Coherence of assistance and assisted maximally coherent states

TL;DR

This paper explores the coherence of assistance in quantum states, establishing a unified framework with entanglement, and demonstrates that all full-rank states are distillable through assisted coherence distillation.

Contribution

It introduces a general coherence of assistance, links it to entanglement, and provides necessary conditions for assisted maximally coherent and entangled states.

Findings

Coherence and entanglement of assistance are in one-to-one correspondence.

Assisted coherence and entanglement measures are strictly larger than convex roof measures.

All full-rank quantum states are distillable via assisted coherence distillation.

Abstract

Coherence and entanglement are fundamental concepts in resource theory. The coherence (entanglement) of assistance is the coherence (entanglement) that can be extracted assisted by another party with local measurement and classical communication. We introduce and study the general coherence of assistance. First, in terms of real symmetric concave functions on the probability simplex, the coherence of assistance and the entanglement of assistance are shown to be in one-to-one correspondence. We then introduce two classes of quantum states: the assisted maximally coherent states and the assisted maximally entangled states. They can be transformed into maximally coherent or entangled pure states with the help of another party using local measurement and classical communication. We give necessary conditions for states to be assisted maximally coherent or assisted maximally entangled. Based on these, a unified framework between coherence and entanglement including coherence (entanglement) measures, coherence (entanglement) of assistance, coherence (entanglement) resources is proposed. Then we show that the coherence of assistance as well as entanglement of assistance are strictly larger than the coherence of convex roof and entanglement of convex roof for all full rank density matrices. So all full rank quantum states are distillable in the assisted coherence distillation.