Switching between relaxation hotspots and coldspots in disordered spin qubits

Abstract

We develop a valley-dependent envelope function theory that can describe the effects of arbitrary configurations of interface steps and miscuts on the qubit relaxation time. For a given interface roughness, we show how our theory can be used to find the valley-dependent dipole matrix elements, the valley splitting, and the spin-valley coupling as a function of the electromagnetic fields in a Si/SiGe quantum dot spin qubit. We demonstrate that our theory can quantitatively reproduce and explain the result of experimental measurements for the spin relaxation time with only a minimal set of free parameters. Investigating the sample dependence of spin relaxation, we find that at certain conditions for a disordered quantum dot, the spin-valley coupling vanishes. This, in turn, completely blocks the valley-induced qubit decay. We show that the presence of interface steps can in general give rise to a strongly anisotropic behavior of the spin relaxation time. Remarkably, by properly tuning the gate-induced out-of-plane electric field, it is possible to turn the spin-valley hotspot into a ``coldspot" at which the relaxation time is significantly prolonged and where the spin relaxation time is additionally first-order insensitive to the fluctuations of the magnetic field. This electrical tunability enables on-demand fast qubit reset and initialization that is critical for many quantum algorithms and error correction schemes. We, therefore, argue that the valley degree of freedom can be used as an advantage for Si spin qubits.

arXiv comment14+6 pages, 11 figures, 3 tabels

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• Practical Strategies for Enhancing the Valley Splitting in Si/SiGe Quantum Wells
• Strong electron-electron interactions in Si/SiGe quantum dots
• Coherent spin-valley oscillations in silicon
• Linear-in-momentum spin orbit interactions in planar Ge/GeSi heterostructures and spin qubits
• Valley-Free Silicon Fins Caused by Shear Strain
• Valley splitting depending on the size and location of a silicon quantum dot
• Theory of Silicon Spin Qubit Relaxation in a Synthetic Spin-Orbit Field
• Phonon-limited valley life times in single-particle bilayer graphene quantum dots
• Electrical Interconnects for Silicon Spin Qubits
• Omnidirectional shuttling to avoid valley excitations in Si/SiGe quantum wells
• Phonon-induced frequency shift in semiconductor spin qubits