# Non-commutative Clark measures for the free and abelian Toeplitz algebras

## TL;DR

This paper introduces a non-commutative Aleksandrov-Clark measure for elements in the operator-valued free Schur class, establishing a bijection with completely positive maps on the free disk algebra and relating it to classical AC measures.

## Contribution

It constructs a non-commutative AC measure for free Schur class elements and links these measures to classical AC measures via free liftings.

## Key findings

- Defines a bijection between free Schur class and non-commutative AC measures.
- Relates non-commutative AC measures to classical AC measures through free liftings.
- Establishes the relationship between free and commutative Toeplitz algebra measures.

## Abstract

We construct a non-commutative Aleksandrov-Clark measure for any element in the operator-valued free Schur class, the closed unit ball of the free Toeplitz algebra of vector-valued full Fock space over $\mathbb{C} ^d$. Here, the free (analytic) Toeplitz algebra is the unital weak operator topology (WOT)-closed algebra generated by the component operators of the free shift, the row isometry of left creation operators. This defines a bijection between the free operator-valued Schur class and completely positive maps (non-commutative AC measures) on the operator system of the free disk algebra, the norm-closed algebra generated by the free shift. Identifying Drury-Arveson space with symmetric Fock space, we determine the relationship between the non-commutative AC measures for elements of the operator-valued commutative Schur class (the closed unit ball of the WOT-closed Toeplitz algebra generated by the Arveson shift) and the AC measures of their free liftings to the free Schur class.