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New Entanglement-Assisted Codes and Mathematical Structures in Quantum Error Correction

Serge Adonsou

Published Sep 1, 2026• 0 citations
OpenAlex

Abstract

Quantum information processing promises exponential advantages for certain computational and communication tasks, but practical quantum devices are inherently vulnerable to decoherence and operational imperfections. This thesis develops new algebraic and analytical tools for quantum error correction (QEC) aimed at unifying entanglement-assisted coding theory with operator-algebra frameworks, while also providing mathematically rigorous insights for continuous-variable photonic implementations. First, we introduce the framework of entanglement-assisted operator algebra quantum error correction (EA-OAQEC), extending entanglement-assisted QEC in an operator-algebra context. Built on a stabilizer-based formalism, EA-OAQEC unifies and generalizes subspace, subsystem, and hybrid classical-quantum entanglement-assisted codes. We establish a master error-correction theorem, define a generalized distance notion, and develop constructive techniques including gauge fixing, clean-qubit transformations, and entanglement-assisted gauge-fixing procedures. Second, we study general logical operators: unitaries that preserve a stabilizer codespace beyond the traditional Pauli normalizer. We derive explicit structure theorems for the centralizer and normalizer in the full unitary setting and show how normalizer transformations can be parameterized via classical bit matrix multiply complement (BMMC) permutations. Finally, motivated by photonic quantum computing, we analyze finite-rank compressions of the continuous position and momentum operators relevant to Gottesman-Kitaev-Preskill (GKP) codes. We prove that the spectra of these compressions are governed by the roots of classical Hermite polynomials and connect the compressed operators to physically realizable approximations of displacement operations and finite-energy GKP states.

