Ramsey Interferometry Quantifies Spectator-Crosstalk in Silicon Carbide S=3/2 Qudits

Why It Matters

Spectator‑crosstalk limits gate fidelity in multilevel quantum processors, so its precise quantification is essential for scalable silicon‑carbide quantum hardware.

Key Takeaways

• Broadband Ramsey maps spectator crosstalk in SiC qudits.
• Six-branch structure matches analytic predictions without frequency fitting.
• Off‑resonant pulses cause coherent leakage between spin sublevels.
• Framework enables pulse calibration and error‑corrected qudit control.

Pulse Analysis

Silicon‑vacancy centres in 4H‑SiC host a spin‑3/2 ground state that naturally forms a four‑level qudit, offering higher information density than conventional two‑level qubits. Their compatibility with wafer‑scale fabrication, long coherence times, and integrated photonics makes them attractive candidates for quantum networks and repeaters. However, the dense manifold of transitions also introduces unwanted couplings, a challenge that has hindered reliable gate operations and error‑correction schemes in solid‑state platforms.

Broadband Ramsey interferometry provides a sensitive probe of phase evolution across multiple transitions, allowing researchers to resolve the subtle spectator‑crosstalk that arises when short, broadband microwave pulses unintentionally drive off‑resonant level pairs. By assigning compact amplitudes to each spectral line and validating the resulting six‑branch detuning map against both analytic models and time‑domain simulations, the study demonstrates unprecedented agreement without any post‑hoc frequency fitting. This level of precision enables in‑situ pulse calibration, reducing coherent leakage and improving the fidelity of quantum‑gate implementations.

The ability to both suppress and harness spectator transitions opens new pathways for hardware‑efficient quantum error correction and multi‑parameter sensing. Accurate characterisation of multilevel dynamics will accelerate the integration of SiC qudits into larger quantum processors, where reduced circuit depth and richer logical encodings are critical. Future work will likely explore pulse‑shaping strategies to tailor crosstalk, assess its impact on dynamical decoupling, and extend the methodology to other colour‑centre platforms, cementing silicon carbide’s role in the next generation of scalable quantum technologies.