Courtesy of centre
for quantum computation.

#
Quantum information

###
Is information local?

All of the basic laws of physics that are known to approximate nature to
some

reasonable degree can be expressed as fields evolve in space and time
according to

*hyperbolic partial differential equations.*

This is true for all quantum fields in the "Standard Model" of particle
physics and the classical

gravitational field in General Relativity.
Normally an evolution that can be fully described with partial differential
equations

means that nature is "local", i.e. to describe what happens or is known
at a

certain place depends only on what happens in its immediate neighbourhood.

Still, quantum mechanics *seems* to imply that this is not true
in certain

situations. This leaves a tension between the basic field equations
of physics and

the idea of non-local quantum information, that has been

impossible to understand for me.

Recently David
Deutsch , a pioneer of quantum computing, argued in an interview
that

*within Everett´s * *relative-state
interpretation* of quantum mechanics we can:

"...blow the 'quantum non-locality' misconception clean out of the
water."

In my mind, if true, this would be a most convincing argument
in favour of the relative-state

(or "many-worlds" MWI) interpretation.

Contrary to this view many MWI-specialists, like e.g. Hans-Dieter Zeh,
are adamant that even in the MWI

non-locality is unavoidable. I had an e-mail
discussion about these opposing views in the spring

of 2001 with Henry Stapp. I also asked David Deutsch for his standpoint
on this issue see

here for his answer. In view
of the motto of this site, it comes as no surprise that David Deutsch

likes Karl Popper.

###
Can the many-worlds interpretation be tested?

Based on an experiment done by Y.Kim and Y.Shih [quant-ph/9905039]
Rainer
Plaga recently

proposed an practical test of the relative state interpretation:

"*An extension of ``Popper´s experiment``* *can
test interpretations of* *quantum mechanics*

[quant-ph/0010030]
"(Found.Phys.Lett. **13,** 461(2000)).

Since this paper was published, there have been controversial discussions
if Kim and Shih

gave a correct account of the meaning of their experimental results.
I do not think anymore

that they did, see here
why. See also quant-ph/0005063
by Tony Short. This withdraws the basis from my paper.

The search for a practical test - or a proof of its impossibility -
of the relative-state

interpretation is this still on.

Return
to home