近日，荷兰代尔夫特理工大学的Christian Kraglund Andersen课题组与荷兰莱登大学的Bernard van Heck以及美国伊利诺伊大学香槟分校的Andersen Angela等人合作并取得一项新进展。经过不懈努力，他们实现了超导自旋量子比特强耦合到传输子（transmon）量子比特的直接操纵。相关研究成果已于2023年5月22日在国际知名学术期刊《自然—物理学》上发表。

在这项研究中，研究人员采用了具有较大电荷能的静电定义的量子点约瑟夫森结，形成了自旋分裂的双重基态。通过在磁场中调谐量子比特频率，他们能够直接操纵量子比特的自旋，在10GHz的频率范围内对其性能进行调控。利用全电动微波驱动，他们成功产生了超过200MHz的拉比频率。此外，他们还将Andreev自旋量子比特嵌入到超导传输子（transmon）量子比特中，成功展示了强相干的量子比特-量子比特耦合。这些结果是将超导和半导体量子比特的优势结合形成混合架构的关键步骤。

据了解，半导体中的自旋量子比特是生产高度可扩展的量子计算设备的有前途的平台。然而，在较大距离上实现多量子比特的相互作用是困难的。为了克服这个问题，超导自旋量子比特提供了一种替代方法，利用Andreev能级的自旋自由度来编码量子比特。这些Andreev自旋量子比特具有固有的自旋-超电流耦合，使得可以利用电路量子电动力学的最新进展。然而，第一个实现的Andreev自旋量子比特将量子比特编码在半导体弱链接的激发态中，导致频繁从计算子空间中衰变。此外，需要间接的拉曼跃迁也阻碍了快速的量子比特操纵。

附：英文原文

Title: Direct manipulation of a superconducting spin qubit strongly coupled to a transmon qubit

Author: Pita-Vidal, Marta, Bargerbos, Arno, itko, Rok, Splitthoff, Lukas J., Grnhaupt, Lukas, Wesdorp, Jaap J., Liu, Yu, Kouwenhoven, Leo P., Aguado, Ramn, van Heck, Bernard, Kou, Angela, Andersen, Christian Kraglund

Issue&Volume: 2023-05-22

Abstract: Spin qubits in semiconductors are a promising platform for producing highly scalable quantum computing devices. However, it is difficult to realize multiqubit interactions over extended distances. Superconducting spin qubits provide an alternative by encoding a qubit in the spin degree of freedom of an Andreev level. These Andreev spin qubits have an intrinsic spin–supercurrent coupling that enables the use of recent advances in circuit quantum electrodynamics. The first realization of an Andreev spin qubit encoded the qubit in the excited states of a semiconducting weak link, leading to frequent decay out of the computational subspace. Additionally, rapid qubit manipulation was hindered by the need for indirect Raman transitions. Here we use an electrostatically defined quantum dot Josephson junction with large charging energy, which leads to a spin-split doublet ground state. We tune the qubit frequency over a frequency range of 10GHz using a magnetic field, which also enables us to investigate the qubit performance using direct spin manipulation. An all-electric microwave drive produces Rabi frequencies exceeding 200MHz. We embed the Andreev spin qubit in a superconducting transmon qubit, demonstrating strong coherent qubit–qubit coupling. These results are a crucial step towards a hybrid architecture that combines the beneficial aspects of both superconducting and semiconductor qubits.

DOI: 10.1038/s41567-023-02071-x

Source: https://www.nature.com/articles/s41567-023-02071-x