Peking University Dramatically Improves Coherence of Solid-State Quantum Bits with New Scanning Probe Technology

Recently, based on the self-developed qPlus-type scanning probe microscope system, Professor Jiang Ying's team from the Center for Quantum Materials Science, School of Physics, Peking University, and the Center for Advanced Materials Research on Light Elements, Peking University, in collaboration with Associate Professor Yang Sen from Hong Kong University of Science and Technology and Professor Jörg Wrachtrup from the University of Stuttgart, Germany, has developed a new technique for controlled manipulation of the electron spin library on the near surface of diamond, which significantly The new technique improves the coherence of shallow solid-state quantum bits (the coherence time T2 can be extended by up to 20 times) and is expected to break the bottleneck of applications in the field of quantum sensing. The research results were published in Nature Physics on Aug. 25.

Figure 1 a: the model diagram of the self-developed scanning quantum sensing microscope system, from which all the data of this work were obtained; b: the physical photo of the core probe of the scanning quantum sensing microscope system

In recent years, Jiang Ying's group has successfully integrated quantum sensing technology and qPlus-type scanning probe technology to develop a scanning quantum sensing microscope (Figure 1), which is the first time in the world to realize NV-based nanoscale electric field imaging and charge state modulation.

On this basis, Jiang Ying's group further collaborated with Yang Sen's group to develop an innovative "Pull-and-Push Method" based on needle tip manipulation for diamond near-surface electron spin noise. The method utilizes the local strong electric field of a conducting needle tip to manipulate the charge precisely at the nanoscale, and achieves efficient suppression of electron spin noise at the near surface of diamond under room temperature atmospheric environment, and significantly improves the coherence and detection sensitivity of shallow NV. The method is particularly effective for NVs within 5 nm in depth, where the coherence time (T2) can be enhanced up to 20 times and the detection sensitivity can be improved by about 80 times, approaching the theoretical detection limit of a single proton nuclear spin (Figure 2).

Fig. 2 a and b: Schematic diagram of the manipulation of the near-surface electron spin library of diamond using the SPM pin-tip local strong electric field (Pull-and-Push Method); c: Significant enhancement of the coherence of the shallow NV color center (20-fold enhancement of T2 time) based on the pin-tip manipulation method; d: Sensitivity of the detection of the shallow NV color center after the enhancement of the coherence approximating a single proton; e: The sensitivity of the pin-tip manipulation method on the NV color-center T2 time enhancement multiplication statistics. This method is particularly effective for color centers within 5 nm depth.

This work not only provides a novel method to suppress the decoherence of shallow NV, but also is expected to break the bottleneck of its application in the field of quantum sensing, and can be widely applied to solid-state quantum bit systems in diamond, silicon carbide, boron nitride and other materials.

Article Link:

https://www.nature.com/articles/s41567-022-01719-4