Distances between pure quantum states induced by a distance matrix

Abstract

With the help of a given distance matrix of size $n$, we construct an infinite family of distances $d_p$ (where $p\ge 2$) on the complex projective space $\mathbb{P}({\mathbb{C}}^n)$ modelling the space of pure states of an $n$-level quantum system. The construction can be seen as providing a natural way to isometrically embed any given finite metric space into the space of pure quantum states 'spanned' upon it. In order to show that the maps $d_p$ are indeed distance functions -- in particular, that they satisfy the triangle inequality -- we employ methods of analysis, multilinear algebra and convex geometry, obtaining a nontrivial auxiliary convexity result in the process. In addition, a way of extending distances $d_p$ onto mixed states is proposed for a broad class of distance matrices.

27 pages, 1 figure