## Quantum Measurements Without Sums

Citations: | 23 - 8 self |

### BibTeX

@MISC{Coecke_quantummeasurements,

author = {Bob Coecke and Dusko Pavlovic},

title = {Quantum Measurements Without Sums},

year = {}

}

### OpenURL

### Abstract

Sums play a prominent role in the formalisms of quantum mechanics, be it for mixing and superposing states, or for composing state spaces. Surprisingly, a conceptual analysis of quantum measurement seems to suggest that quantum mechanics can be done without direct sums, expressed entirely in terms of the tensor product. The corresponding axioms define classical spaces as objects that allow copying and deleting data. Indeed, the information exchange between the quantum and the classical worlds is essentially determined by their distinct capabilities to copy and delete data. The sums turn out to be an implicit implementation of this capabilities. Realizing it through explicit axioms not only dispenses with the unnecessary structural baggage, but also allows a simple and intuitive graphical calculus. In category-theoretic terms, classical data types are †-compact Frobenius algebras, and quantum spectra underlying quantum measurements are Eilenberg-Moore coalgebras induced by these Frobenius algebras. An earlier version of this paper has been in circulation since November 2005 with the somewhat different title Quantum measurements as coalgebras. 1 1