Detecting Quantum Causality In Quantum Evolution

In this paper,we investigate problems about causalities in quantum evolutions,especially the quantum causal inference problem.A criterion resulting from a set of measurements is proposed to discriminate between quantum causalities and quantum common causes.The matrix of the correlations between the measurements turns out to be closely relevant with the Bloch sphere representation of qubits.Even if quantum causalities and quantum common causes are mixed probabilistically,we can tell the range of the possibility of quantum causalities or quantum common causes from the criterion proposed.Also,we have considered the faster-than-light diffusions in quantum evolutions such as quantum random walks.It is found that continues-time quantum walks in a 1-dimentional space predict faster-than-light diffusions if the initial state of the walker is well chosen.This demands a more cautious analysis on the continues-time quantum walks to make it consistent with theories about causalities.