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Wielding the ZX-calculus, Flexsymmetry, Mixed States, and Scalable Notations

Titouan Carette

Published Nov 23, 2021• 0 citations
OpenAlex

Abstract

This thesis is about the application of graphical languages to quantum computing. By graphical language, we mean the use of diagrams, similar to circuits, representing the evolution of quantum systems. The thesis introduces those languages in the formalism of category theory and focuses mainly on one language: the ZX-calculus, and its close relatives, the ZW-calculus and ZH-calculus. The notion of flexsymmetry is introduced, describing diagrams whose inputs and outputs are all interchangeable. This notion is used to classify all languages similar to the ZX-calculus. It is shown that the only admissible languages are the ZX-calculus, the ZH-calculus, and the ZW-calculus. Then is tackled the question of extending those languages to mixed-state quantum mechanics. A general categorical construction is proposed and is applied to provide extensions of the different languages. Finally, the thesis introduces notations allowing to handle in a compact way quantum algorithms relying on arbitrary large diagrams. To challenge their efficiency, those notations are used to show the correction of various quantum algorithms.

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We introduce the Scalable ZX-calculus (SZX-calculus for short), a formal and compact graphical language for the design and verification of quantum computations. The SZX-calculus is an extension of the ZX-calculus, a powerful framework that captures graphically the fundamental properties of quantum mechanics through its complete set of rewrite rules. The ZX-calculus is, however, a low level language, with each wire representing a single qubit. This limits its ability to handle large and elaborate quantum evolutions. We extend the ZX-calculus to registers of qubits and allow compact representation of sub-diagrams via binary matrices. We show soundness and completeness of the SZX-calculus and provide two examples of applications, for graph states and error correcting codes.

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The ZX-calculus was introduced as a graphical language able to represent specific quantum primitives in an intuitive way. The recent completeness results have shown the theoretical possibility of a purely graphical description of quantum processes. However, in practice, such approaches are limited by the intrinsic low level nature of ZX calculus. The scalable notations have been proposed as an attempt to recover an higher level point of view while maintaining the topological rewriting rules of a graphical language. We demonstrate that the scalable ZX-calculus provides a formal, intuitive, and compact framework to describe and prove quantum algorithms. As a proof of concept, we consider the standard oracle-based quantum algorithms: Deutsch-Jozsa, Bernstein-Vazirani, Simon, and Grover algorithms, and we show they can be described and proved graphically.

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Completeness of Graphical Languages for Mixed State Quantum Mechanics

Titouan Carette, Emmanuel Jeandel, Simon Perdrix +1 more

There exist several graphical languages for quantum information processing, like quantum circuits, ZX-calculus, ZW-calculus, and so on. Each of these languages forms a †-symmetric monoidal category (†-SMC) and comes with an interpretation functor to the †-SMC of finite-dimensional Hilbert spaces. In recent years, one of the main achievements of the categorical approach to quantum mechanics has been to provide several equational theories for most of these graphical languages, making them complete for various fragments of pure quantum mechanics. We address the question of how to extend these languages beyond pure quantum mechanics to reason about mixed states and general quantum operations, i.e., completely positive maps. Intuitively, such an extension relies on the axiomatisation of a discard map that allows one to get rid of a quantum system, an operation that is not allowed in pure quantum mechanics. We introduce a new construction, the discard construction , which transforms any †-symmetric monoidal category into a symmetric monoidal category equipped with a discard map. Roughly speaking this construction consists in making any isometry causal. Using this construction, we provide an extension for several graphical languages that we prove to be complete for general quantum operations. However, this construction fails for some fringe cases like Clifford+T quantum mechanics, as the category does not have enough isometries.

