Progress in Quantum Information and Computational Cooperation Research of Diamond Nitrogen Vacancy Center in Physics

The central structure of nitrogen vacancy in diamonds has been discovered since 1997. Since it has been conducting quantum information research, it has a long electron spin decoherence time at room temperature, a pure spin environment and superfine refinement with surrounding nuclear spins. Role, people have carried out a variety of research, including the realization of single qubit and multi-qubit control, quantum registers, double qubit logic gate operations, the preparation of three qubit entangled states and the recent dynamic decoupling to extend the retreat The study of coherence time demonstrates the broad prospects of this system in solid-state quantum information and computation.

In the past few years, Pan Xinyu, a researcher at the Institute of Physics of the Chinese Academy of Sciences/Beijing National Laboratory for Condensed Matter Physics, has independently designed and built two sets of laser scanning confocal fluorescence microscopy systems. The research and development of microwave near-field antennas has carried out a series of quantum information research based on diamond nitrogen vacancy centers.

Recently, Associate Researcher Pan Xinyu and Fan Wei, researchers, have implemented the optimized phase quantum cloning machine for the first time in a solid state system at room temperature. In the two two-level systems formed by the Zeeman effect in the center of the diamond nitrogen vacancy, the encoding of three quantum states is realized. The preparation of the initial state and the realization of the quantum cloning machine through the laser pumping and the two independent radiation fields of the microwave A combination of methods is implemented. The average fidelity of the clones of the experimental results reached 85.2%, which is close to the maximum fidelity of 85.4% predicted by theoretical calculations. The results of the study were published in Applied Physics Letters [99, 051113 (2011)].

In addition, Associate Professor Pan Xinyu and Professor Liu Renbao of the Chinese University of Hong Kong collaborated to study the noise fluctuation effect of electron spin at the center of diamond nitrogen vacancy at room temperature. Fluctuations in the local field can lead to decoherence of the quantum system. It is generally believed that thermal noise is many times stronger than quantum noise at room temperature unless there is a human method to suppress thermal noise such as spin echo. At the room temperature, the team successfully observed the strong quantum noise fluctuation effect of the electron spin at the center of the nitrogen vacancy of the diamond on the surrounding nuclear spin environment. It has been found that the competitive relationship between quantum fluctuations and thermal noise can be adjusted by the applied magnetic field. As the external magnetic field increases, the process of gradual change from thermal noise to quantum noise and back to thermal noise is observed. The experiment was based on Ramsey interferometry, and the experimental results were in good agreement with the numerical simulation. The results of the study were published in Scientific Reports [2, 432 (2012)].

The above work was funded by the “973” project of the Ministry of Science and Technology and the National Natural Science Foundation, the Hong Kong Research Grants Council and the Chinese University of Hong Kong.

Figure 1 Measurement results of a quantum cloning experiment. The black point is the experimentally measured Rabi oscillation curve, the red line is the fitting curve, and the a picture is the measured electronic population of the ms=0 state after the cloning operation. The theoretical prediction value is 33%, and the b picture is the measured cloth. At 48%, the theoretical prediction is 50%.

Fig. 2 The Ramsey signal of the electron spin at the center of the diamond nitrogen vacancy. Under different applied magnetic fields, the decoherence time and the n of the fitted curve change with the magnetic field, thus exhibiting different noise fluctuation effects.

Figure 3. Decoherence time of three different nitrogen vacancy centers and the relationship between n and applied magnetic field.