We report on a microwave planar ring antenna specifically designed for optically-detected magnetic resonance (ODMR) of nitrogen-vacancy (NV) centers in diamond. It has the resonance frequency at around 2.87 GHz with the bandwidth of 400 MHz, ensuring that ODMR can be observed under external magnetic fields up to 100 G without the need of adjustment of the resonance frequency. It is also spatially uniform within the 1-mm-diameter center hole, enabling the magnetic-field imaging in the wide spatial range. These features facilitate the experiments on quantum sensing and imaging using NV centers at room temperature.
Nitrogen-vacancy (NV) centers in diamond are considered sensors for detecting magnetic fields. Pulsed optically detected magnetic resonance (ODMR) is typically used to detect AC magnetic fields; however, this technique can only be implemented after careful calibration that involves aligning an external static magnetic field, measuring continuous-wave (CW) ODMR, determining the Rabi frequency, and setting the microwave phase. In contrast, CW-ODMR can be simply implemented by continuous application of green CW laser and a microwave filed. In this letter, we report a method that uses NV centers and CW-ODMR to detect AC magnetic fields. Unlike conventional methods that use NV centers to detect AC magnetic fields, the proposed method requires neither a pulse sequence nor an externally applied DC magnetic field; this greatly simplifies the procedure and apparatus needed to implement this method. This method provides a sensitivity of 2.5 µT/ Hz at room temperature. Thus, this simple alternative to existing AC magnetic field sensors paves the way for a practical and feasible quantum sensor.
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 C3ν 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 multi-frequency 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 detection of small magnetic fields is important in the field of metrology, because there are many potential applications in biology and medical science. The performance of a magnetic field sensor is characterized by its spatial resolution and sensitivity; therefore, a significant amount of effort has been devoted to creating a device that can measure small magnetic fields in a local region [1][2][3].Nitrogen vacancy (NV) centers in diamond are fascinating candidates with which to construct a magnetic field sensor [4][5][6][7]. The NV center is a spin 1 system, and the frequency of the | ± 1 states can be shifted by magnetic fields. We can use this system as an effective two-level system spanned by |0 and |1 with a frequency selectivity where | − 1 is significantly detuned. We can implement gate operations of the spins in NV centers using microwave pulses [8][9][10][11]. It is possible to detect DC (AC) magnetic fields by implementing a Ramsey interference (spin echo) measurement [4][5][6]. Moreover, NV centers have a long coherence time, e.g., a few milli-seconds at a room temperature and a second at low temperature [12][13][14]. In addition, because the NV centers can be strongly coupled with optical photons, we can read out the state of the NV centers via fluorescence from the optical transitions [9,10]. The NV centers can be embedded in nanocrystals, which allows the NV centers to interact with local magnetic fields [15]. These properties are prerequisite to realizing a high-performance sensor for magnetic fields.Recently, vector magnetic field sensing by NV centers has become an active area of interest [16][17][18][19][20][21]. The NV center is aligned along one of four different axes due to C 3ν symmetry. The Zeeman energies of the NV centers are determined by gµ b B · d j (j = 1, 2, 3, 4) where g denotes the g factor, µ b denotes a Bohr magneton, B denotes the magnetic fields, and d j denotes the direction of the j-th NV axis. By sequentially performing Ramsey interference or spin echo measurements on NV centers with...
Recently we have demonstrated AC magnetic field sensing scheme using a simple continuous-wave optically detected magnetic resonance of nitrogen-vacancy centers in diamond [Appl. Phys. Lett. 113, 082405 (2018)]. This scheme is based on electronic spin double resonance excited by continuous microwaves and radio-frequency (RF) fields. Here we measured and analyzed the double resonance spectra and magnetic field sensitivity for various frequencies of microwaves and RF fields. As a result, we observed a clear anticrossing of RF-dressed electronic spin states in the spectra and estimated the bandwidth to be approximately 5 MHz at the center frequency of 9.9 MHz.
Operando analysis of electron devices provides key information regarding their performance enhancement, reliability, thermal management, etc. For versatile operando analysis of devices, the nitrogen-vacancy (NV) centers in diamonds are potentially useful media owing to their excellent sensitivity to multiple physical parameters. However, in single crystal diamond substrates often used for sensing applications, placing NV centers in contiguity with the active channel is difficult. This study proposes an operando analysis method using a nanodiamond thin film that can be directly formed onto various electron devices by a simple solution-based process. The results of noise analysis of luminescence of the NV centers in nanodiamonds show that the signal-to-noise ratio in optically detected magnetic resonance can be drastically improved by excluding the large 1/ f noise of nanodiamonds. Consequently, the magnetic field and increase in temperature caused by the device current could be simultaneously measured in a lithographically fabricated metal microwire as a test device. Moreover, the spatial mapping measurement is demonstrated and shows a similar profile with the numerical calculation.
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