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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)
This article discusses the intimate relationship between quantum mechanics, information theory, and relativity theory. Taken together these are the foundations of present-day theoretical physics, and their interrelationship is an essential part of the theory. The acquisition of information from a quantum system by an observer occurs at the interface of(More)
Quantum theory is incompatible with the following propositions. (1) The result of the measurement of an operator A depends solely on A and on the system being measured. (2) If operators A and B commute, the result of a measurement of their product AB is the product of the results of separate measurements of A and orB. Various quantum "paradoxes" [ 1-5 ] are(More)