Leblanc Axel, Tangchingchai Chotivut, Sadre Momtaz Zahra, Kiyooka Elyjah, Hartmann Jean-Michel, Gustavo Frédéric, Thomassin Jean-Luc, Brun Boris, Schmitt Vivien, Zihlmann Simon, Maurand Romain, Dumur Étienne, De Franceschi Silvano, Lefloch François
Univ. Grenoble Alpes, CEA, Grenoble INP, IRIG-PHELIQS, 38000, Grenoble, France.
Institut Néel, CNRS/UGA, Grenoble, 38042, France.
Nat Commun. 2025 Jan 25;16(1):1010. doi: 10.1038/s41467-025-56245-7.
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 component accounts for more than 95% of the total supercurrent. This result demonstrates a new promising route towards parity-protected superconducting qubits.
混合超导 - 半导体约瑟夫森场效应晶体管（JoFET）作为具有栅极可调临界电流的约瑟夫森结发挥作用。此外，它们可以具有包含超导相位差多个谐波的非正弦电流 - 相位关系（CPR），这是一种迄今未得到充分利用的特性。在这里，我们利用这种多谐波特性来创建一个具有几乎完美π周期CPR的约瑟夫森电路元件，这表明电荷为4e的超电流传输占主导地位。我们使用具有低电感铝臂的超导量子干涉器件（SQUID）和两个名义上相同的JoFET实现了这样一个约瑟夫森元件，该元件最近被提议作为受保护超导量子比特的构建块。后者由嵌入高迁移率二维空穴气的SiGe/Ge/SiGe量子阱异质结构制成。通过仔细调整JoFET栅极电压并将通过SQUID的磁通量精细调节到接近半个磁通量子，我们实现了一种状态，其中 分量占总超电流的95％以上。这一结果展示了通往宇称保护超导量子比特的一条新的有前景的途径。
