Wang Chien-An, Ercan H Ekmel, Gyure Mark F, Scappucci Giordano, Veldhorst Menno, Rimbach-Russ Maximilian
QuTech and Kavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands.
Electrical and Computer Engineering Department, University of California, Los Angeles, California 90095 USA.
npj Quantum Inf. 2024;10(1):102. doi: 10.1038/s41534-024-00897-8. Epub 2024 Oct 17.
Hole-based spin qubits in strained planar germanium quantum wells have received considerable attention due to their favorable properties and remarkable experimental progress. The sizeable spin-orbit interaction in this structure allows for efficient qubit operations with electric fields. However, it also couples the qubit to electrical noise. In this work, we perform simulations of a heterostructure hosting these hole spin qubits. We solve the effective mass equations for a realistic heterostructure, provide a set of analytical basis wavefunctions, and compute the effective g-factor of the heavy-hole ground state. Our investigations reveal a strong impact of highly excited light-hole states located outside the quantum well on the g-factor. We find that sweet spots, points of operations that are least susceptible to charge noise, for out-of-plane magnetic fields are shifted to impractically large electric fields. However, for magnetic fields close to in-plane alignment, partial sweet spots at low electric fields are recovered. Furthermore, sweet spots with respect to multiple fluctuating charge traps can be found under certain circumstances for different magnetic field alignments. This work will be helpful in understanding and improving the coherence of germanium hole spin qubits.
由于其良好的特性和显著的实验进展，应变平面锗量子阱中的空穴基自旋量子比特受到了广泛关注。这种结构中可观的自旋 - 轨道相互作用使得利用电场进行高效的量子比特操作成为可能。然而，它也会将量子比特与电噪声耦合。在这项工作中，我们对包含这些空穴自旋量子比特的异质结构进行了模拟。我们求解了一个实际异质结构的有效质量方程，提供了一组解析基波函数，并计算了重空穴基态的有效g因子。我们的研究揭示了量子阱外高度激发的轻空穴态对g因子有强烈影响。我们发现，对于面外磁场，最不易受电荷噪声影响的操作点（即“甜点”）被转移到了不切实际的大电场处。然而，对于接近面内取向的磁场，在低电场下可以恢复部分“甜点”。此外，在某些情况下，针对不同的磁场取向，可以找到相对于多个波动电荷陷阱的“甜点”。这项工作将有助于理解和提高锗空穴自旋量子比特的相干性。
