SiC Quantum Sensing Technologies

• SiC Quantum Sensing Technologies are advanced sensors that use optically addressable spin defects to measure magnetic, electric, and thermal fields at the nanoscale.
• They employ various intrinsic defect centers—silicon vacancies, divacancies, and nitrogen vacancies—with unique spin and optical properties that enable quantitative nanoscale measurements.
• Wafer-scale integration and robust device engineering facilitate scalable, high-fidelity sensor platforms for applications in metrology, bioimaging, and noninvasive field imaging.

Silicon Carbide (SiC)-Quantum Sensing Technologies constitute an advanced platform for employing optically addressable spin defects in SiC as quantitative, broadband nanoscale probes of magnetic, electric, and thermal fields. This class of solid-state quantum sensors leverages a diverse family of intrinsic paramagnetic color centers—including silicon vacancies (VSi), divacancies (PL5 and others), and nitrogen-vacancy (NV) centers—each offering distinct spin multiplicities, zero-field splittings, and optical transitions in the near-infrared (NIR) spectral window. SiC stands out for its industry-compatible, wafer-scale processing and robust defect engineering, which enables high-fidelity, scalable quantum devices. Below is a comprehensive overview detailing the electronic structure, sensing modalities, nanoscale capabilities, and device integration prospects of SiC-based quantum sensors.

1. Defect Centers in SiC and Their Spin Properties

Several classes of deep-level point defects in SiC function as quantum spin sensors, each with unique spin Hamiltonians and optical characteristics.

• Silicon Vacancy (VSi) Centers: In 4H-SiC, the prominent V2 site yields a negatively charged S=3/2 ground state, described by:

$$H = D\left(S_z^2 - \frac{5}{4}\right) + g \mu_B \mathbf{B}\cdot\mathbf{S}$$

with $D \approx 35$ MHz ($2D \approx 70$ MHz splitting), $g \approx 2.0$, and Zeeman splitting under external magnetic field. The quartet structure provides two Kramers doublets $|m_S|=3/2$, $|m_S|=1/2$ (Singh et al., 2022, Soykal et al., 2016).

• Divacancy (VSi–VC) and PL5 Centers: PL5 is a symmetrically distinct divacancy in 4H-SiC with ground state $S=1$:

$$H = D S_z^2 + E(S_x^2 - S_y^2) + g \mu_B \mathbf{B}\cdot \mathbf{S}$$

where $D \approx 1.36$ GHz, $E \approx 16$ MHz. The substantial axial ZFS is critical for robust ODMR at zero and moderate external field (Liu et al., 27 Dec 2025).

• Nitrogen Vacancy (NV) in SiC: S=1 ground state, similar in structure to the diamond NV− center, with site-dependent ZFS (e.g., $D=1284$–$1349$ MHz for various sites in 4H-SiC) and sharp ZPL near 1.17–1.24 µm (Mu et al., 2020).

All these centers are optically addressable in the NIR (850–1200 nm), compatible with biological tissue windows and fiber optics (Muzha et al., 2014).

2. Optical and Microwave Sensing Modalities

Quantum sensing in SiC employs optically detected magnetic resonance (ODMR) and related techniques:

• Initialization/Readout: Non-resonant and resonant laser excitation (e.g., 905 nm for PL5, 785 or 917 nm for VSi) polarizes the electronic spin manifold and enables spin-dependent photoluminescence (PL) for readout (Liu et al., 27 Dec 2025, Singh et al., 2022).
• ODMR Protocols: Microwave (or RF) drives on-resonant transitions within the spin multiplet, producing PL dips at transition frequencies. Resonant optical excitation at cryogenic temperatures can maximize contrast (up to 50%) for specific sites, whereas off-resonant protocols yield modest room-temperature contrasts (sub-1%) (Tathfif et al., 1 Dec 2025).
• Advanced Modulation: Dual-frequency or duplex-qubit protocols for VSi (S=3/2) centers simultaneously address both $|\pm3/2\rangle \leftrightarrow |\pm1/2\rangle$ transitions, effectively doubling ODMR contrast and enhancing magnetic sensitivity (e.g., to $\sim1.4\,\mu$T/Hz$^{1/2}$ in dense ensembles) (Tahara et al., 2024).
• Microwave-Free Relaxometry: Near zero-field, spectroscopy of spin-level anti-crossings (LACs) in the VSi quartet enables all-optical relaxometric detection of local fields with spatial resolutions down to hundreds of nanometers, without MW hardware (Bulancea-Lindvall et al., 2022, Suhana et al., 18 Sep 2025).

