Complete characterization of the state of a quantum system made up of subsystems requires determination of relative phase, because of interference effects between the subsystems. For a system of qubits used as a quantum computer this is especially vital, because the entanglement, which is the basis for the quantum advantage in computing, depends intricately on phase. We present here a first step towards that determination, in which we use a two-qubit quantum system as a quantum neural network, which is trained to compute and output its own relative phase.
@article{arxiv.1301.2808,
title = {A quantum neural network computes its own relative phase},
author = {E. C. Behrman and J. E. Steck},
journal= {arXiv preprint arXiv:1301.2808},
year = {2013}
}