I Quantum Causal Modelling: Mathematics

I have been trying to read through the following paper: https://iopscience.iop.org/article/10.1088/1367-2630/18/6/063032/pdf, but am stuck at the parts from page 6 onwards.

What is the "approach/formalism" used in the following sections of the paper, and are there any gentle introductions (available online, preferably) to this topic I can read through that may help me understand what's in the paper? I have seen similar mathematics appear in quite a few QM papers now and can't help but wonder if it's important.

Thanks in advance.
Perhaps I should have been more specific in my question, apologies:

Could anyone recommend some introductory materials to
1. "Process Matrix Formalism" - as mentioned in the abstract
2. Completely Positive Trace Preserving maps, Choi–Jamiołkowski isomorphism, and how they are used in QM

Thanks in advance.

Want to reply to this thread?

"Quantum Causal Modelling: Mathematics" You must log in or register to reply here.

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving

Hot Threads