[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
uncertainty
principle via quantum cloning, or via quantum memories ....
...... Of course, given the peculiar structure & formalism of QM, it is
possible
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 .....
s.
The quantum mechanics of time travel through post-selected teleportation
http://arxiv.org/abs/1007.2615
Seth Lloyd, Lorenzo Maccone, Raul Garcia-Patron, Vittorio Giovannetti, Yutaka
Shikano
Closed timelike curves via post-selection: theory and experimental
demonstration
http://arxiv.org/abs/1005.2219
Seth Lloyd, Lorenzo Maccone, Raul Garcia-Patron, Vittorio Giovannetti, Yutaka
Shikano,
Stefano Pirandola, Lee A. Rozema, Ardavan Darabi, Yasaman Soudagar, Lynden K.
Shalm,
Aephraim M. Steinberg
see also popular pages like ....
http://www.technologyreview.com/blog/arxiv/25494/
http://www.wired.com/wiredscience/2010/07/time-travel/
http://www.santafe.edu/news/item/time-travel-testing-grandfather-paradox-
Lloyd/
http://www.sciencenews.org/view/generic/id/61301/title/Taming_time_travel
http://www.centauri-dreams.org/?p=13568
Any quantum state can be cloned in the presence of closed timelike curves
D. Ahn, T. C. Ralph, R. B. Mann
http://arxiv.org/abs/1008.0221
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
Renner
http://arxiv.org/abs/0909.0950
http://www.ethlife.ethz.ch/archive_articles/100726_Heisenberg_su/index_EN
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
http://arxiv.org/PS_cache/quant-ph/pdf/0109/0109022v2.pdf
Quantum Theory Looks at Time Travel
Daniel M. Greenberger, Karl Svozil
http://arxiv.org/abs/quant-ph/0506027
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
http://arxiv.org/abs/quant-ph/0205182
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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