After more than three years of hard work, the research team of Professor Du Jiangfeng of the University of Science and Technology of China has built a series of internationally advanced optical detection magnetic resonance experimental platforms, and carried out cutting-edge science such as quantum computing and weak magnetic signal sensitive detection based on diamond doped single spin Research has made a series of important progress. Related results were published in 2014 "Nature", "Nature • Physics" and "Physical Review Letters".
Precise manipulation of qubits is one of the core problems of quantum computing. For electronic spin qubits, nuclear spin thermal reservoir noise and driving field noise make precise manipulation extremely challenging. Professor Du Jiangfeng's research team used two novel methods to effectively suppress these two types of noise and achieve precise manipulation of single electron spins. The relevant results were published in the Physical Review Letters. In addition, Professor Du Jiangfeng cooperated with the University of Stuttgart, Germany, and achieved quantum error correction in the solid-state spin system through experiments. The work was published in Nature. These achievements are of great significance to the practical application of quantum computing and sensitive detection in the future.
Electron spin will feel the nuclear spin thermal reservoir noise in the surrounding environment. The impact of this magnetic field fluctuation noise on electron spins not only appears to destroy quantum states, but also greatly restricts the quality of the quantum system of manipulation. Du Jiangfeng's research group Rong Xing and others took advantage of pulse manipulation in the field of magnetic resonance and extended a dynamic error correction logic gate used to resist gradient magnetic field fluctuation noise to suppress the more general magnetic field fluctuation noise. The experimental results show that the external magnetic field noise is effectively suppressed to the sixth order, and the quantum coherence time is extended to 690 ± 40 microseconds, which is two orders of magnitude longer than the free induction decay time, and far exceeds the quantum coherence time under ordinary pulse control , Reached the T1rho (660 ± 80 microseconds) limit. For the first time, this work successfully pushed the precise control of electron spins beyond the T2 limit to the T1 level, which greatly extended the time that electron spin qubits can be manipulated, making more complex and precise manipulation possible, thus It provides key technologies for quantum calculation and sensitive detection based on electron spin.
In addition, the driving field that controls the electronic spin will introduce additional noise. When the noise of the spin thermal reservoir in the environment is effectively suppressed, the driving field noise will become an important factor restricting the quality of the manipulation. Du Jiangfeng's research group Zhou Jingwei and others used fast microwave frequency modulation to realize the first time Landau-Zener (LZ) tunneling in the time domain for more than 100 times, and observed a new type of Rabbi oscillation caused by multiple tunneling. Theoretical and experimental results show that this new type of Rabbi oscillation can effectively suppress the noise introduced by the driving field, thus providing a brand-new means for achieving precise control. This work will not only help to deeply understand the important physical processes related to LZ tunneling and Rabbi oscillation, but also have important value for the application of quantum control technology in quantum computing, biochemistry and other fields.
Quantum error correction is also a scheme that can effectively combat noise, and is the key to achieving fault-tolerant quantum computing. Professor Du Jiangfeng cooperated with the University of Stuttgart in Germany to extend the optimal control method in nuclear magnetic resonance to optical detection magnetic resonance, realizing high-precision manipulation of a complex quantum system composed of one electron spin and three nuclear spins, thereby achieving solid state Quantum error correction in the spin system. This work laid a solid foundation for the practical application of quantum computing based on solid-state spin system.
Accurate quantum manipulation and effective suppression of environmental noise are also of great significance for the sensitive detection of weak signals. Du Jiangfeng's research group Shi Development et al. Used nitrogen-vacancy solid-state single-electron spin quantum interferometer in doped diamond to convert the weak magnetic signal generated by the micro-spin system into the phase of the interferometer, and used multi-pulse dynamic decoupling technology and An external magnetic field is used to effectively suppress the environmental noise, and the detection of single-core spin pairs and their atomic-scale structural analysis under the atmospheric environment at room temperature have been successfully achieved. This work shows that dynamic decoupling technology combined with single-spin probes is a powerful tool for single molecule structure analysis and spectroscopic analysis, which can help us obtain material composition and structure information at the nanometer or even atomic scale, and develop microcosm for various fields such as physical biology Research provides new methods.
The work of Professor Du Jiangfeng's research group has raised the ability to manipulate spin quantum systems to a new level, and the methods developed in these works can be applied to a variety of important qubit systems, such as quantum dots, ion traps, super Conduct qubits, etc. Therefore, these important developments have laid a solid foundation for frontier fields such as quantum computing and sensitive detection of weak magnetic signals.
The above research was supported by the National Fund Committee, the Ministry of Science and Technology, and the Chinese Academy of Sciences.
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