



01538nas a2200157   4500008004100000245007800041210006900119260001500188520103700203100001601240700001701256700002201273700002501295700002301320856003701343       2018                        eng d00aDistributed Quantum Metrology and the Entangling Power of Linear Networks0 aDistributed Quantum Metrology and the Entangling Power of Linear  c2018/07/253 a<p><span style="font-family: &quot;Lucida Grande&quot;, helvetica, arial, verdana, sans-serif; font-size: 14.4px;">We derive a bound on the ability of a linear optical network to estimate a linear combination of independent phase shifts by using an arbitrary non-classical but unentangled input state, thereby elucidating the quantum resources required to obtain the Heisenberg limit with a multi-port interferometer. Our bound reveals that while linear networks can generate highly entangled states, they cannot effectively combine quantum resources that are well distributed across multiple modes for the purposes of metrology: in this sense linear networks endowed with well-distributed quantum resources behave classically. Conversely, our bound shows that linear networks can achieve the Heisenberg limit for distributed metrology when the input photons are hoarded in a small number of input modes, and we present an explicit scheme for doing so. Our results also have implications for measures of non-classicality.</span></p>1 aGe, Wenchao1 aJacobs, Kurt1 aEldredge, Zachary1 aGorshkov, Alexey, V.1 aFoss-Feig, Michael  uhttps://arxiv.org/abs/1707.06655