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

TL;DR

This paper investigates spectator-transition crosstalk in a spin-3/2 silicon vacancy qudit in silicon carbide using broadband Ramsey interferometry, providing a detailed framework for understanding and controlling multilevel quantum systems.

Contribution

It introduces a spectrator-aware analytical and numerical framework for quantifying and managing crosstalk in multilevel qudits, enhancing control strategies in quantum technologies.

Findings

Spectator crosstalk manifests as multiple lines in Ramsey spectra.

Analytic mapping predicts a six-branch structure of energy differences.

Numerical simulations match experimental spectral features.

Abstract

Color center spins in 4H-SiC offer a rare combination of wafer-scale materials maturity with long spin coherence and chip-level photonics, making them promising building blocks for scalable quantum technologies. In particular, the silicon vacancy hosts an S=3/2 ground state, a native qudit that enables compact encodings and subspace-selective control, but also introduces spectator transitions: short, detuned pulses can coherently drive non-addressed level pairs and create crosstalk. Here we use broadband Ramsey interferometry to reveal and quantify such spectator-transition crosstalk. Experimentally, the Ramsey Fourier spectra display multiple lines beyond the addressed single-quantum transition. Analytically, we map each line to a pairwise energy difference between qudit levels of the rotating-frame Hamiltonian and assign its weight via compact amplitudes set by the prepared state and the microwave pulse parameters, predicting a deterministic six-branch structure. Numerical time-domain propagation with the experimental sampling reproduces the detuning map, and the measured peak positions coincide with the analytic branch lines without frequency fitting. Together these results provide a practical, spectator-aware framework for multilevel control in the silicon vacancy qudit. The approach offers clear guidance to suppress crosstalk or, conversely, to exploit spectator lines, for example as additional constraints for in situ pulse calibration and for phase-sensitive quantum state and process estimation.