3. Sensing Modalities and Nanoscale Noise Spectroscopy

State-of-the-art SiC quantum sensors have achieved real-time, nanoscale noise spectroscopy of charge and spin environments:

• Single-Charge Tunneling and RTN Detection: Single PL5 centers allow direct observation of discrete charge-state tunneling via stochastic Stark shifts of the ODMR frequency. Plateau analysis in time-resolved traces can localize individual traps to within ~10 nm of the sensor (Liu et al., 27 Dec 2025).
• Broadband Noise Spectroscopy: Hahn-echo and multi-pulse (e.g., XY8) dynamical decoupling pulse sequences reconstruct environmental noise spectral density $S(\omega)$ from Hz to MHz ranges. The filter function formalism is central: coherence decay $\chi(\tau)$ relates to $S(\omega)$ via

$$\chi(\tau) = \int_0^\infty \frac{S(\omega)}{\pi\omega^2} F(\omega, \tau) d\omega$$

Fitting decay curves as a function of pulse separation yields the environmental spectrum across frequency bands (Liu et al., 27 Dec 2025).

• $T_1$ Relaxometry and Nanoscale EPR: Mapping $1/T_1$ as a function of bias field identifies proximate paramagnetic defects through resonance with target spin Larmor frequencies. This enables localized electron paramagnetic resonance (EPR) spectroscopy at nanoscale, providing the first room-temperature EPR fingerprints of charge defects in SiC (Liu et al., 27 Dec 2025).

The combination of these methodologies forms a full-spectrum toolkit for studying charge, spin, and phonon contributions to decoherence and device instability.

4. Ensemble Sensing, Device Architectures, and Integration

Scalable architectures exploit ensembles of spin centers and integrate photonic structures:

• Wafer-Scale Magnetometer Chips: Integration of V2 color centers into planar waveguides (e.g., 9 μm-thick epitaxial 4H-SiC on $n^{++}$ substrates, SiO$_2$ cladding) yields device architectures compatible with CMOS processes. Ensemble excitation and waveguiding enable sensor shot-noise-limited sensitivities $<300$ nT/Hz$^{1/2}$ (CW), or $\sim 10$ nT/Hz$^{1/2}$ (echo). High collection efficiency and uniform B$_1$ field profiles are achieved without complex microcavity patterning (Stuermer et al., 13 Jan 2026).
• Widefield Quantum SiC Microscopy (QSiCM): Camera-based platforms with spatial multiplexing enable per-pixel imaging ($\sim$30 μm resolution, 50 ms frames) of current-induced magnetic fields, with dual-frequency and MW-free readout (sensitivity $\sim$2 μT/Hz$^{1/2}$ per pixel). This approach is robust to strain, temperature drift, and scalable to wafer areas (Suhana et al., 18 Sep 2025).
• Hybrid Nanomagnonic-Photonic Systems: Devices combining shallow V2 centers with adjacent YIG nanostripes harness high magnetic field gradients for sub-nanometer slice addressing in biological and condensed matter targets, enabling OD-PELDOR spectroscopy and single external spin sensitivity (Tribollet, 2019, Tribollet, 2019).
• Fiber-Integrated and Nanocrystal Sensors: SiC nanocrystals (down to ~60 nm) with preserved spin and PL properties extend quantum sensing to fiber-integrated, minimally invasive, or deep-tissue bioimaging applications (Muzha et al., 2014, Quan et al., 2022).

5. Figures of Merit: Sensitivities, Coherence, and Operational Regimes

Key performance metrics in SiC-based quantum sensing are as follows:

Center/Device	T$_2$ (Echo)	Contrast ($C$)	Sensitivity (nT/Hz$^{1/2}$)	Notable Features
PL5 (Single, RT)	$\sim100-500\,\mu$s	$\sim0.5\%$	$<1$ (ensemble, lab)	Giant Stark $E$, robust to stress
V2 (Ensemble)	$2.8\,\mu$s	$0.6\%-1\%$	$\sim$10 (waveguide)	On-chip, scalable architecture
V2 (Single, cryo)	$>100\,\mu$s	$>10\%$ (ZPL)	$\sim 1.5$ (resonant)^*	Resonant, subensemble, low T
VSi (Single)	$100\,\mu$s	$1\%$	$40$ (Ramsey)	S=3/2, nT-level, telecom emission
QSiCM (Widefield)	$-$	$-$	$2\,\mu$T (per pixel)	Spatial multiplexing, MW-free option

^*Numbers denote best shot-noise-limited sensitivity; actual device-limited values may be higher depending on collection efficiency and contrast.

