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An unknown quantum state ji can be disassembled into, then later reconstructed from, purely classical information and purely nonclassical EPR correlations. To do so the sender, \Alice," and the receiver, \Bob," must prearrange the sharing of an EPR-correlated pair of particles. Alice makes a joint measurement on her EPR particle and the unknown quantum(More)
We consider the Bennett-Brassard cryptographic scheme, which uses two conjugate quantum bases. An eavesdropper who attempts to obtain information on qubits sent in one of the bases causes a disturbance to qubits sent in the other basis. We derive an upper bound to the accessible information in one basis, for a given error rate in the conjugate basis.(More)
Bell inequalities are derived for any number of observers, any number of alternative setups for each one of them, and any number of distinct outcomes for each experiment. It is shown that if a physical system consists of several distant subsystems, and if the results of tests performed on the latter are determined by local variables with objective values,(More)
We inquire under what conditions some of the information in a quantum signal source, namely a set of pure states a emitted with probabilities p a , can be extracted in classical form by a measurement leaving the quantum system with less entropy than it had before, but retaining the ability to regenerate the source state exactly from the classical(More)
Popper conceived an experiment whose analysis led to a result that he deemed absurd. Popper wrote that his reasoning was based on the Copenhagen interpretation and therefore invalidated the latter. Actually, Popper's argument involves counterfactual reasoning and violates Bohr's complementarity principle. The absurdity of Popper's result only confirms(More)
I was the referee who approved the publication of Nick Herbert's FLASH paper, knowing perfectly well that it was wrong. I explain why my decision was the correct one, and I briefly review the progress to which it led. The no-cloning theorem [1, 2] is of fundamental importance in quantum theory. It asserts that no quantum amplifier can duplicate accurately(More)