One of the key issues in quantum computation is to realize precise control over quantum qubits in the realistic system. It is of great challenge to perform the accurate controlling the electron spin qubits, due to the noises aroused from the nuclear spin bath and the driving field. Prof. Du’s group has utilized two novel methods to suppress the noises and realized precise control of the electron spins. These results have been published in Physical Review Letters. [Phys. Rev. Lett. 112, 010503 (2014)] [Phys. Rev. Lett. 112, 050503 (2014)] Prof. Du and his cooperators in University Stuttgart have experimentally realized the quantum error correction in diamonds, which is another effective method to overcome the noise effect. This result has been reported in Nature. [Nature 506, 204 (2014)]

The electron spin suffers the noise resulted by the around nuclear spin bath. This noise will not only destroy the quantum states of the electron spin, but also will deteriorate the quality of the quantum gates. Prof. Du’s group adopted a type of dynamically corrected gats, originally proposed for suppressing the fluctuation of gradient magnetic field specific for double quantum dots, to realize robust and high-fidelity quantum gates in the presence of fluctuation of static magnetic field. The results show that the noise was suppressed to 6th order and the quantum gate’s performance was pushed to T1rho limit. This work promotes the quality of quantum operation to the limit of T1 for the first time, and promises more quantum gates due to the longer coherence time. Their work is expected to have various applications in quantum information processing, high resolution spectroscopy, and various quantum metrologies, where high-fidelity quantum gates are required.[Phys. Rev. Lett. 112, 050503 (2014)]

On the other hand, fluctuations of the driving field will introduce additional noise. While the intrinsic spin bath noise has been suppressed efficiently, fluctuation of the driving field amplitude emerges and become dominant. With fast frequency modulation of the control fields, Prof. Du’s group experimentally observed a new Rabi Oscillations (ROs) resulting from more than 100 Landau-Zener (LZ) transitions. Detailed experimental studies together with theoretical analysis indicate that fluctuations of the driving field can be suppressed in the new ROs relative to common ROs under the same driving microwave power. This provides an alternative way to realize precise and robust quantum control. Such studies open a door for further studies of various quantum dynamical phenomena related to LZ-Rabi, with profound impacts in many fields, including quantum computing, strong-driving physics, as well as quantum chemistry and even possibly biological systems. [Phys. Rev. Lett. 112, 010503 (2014)]

Quantum error correction (QEC), an effective method to fight against the noisy environment, is a key to realize fault-tolerant quantum computation. Cooperating with German research group, Prof. Jiangfeng Du succeeds in realizing quantum error correction in diamond. They extend the widely used optimal control techniques in nuclear magnetic resonance to optical detection magnetic resonance of the single spin system and secessfully perform QEC in a complex quantum system which consists of a single electron spin and three nuclear spins. This work sets a millstone on the path towards future practical quantum computation. [Nature 506, 204 (2014)]

Precise quantum control and effectivly supressing noise of the environment are also of great importance for quantum metrology. Prof. Jiangfeng Du's group recently succeeded in sensing and atomic-scale analysis of single nuclear spin clusters in diamond at room temperature via quantum interferometer.　The dynamical decoupling operations and thousands Gauss external magnetic field are employed to realize ‘lock-in detection’ of weak magnetic signalby suppressingthe noise and amplifying the weak signal. This work indicates that, in combination with advanced material-surface engineering, central spin decoherence under dynamical decoupling controls may be a useful probe for NMR single-molecule structure analysis, thus provide insights for micro-scale research in physics, biology and other fields. [Nature Physics 10, 21 (2014)]

These important progresses made by Prof. Jiangfeng Du’s group have advanced the precision of quantum controls to a new level. Furthermore, these techniques can be applied in other important quantum systems, including quantum dot, trapped ion, superconducting circuits. These important progresses are expected to have various applications in quantum information processing, high resolution spectroscopy, and various quantum metrologies.

The above works are supported by National Natural Science Foundation, Ministry of Science and Technology, and the Chinese Academy of Sciences.

(RUI Ying, Shool of Physcal Sciences, Hefei National Laboratory for Physical Sciences at the Microscale)