On the Interference of Probabilities

P. D. Finch

Andrei Yu. Khrennikov

We describe methodology of cognitive experiments (based on interference of probabilities for mental observables) which could verify quantum-like structure of mental information, namely, interference of probabilities for incompatible observables. In principle, such experiments can be performed in psychology, cognitive, and social sciences. In fact, the general contextual probability theory predicts not only quantum-like trigonometric (cos θ) interference of probabilities, but also hyperbolic (cosh θ) interference of probabilities (as well as hyper-trigonometric). In principle, statistical data obtained in experiments with cognitive systems can produce hyperbolic (cosh θ) interference of probabilities. We introduce a wave function of (e.g., human) population. In general, we should not reject the possibility that cognitive functioning is neither quantum nor classical. We discuss the structure of state spaces for cognitive systems.

Andrei Yu. Khrennikov

Daniel Braun, Bertrand Georgeot

We study the importance of interference for the performance of Shor's factoring algorithm and Grover's search algorithm using a recently proposed interference measure. To this aim we introduce systematic unitary errors, random unitary errors, and decoherence processes in these algorithms. We show that unitary errors which destroy the interference destroy the efficiency of the algorithm, too. However, unitary errors may also create useless additional interference. In such a case the total amount of interference can increase, while the efficiency of the quantum computation decreases. For decoherence due to phase flip errors, interference is destroyed for small error probabilities, and converted into destructive interference for error probabilities approaching 1, leading to success probabilities which can even drop below the classical value. Our results show that in general, interference is necessary in order for a quantum algorithm to outperform classical computation, but large amounts of interference are not sufficient and can even lead to destructive interference with worse than classical success rates.

Domenico Costantini, Carlo Ferigato

Abstract Pascual Jordan was the first to propose the law of interference of probability amplitudes as a principle of quantum mechanics. We analyze the role of probabilistic ideas played in this proposal from a historical perspective. In particular, we point out the relation between the usual theory of probability that Jordan called elementary and quantum mechanics. Jordan was the first to stress the analogy between the law of total probability and the law of interference. In this regard, we speculate about the intellectual path Jordan might have followed in order to arrive at the interference law. We do not oppose the usual probability to quantum probability. Instead, we are convinced, as Jordan was, that the rules of quantum mechanics are the rules of a probability theory that has ceased to be elementary.

Andrei Yu. Khrennikov