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Optimization of simultaneous measurement of magnetic field and temperature measurement by silicon vacancy quantum sensor using simultaneous resonance

Tanaka Tomoaki, Yamazaki Yuichi, Kojima Kazutoshi, Ohshima Takeshi

Published Nov 29, 2022• 0 citations
OpenAlex

Abstract

Background and Purpose Silicon vacancies (VSi) in silicon carbide (SiC) have attracted great attention because we can measure magnetic field and temperature in some devices by fabricating VSi in the devices1,2. Simultaneous measurement of magnetic field and temperature using SiC-VSi quantum sensor requires simultaneous Optically Detected Magnetic Resonance (ODMR) measurement of the ground and excited states. However, the ODMR contrast (= sensitivity) of the excited state is about one order of magnitude smaller than that of the ground state. So, the temperature measurement is time-consuming. To solve this problem, we have proposed and demonstrated a new temperature measurement method, Simultaneous Resonance (SR) ODMR, which based on the modulation of the ODMR contrast of the ground state by simultaneous resonance of the ground and excited states3. This method converts part of the contrast of the ground state into that of the excited state. In order to perform magnetic field and temperature measurements with high sensitivity, it is necessary to optimize the RF power ratio which is related to the contrast ratio between the ground and excited states to minimize the measurement time. Therefore, the purpose of our study is to optimize the power ratio of the RF using the simultaneous measurement by SR ODMR. Methods and Results VSi dots were fabricated on p-type 4H-SiC epitaxial thin film (5.6 µm) using a particle beam writing (ion species: He, Energy: 0.5 MeV, irradiation dose: 3×105 /dots). The size and depth of the dots are 5×5 µm2 and ~1 µm, respectively. Three signal generators were used for the measurements, one fixed at the resonance frequency of the ground state (70 MHz) for SR, and the others swept near those of the ground and excited states (20-170, 300-600 MHz) for the ground state and SR ODMR measurements, respectively. Figure 1 shows the spectra of ground and SR excited states by ODMR simultaneous measurements. Signal intensities indicated by red and blue arrows are observed. The former is a resonance of the ground state, and the latter is that of the excited states. We can find that another dip indicated by green arrow around 500 MHz exists. The sweep condition indicates that this frequency corresponds to 70 MHz of the ground state measurement. This suggests that the resonance of the ground state occurs in both the ground state and SR ODMR measurements. As a result of their competition, the dip appears at around the 500 MHz on the SR ODMR side. We measured the changing of ODMR contrast of the ground and excited states when we change the RF power of signal generators. The signal intensity was almost the same at the RF power ratio of 1:9 for SR and ground state ODMR. At this condition, the contrast of SR is more than four times that of traditional excited state measurement. This suggests that we achieved faster measurement than conventional simultaneous ground and excited states measurement.

