Asymmetric Spectrum And Quantum Metrology In Ultra-low-Field Nuclear Magnetic Resonance

Nuclear magnetic resonance(NMR)is one of the most powerful analytical tools in the field of chemistry and biology.However,traditional high-field NMR requires a bulky,costly superconducting magnet.This also leads to problems such as inhomoge-neous broadening of the spectra and truncation of the internal spin interaction,which limits the application of the technology to a certain extent.With the advent of high-sensitivity magnetic field detectors,ultra-low-field NMR has attracted a wide atten-tion.Ultra-low-field NMR has unique advantages over high-field NMR.For example,there is no need for superconducting magnets,high absolute spectral resolution,strong coupling between nuclear spins,etc.Therefore,it complements high-field NMR and broadens the application of NMR in scientific research.Recently,a series of ultra-low-field NMR studies have been carried out using atom-ic magnetometers,and remarkable results have been achieved.Using the home-built ultra-low-field NMR spectrometer,I research on the topic of " ultra-low-field nuclear magnetic resonance spectroscopy and its application in precision measurement".The specific content includes the following two aspects:(1)Theoretical and experimental research on the asymmetric spectrum of ultra-low-field NMR based on atomic magnetometer.Ultra-low-field NMR asymmetric spec-tra are ubiquitous,but not yet understood.By establishing and testing the response mod-el of the atomic magnetometer and the nuclear magnetic system to the external weak magnetic field,the origin of the ultra-low-field NMR asymmetric spectrum is explained for the first time,which further reveals the rich extra information contained in this asym-metric spectrum.For example,the Lande g factor of the nuclear energy level,the light shift field of the alkali metal cell.(2)Experimental implementation of noise-enhanced quantum hypothesis testing.In the home-built ultra-low-field NMR experimental platform,I correlate the magnetic field to be measured with noise by applying a specific control magnetic field,which ex-perimentally confirms the testing success probability of noise enhancement.This work shows that environmental impacts in open systems are not always harmful,instead,it can be effectively utilized to achieve higher performance metrics.It provides strong evidence for how to effectively accomplish quantum information processing tasks in the real environment.