Magnetic Sensing inside a Diamond Anvil Cell via Nitrogen-Vacancy Center Spins

　　Research into high pressure has opened a new frontier for scientists in various fields,with new materials,structures,and emergent physical properties being reported.Under high-pressure conditions,simple compounds have shown complicated phase diagrams.For example,eight phases have been reported in dense ice,six in solid oxygen,and six in solid hydrogen,while many pure elements are superconductors under high pressure.Hydrogen is expected to be a room temperature superconductor,and many studies have explored its metallic state.Recently,superconductive behavior in hydride has attracted more attention,as the superconductor phase transition temperature has been reported as being over 260K,which is the outdoor temperature at most areas in the northern hemisphere winter.

　　The diamond anvil cell-based high-pressure technique is a unique tool for creating new states of matter and for understanding the physics underlying some exotic phenomena.In situ sensing of spin and charge properties under high pressure is crucially important but remains technically challenging.While the nitrogen-vacancy(NV)center in diamond is a promising quantum sensor under extreme conditions,its spin dynamics and the quantum control of its spin states under high pressure remain elusive.In this study,we demonstrate coherent control,spin relaxation,and spin dephasing measurements for ensemble NV centers up to 32.8GPa.With this in situ quantum sensor,we investigate the pressure-induced magnetic phase transition of a micron-size permanent magnet Nd2Fe14B sample in a diamond anvil cell,with a spatial resolution of∼2µm,and sensitivity of∼20µT/Hz1/2.This scheme could be generalized to measure other parameters such as temperature,pressure and their gradients under extreme conditions.This will be beneficial for frontier research of condensed matter physics and geophysics.

　　In summary,we have demonstrated fast coherent manipulation of ensemble NV spins,up to 32.8GPa,and the measured spin coherence and spin relaxation time have little difference as compared to those measured under ambient conditions.We have used in situ and sensitive quantum sensors to study the pressure induced magnetic phase transition of Nd2Fe14B.To improve the spatial resolution and reusability of the DAC chamber,shallow NV centers on the diamond culet could be employed.To improve microwave[]transmission efficiency,coplanar waveguides could be deposited on the DAC culet,which is compatible with much higher pressures.

　　Diamond,as one of the most special materials in natural world,is featured with the highest hardness,low friction coefficient,high elasticity modulus,high thermal conductivity,high insulation class,wide energy gap,great sound propagation rate and favorable chemical stability,which are presented in below Table.In spite of such unique features,the natural diamond has always been existed in the form of gem,with its variability and rareness sharply limiting its application.Luoyang Yuxin Diamond Co.,Ltd‘s CVD Diamond film,on the other hand,integrates such physical and chemical properties,with lower cost than natural diamond and applicable to be made into various shapes,thus enjoying extensive application prospect in electronic industry,optical field and mechanical industry.