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Wielding the ZX-calculus : Flexsymmetry, Mixed States and Scalable Notations

Titouan Carette

Manier le ZX-calcul : flexsymétrie, systèmes ouverts et limandes Cette thèse concerne l'application de langages graphiques à l'informatique quantique. Par langages graphiques on entends l'usage de diagrammes, très similaire au circuits, représentant des évolutions de systèmes quantique. La thèse introduit ces langages dans le formalisme de la théorie des catégories et s’intéresse en particulier a un langage : le ZX-calcul, ainsi qu'a ses proche parent le ZW-calcul et le ZH-calcul. La notion de flexsymmetrie est introduite, décrivant des diagrammes dont les entrés et sorties sont toutes interchangeables entre elles. La notion et ensuite utilisée pour classifier tout les langage similaire au ZX-calcul. Il est montré que les seuls langages admissibles sont le ZX-calcul, le ZW-calcul et le ZH-calcul. Ensuite est abordée la question de l'extension de ces langages au cas de systèmes mixtes classique-quantique. Une construction catégorique générale est proposée et est utilisée pour étendre les différent langages. Enfin la thèse introduit des notations permettant de représenter de manière compact des algorithmes quantiques mettant en jeux des diagrammes arbitrairement grand. Afin d'en éprouver l'efficacité, ces notations sont utilisé pour montrer graphiquement la correction de différents algorithmes quantiques.

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An Algebraic Axiomatisation of ZX-calculus

Quanlong Wang

ZX-calculus is a graphical language for quantum computing which is complete in the sense that calculation in matrices can be done in a purely diagrammatic way. However, all previous universally complete axiomatisations of ZX-calculus have included at least one rule involving trigonometric functions such as sin and cos which makes it difficult for application purpose. In this paper we give an algebraic complete axiomatisation of ZX-calculus instead such that there are only ring operations involved for phases. With this algebraic axiomatisation of ZX-calculus, we are able to establish for the first time a simple translation of diagrams from another graphical language called ZH-calculus and to derive all the ZX-translated rules of ZH-calculus. As a consequence, we have a great benefit that all techniques obtained in ZH-calculus can be transplanted to ZX-calculus, which can't be obtained by just using the completeness of ZX-calculus.

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A Recipe for Quantum Graphical Languages

Titouan Carette, Emmanuel Jeandel

Different graphical calculi have been proposed to represent quantum computation. First the ZX-calculus [Coecke and Duncan, 2011], followed by the ZW-calculus [Hadzihasanovic, 2015] and then the ZH-calculus [Backens and Kissinger, 2018]. We can wonder if new ZX-like calculi will continue to be proposed forever. This article answers negatively. All those language share a common core structure we call Z^*-algebras. We classify Z^*-algebras up to isomorphism in two dimensional Hilbert spaces and show that they are all variations of the aforementioned calculi. We do the same for linear relations and show that the calculus of [Bonchi et al., 2017] is essentially the unique one.

