Giant Anisotropy of Spin Relaxation and Spin-Valley Mixing in a Silicon Quantum Dot

Abstract

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.

An Operation Guide of Si-MOS Quantum Dots for Spin Qubits

“…Due to the existence of the interfacial electric field, the quadruple degenerate and the double degenerate split further and form valley-level splits [57]. Unlike the orbital state, the splitting energy of the two lowest valley states (E VS ) in silicon QDs is similar to the Zeemen splitting energy (E Z ) under the applied magnetic field in our experiment [36][37][38][39]64,65]. Therefore, it is important to determine the splitting energy of the valley state.…”

“…According to Figure 4a, the E VS of the second electron is 170 µeV, and the E VS of the third one is 245 µeV. The difference between the E VS of these two electrons is caused by the different LP voltages [38].…”

“…By using the high vacuum activation annealing technique, we improve the mobility of Si-MOS devices by a factor of two, reaching 1.5 m 2 /(V•s) [61]. In this work, we use a DQD that has a similar structure (Ref [38]) and was fabricated in our lab's clean room. As shown in Figure 1a, the aluminum electrodes are vaporized on top of the silicon oxide by electron beam evaporation techniques.…”

“…Here, we tune the energy level of the first four electrons by changing the magnetic field of which the direction of is along the surface of the device and perpendicular to the one-dimensional channel formed by the QD, as shown in Figure 1a. Figure 4a shows the transition lines of the first four electrons in the device in Ref [38]. The voltage of the first transition line of the QD decreases as the magnetic field increases, while the fourth line increases.…”

“…Nowadays, the single-qubit operations of spin qubits achieve fidelities of 99.9% [28,29], the two-qubit operation fidelities are above 99% as reported [30], the spin-photon coupling rates are more than 10 megahertz [31][32][33], and the qubit operation temperature is higher than 1 kelvin [34,35]. In the meantime, experiments on other properties of silicon QDs, including valley states [36][37][38], orbital states [39], and noise spectra [40,41], have been carried out. Furthermore, experimental approaches and techniques for characterizing features of QDs from other systems, e.g., charge stability diagrams [42][43][44], random telegraph signals (RTS) [45][46][47][48], Elzerman readout [49,50], Pauli spin blockade (PSB) readout [51,52], electron spin resonance (ESR) [53,54], and electron dipole spin resonance (EDSR) [55,56], have been applied in silicon QDs as well.…”