Embedding Stabilizer Codes and Leakage Correction in Multilevel Quantum Systems

Leakage beyond the computational subspace is a major source of error in multilevel quantum hardware. We show that any $[[n,k,d]]$ stabilizer code can be embedded isometrically into a single $D$-dimensional system while preserving its complete error-correcting structure. We further derive a necessary and sufficient condition for exact leakage correction, proving that leakage is correctable precisely when it does not distinguish between logical states. These results establish a unified framework for quantum error correction in multilevel quantum systems.