A world record! USTC achieves ultrafast manipulation of semiconductor qubits
The team of Academician Guo Guangcan from the University of Science and Technology of China has made important progress in the study of spin qubit manipulation in silicon-based semiconductors. The team, Professor Guoping Guo, Researcher Li Haiou, Researcher Zhang Jianjun, Institute of Physics, Chinese Academy of Sciences, and others, in cooperation with researchers from the United States and Australia, as well as Benyuan Quantum Computing Company, achieved ultrafast manipulation of silicon-based spin qubits, with a spin flip rate of more than 540MHz, which is the highest value reported internationally. The research results were published online in the internationally renowned journal Nature Communications on January 11.
Silicon-based semiconductor spin qubits have become one of the core directions of quantum computing research due to their long quantum decoherence time, high manipulation fidelity, and high scalability compatible with modern semiconductor process technologies. High manipulation fidelity requires faster manipulation rates for bits with longer quantum decoherence times. Using the electron spin resonance method to realize the spin bit flipping scheme has a slower bit manipulation rate. The researchers found that the use of electric dipole spin resonance can achieve a faster rate of spin bit manipulation. The electric dipole spin resonance is mainly realized through the "artificial spin-orbit coupling" generated by the micro-magnet structure embedded in the device, which makes the spin qubit feel stronger charge noise, thereby reducing the spin qubit's The decoherence time, while reducing the average manipulation fidelity of spin qubit arrays, hinders the two-dimensional expansion of silicon-based spin qubit cells. A feasible and effective solution is spin qubit manipulation using the spin-orbit coupling that occurs naturally in materials.
The hole carriers in silicon-based quantum dots are in the P orbital state, so they naturally have strong intrinsic spin-orbit coupling effects and weak hyperfine interactions. Using the electric dipole spin resonance technology, the full electrical control of the hole spin qubit can be realized through an alternating electric field, which greatly simplifies the preparation process of the qubit and is conducive to the realization of two-dimensional silicon-based spin qubit units. dimensional expansion. In view of this, in recent years, the study of spin-orbit coupling in silicon-based hole systems and the realization of ultrafast spin qubit manipulation have become hotspots in the field.
The direction of the spin-orbit coupling field will affect the spin bit manipulation rate and the fidelity of bit initialization and reading. Measuring and determining the direction of the spin-orbit coupling field is the primary task. Measurement and control of the Landau g-factor tensor and spin-orbit coupling field direction in hole quantum dots [Nano Letters 21, 3835-3842 (2021)]. On this basis, Li Haiou et al. further optimized the device performance, completed the Pauli spin blocking readout of spin qubits in double quantum dots with highly tunable coupling strength, and observed multi-level electric dipole spins resonance spectrum. By tuning and selecting different spin-flipping modes, ultrafast manipulation of spin qubits with spin-flipping rates exceeding 540 MHz is achieved. Through modeling analysis, the researchers revealed that the main contribution of the ultrafast spin qubit manipulation rate comes from the strong spin-orbit coupling effect (ultrashort spin-orbit coupling length) of the system. The results show that the germanium-silicon hole spin qubit system is one of the important candidates for realizing fully electronically controlled semiconductor quantum computing, which opens up a new field for semiconductor quantum computing research.
(a) Schematic diagram of GeSi nanowire-hole double quantum dots and spin-bit manipulation, (b) the spin-bit flip rate increases with microwave power, (c) when the microwave power is 9 dBm, the spin-bit The control rate can reach 542MHz.
Academician Guo Guangcan and the team of Professor Guo Guoping have been deeply involved in the field of silicon-based semiconductor quantum computing for more than ten years, and have harvested a series of research results. In recent years, the team has used microwave superconducting resonators to realize the excitation energy spectrum measurement of semiconductor double quantum dots, and used microwave resonators to detect a new phenomenon of interference of semiconductor quantum dots driven by microwaves; applying machine learning to quantum computing effectively improves The reading fidelity of the quantum chip is improved, and the reading crosstalk effect is greatly suppressed. Among them, Yuanyuan Quantum, the research cooperation unit, is also the only enterprise in China that conducts both superconducting quantum computing and silicon-based semiconductor quantum computing engineering. In April 2021, Yuanyuan Quantum cooperated with Jinghe Technology to establish the first joint laboratory of quantum computing chips in China, leading the development of domestic silicon-based quantum computers.
Paper link:https://doi.org/10.1038/s41467-021-27880-7
