It is well known that for Si quantum dots (QDs), at a certain magnetic field that is commonly referred to as the "hot spot", the electron spin relaxation rate ( ) can be drastically enhanced due to strong spin-valley mixing. Here, we experimentally find that with a valley splitting of ~78 µeV, this "hot spot" spin relaxation can be suppressed by more than 2 orders of magnitude when the in-plane magnetic field is oriented at an optimal angle, about 9° from the 100 sample plane. This directional anisotropy exhibits a sinusoidal modulation with a 180° periodicity. We explain the magnitude and phase of this modulation using a model that accounts for both spin-valley mixing and intravalley spin-orbit mixing. The generality of this phenomenon is also confirmed by tuning the electric field and the valley splitting up to ~268 µeV.

Two-dimensional (2D) materials are a family of layered materials exhibiting rich exotic phenomena, such as valleycontrasting physics. Down to single-particle level, unraveling fundamental physics and potential applications including quantum information processing in these materials attracts significant research interests. To unlock these great potentials, gate-controlled quantum dot architectures have been applied in 2D materials and their heterostructures. Such systems provide the possibility of electrical confinement, control, and manipulation of single carriers in these materials. In this review, efforts in gate-controlled quantum dots in 2D materials are presented. Following basic introductions to valley degree of freedom and gate-controlled quantum dot systems, the up-to-date progress in etched and gate-defined quantum dots in 2D materials, especially in graphene and transition metal dichalcogenides, is provided. The challenges and opportunities for future developments in this field, from views of device design, fabrication scheme, and control technology, are discussed. The rapid progress in this field not only sheds light on the understanding of spin-valley physics, but also provides an ideal platform for investigating diverse condensed matter physics phenomena and realizing quantum computation in the 2D limit.

To improve mobility of fabricated silicon metal-oxide-semiconductor (MOS) quantum devices, forming gas annealing is a common method used to mitigate the effects of disorder at the Si/SiO2 interface. However, the importance of activation annealing is usually ignored. Here, we show that a high vacuum environment for implantation activation is beneficial for improving mobility compared to nitrogen atmosphere. Low-temperature transport measurements of Hall bars show that peak mobility can be improved by a factor of two, reaching 1.5 m 2 /(V • s) using high vacuum annealing during implantation activation. Moreover, the charge stability diagram of a single quantum dot is mapped, with no visible disturbance caused by disorder, suggesting the possibility of fabricating high-quality quantum dots on commercial wafers. Our results may provide valuable insights into device optimization in silicon-based quantum computing.

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The high spin states of 87 Nb have been studied by using the 58 Ni (32 S , 3p)87 Nb reaction at beam energy 95–105 MeV and the reaction 58 Ni (35 Cl , 2pα) at 124 MeV. γ-γ coincidence relations, angular distributions of γ-rays, excitation functions and DCO ratios were measured. High spin states in 87 Nb have been established up to spin of 37/2ℏ and excitation energy of 7 MeV. CSM calculation was carried out with parameters of configuration dependence of nuclear shape. The nature and configuration of every band in 87 Nb are discussed.