Quantum error correction and generalized numerical ranges

TL;DR

This paper explores the geometric properties of joint higher rank numerical ranges and their implications for quantum error correction, revealing conditions under which these ranges are star-shaped or convex, especially in large or infinite-dimensional spaces.

Contribution

It introduces new geometric insights into joint higher rank numerical ranges and their relation to quantum error correction, extending understanding to infinite-dimensional operators.

Findings

Joint higher rank numerical ranges are star-shaped in large Hilbert spaces.

These ranges contain non-empty convex subsets under certain conditions.

Infinite-dimensional cases relate to joint essential numerical ranges.

Abstract

For a noisy quantum channel, a quantum error correcting code exists if and only if the joint higher rank numerical ranges associated with the error operators of the channel is non-empty. In this paper, geometric properties of the joint higher rank numerical ranges are obtained and their implications to quantum computing are discussed. It is shown that if the dimension of the underlying Hilbert space of the quantum states is sufficiently large, the joint higher rank numerical range of operators is always star-shaped and contains a non-empty convex subset. In case the operators are infinite dimensional, the joint infinite rank numerical range of the operators is a convex set closely related to the joint essential numerical ranges of the operators.