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Background and Purpose Silicon vacancies (VSi) in silicon carbide (SiC) have attracted great attention because we can measure magnetic field and temperature in some devices by fabricating VSi in the devices1,2. Simultaneous measurement of magnetic field and temperature using SiC-VSi quantum sensor requires simultaneous Optically Detected Magnetic Resonance (ODMR) measurement of the ground and excited states. However, the ODMR contrast (= sensitivity) of the excited state is about one order of magnitude smaller than that of the ground state. So, the temperature measurement is time-consuming. To solve this problem, we have proposed and demonstrated a new temperature measurement method, Simultaneous Resonance (SR) ODMR, which based on the modulation of the ODMR contrast of the ground state by simultaneous resonance of the ground and excited states3. This method converts part of the contrast of the ground state into that of the excited state. In order to perform magnetic field and temperature measurements with high sensitivity, it is necessary to optimize the RF power ratio which is related to the contrast ratio between the ground and excited states to minimize the measurement time. Therefore, the purpose of our study is to optimize the power ratio of the RF using the simultaneous measurement by SR ODMR. Methods and Results VSi dots were fabricated on p-type 4H-SiC epitaxial thin film (5.6 µm) using a particle beam writing (ion species: He, Energy: 0.5 MeV, irradiation dose: 3×105 /dots). The size and depth of the dots are 5×5 µm2 and ~1 µm, respectively. Three signal generators were used for the measurements, one fixed at the resonance frequency of the ground state (70 MHz) for SR, and the others swept near those of the ground and excited states (20-170, 300-600 MHz) for the ground state and SR ODMR measurements, respectively. Figure 1 shows the spectra of ground and SR excited states by ODMR simultaneous measurements. Signal intensities indicated by red and blue arrows are observed. The former is a resonance of the ground state, and the latter is that of the excited states. We can find that another dip indicated by green arrow around 500 MHz exists. The sweep condition indicates that this frequency corresponds to 70 MHz of the ground state measurement. This suggests that the resonance of the ground state occurs in both the ground state and SR ODMR measurements. As a result of their competition, the dip appears at around the 500 MHz on the SR ODMR side. We measured the changing of ODMR contrast of the ground and excited states when we change the RF power of signal generators. The signal intensity was almost the same at the RF power ratio of 1:9 for SR and ground state ODMR. At this condition, the contrast of SR is more than four times that of traditional excited state measurement. This suggests that we achieved faster measurement than conventional simultaneous ground and excited states measurement.
The V2 silicon vacancy defect in 4H-SiC has emerged as a promising system for quantum technologies due to its favorable optical and spin properties and the advantages of the SiC host. However, the readout contrast - an important benchmark for quantum sensing - of V2 ensembles for optically-detected magnetic resonance (ODMR) is relatively low, usually <1%\%% at room temperature. To overcome this challenge, we resonantly excite the V2 ensembles at cryogenic temperatures and compare the results with the off-resonant case. We report a maximum ODMR contrast of 50%\%% with only 2 μμμW of resonant laser power, almost 100 times improvement over off-resonant excitation. We attribute this high readout contrast to a subset of V2 centers that have one spin-selective optical transition resonant with the laser. The ODMR contrast decreases with temperature, approaching the non-resonant contrast by 60 K, likely due to broadening of the optical transition linewidths. We achieve a maximum sensitivity of 100 nT/Hz\sqrt{Hz}Hz​ with a resonant laser power of 300 μμμW, while 100 times more non-resonant excitation power is needed to achieve comparable sensitivity.
Silicon vacancy centers in silicon carbide are promising candidates for storing and manipulating quantum information. Implementation of fast quantum gates is an essential requirement for quantum information processing. In a low magnetic field, the resonance frequencies of silicon vacancy spins are in the range of a few MHz, the same order of magnitude as the Rabi frequencies of typical control fields. As a consequence, the rotating wave approximation becomes invalid and nonlinear processes like the absorption and emission of multiple photons become relevant. This paper focuses on multi-photon transitions of negatively charged silicon vacancies driven by a strong RF field. We present continuous-wave optically detected magnetic resonance (ODMR) spectra measured at different RF powers to identify the 1-, 2-, and 3 RF photon transitions of different types of the silicon vacancy in the 6H6H6H-SIC polytype. Time-resolved experiments of Rabi oscillations and free induction decays of these multiple RF photon transitions were observed. Apart from zero-field data, we also present spectra in magnetic fields with different strength and orientation with respect to the system's symmetry axis.
