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Experimental delayedchoice entanglement swapping. Nature Phys
, 2012
"... Motivated by the question of which kind of physical interactions and processes are needed for the production of quantum entanglement, Peres has put forward the radical idea of delayedchoice entanglement swapping. There, entanglement can be ‘produced a posteriori, after the entangled particles have ..."
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Motivated by the question of which kind of physical interactions and processes are needed for the production of quantum entanglement, Peres has put forward the radical idea of delayedchoice entanglement swapping. There, entanglement can be ‘produced a posteriori, after the entangled particles have been measured and may no longer exist’. Here, we report the realization of Peres’s gedanken experiment. Using four photons, we can actively delay the choice of measurement— implemented through a highspeed tunable bipartitestate analyser and a quantum randomnumber generator—on two of the photons into the timelike future of the registration of the other two photons. This effectively projects the two already registered photons onto one of two mutually exclusive quantum states in which the photons are either entangled (quantum correlations) or separable (classical correlations). This can also be viewed as ‘quantum steering into the past’. In the entanglement swapping 1–3 procedure, two pairs of entangled photons are produced, and one photon from each pair is sent to Victor. The two other photons from each pair are sent to Alice and Bob, respectively. If Victor projects his two photons onto an entangled state, Alice’s and Bob’s photons are entangled although they have never interacted or shared any common past.
From Quantum to Classical Dynamics: a Landau Continuous Phase Transition with Spontaneous Superposition Breaking
 quantph/0409010 v1 1 Sep 2004
"... Developing an earlier proposal (Ne’eman, Damnjanović,etc.), we show herein that there is a Landau continuous phase transition from the exact quantum dynamics to the effectively classical one, occurring via spontaneous superposition breaking (effective hiding), as a special case of the corresponding ..."
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Developing an earlier proposal (Ne’eman, Damnjanović,etc.), we show herein that there is a Landau continuous phase transition from the exact quantum dynamics to the effectively classical one, occurring via spontaneous superposition breaking (effective hiding), as a special case of the corresponding general formalism (Bernstein). Critical values of the order parameters for this transition are determined by Heisenberg’s indeterminacy relations, change continuously, and are in excellent agreement with the recent and remarkable experiments with Bose condensation. It is also shown that such a phase transition can sucessfully model selfcollapse (selfdecoherence), as an effective classical phenomenon, on the measurement device. This then induces a relative collapse (relative decoherence) as an effective quantum phenomenon on the measured quantum object by measurement. We demonstrate this (including the case of BoseEinstein condensation) in the wellknown cases of the SternGerlach spin measurement, Bell’s inequality and the recently discussed quantum superposition on a mirror à la Marshall et al. These results provide for a proof that quantum mechanics, in distinction to all absolute collapse and hiddenvariable theories, is local and objective. There now appear no insuperable obstacles to solving the open problems in quantum theory of measurement and foundation of quantum mechanics, and strictly within the standard quantummechanical formalism. Simply put, quantum mechanics is a field theory over the Hilbert space, the classical mechanics characteristics of which emerge through spontaneous superposition breaking. 1 1