Random states for robust quantum metrology

by Prof. Maciej Lewenstein

Friday 29 Apr 2016, 11:00 → 12:00 Europe/Budapest

Meeting Room

We study how useful random states are for quantum metrology, i.e., surpass the classical limits imposed on precision in the canonical phase estimation scenario. First, we prove that random pure states drawn from the Hilbert space of distinguishable particles typically do not lead to super-classical scaling of precision even whenallowing for local unitary optimization. Conversely, we show that random states from the symmetric subspacetypically achieve the optimal Heisenberg scaling without the need for local unitary optimization. Surprisingly,the Heisenberg scaling is observed for states of arbitrarily low purity and preserved under finite particle losses. Moreover, we prove that for such states a standard photon-counting interferometric measurement suffices to typically achieve the Heisenberg scaling of precision for all possible values of the phase at the same time. Finally, we demonstrate that metrologically useful states can be prepared with short random optical circuitsgenerated from three types of beam-splitters and a non-linear (Kerr-like) transformation. http://arxiv.org/1602.05407