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Quantum information processing promises exponential advantages for certain computational and communication tasks, but practical quantum devices are inherently vulnerable to decoherence and operational imperfections. This thesis develops new algebraic and analytical tools for quantum error correction (QEC) aimed at unifying entanglement-assisted coding theory with operator-algebra frameworks, while also providing mathematically rigorous insights for continuous-variable photonic implementations. First, we introduce the framework of entanglement-assisted operator algebra quantum error correction (EA-OAQEC), extending entanglement-assisted QEC in an operator-algebra context. Built on a stabilizer-based formalism, EA-OAQEC unifies and generalizes subspace, subsystem, and hybrid classical-quantum entanglement-assisted codes. We establish a master error-correction theorem, define a generalized distance notion, and develop constructive techniques including gauge fixing, clean-qubit transformations, and entanglement-assisted gauge-fixing procedures. Second, we study general logical operators: unitaries that preserve a stabilizer codespace beyond the traditional Pauli normalizer. We derive explicit structure theorems for the centralizer and normalizer in the full unitary setting and show how normalizer transformations can be parameterized via classical bit matrix multiply complement (BMMC) permutations. Finally, motivated by photonic quantum computing, we analyze finite-rank compressions of the continuous position and momentum operators relevant to Gottesman-Kitaev-Preskill (GKP) codes. We prove that the spectra of these compressions are governed by the roots of classical Hermite polynomials and connect the compressed operators to physically realizable approximations of displacement operations and finite-energy GKP states.
We introduce a framework for entanglement-assisted quantum error correcting codes that unifies the three original frameworks for such codes called EAQEC, EAOQEC, and EACQ under a single umbrella. The unification is arrived at by viewing entanglement-assisted codes from the operator algebra quantum error correction perspective, and it is built upon a recently established extension of the stabilizer formalism to that setting. We denote the framework by EAOAQEC, and we prove a general error correction theorem for such codes, derived from the algebraic perspective, that generalizes each of the earlier results. This leads us to a natural notion of distance for such codes, and we derive a number of distance results for subclasses of the codes. We show how EACQ codes form a proper subclass of the entanglement-assisted subspace codes defined by EAOAQEC. We identify and construct new classes of entanglement-assisted subsystem codes and entanglement-assisted hybrid classical-quantum codes that are found outside of the earlier approaches.
Entanglement-assisted (EA) stabilizer codes enhance the rate of error correction in relation to codes with no pre-shared entanglement. Meanwhile, bosonic error-correcting codes, such as the Gottesman-Kitaev-Preskill (GKP) code, can be concatenated with qubit stabilizer codes to significantly reduce the logical failure probability of those stabilizer codes. First, we combine the above two concepts to propose an EA version of the qubit-into-oscillators concatenated code that chains an EA-stabilizer (outer) code with a GKP (inner) code. As an example we present a three-qubit EA-repetition concatenated with a GKP code. Second, we propose an EA version of the non-Gaussian oscillator-into-oscillators concatenated code that chains a GKP (outer) code with an EA-stabilizer (inner) code. As an example we present a GKP code concatenated with a three-qubit EA repetition code that uses two maximally entangled modes (emodes) and suppresses the variances of both position and momentum quadrature errors of a data mode. Furthermore, we generalize the latter example to a family of GKP code concatenated with a nnn-qubit EA repetition code that uses n−1{n-1}n−1 emodes and suppresses the variances of both position and momentum quadrature errors of a data mode by a factor 1/n{1/n}1/n.
We introduce a stabilizer formalism for the general quantum error correction framework called operator algebra quantum error correction (OAQEC), which generalizes Gottesman's formulation for traditional quantum error correcting codes (QEC) and Poulin's for operator quantum error correction and subsystem codes (OQEC). The construction generates hybrid classical-quantum stabilizer codes and we formulate a theorem that fully characterizes the Pauli errors that are correctable for a given code, generalizing the fundamental theorems for the QEC and OQEC stabilizer formalisms. We discover hybrid versions of the Bacon-Shor subsystem codes motivated by the formalism, and we apply the theorem to derive a result that gives the distance of such codes. We show how some recent hybrid subspace code constructions are captured by the formalism, and we also indicate how it extends to qudits.
This thesis investigates the algebraic structure, construction, encoding, and decoding of quasi-cyclic (QC) and quasi-twisted (QT) codes and their applications to quantum error correction. For selected repeated-root and simple-root QC codes, generator-matrix-based construction methods are developed using the Generalized Discrete Fourier Transform (GDFT) and Discrete Fourier Transform (DFT), respectively. These methods enable efficient encoding by matrix-vector multiplication and provide computational advantages over codeword-based constructions. Spectral decoding procedures are also studied, including a GDFT-based folding framework that relates decoding of repeated-root QC codes to that of associated simple-root codes. Furthermore, a correspondence between certain repeated-root QC codes over finite fields and simple-root QT codes over finite chain rings is established. Building on these classical structures, one-generator QT codes of index 3 are investigated for quantum-code construction. Their Hermitian duals are characterized, and sufficient conditions for Hermitian self-orthogonality are derived, yielding stabilizer quantum error-correcting codes with good and, in several cases, optimal parameters. Structured syndrome-based decoding is developed by relating stabilizer measurements to classical decoding of the underlying QT codes. An extension technique preserving Hermitian self-orthogonality is introduced, producing additional stabilizer codes and corresponding decoding procedures. Finally, entanglement-assisted quantum error-correcting codes are constructed from 1-generator QT codes through Hermitian rank conditions, yielding maximal-entanglement codes with competitive parameters. Overall, the thesis establishes QC and QT codes as a unified algebraic framework for efficient classical coding, stabilizer quantum error correction, and entanglement-assisted quantum coding.
Clifford codes are a natural generalization of quantum stabilizer codes based primarily on representation theory. This class of codes has previously been extended to the setting of quantum subsystem codes. We formulate a two-fold generalization of Clifford codes, for both the hybrid classical and quantum information and projective representation theory settings. This leads to new classes of hybrid subspace and subsystem Clifford codes. We extend the fundamental representation theoretic quantum error correction theorem to include these codes, based on the operator algebra quantum error correction framework. We also discuss several examples throughout the presentation, of both stabilizer and non-stabilizer type.
Quantum error correction is an essential ingredient in the development of quantum technologies. Its subject is to investigate ways to embed quantum Hilbert spaces into a physical system such that this subspace is robust against small imperfections in the physical systems. This task is exceedingly complex: for one, this is due to the vast diversity of possible physical systems with different structure to use. For another, every physical setting also comes with its own imperfections that need to be protected against. Bred by the complexity of a technological ambition, research on quantum error correction has developed into a large field of research that ranges from engineering of small systems with a single photon to the creation of macroscopic topological phases of matter and models of complex emergent physics. A quintessential tool in quantum error correction is the stabilizer formalism, which tames quantum systems by enforcing symmetries. A Gottesman-Kitaev-Preskill (GKP) code is a stabilizer code that creates a logical subspace within an infinite dimensional Hilbert space by endowing it with translational symmetries. While in practice the infinitude of the Hilbert space, as well as the infinitude of the translational symmetry group are considered as obstacles for implementation, in theory these are precisely the features that make the theory of GKP codes particularly rich, well behaved and well-connected to fascinating topics in mathematics. The purpose of this thesis is to explore these connections: to understand the coding theoretic and practical properties of GKP codes, utilizing its rich mathematical foundation, and to provide a foundation for future research. Along this journey we discover -- through the looking glass of GKP codes -- how quantum error correction fits into a fabulous mathematical world and formulate a series of dreams about possible directions of research.