Laboratoire de Physique Théorique
Toulouse - UMR 5152

In order to get accuracies below the shot-noise limit in interferometric measurements based on distinguishable qubits, entangled states are necessary and most often obtained by squeezing techniques. We show that, in the case of identical qubits, as for experiments with trapped ultracold atoms, what is necessary is non-locality and this can be provided by the interferometer itself and not by the input state. This is due to the peculiar character of identical particle entanglement that requires an observable based (algebraic) rather than a Hilbert space formulation.