Adrian Kent, Cavendish Lab "summons" quantum spirits. #2 11-6-11

On Nov 6, 2011, at 1:04 PM, Paul Zielinski wrote:

He claims that his "non-summoning" theorem follows from the no-cloning theorem and and the no-signaling
principle, and that it fundamentally distinguishes relativistic QFT from both non-relativistic QM and classical
relativity.

Yes, I know that much. Can you clearly explain what "summoning" means operationally and how it is important for any practical application?

I plan to look through Kent's papers - some of the titles are intriguing.

I agree it's important to distinguish no-cloning from no signaling. No-cloning is sufficient for no-signaling, but not necessary.
No-cloning was only for Nick Herbert's laser amplifier approach to signal non-locality.

The basic error of all the no-signalers seems to be the denial of distinguishablilty of non-orthogonal states.  This is manifestly false in my opinion. Glauber coherent states are the counter-example.


As to Brian's objections, they do say

"We suppose that both parties have arbitrarily efficient technology,

non-physical

limited only by the relevant causal
structure and physical theory. In particular, to simplify the discussion initially, we suppose that Alice
and Bob can independently and securely access any relevant point in space-time and instantaneously
process and exchange information there.

non-physical

We also suppose that their preparations, information processing,
communications and measurements are error-free and have unbounded precision and capacity. We will
relax these idealized and somewhat unphysical assumptions later."

Yes, I saw that when I skimmed it first time round. Does he actually talk about a realistic case in that paper? I don't think so.

It would help if he, at the beginning ,gave a motive - value added of what "summoning" really means?