Recently, Professor Jiang Ying and J? Professor rg Wrachtrup and Professor YEUNG Sum of the Chinese University of Hong Kong have jointly developed a scanning quantum sensing microscope, which uses solid qubits and nitrogen vacancy (NV) centers as quantum sensors. They realized the nano-scale electric field imaging based on NV and its charge state control for the first time, showing the possibility of scanning NV electricity. The work entitled "Nano-electric field imaging based on quantum sensor and its charge state control under environmental conditions" has been published in the journal Nature Communication.
Nitrogen vacancy center is a point defect in diamond, which is considered as one of the most promising solid-state qubits in quantum computing, quantum information and quantum sensing. NV can be used as a powerful quantum sensor to quantitatively detect subtle magnetic/electrical signals by monitoring the coherent evolution of quantum states in the process of interaction with the surrounding environment. Because of the long coherence time of NV, it can reach ~ms even under environmental conditions, so it is extremely sensitive and can even be used to detect the spin of a single nucleus/electron. Combining shallow NV with scanning probe microscope (SPM), we can construct scanning magnetic measurement technology and realize quantitative magnetic imaging in nanometer scale. However, due to the relatively weak coupling strength between NV and electric field, there are strict requirements for the coherence of shallow NV and the stability of SPM system, so far, nano-scale electric field mapping has not been realized.
Professor Jiang Ying and his team have been committed to the development of advanced scanning probe microscope system for a long time. Recently, they developed a new generation of qplus Atomic Force Microscope (AFM), which improved the resolution and sensitivity of SPM to the classical limit and made it possible to directly image hydrogen atoms in water molecules. On this basis, the team integrated the quantum sensing technology based on nvl into the SPM system based on qplu to form the so-called scanning quantum sensing microscope. Because of the high stability of qPlus sensor, it can work at a small amplitude (~ 100 pm) near the surface of the needle tip, which is very important for maintaining good coherence and resolution of shallow NV. The team can draw the local electric field from the biased metal tip with a spatial resolution of about 10 nm and a sensitivity close to the elemental charge. In the future, this technology can be applied to study the local charge, polarization and dielectric response of functional materials from a microscopic point of view.
Using this new system, the team also realized the reversible control of a single NV charge state (NVˉ, NV+ and NV0), in which NVˉ acts as a quantum sensor, while NV+ and NV0 are the basic building blocks of quantum storage to improve the signal-to-noise ratio of quantum sensing. The researchers found that with the help of photon ionization excitation laser, the polarization/depolarization of local diamond surface can be realized by using local electric field sharp polarization technology, and the nano-precision of NV charge state switch can be induced (as low as 4.6 nautical miles). This discovery will help to purify the direct electrostatic environment of NV, enhance the coherence of NV and establish a quantum network based on NV.