Delayed choice for entanglement swapping

Two observers (Alice and Bob) independently prepare two sets of singlets. They test one particle of each singlet along an arbitrarily chosen direction and send the other particle to a third observer, Eve. At a later time, Eve performs joint tests on pairs of particles (one from Alice and one from Bob). According to Eve's choice of test and to her results, Alice and Bob can sort into subsets the samples that they have already tested, and they can verify that each subset behaves as if it consisted of entangled pairs of distant particles, that have never communicated in the past, even indirectly via other particles.Comment: 7 pages, LaTeX, to appear in special issue of J. Modern Optic

Reply to the comment of Y. Aharonov and L. Vaidman on ``Time asymmetry in quantum mechanics: a retrodiction paradox''

In the standard physical interpretation of quantum theory, prediction and retrodiction are not symmetric. The opposite assertion by some authors results from their use of non-standard interpretations of the theory.Comment: final version in Physics Letters A 203 (1995) 15

Opposite momenta lead to opposite directions

When a particle decays into two fragments, the wavefunctions of the latter are spherical shells with expanding radii. In spite of this spherical symmetry, the two particles can be detected only in opposite directions.Comment: 3 pages LaTeX, submitted to American Journal of Physic

What is actually teleported?

There are no ``unknown quantum states.'' It's a contradiction in terms. Moreover, Alice and Bob are only inanimate objects. They know nothing. What is teleported instantaneously from one system (Alice) to another system (Bob) is the applicability of the preparer's knowledge to the state of a particular qubit in these systems. The operation necessitates dual classical and quantum channels. Other examples of dual transmission, including ``unspeakable information,'' will be presented and discussed. This article also includes a narrative of how I remember that quantum teleportation was conceived.Comment: preliminary version, to be submitted to IBM Journal of R&