It is possible to entangle two photons that have never interacted before by using two down-conversion sources and then subjecting one photon from each entangled pair to a Bell-state measurement. This causes the other two photons, which have never interacted, to become entangled.
Further Links for Consideration
The basics of two-party entanglement
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http://xxx.arxiv.org/abs/quant-ph/9511030
http://xxx.arxiv.org/abs/quant-ph/9511027
http://xxx.arxiv.org/abs/quant-ph/9604024
http://xxx.arxiv.org/abs/quant-ph/9707035
http://xxx.arxiv.org/abs/quant-ph/9709029
http://xxx.arxiv.org/abs/quant-ph/9801069
http://xxx.arxiv.org/abs/quant-ph/9811053
http://xxx.arxiv.org/abs/quant-ph/9905071
Basics of multiparty entanglement
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http://xxx.arxiv.org/abs/quant-ph/9907047
http://xxx.arxiv.org/abs/quant-ph/9908073
http://xxx.arxiv.org/abs/quant-ph/9912039
http://xxx.arxiv.org/abs/quant-ph/0005115
Basics of secret sharing
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http://xxx.arxiv.org/abs/quant-ph/9806063
We have engineered an entangled state made of two atoms and the cavity mode. The entanglement is produced in a succession of controlled steps addresssing the particles individually. The sequence is fully programmable and could be configured to produce any quantum state. We have chosen here to prepare a triplet of entangled particles of the GHZ type. The entanglement has been demonstrated by experiments performed in two orthogonal basis. The procedure can, in principle, operate on larger numbers of particles, opening the way to new fundamental tests of quantum theory.
Test of the Quantenteleportation
over long distances in the duct system of Vienna
Working group
Quantity of experiment and the Foundations OF Physics
Professor Anton Zeilinger
Quantum physics questions the classical physical conception of the world and also the everyday life understanding, which is based on our experiences, in principle. In addition, the experimental results lead to new future technologies, which a revolutionizing of communication and computer technologies, how we know them, promise.
In order to exhaust this technical innovation potential, the project "Quantenteleportation was brought over long distances" in a co-operation between WKA and the working group by Professor Anton Zeilinger into being. In this experiment photons in the duct system "are teleportiert" of Vienna, i.e. transferred, the characteristics of a photon to another, removed far. First results are to be expected in the late summer 2002.
Dear Plato,
ReplyDeleteThe electron is nowadays supposed to be in an almost metaphysical superposition of spin states until measured, which indirectly (via the EPR-Bell-Aspect work) leads to the entanglement concept you mention. But Dr Thomas Love of California State University last week sent me a preprint, “Towards an Einsteinian Quantum Theory”, where he shows that the superposition principle is a fallacy, due to two versions of the Schroedinger equation: a system described by the time-dependent Schroedinger equation isn’t in an eigenstate between interactions.
“The quantum collapse occurs when we model the wave moving according to Schroedinger (time-dependent) and then, suddenly at the time of interaction we require it to be in an eigenstate and hence to also be a solution of Schroedinger (time-independent). The collapse of the
wave function is due to a discontinuity in the equations used to model the physics, it is not inherent in the physics.”
In the same report, page 133, Dr Love explains that von Neumann's proof of the impossibility of hidden variables is false because it replies on the validity of the principle of superposition.
So we can, and if we are objective, we must move on to make calculations with a causal model of reality. Feynman knew this 42 years ago, as shown in his Nov 1964 Cornell lectures filmed for BBC TV, "The Character of Physical Law" (broadcast on BBC2 in 1965), published in his book Character of Physical Law, pp. 171-3):
"The inexperienced [theorists who have never made contact with reality by getting a theory which predicts something measurable], and crackpots, and people like that, make guesses that are simple, but [with extensive knowledge of the actual facts rather than speculative theories of physics] you can immediately see that they are wrong, so that does not count. ... There will be a degeneration of ideas, just like the degeneration that great explorers feel is occurring when tourists begin moving i on a territory."
On page 38 of this book, Feynman has a diagram which looks basically like this: >E S<, where E is earth and S is sun. The arrows show the push that causes gravity. This is the LeSage gravity scheme, which I now find Feynman also discusses (without the diagram) in his full Lectures on Physics. He concludes that the mechanism in its form as of 1964 contradicted the no-ether relativity model and could not make any valid predictions, but finishes off by saying (p. 39):
"'Well,' you say, 'it was a good one, and I got rid of the mathematics for a while. Maybe I could invent a better one.' Maybe you can, because nobody knows the ultimate. But up to today [1964], from the time of Newton, no one has invented another theoretical description of the mathematical machinery behind this law which does not either say the same thing over again, or make the mathematics harder, or predict some wrong phenomena. So there is no model of the theory of gravitation today, other the mathematical form."
Does this mean Feynman is after physical mechanism, or is happy with the mathematical model? The answer is there on page 57-8:
"It always bothers me that, according to the laws as we understand them today, it takes a computing machine an infinite number of logical operations to figure out what goes on in no matter how tiny a region of space, and no matter how tiny a region of time. How can all that be going on in that tiny space? Why should it take an infinite amount of logic to figure out what one tiny piece of space/time is going to do? So I have often made the hypothesis that ultimately physics will not require a mathematical statement, that in the end the machinery will be revealed, and the laws will turn out to be simple, like the chequer board with all its apparent complexities."
Best wishes,
nigel