For high-bias operation devices such as silicon carbide (SiC) power devices, early detection of failure mechanisms is essential to ensure reliability. This requires a method to map high electric fields with high spatial resolution, which has not been realized until now. Here we report that the silicon vacancy (Vsi) in SiC has outstanding characteristics for detecting electric fields applied in various directions within a high-biased SiC device. Vsi exhibits an equivalent response to electric field components parallel (Epara) and perpendicular (Eperp) to the c-axis, a feature unique among quantum sensors, and the responsiveness to Epara and Eperp enables detection of arbitrary electric fields encountered in cutting-edge SiC power devices. We confirmed high electric field detection of ~2.3 MV/cm, which is ~90% of the breakdown electric field of a 4H-SiC with typical carrier concentration. Selectively formed Vsi enables high-resolution mapping of electric field distribution. Vsi-based quantum sensors bring data-driven research and development methodologies as well as device degradation diagnosis.
The nitrogen-vacancy (NV) center is a promising candidate to realize practical quantum sensors with high sensitivity and high spatial resolution at room temperature and atmospheric pressure. In conventional high-frequency AC magnetometry with NV centers, the setup requires a pulse sequence with an appropriate time synchronization and strong microwave power. To avoid these practical difficulties, AC magnetometry using continuous-wave optically detected magnetic resonance (CW-ODMR) was recently demonstrated. That previous study utilized radio frequency (RF)-dressed states generated by the coherent interaction between the electron spin of the NV center and the RF wave. However, the drawback of this method is that the detectable frequency of the AC magnetic fields is fixed. Here, we propose and demonstrate frequency-tunable magnetic field sensing based on CW-ODMR. In the new sensing scheme, we obtain RF double-dressed states by irradiation with RF fields at two different frequencies. One creates the RF-dressed states and changes the frequency of the target AC field. The other is a target AC field that induces a change in the CW-ODMR spectrum by generating the RF double-dressed states through coherent interaction with the RF-dressed states. The sensitivity of our method is estimated to be comparable to or even higher than that of the conventional method based on the RF field with a single frequency. The estimated bandwidth is 7.5 MHz, higher than that of the conventional method using the RF-dressed states. Our frequency-tunable magnetic field sensor based on CW-ODMR paves the way for new applications in diamond devices.
The silicon vacancy center in Silicon Carbide (SiC) provides an optically addressable qubit at room temperature in its spin- 32\frac{3}{2}23​ electronic state. However, optical spin initialization and readout are less efficient compared to those of spin-1 systems, such as nitrogen-vacancy centers in diamond, under non-resonant optical excitation. Spin-dependent fluorescence exhibits contrast only between ∣m=±3/2⟩| m=\pm 3/2\left.\right\rangle∣m=±3/2⟩ and ∣m=±1/2⟩| m=\pm 1/2\left.\right\rangle∣m=±1/2⟩ states, and optical pumping does not create a population difference between ∣+1/2⟩| +1/2\left.\right\rangle∣+1/2⟩ and ∣−1/2⟩| -1/2\left.\right\rangle∣−1/2⟩ states. Thus, operating one qubit (e.g., {∣+3/2⟩,∣+1/2⟩}\left\{| +3/2\left.\right\rangle ,| +1/2\left.\right\rangle \right\}{∣+3/2⟩,∣+1/2⟩} states) leaves the population in the remaining state ( ∣−1/2⟩| -1/2\left.\right\rangle∣−1/2⟩ ) unaffected, contributing to background in optical readout. To mitigate this problem, we propose a sensing scheme based on duplex qubit operation in the quartet, using microwave pulses with two resonant frequencies to simultaneously operate {∣+3/2⟩,∣+1/2⟩}\left\{| +3/2\left.\right\rangle ,| +1/2\left.\right\rangle \right\}{∣+3/2⟩,∣+1/2⟩} and {∣−1/2⟩,∣−3/2⟩}\left\{| -1/2\left.\right\rangle ,| -3/2\left.\right\rangle \right\}{∣−1/2⟩,∣−3/2⟩} . Experimental results demonstrate that this approach doubles signal contrast in optical readout and improves sensitivity in AC magnetometry compared to simplex operation.
Silicon carbide (SiC) has become a key player in the realization of scalable quantum technologies due to its ability to host optically addressable spin qubits and wafer-size samples. Here, we have demonstrated optically detected magnetic resonance (ODMR) with resonant excitation and clearly identified the ground state energy levels of the NV centers in 4H-SiC. Coherent manipulation of NV centers in SiC has been achieved with Rabi and Ramsey oscillations. Finally, we show the successful generation and characterization of single nitrogen vacancy (NV) center in SiC employing ion implantation. Our results highligh the key role of NV centers in SiC as a potential candidate for quantum information processing.