A Quantum-Feedforward And Classical-Feedback Separating Structure Adapted With Monodirectional Measurements; Blind Qubit Uncoupling Capability And Links With ICA
Yannick Deville, Alain Deville

This paper deals with Blind Quantum Source Separation (BQSS).
The proposed separating system only receives observed quantum
states, each obtained after two quantum bits (qubits) were first independently
initialized with values that this system does not know and
then coupled according to a quantum operator involving parameter
values that the separating system does not know a priori. This system
aims at restoring the information contained in the initial qubit
states. We previously tackled this problem by first converting the
observed quantum state into data which have a classical (i.e. non-quantum)
form and then only processing the latter data with classical
means. We here propose a new approach, based on a separating
system which uses quantum processing means (consisting of a specific
unitary operator) in its feedforward path. Classical processing
is only used in the feedback path of this system, to adapt its transfer
function. The proposed adaptation method is based on binary-valued
monodirectional output measurements and related to quantum disentanglement.
We also analyze its relationships with classical Independent
Component Analysis. We prove that this BQSS method partly
restores the initial two-qubit states: it determines their components
up to some phase and permutation indeterminacies.