Title Page
Abstract
국문초록
Preface
Contents
List of Abbreviations and Symbols 26
Chapter 1. Introduction 31
Chapter 2. Quantum Sensing with Single Spin in Diamond 37
2.1. The Nitrogen-Vacancy center in diamond 37
2.1.1. Electronic structures 39
2.1.2. Optical transitions 40
2.2. Magnetic field sensing 49
2.2.1. Electron spin resonance with Zeeman split 49
2.2.2. Rabi oscillation 53
2.2.3. Ramsey measurement 56
2.2.4. Echo measurement 61
2.2.5. Spin-lattice relaxation measurement 63
Chapter 3. Nanoscale Imaging Experiment Setup 65
3.1. Confocal optics 65
3.2. Microwave and electronics setups 75
3.3. Scanning probe microscope 80
3.3.1. Imaging method example for various magnetic samples 91
3.4. Experiment in cryostat 95
Chapter 4. Magnetic Nanowire 101
4.1. Ferromagnetic nanowires and diamond NV centers 104
4.2. Experimental setup and ODMR measurement 104
4.3. Magnetic field simulation 105
4.4. Magnetic field imaging in confocal optics 106
4.5. Ramsey measurement applications 109
4.6. Conclusions 112
Chapter 5. Point-Contacted Graphene Devices 113
5.1. Point contacted graphene 114
5.2. Magnetic imaging using scanning NV microscope 117
5.3. Current profile reconstruction 120
5.4. Conclusions 126
Chapter 6. Dynamics in Permalloy 127
6.1. Experimental details 128
6.2. Static magnetic field imaging 130
6.3. Domain driven by external field 132
6.4. Rabi frequency calculation 135
6.5. Driven imaging in external static field 137
6.6. Conclusions 138
Chapter 7. Conclusions 139
Bibliography 141
Appendices 159
Appendix A. Spin Operator Calculation 159
A.1. Spin operator definitions 159
A.2. Rotating frame calculation 160
Appendix B. Magnetic Field Decomposition and Current Reconstruction 163
B.1. Magnetic field decomposition 163
B.2. Current reconstruction 165
Index 167
Curriculum Vitae 168
Table 3.1. Optical components used for confocal optics. The positions of the components are shown in Figure 3.3. 69
Table 3.2. Electronics and Microwave components. This is utilized to design a microwave and measurement system as illustrated in the Figure 3.6. 76
Table 3.3. Tuning forks based scanning probe microscope electronics. This is used to build the scanning probe electronics as seen in the Figure 3.10. 83
Figure 1.1. (a) The Hope diamond. Photo taken at Smithsonian National Museum of Natural History, July 2022. (b) Natural colored diamonds. Photo taken at Natural History Museum... 32
Figure 1.2. This word frequency and word cloud show which words are used a lot in this dissertation. 36
Figure 2.1. NV center structures. (a) NV center oriented along [111] crystal direction in a diamond unit cell which size is 3.57Å. Carbon atoms are represented by black spheres, a... 38
Figure 2.2. (a) Electronics energy level in the band gap of a diamond. There are energy states of several charge states of NV centers and ionized nitrogen. (b) Charge state readout via... 39
Figure 2.3. NV center energy level focused its photonic state. (a) Optical transition levels. In spin triplet, Green arrows refer excitation light such as 532nm laser, and red arrows refer... 41
Figure 2.4. Spin readout time analysis. (a) After state preparation, Green laser was used for optical pumping and syncronized readout time window with vary start time from excitation.... 44
Figure 2.5. Depopulation time measurement. (a) Pulse sequence for depopulation measurement. "π" means pi pulse. (b) Result of depopulation time for time. 45
Figure 2.6. Laser power and initialization and photon counts. (a) Normalized photoluminescence result from time trace when initialization with different pumping laser powers. (b)... 47
Figure 2.7. Optically detected magnetic resonance. (a) CW-ESR measurement pulse scheme. Optical pumping, microwave driving and photon counting are operated in same time when... 48
Figure 2.8. ESR spectrum on varying magnetic field. (a) ESR spectrum on magnetic field. (b) ESR spectrum with varying magnetic field. Darker Vshapeshows Zeeman split. (c)... 51
Figure 2.9. Contrast and linewidth are depending on laser and microwave power. (a) Contrast vs. Laser power. (b) Contrast vs. Microwave power. (b) Linewidth vs. Microwave power. 53
