Experimental Investigation Of Quantum Coherence Protection Based On Nitrogen-Vacancy Center In Diamond

Quantum information science is an emerging interdisciplinary in the 21 st century,in which the quantum technologies,such as quantum computing,quantum simulation and quantum metrology,are gradually changing people’s lives.Benefit from the quantumcoherence-based fundamental mechanism,the performances of quantum technologies are greater than that of classical technologies,such as quantum computers owning the advantage of natural parallelism,and quantum sensors beating the classical limitation.However,quantum coherence is pretty fragile.Generally,the realization of quantum technologies depends on the open quantum systems,which often experience the decoherence caused by the coupled environment.The decoherence mainly limits the development of quantum technologies.Thus,how to realize the better coherence protection of open quantum systems receives much concern from associate scholars.In this thesis,three experimental researches for quantum coherence protection have been mainly completed based on the nitrogen-vacancy(NV)center in diamond.The following works are related.(1)Experimental demonstration of an improved dynamical-decoupling(DD)spectral analysis method.A traversal periodic-signal identification approach is introduced for separating multiple 13 C nuclear-spin coupling signals from the room-temperature DD spectra,and a deep-learning model is established for efficiently and accurately analyzing the corresponding hyperfine interaction parameters of separated 13 C nuclear spins.This method provides a novel experimental technique for formulating the coherence protection schemes of NV-center electron spin.(2)Experimental demonstration of an electron-spin coherence protection scheme based on feedforward quantum control.Real-time measurement of the electron-spin resonance frequency is realized with the assistance of a purpose-built mixed-signal data acquisition system,and an LSTM-based deep-learning model is designed and accomplished for predicting the electron-spin resonance frequency trends in future.With the prediction,the feedforward quantum control and coherence protection of single electron spin are realized,resulting in a three-fold improvement of Ramsey spectral line-width reduction.(3)Experimental demonstration of a quantum autoencoder for coherence protection of two-qubit entangled state.This autoencoder has the capability of preserving the entanglement based on decoherence-free subspace approach.Moreover,it trains itself in the way of unsupervised learning based on hybrid quantum-classical approach,which suppresses some unknown errors introduced by classical systems.With this autoencoder,an improvement with a three orders of magnitude in the decoherence time of NV-center two-qubit entangled state is realized.