As one of the most promising candidates of solid-state qubits, nitrogen-vacancy (NV) centers in diamonds have been paid much attention for experimental quantum information processings, such as their energy level structures characterized by microwave absorption probes. In this paper we develop a simplified steady-state spectral method to exactly solve the driven three-level atomic system for fitting the measured microwave absorptions of the NV centers in diamonds. Due to the energy level structures of the NV centers in diamonds which are controllable by applying external magnetic fields, the precision measurements of the ESR spectra of the NV centers in diamond can be used to precisely detect the applied magnetic fields with nanometer spatial scale resolutions. Our steady-state spectral simulations show that the Bz-component (parallel with the axis of the NV centers) of the applied magnetic fields causes the symmetric Zeeman shifts in the zero-field splitting levels, while the B⊥-component (perpendicular to the NV axis mainly) causes the asymmetric Zeeman shifts. Therefore, by exactly probing the steady-state Zeeman shift absorption spectra of the NV centers in diamonds the applied magnetic fields can be detected precisely, at least theoretically.
As one of the most promising candidates of solid-state qubits, nitrogen-vacancy (NV) centers in diamonds have been paid much attention for experimental quantum information processings, such as their energy level structures characterized by microwave absorption probes. In this paper we develop a simplified steady-state spectral method to exactly solve the driven three-level atomic system for fitting the measured microwave absorptions of the NV centers in diamonds. Due to the energy level structures of the NV centers in diamonds which are controllable by applying external magnetic fields, the precision measurements of the ESR spectra of the NV centers in diamond can be used to precisely detect the applied magnetic fields with nanometer spatial scale resolutions. Our steady-state spectral simulations show that the Bz-component (parallel with the axis of the NV centers) of the applied magnetic fields causes the symmetric Zeeman shifts in the zero-field splitting levels, while the B⊥-component (perpendicular to the NV axis mainly) causes the asymmetric Zeeman shifts. Therefore, by exactly probing the steady-state Zeeman shift absorption spectra of the NV centers in diamonds the applied magnetic fields can be detected precisely, at least theoretically.
An ensemble of nitrogen-vacancy (NV) centers in diamond is an attractive device to detect small magnetic fields. In particular, by exploiting the fact that the NV center can be aligned along one of four different axes due to ${C}_{3\ensuremath{\nu}}$ symmetry, it is possible to extract information concerning vector magnetic fields. However, in the conventional scheme, low readout contrasts of the NV centers significantly decrease the sensitivity of the vector-magnetic-field sensing. Here, we propose a way to improve the sensitivity of the vector-magnetic-field sensing of the NV centers using multifrequency control. Since the Zeeman energy of the NV centers depends on the direction of the axis, we can independently control the four types of NV centers using microwave pulses with different frequencies. This allows us to use every NV center for the vector field detection in parallel, which effectively increases the readout contrast. Our results pave the way to realize a practical diamond-based vector field sensor.
The measurement of vector magnetic fields with high sensitivity and spatial resolution is important for both fundamental science and engineering applications. In particular, magnetic-field sensing with nitrogen-vacancy (NV) centers in diamond is a promising approach that can outperform existing methods. Recent studies have demonstrated vector dc magnetic-field sensing with perfectly aligned NV centers, which showed a higher readout contrast than NV centers having four equally distributed orientations. However, to estimate the azimuthal angle of the target magnetic field with respect to the NV axis in these previous approaches, it is necessary to apply a strong reference dc magnetic field, which can perturb the system to be measured. This is a crucial problem, especially when attempting to measure vector magnetic fields from materials that are sensitive to applied dc magnetic fields. Here, we propose a method to measure vector dc magnetic fields using perfectly aligned NV centers without reference dc magnetic fields. This method can be performed even with a single NV center. More specifically, we use the direction of linearly polarized microwave fields to induce Rabi oscillation as a reference and we estimate the azimuthal angle of the target fields from the Rabi frequency. We further demonstrate the potential of our method to improve sensitivity by using entangled states to overcome the standard quantum limit. Our method of using a reference microwave field is an alternative technique for sensitive vector dc magnetic-field sensing.
Precision measurements of electric current flow in motors and power converters is indispensable for efficient digital control by monitoring their energy use. Nitrogen-vacancy (NV) centers in a crystalline diamond are promising candidates for sensitive magnetometry and electric current measurements. In a diamond quantum sensor with NV centers, the Zeeman splitting of the electron spin state of the NV center can be utilized to detect magnetic field. This is because the splitting of the spectral line is proportional to the external magnetic field strength, and the arbitrary constant of the gyromagnetic ratio is independent of both frequency and magnetic field. Then, the Zeeman splitting can be measured with optically detected magnetic resonance (ODMR) spectroscopy.
In modern-day quantum metrology, quantum sensors are widely employed to detect weak magnetic fields or nanoscale signals. Quantum devices, exploiting quantum coherence, are inevitably connected to physical constants and can achieve accuracy, repeatability, and precision approaching fundamental limits. As a result, these sensors have shown utility in a wide range of research domains spanning both science and technology. A rapidly emerging quantum sensing platform employs atomic-scale defects in crystals. In particular, magnetometry using nitrogen-vacancy (NV) color centers in diamond has garnered increasing interest. NV systems possess a combination of remarkable properties, optical addressability, long coherence times, and biocompatibility. Sensors based on NV centers excel in spatial resolution and magnetic sensitivity. These diamond-based sensors promise comparable combination of high spatial resolution and magnetic sensitivity without cryogenic operation. The above properties of NV magnetometers promise increasingly integrated quantum measurement technology, as a result, they have been extensively developed with various protocols and find use in numerous applications spanning materials characterization, nuclear magnetic resonance (NMR), condensed matter physics, paleomagnetism, neuroscience and living systems biology, and industrial vector magnetometry. In this chapter, NV centers are explored for magnetic sensing in a number of contexts. In general, we introduce novel regimes for magnetic-field probes with NV ensembles. Specifically, NV centers are developed for sensitive magnetometers for applications where microwaves (MWs) are prohibitively invasive and operations need to be carried out under zero ambient magnetic field. The primary goal of our discussion is to improve the utility of these NV center-based magnetometers.
The physical properties of diamond crystals, such as color or electrical conductivity, can be controlled via impurities. In particular, when doped with nitrogen, optically active nitrogen-vacancy centers (NV), can be induced. The center is an outstanding quantum spin system that enables, under ambient conditions, optical initialization, readout, and coherent microwave control with applications in sensing and quantum information. Under optical and radio frequency excitation, the Zeeman splitting of the degenerate states allows the quantitative measurement of external magnetic fields with high sensitivity. This study provides a pedagogical introduction to the properties of the NV centers as well as a step-by-step process to develop and test a simple magnetic quantum sensor based on color centers with significant potential for the development of highly compact multisensor systems.
Nitrogen-vacancy (NV) centers in a bulk diamond are often employed to realize measurement of multiple physical quantities, which depends on orientation information of NV axis. We report a fast and effective method to determine the orientation of NV axis with the aid of a static magnetic field. By measuring the optically detected magnetic resonance spectra, we can precisely extract the polar angle information between the NV axis and the known magnetic field. Combining with the polar angle information of different kinds of NV centers, we employ the Nelder–Mead algorithm to get the optimal solution of the orientation of NV axis. This method is simple and efficient, and is easily applied in NV-based quantum sensing.