English

Four-dimensional operator systems without the lifting property

Operator Algebras 2025-08-04 v1 Functional Analysis

Abstract

The purpose of this note is to provide a family of explicit examples of 44-dimensional operator systems contained in the Calkin algebra Q(H)\mathcal{Q}(\mathcal{H}) on a separable infinite-dimensional Hilbert space H\mathcal{H} for which the identity map has no unital completely positive (ucp) lift to B(H)\mathcal{B}(\mathcal{H}) with respect to the canonical quotient map π:B(H)Q(H)\pi:\mathcal{B}(\mathcal{H}) \to \mathcal{Q}(\mathcal{H}). More specifically, to each unital CC^*-algebra A\mathcal{A} generated by nn unitaries and unital *-homomorphism ρ:AQ(H)\rho:\mathcal{A} \to \mathcal{Q}(\mathcal{H}) with no ucp lift, we construct a four-dimensional operator subsystem S\mathcal{S} of Mn+1(A)M_{n+1}(\mathcal{A}) without the lifting property. As a result, for each n2n \geq 2 we exhibit a four-dimensional operator system S\mathcal{S} in Mn+1(Cr(Fn))M_{n+1}(C_r^*(\mathbb{F}_n)) without the lifting property. We also obtain explicit examples where the generalized Smith-Ward problem for liftings of joint matrix ranges for three self-adjoint operators has a negative answer.

Keywords

Cite

@article{arxiv.2508.00113,
  title  = {Four-dimensional operator systems without the lifting property},
  author = {Samuel J. Harris},
  journal= {arXiv preprint arXiv:2508.00113},
  year   = {2025}
}

Comments

9 pages

R2 v1 2026-07-01T04:28:30.372Z