[ExI] Probability Processor

scerir scerir at libero.it
Tue Aug 17 10:12:10 UTC 2010

BTW, it is also interesting to point out there are some vague ideas
about radically different processors: 

1) How to exploit the apparent "timelessness" of the quantum
domain, in other words it would be a sort of computation "on closed
timelike curves - CTC", usually called hypercomputation. 

2) Another vague idea seems to consist  in efforts to "bypass" the 
principle via quantum cloning, or via quantum memories ....
...... Of course, given the peculiar structure & formalism of QM, it is 
to keep a sort "chronology protection principle", that is to say that
the "grandfather paradox" is impossible (see paper below by Greenberger
and Svozil).  

Some materials here below .....


The quantum mechanics of time travel through post-selected teleportation
Seth Lloyd, Lorenzo Maccone, Raul Garcia-Patron, Vittorio Giovannetti, Yutaka 

Closed timelike curves via post-selection: theory and experimental 
Seth Lloyd, Lorenzo Maccone, Raul Garcia-Patron, Vittorio Giovannetti, Yutaka 
Stefano Pirandola, Lee A. Rozema, Ardavan Darabi, Yasaman Soudagar, Lynden K. 
Aephraim M. Steinberg

see also popular pages like ....

Any quantum state can be cloned in the presence of closed timelike curves
D. Ahn, T. C. Ralph, R. B. Mann
Abstract: The possible existence of closed timelike curves (CTCs) draws 
attention to fundamental questions about what is physically possible and what 
is not. An example is the "no cloning theorem" in quantum mechanics, which 
states that no physical means exists by which an unknown arbitrary quantum 
state can be reproduced or copied perfectly. We show here that this theorem can 
be circumvented in the presence of closed timelike curves, allowing the cloning 
of an unknown arbitrary quantum state. Since the "no cloning theorem" has 
played a central role in the development of quantum information science, it is 
clear that the existence of CTCs would radically change the rules for quantum 
information technology. Nevertheless we show that this type of cloning does not 
violate no-signalling criteria. 

The Uncertainty Principle in the Presence of Quantum Memory
Mario Berta, Matthias Christandl, Roger Colbeck, Joseph M. Renes, Renato 
Abstract: The uncertainty principle lies at the heart of quantum theory, 
illuminating a dramatic difference with classical mechanics. The principle 
bounds the uncertainties of the outcomes of any two observables on a system in 
terms of the expectation value of their commutator. It implies that an observer 
cannot predict the outcomes of two incompatible measurements to arbitrary 
precision. However, this implication is only valid if the observer does not 
possess a quantum memory, an unrealistic assumption in light of recent 
technological advances. In this work we strengthen the uncertainty principle to 
one that applies even if the observer has a quantum memory. We provide a lower 
bound on the uncertainty of the outcomes of two measurements which depends on 
the entanglement between the system and the quantum memory. We expect our 
uncertainty principle to have widespread use in quantum information theory, and 
describe in detail its application to quantum cryptography.

Anton Zeilinger et al had a different idea, years ago

Quantum Theory Looks at Time Travel
Daniel M. Greenberger, Karl Svozil
they make good points, to show the inconsistency of paradoxes,
at least from the quantum p.o.v.

See also the so called "inverse EPR" that is the entanglement due to an "ex 
post" measurement, 
or interaction, or whatever, that is to say that (more or less) you can 
entangle something in the past, 
from the future, with all those weird effects ..... (might be interesting, 
having in mind hypercomputations!)

'Time-Reversed EPR and the Choice of Histories in Quantum Mechanics'
Avshalom C. Elitzur, Shahar Dolev, Anton Zeilinger
Abstract: When a single photon is split by a beam splitter, its two `halves' 
can entangle two distant atoms into an EPR pair. We discuss a time-reversed 
analogue of this experiment where two distant sources cooperate so as to emit a 
single photon. The two `half photons,' having interacted with two atoms, can 
entangle these atoms into an EPR pair once they are detected as a single 
photon. Entanglement occurs by creating indistinguishabilility between the two 
mutually exclusive histories of the photon. This indistinguishabilility can be 
created either at the end of the two histories (by `erasing' the single 
photon's path) or at their beginning (by `erasing' the two atoms' positions). 

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