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arXiv:2507.18175 · Journal of Combinatorial Theory Series A

Optimal quantum (r,δ)-locally repairable codes via classical ones

Kun Zhou, Meng Cao

Published Apr 23, 2026• 3 citations
arXivHTMLPDF
DOI
10.1016/j.jcta.2026.106212

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Matrix-product (MP) codes provide an efficient approach for constructing long classical codes by combining a defining matrix with several shorter constituent codes. Employing non-singular by columns (NSC) quasi-unitary matrices as the defining matrices of MP codes enables the construction of various types of quantum codes. The existence of infinite families ofN×NNSC quasi-unitary matrices over Fq2forN = qorq+2 ≤ N ≤q2, whereq≠ 2 is a prime power, was posed as an open problem in the literature and remains largely unresolved. In this paper, we introduce a novel method for constructing NSC quasi-unitary matrices based on a generalized orthogonality relation for cyclic groups. We prove that (2m+ 1) × (2m+ 1) NSC quasi-unitary matrices always exist over Fq2whenever 2m| (q2–1). This result establishes, for the first time, the existence of six new infinite families of NSC quasi-unitary matrices, providing solutions to the aforementioned open problem. The number of such matrices within our framework is also determined. As a key application, we leverage NSC quasi-unitary matrices to construct optimal pure quantum (r; δ)-locally repairable codes (LRCs). We propose an effective method for constructing optimal pure quantum (r; δ)- LRCs from MP codes whose defining matrices are NSC quasiunitary matrices. Based on this method, we explicitly construct two new infinite families of optimal pure quantum (r; δ)-LRCs with flexible parameters.
For a general entanglement-assisted or unassisted quantum error-correcting code, a set of erasures, and an associated repair group, we propose a linear algebraic procedure to compute a reduced set of observables and a reduced repair group of codeword qudits for correcting the given erasures. The procedure has cubic complexity in the repair group size and the computed set of observables has the smallest possible size for correcting the given erasures. We specialize the general procedure to quantum codes constructed from Euclidean and Hermitian orthogonality, and provide closed-form upper bounds on the size of reduced repair groups for those special cases. Based on these closed-form bounds, we propose quantum counterparts of the information locality of classical local recovery.
This PhD thesis addresses two current problems belonging to the fields of classical and quantum information theory. The first is the repair problem in distributed and cloud storage systems in the setting where multiple nodes may fail simultaneously. These codes are called (r,\delta)-locally recoverable codes. To handle it, we consider monomial-Cartesian codes, resulting in new (r,\delta)-locally recoverable codes. The other problem is the construction of good quantum error-correcting codes. Those we provide are quantum stabilizer codes derived from two families of classical codes: generalized (or twisted) monomial-Cartesian codes and evaluation codes at the roots of trace-depending polynomials. Both quantum code constructions have excellent parameters.