitt: Univ. Grenoble Alpes
Simon Zihlmann: Univ. Grenoble Alpes
Romain Maurand: Univ. Grenoble Alpes
Étienne Dumur: Univ. Grenoble Alpes
Silvano Franceschi: Univ. Grenoble Alpes
François Lefloch: Univ. Grenoble Alpes

Nature Communications, 2025, vol. 16, issue 1, 1-7

Abstract: Abstract Hybrid superconductor-semiconductor Josephson field-effect transistors (JoFETs) function as Josephson junctions with gate-tunable critical current. Additionally, they can feature a non-sinusoidal current-phase relation (CPR) containing multiple harmonics of the superconducting phase difference, a so-far underutilized property. Here we exploit this multi-harmonicity to create a Josephson circuit element with an almost perfectly π-periodic CPR, indicative of a largely dominant charge-4e supercurrent transport. We realize such a Josephson element, recently proposed as building block of a protected superconducting qubit, using a superconducting quantum interference device (SQUID) with low-inductance aluminum arms and two nominally identical JoFETs. The latter are fabricated from a SiGe/Ge/SiGe quantum-well heterostructure embedding a high-mobility two-dimensional hole gas. By carefully adjusting the JoFET gate voltages and finely tuning the magnetic flux through the SQUID close to half a flux quantum, we achieve a regime where the $$\sin (2\varphi )$$ sin ( 2 φ ) component accounts for more than 95% of the total supercurrent. This result demonstrates a new promising route towards parity-protected superconducting qubits.

Date: 2025
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DOI: 10.1038/s41467-025-56245-7

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