Figure 2.10. (a) Rabi oscillation pulse scheme. Every pulse is synchronized. The microwave pulse is controlled by a switch, and the measurement is performed by varying the duration... 55
Figure 2.11. Ground state energy level and hyper fine interaction of NV centers with ¹⁴N and ¹⁵N. Ground state crystal field split is D₀=2.87GHz in room temperature. 56
Figure 2.12. Ramsey measurement. (a) and (b) Hyperfine structure of NV center with ¹⁴N and ¹⁵N. (c) Ramsey experiment pulse scheme. There are 3 valleys in (b) with mI=0,±1... 58
Figure 2.13. Qualitative graphical description of decoherence and T₂★ when Ramsey measurement.[이미지참조] 60
Figure 2.14. Hahn-Echo measurement. (a) Pulse scheme of Echo measurement. (b) Graphical representation of Echo measurement in the Bloch sphere. (c) Echo measurement example... 62
Figure 2.15. T₁ measurement (a) Pulse scheme of T₁ measurement. If the π pulse displayed in the dahsed round bracket is utilized, it prepares |1> state, and if it is not, it prepares |0>... 63
Figure 3.1. A cartoon describing dissertation experiments. In the middle of the figure is a diamond probe with a small red arrow indicating to a single NV center. Above this, an optics... 66
Figure 3.2. Vibration level on an optical table and a floor. (a) Time trace of vertical velocity. (b) Frequency spectrum of velocity. (c) Time trace of vertical distance. (d) Frequency... 67
Figure 3.3. Optical components of confocal microscopy. Each components details are written in Table 3.1. 68
Figure 3.4. AOM delay measurement. (a) The pulse sequence for AOM delay measurement. (b) Photoluminescence data vs. time result of AOM delay measurement. 70
Figure 3.5. (a) Schematics of 4−F scanning microscope. (b) Collection from NV to the end of objective lens. (c) Optical image acquired by confocal optics. Scale bar 1µm.[이미지참조] 73
Figure 3.6. Electronic parts. Each components details are written in Table 3.2. 77
Figure 3.7. AOM leakage reduction (a) Tank circuit diagram. (b) The Bode plot of the tank circuit. (c) Double passed AOM optics. 78
Figure 3.8. NV Imaging methods. (a) Scanning magnetic samples using a diamond tip. (b) Magnetic sample on diamond substrate. (c) Nano-diamonds on magnetic samples. (d) Wide-... 81
Figure 3.9. NV Scanning method. (a) A fabricated diamond probe. (b) Nano-diamond attached at the end of AFM cantilever. (c) Mangetic samples attached at the end of AFM... 82
Figure 3.10. Scanning probe microscope electronics. Each components details in Table 3.3. 83
Figure 3.11. Confocal microscope images of diamond scanning probes. (a,d) UCSB probe images. (b,e) QNami probe images. (c,f) QZabre probe images. Scale bars 20µm for (a-c).... 84
Figure 3.12. (a) Whole side view, and (b) Side view, and (c) Top view photo of scanning systems. Scale bars 1cm for (a-c). (d) Diamond probe, sample, microwave. (e) Diamond... 85
Figure 3.13. Schematics of tuning forks. (a) Drawing of a structure and electrodes of tuning forks. (b) Equivalent RLC circuit of tuning forks. 87
Figure 3.14. Lock-In signal. (a) Amplitude vs. frequency. (b) Amplitude vs. distance. (c) Phase vs. frequency. (d) Phase vs. distance. (e) Comparison distance 88
Figure 3.15. PL vs. distance from surface. 89
Figure 3.16. Tuning forks amplitude measurement. (a) Optical images of single NV center at diamond probe. Scale bars 1µm. (b) Line cut of PL image where TF ON. (c) TF Amplitude... 90
Figure 3.17. The spatial resolution of magnetic field imaging is determined by the distance between the tip and the sample. (a) Magnetic field values along two parallel wires at different... 91
Figure 3.18. Example of ESR spectrum and magnetic field measurement scheme. (a) Drawing of ESR spectrum as a function of microwave frequency. (b) The photoluminescence... 92
Figure 3.19. Examples for contour image of the magnetic skyrmion sample. This sample is made with Ta(1.5)/Pt(2)/Co(0.3-1.5)/Pt(5)/Ta(2) on MgO(001) Substrate. As the external... 93
Figure 3.20. Various magnetic imaging of ferromagnetic film with IrMn(5). (a) Full ESR measurement image. (b)Dual microwave frequency image. (c-g)Contour image with several... 94
