This paper surveys joint work with Samson Abramsky. I will somewhat informally discuss the main results of a series of papers in a pedestrian not too technical way. These include: . 'The logic of entanglement', that is, the identification and abstract axiomatization of the 'quantum information-flow' which enables protocols such as quantum teleportation. To this means we define strongly compact closed categories which abstractly capture the behavioral properties of quantum entanglement. . 'Postulates for an abstract quantum formalism' in which classical information-flow (e.g. token exchange) is part of the formalism. As an example, we provide a purely formal description of quantum teleportation and prove correctness in abstract generality. In this formalism types reflect kinds contra the essentially typeless von Neumann formalism. Hence even concretely this formalism manifestly improves on the usual one. .'Towards a high-level approach to quantum informatics'. Indeed the above discussed work can be conceived as aiming to solve: ???/von Neumann quantum formalism ≈ high-level language/low-level language
This paper surveys joint work with Samson Abramsky. I will somewhat informally discuss the main results of a series of papers in a pedestrian not too technical way. These include: . 'The logic of entanglement', that is, the identification and abstract axiomatization of the 'quantum information-flow' which enables protocols such as quantum teleportation. To this means we define strongly compact closed categories which abstractly capture the behavioral properties of quantum entanglement. . 'Postulates for an abstract quantum formalism' in which classical information-flow (e.g. token exchange) is part of the formalism. As an example, we provide a purely formal description of quantum teleportation and prove correctness in abstract generality. In this formalism types reflect kinds contra the essentially typeless von Neumann formalism. Hence even concretely this formalism manifestly improves on the usual one. .'Towards a high-level approach to quantum informatics'. Indeed the above discussed work can be conceived as aiming to solve: ???/von Neumann quantum formalism ≈ high-level language/low-level language
Quantum information and computation is concerned with the use of quantum-mechanical systems to carry out computational and information-processing tasks (Nielsen and Chunag, 2000). In the few short years that this approach has been studied, a number of remarkable concepts and results have emerged, most notably:a couple of spectacular algorithms and a number of information protocols, exemplified by quantum teleportation, which exploit quantum entanglement in an essential fashion. The current tools available for developing quantum algorithms and protocols are deficient on two main levels: firstly, they are too low-level and at a more fundamental level, the standard mathematical framework for quantum mechanics (which is essentially due to von Neumann (1932)) is actually insufficiency comprehensive for informatic purposes. In joint work with Bob Coecke, we have recently made some striking progress in addressing both these points. They have recast the von Neumann formalism at a more abstract and conceptual level, using category theory.
We study quantum information and computation from a novel point of view. Our approach is based on recasting the standard axiomatic presentation of quantum mechanics, due to von Neumann, at a more abstract level, of compact closed categories with biproducts. We show how the essential structures found in key quantum information protocols such as teleportation, logic-gate teleportation, and entanglement-swapping can be captured at this abstract level. Moreover, from the combination of the --apparently purely qualitative-- structures of compact closure and biproducts there emerge `scalars` and a `Born rule'. This abstract and structural point of view opens up new possibilities for describing and reasoning about quantum systems. It also shows the degrees of axiomatic freedom: we can show what requirements are placed on the (semi)ring of scalars C(I,I), where C is the category and I is the tensor unit, in order to perform various protocols such as teleportation. Our formalism captures both the information-flow aspect of the protocols (see quant-ph/0402014), and the branching due to quantum indeterminism. This contrasts with the standard accounts, in which the classical information flows are `outside' the usual quantum-mechanical formalism.
Quantum information and computation is concerned with the use of quantum-mechanical systems to carry out computational and information-processing tasks (Nielsen and Chunag, 2000). In the few short years that this approach has been studied, a number of remarkable concepts and results have emerged, most notably:a couple of spectacular algorithms and a number of information protocols, exemplified by quantum teleportation, which exploit quantum entanglement in an essential fashion. The current tools available for developing quantum algorithms and protocols are deficient on two main levels: firstly, they are too low-level and at a more fundamental level, the standard mathematical framework for quantum mechanics (which is essentially due to von Neumann (1932)) is actually insufficiency comprehensive for informatic purposes. In joint work with Bob Coecke, we have recently made some striking progress in addressing both these points. They have recast the von Neumann formalism at a more abstract and conceptual level, using category theory.
These lecture notes survey some joint work with Samson Abramsky as it was presented by me at several conferences in the summer of 2005. It concerns `doing quantum mechanics using only pictures of lines, squares, triangles and diamonds'. This picture calculus can be seen as a very substantial extension of Dirac's notation, and has a purely algebraic counterpart in terms of so-called Strongly Compact Closed Categories (introduced by Abramsky and I in quant-ph/0402130 and [4]) which subsumes my Logic of Entanglement quant-ph/0402014. For a survey on the `what', the `why' and the `hows' I refer to a previous set of lecture notes quant-ph/0506132. In a last section we provide some pointers to the body of technical literature on the subject.
Elaborating on our joint work with Abramsky in [S. Abramsky, B. Coecke, B. (2004) A categorical semantics of quantum protocols. Proceedings of the 19th Annual IEEE Symposium on Logic in Computer Science (LiCS'04), IEEE Computer Science Press. Extended version including proofs at arXiv:quant-ph/0402130, S. Abramsky, B. Coecke, (2005) Abstract physical traces. Theory and Applications of Categories 14, 111–124] we further unravel the linear structure of Hilbert spaces into several constituents. Some prove to be very crucial for particular features of quantum theory while others obstruct the passage to a formalism which is not saturated with physically insignificant global phases. First we show that the bulk of the required linear structure is purely multiplicative, and arises from the strongly compact closed tensor which, besides providing a variety of notions such as scalars, trace, unitarity, self-adjointness and bipartite projectors [S. Abramsky, B. Coecke, B. (2004) A categorical semantics of quantum protocols. Proceedings of the 19th Annual IEEE Symposium on Logic in Computer Science (LiCS'04), IEEE Computer Science Press. Extended version including proofs at arXiv:quant-ph/0402130, S. Abramsky, B. Coecke, (2005) Abstract physical traces. Theory and Applications of Categories 14, 111–124], also provides Hilbert-Schmidt norm, Hilbert-Schmidt inner-product, and in particular, the preparation-state agreement axiom which enables the passage from a formalism of the vector space kind to a rather projective one, as it was intended in the (in)famous Birkhoff & von Neumann paper [G. Birkhoff, J. von Neumann, (1936) The logic of quantum mechanics. Annals of Mathematics 37, 823–843]. Next we consider additive types which distribute over the tensor, from which measurements can be build, and the correctness proofs of the protocols discussed in [S. Abramsky, B. Coecke, (2004) A categorical semantics of quantum protocols. Proceedings of the 19th Annual IEEE Symposium on Logic in Computer Science (LiCS'04), IEEE Computer Science Press. Extended version including proofs at arXiv:quant-ph/0402130] carry over to the resulting weaker setting. A full probabilistic calculus is obtained when the trace is moreover linear and satisfies the diagonal axiom, which brings us to a second main result, characterization of the necessary and sufficient additive structure of a both qualitatively and quantitatively effective categorical quantum formalism without redundant global phases. Along the way we show that if in a category a (additive) monoidal tensor distributes over a strongly compact closed tensor, then this category is always enriched in commutative monoids.