Nanoscale Magnetic Resonance Fourier Imaging Using Nitrogen-Vacancy Color Centers In Diamond

In recent years,the nitrogen-vacancy(NV)center in diamond has become a quantum probe with high sensitivity and high spatial resolution due to its superior properties,e.g.its atomic scale size and ultra-long coherence time.Since German and American scientists proposed a nanoscale magnetic resonance imaging(MRI)scheme on NV centers under ambient condition in 2008,rapid progresses have been made in the field of nanoscale MRI.Widefield imaging and scanning probe microscope are the widely used techniques to realize nanoscale magnetic resonance imaging.These methods can only detect the information on the sample surface and thus it’s not feasible to achieve threedimensional imaging.While realizing the 3D superresolution imaging and structure analysis of single molecules are the highly desired goals we have been pursuing.Combining the high sensitivity quantum probe NV center with the Fourier imaging technology of traditional MRI,three-dimensional gradient magnetic field is used to phase-encode the sample space information.Then the real space information can be obtained by Fourier transforming the signal in phase space.It is expected to realize the 3D imaging of single molecules in vitro or the structural analysis of protein molecules.My work during my doctoral period was mainly accomplished on the homebiult single-spin Fourier MRI platform.We also developed related technologies to realize the nano-resolution localization of the system from one to a few and finally to multiple NV centers in diamond.This provides a solid foundation for 3D superresolution imaging of single molecule afterwards.This paper consists of the following content:1.We have independently built a single-spin Fourier MRI experimental platform based on NV centers.This platform is a highly integrated optical fiber collection experimental platform.This confocal platform with fiber-collection technique has a satisfactory performance on the stability.Even under the condition of air conditioned temperature control device,the whole apparatus drift is within 1 μm for 35h.By using this fiber-based collection approach,the whole setup can be quickly recovered to the optimal status even under severe temperature fluctuation.Moreover,we designed gradient microcoils for different experimental samples,including large-and small-sized gradient magnetic field chips.The maximum gradient magnetic fields we can achieve are 0.02 mT/μm and 0.74 mT/μm,respectively,and we also developed a whole set of pulse gradient field generation and control methods.On the above mentioned robust and integrated Fourier optically detected magnetic resonance setup,we realize the nanoscale localization of a single NV center with Fourier imaging technique,the resolution of which becomes the highest index for this method(1.8 nm).2.Aiming at the scientific problem of single-spin Fourier MRI in diamond,the nano-resolution phase encoding of a single NV center is realized by using the technique of combining NV center and Fourier imaging.We proposed a noval method of photoswitching of NV centers quantum states controlled by the gradient magnetic field.We realized the super-resolution localization of two NV centers in the same orientation within diffraction limit,with the localization accuracy below 1 nm.In current experimental condition,the ultimate resolution we can achieve theoretically is 0.15 nm.In addition,we also demonstrate the selectively addressing of these two NV centers.We independently characterize their coherent properties,which is applicant for the implementation of quantum sensing.3.After realizing the super-resolution localization of two adjacent NV centers in diamond,we turned our goal to multi-dimensional super-resolution localization of multiple NV centers in the ensemble sample.The 1D and 2D super-resolution imaging of the ensemble NVs was achieved under the condition of stable gradient magnetic field provided by current source.At the same time,we also studied the 2D super-resolution imaging in three different directions,and analyzed the limiting factor of the spatial resolution.For Fourier imaging of a single dimension in this sample,the spatial resolution can reach below 5 nm.In a word,the method of integrating the NV center with Fourier imaging technique can not only realize super-resolution localization and coherent control of NV center,but also provide ideas for the imaging and localization of electron spin or nuclear spin in vitro.This technical method is expected to realize the three-dimensional spatial localization of free radical electrons labeled on single molecules or proteins in vitro.