Figure 3.21. (a) A block diagram of an optical cryostation. (b) Schematic of experiments in the cryostat chamber. The radiation shield to prevent radiation is kept at 30 K, which... 98
Figure 3.22. Temperature and vacuum data were measured during the 36-hour cooling process. (a) Temperature data. Due to the presence of samples and experimental equipment,... 99
Figure 4.1. (a) Schematics of magnetic field imaging of single nanowire. (b) Bar magnet and iron powders. (c) Bar magnet and compasses. Scale bars 2cm. 102
Figure 4.2. Magnetic properties of a single Co nanowire. (a) An SEM image of a single Co nanowire. Scalebar, 2µm. The magnetic hysteresis loop obtained from nanowire arrays... 107
Figure 4.3. Magnetic imaging of a single Co nanowire. (a) 92 NV centers of [111] crystal orientation are used to image magnetic stray field around the nanowire. Circles denote the...[이미지참조] 108
Figure 4.4. Ramsey sequences for sensitive DC measurement. (a) There are three hyperfine resonances in the ODMR spectrum resulting from the coupling between the NV electron spin... 110
Figure 4.5. Comparison of the Ramsey measurement between two NV centers. (a) The Ramsey data obtained from the NV centers marked in the confocal image (b). For clarity, the... 111
Figure 5.1. Graphene point contact devices. (a) Optical image of device #1. A rectangular shape of hBN-encapsulated graphene is patterned to have two narrow channels in the middle... 115
Figure 5.2. Probing magnetic field via ESR. (a) Optically measured ESR spectroscopy of the diamond NV center. The difference in the resonance frequencies corresponds to the amount... 118
Figure 5.3. Reconstruction of current density in device #1. (a) Simulated current density with the supplied current of 100µA. (b) Simulation of magnetic field along the NV axis,... 119
Figure 5.4. Flow diagram of the reconstruction process. Using Ampere's law and Fourier transform, we first convert the real space data of BNV into Fourier space counterparts of BNV,...[이미지참조] 120
Figure 5.5. Effect of the Hanning Window in the reconstructed current density profile. The Hanning Window function used in the reconstruction process contains the cut-off wavelength,... 121
Figure 5.6. Measurement with the opposite directions of current flow. (a) and (b) Measured BNV around a point contact in device #1 but with the reversed direction of current; from leftto...[이미지참조] 122
Figure 5.7. Magnetic field measurement on device #2. (a) Scanned image of BNV. The two top point contacts in the inset are used for the experiment and DC of 200µA is supplied from...[이미지참조] 124
Figure 5.8. Reconstruction of current density in device #2. (a) Close-up measurement of BNV around the drain point contact (the right one in Figure 5.7). (b) and (c) Magnetic images...[이미지참조] 125
Figure 6.1. (a) Experimental Schematics. Diamond probes hosting single NV centers acquire static magnetic field and Rabi oscillation using ODMR on each position of Py. Microwave... 128
Figure 6.2. (a) Magnetic simulation of permalloy square. (b) Magnetic field simulation on permalloy square. (c) Magnetic field imaging using ESR measurement. All scale bars 2µm. 129
Figure 6.3. (a) ESR signal is acquired photoluminescence as a fucntion of microwave frequency. Magnetic field is measured by the frequency difference of valleys in ESR. (b) Dual... 131
Figure 6.4. Magnetic domain evolution in different magnetic field. The domain of east side is parallel to external field with −y direction. Size of east side domain by applying exter-... 132
Figure 6.5. (a) Map of ESR contrast. (b) Rabi frequency is calculated from ESR contrast. (c) Image of Rabi frequency. (d) Data of Rabi oscillation of each point labeled in 1, 2, and... 133
Figure 6.6. (a) The normalized amplitude of oscillating magnetization modulated with frequency ~3GHz for △Mx, (b) △My and (c) △Mz. (d) The sinusoidal magnetic field generated...[이미지참조] 136
Figure 6.7. (a) Static magnetic field image in bias field By=-0.6mT. (b) Image of ODMR contrast. (c) Image of Rabi frequency. All scale bars 2 μm. 138