Silicon carbide wafer+Spectator-transition crosstalk in a spin-3/2 silicon-vacancy qudit in silicon carbide revealed by broadband Ramsey interferometry

This article discusses the use of broadband Ramsey interferometry to analyze spectator-transition crosstalk in a spin-3/2 silicon-vacancy qudit in silicon carbide (4H-SiC). The study highlights how off-resonant microwave pulses can unintentionally excite non-addressed transitions in the qudit, leading to crosstalk between different sublevels.

Key findings of the study include:

1. Experimental Setup: The research uses a broadband Ramsey sequence to measure the response of the silicon-vacancy qudit, revealing multiple spectral lines in the Fourier spectra that are attributed to spectator transitions. The observed crosstalk arises from coherent leakage caused by the excitation of non-targeted level pairs.

2. Multilevel Dynamics: The spin-3/2 ground state of the silicon vacancy in 4H-SiC allows for a natural qudit structure, which can encode more information per physical carrier compared to a standard qubit. However, the close spacing of transitions in the qudit makes it susceptible to off-resonant driving and resulting crosstalk.

3. Simulation and Experimental Agreement: Numerical simulations based on the rotating-frame Hamiltonian are used to predict the spectral branches observed in the Ramsey spectra. These predictions align with the experimental data, showing six distinct frequency components corresponding to different pairwise coherences within the qudit manifold.

4. Spectator Transitions and Crosstalk: The article introduces the concept of spectator transitions—off-resonant pairs that acquire coherence during the Ramsey sequence. These transitions contribute additional spectral features in the observed data. The authors also suggest methods for controlling or exploiting these transitions, depending on the application.

5. Applications and Future Work: The findings provide insights into improving multilevel quantum control, specifically in the context of silicon-vacancy qudits. The study also paves the way for better understanding and exploiting multilevel qudits in quantum computing and sensing applications, and proposes further exploration of pulse parameter regimes to suppress or utilize crosstalk effectively.

In conclusion, the research offers a framework for understanding the multilevel dynamics of silicon-vacancy qudits, quantifying crosstalk, and proposing ways to mitigate it for more accurate quantum state estimation and control.