arXiv:2008.04193•Leibniz international proceedings in informatics•Jan 1, 2020•7 citations
This thesis is about the application of graphical languages to quantum computing. By graphical language, we mean the use of diagrams, similar to circuits, representing the evolution of quantum systems. The thesis introduces those languages in the formalism of category theory and focuses mainly on one language: the ZX-calculus, and its close relatives, the ZW-calculus and ZH-calculus. The notion of flexsymmetry is introduced, describing diagrams whose inputs and outputs are all interchangeable. This notion is used to classify all languages similar to the ZX-calculus. It is shown that the only admissible languages are the ZX-calculus, the ZH-calculus, and the ZW-calculus. Then is tackled the question of extending those languages to mixed-state quantum mechanics. A general categorical construction is proposed and is applied to provide extensions of the different languages. Finally, the thesis introduces notations allowing to handle in a compact way quantum algorithms relying on arbitrary large diagrams. To challenge their efficiency, those notations are used to show the correction of various quantum algorithms.
We introduce the Scalable ZX-calculus (SZX-calculus for short), a formal and compact graphical language for the design and verification of quantum computations. The SZX-calculus is an extension of the ZX-calculus, a powerful framework that captures graphically the fundamental properties of quantum mechanics through its complete set of rewrite rules. The ZX-calculus is, however, a low level language, with each wire representing a single qubit. This limits its ability to handle large and elaborate quantum evolutions. We extend the ZX-calculus to registers of qubits and allow compact representation of sub-diagrams via binary matrices. We show soundness and completeness of the SZX-calculus and provide two examples of applications, for graph states and error correcting codes.
The ZX-calculus was introduced as a graphical language able to represent specific quantum primitives in an intuitive way. The recent completeness results have shown the theoretical possibility of a purely graphical description of quantum processes. However, in practice, such approaches are limited by the intrinsic low level nature of ZX calculus. The scalable notations have been proposed as an attempt to recover an higher level point of view while maintaining the topological rewriting rules of a graphical language. We demonstrate that the scalable ZX-calculus provides a formal, intuitive, and compact framework to describe and prove quantum algorithms. As a proof of concept, we consider the standard oracle-based quantum algorithms: Deutsch-Jozsa, Bernstein-Vazirani, Simon, and Grover algorithms, and we show they can be described and proved graphically.
There exist several graphical languages for quantum information processing, like quantum circuits, ZX-calculus, ZW-calculus, and so on. Each of these languages forms a †-symmetric monoidal category (†-SMC) and comes with an interpretation functor to the †-SMC of finite-dimensional Hilbert spaces. In recent years, one of the main achievements of the categorical approach to quantum mechanics has been to provide several equational theories for most of these graphical languages, making them complete for various fragments of pure quantum mechanics. We address the question of how to extend these languages beyond pure quantum mechanics to reason about mixed states and general quantum operations, i.e., completely positive maps. Intuitively, such an extension relies on the axiomatisation of a discard map that allows one to get rid of a quantum system, an operation that is not allowed in pure quantum mechanics. We introduce a new construction, the discard construction , which transforms any †-symmetric monoidal category into a symmetric monoidal category equipped with a discard map. Roughly speaking this construction consists in making any isometry causal. Using this construction, we provide an extension for several graphical languages that we prove to be complete for general quantum operations. However, this construction fails for some fringe cases like Clifford+T quantum mechanics, as the category does not have enough isometries.
Manier le ZX-calcul : flexsymétrie, systèmes ouverts et limandes Cette thèse concerne l'application de langages graphiques à l'informatique quantique. Par langages graphiques on entends l'usage de diagrammes, très similaire au circuits, représentant des évolutions de systèmes quantique. La thèse introduit ces langages dans le formalisme de la théorie des catégories et s’intéresse en particulier a un langage : le ZX-calcul, ainsi qu'a ses proche parent le ZW-calcul et le ZH-calcul. La notion de flexsymmetrie est introduite, décrivant des diagrammes dont les entrés et sorties sont toutes interchangeables entre elles. La notion et ensuite utilisée pour classifier tout les langage similaire au ZX-calcul. Il est montré que les seuls langages admissibles sont le ZX-calcul, le ZW-calcul et le ZH-calcul. Ensuite est abordée la question de l'extension de ces langages au cas de systèmes mixtes classique-quantique. Une construction catégorique générale est proposée et est utilisée pour étendre les différent langages. Enfin la thèse introduit des notations permettant de représenter de manière compact des algorithmes quantiques mettant en jeux des diagrammes arbitrairement grand. Afin d'en éprouver l'efficacité, ces notations sont utilisé pour montrer graphiquement la correction de différents algorithmes quantiques.
ZX-calculus is a graphical language for quantum computing which is complete in the sense that calculation in matrices can be done in a purely diagrammatic way. However, all previous universally complete axiomatisations of ZX-calculus have included at least one rule involving trigonometric functions such as sin and cos which makes it difficult for application purpose. In this paper we give an algebraic complete axiomatisation of ZX-calculus instead such that there are only ring operations involved for phases. With this algebraic axiomatisation of ZX-calculus, we are able to establish for the first time a simple translation of diagrams from another graphical language called ZH-calculus and to derive all the ZX-translated rules of ZH-calculus. As a consequence, we have a great benefit that all techniques obtained in ZH-calculus can be transplanted to ZX-calculus, which can't be obtained by just using the completeness of ZX-calculus.
Different graphical calculi have been proposed to represent quantum computation. First the ZX-calculus [Coecke and Duncan, 2011], followed by the ZW-calculus [Hadzihasanovic, 2015] and then the ZH-calculus [Backens and Kissinger, 2018]. We can wonder if new ZX-like calculi will continue to be proposed forever. This article answers negatively. All those language share a common core structure we call Z^*-algebras. We classify Z^*-algebras up to isomorphism in two dimensional Hilbert spaces and show that they are all variations of the aforementioned calculi. We do the same for linear relations and show that the calculus of [Bonchi et al., 2017] is essentially the unique one.