A Diagrammatic Approach to Information Transmission in Generalised Switches

Matt Wilson
Giulio Chiribella

The quantum switch is a higher-order operation that takes as an input two quantum processes and combines them in a coherent superposition of two alternative orders. Here we provide an approach to the quantum switch based on the methods of categorical quantum mechanics. Specifically, we represent the quantum switch as a sum of diagrams in the category of finite dimensional Hilbert spaces, or, equivalently, as a sum of diagrams built from Selinger's CPM construction. The sum-of-diagrams picture provides intuition for the activation of classical capacity of completely depolarising channels (CDPCs) and allows for generalisation to N-channel switches. We demonstrate the use of these partially diagrammatic methods by deriving a permutation condition for computing the output of any N-channel switch of CDPCs, we then use that condition to prove that amongst all possible terms, the interference terms associated to cyclic permutations of the N channels are the information-transmitting terms with maximum normalisation

In Benoît Valiron, Shane Mansfield, Pablo Arrighi and Prakash Panangaden: Proceedings 17th International Conference on Quantum Physics and Logic (QPL 2020), Paris, France, June 2 - 6, 2020, Electronic Proceedings in Theoretical Computer Science 340, pp. 333–348.
Published: 6th September 2021.

ArXived at: http://dx.doi.org/10.4204/EPTCS.340.17 bibtex PDF
References in reconstructed bibtex, XML and HTML format (approximated).
Comments and questions to: eptcs@eptcs.org
For website issues: webmaster@eptcs.org