Coherence times (T$_2$) are maximized by isotopic purification and dynamical decoupling (e.g., CPMG, XY8). Self-protection against decoherence, such as in PL5 centers with finite transverse splitting $E_x$, stabilizes T$_2^*$ across wide temperature ranges (Zhou et al., 2017).

6. Applications and Technological Implications

SiC-based quantum sensors have demonstrated and projected applicability in multiple domains:

• Wafer-Scale Quality Assurance and Metrology: Nanoscale noise maps of commercial wafers enable process control and feedback for quantum and power device production (Liu et al., 27 Dec 2025).
• Nanoscale Charge and Spin Environment Characterization: Direct observation and localization of single electron trapping/detrapping events, mapping of broadband environmental noise, and in-situ EPR spectroscopy of paramagnetic defects are now achievable (Liu et al., 27 Dec 2025).
• Biological Sensing and Bioimaging: NIR emission and room-temperature operation in nanocrystals support deep-tissue, fiber-based applications, with intrinsic biocompatibility and potential for hybrid sensors (Muzha et al., 2014).
• Structural Biology: Sub-nanometer dipolar distance resolution for labeled proteins and biomolecules using hybrid nanomagnonic probes (Tribollet, 2019).
• Noninvasive Current and Field Imaging: Widefield QSiCM and scalable chip platforms permit label-free, real-time imaging of currents and fields in electronics, power devices, and potentially live systems (Suhana et al., 18 Sep 2025, Stuermer et al., 13 Jan 2026).

7. Material Engineering, Device Optimization, and Future Prospects

Material and device engineering strategies are central to further sensitivity and scalability:

• Substrate and Defect Selection: High-purity semi-insulating (HPSI) 4H-SiC substrates enable uniform, high-yield PL5 ensemble formation, while defect engineering (electron vs. proton irradiation, annealing) allows control over density, depth, and coherence properties (Li et al., 28 Mar 2025, Stuermer et al., 13 Jan 2026).
• Stress and Strain Management: Quantum coherence of PL5 is shown to be robust under in-plane compressive stress to at least 400 MPa, and no correlation with strain broadening or decoherence is observed to 1200°C (Li et al., 28 Mar 2025).
• Photonic Enhancement: Integration of nanopillars, waveguides, and fiber-coupled or monolithic photonic elements maximizes PL collection efficiency; planar waveguide platforms address $10^5$ more centers for two-to-three orders of magnitude sensitivity improvement over confocal architectures (Stuermer et al., 13 Jan 2026, Muzha et al., 2014).
• Alloying and Isotope Purification: 28Si12C epitaxy reduces spin-bath noise, increases $T_2$, and permits $<$nT/Hz$^{1/2}$ sensitivities in ensembles; further enhancement is anticipated with light trapping and optimized wafer orientation (Suhana et al., 18 Sep 2025).
• Hybrid Approaches: Embedding V2 centers near YIG nanomagnonic stripes creates strong field gradients for single-spin-resolution EPR and structural biology applications; photonic–magnonic hybrids further exploit the flexibility of the SiC platform (Tribollet, 2019).

Enhanced control over charge states, resonant optical protocols at low temperature, and the deployment of multi-modal sensing sequences (ODMR, relaxometry, RTN tracking) mark the next development phase of SiC-quantum sensing technologies for both fundamental and applied settings.

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References: (Liu et al., 27 Dec 2025, Muzha et al., 2014, Tahara et al., 2024, Tribollet, 2019, Bulancea-Lindvall et al., 2022, Suhana et al., 18 Sep 2025, Stuermer et al., 13 Jan 2026, Tribollet, 2019, Singh et al., 2022, Abraham et al., 2020, Quan et al., 2022, Tathfif et al., 1 Dec 2025, Li et al., 28 Mar 2025, Mu et al., 2020, Kraus et al., 2014, Zhou et al., 2017, Soykal et al., 2016)