We generalize past work on quantum sensor networks to show that, for d input parameters, entanglement can yield a factor O(d) improvement in mean squared error when estimating an analytic function of these parameters. We show that the protocol is optimal for qubit sensors, and conjecture an optimal protocol for photons passing through interferometers. Our protocol is also applicable to continuous variable measurements, such as one quadrature of a field operator. We outline a few potential applications, including calibration of laser operations in trapped ion quantum computing.

1 aQian, Kevin1 aEldredge, Zachary1 aGe, Wenchao1 aPagano, Guido1 aMonroe, Christopher1 aPorto, James, V.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1901.0904204213nas a2200241 4500008004100000245006900041210006800110260001500178300001100193490000800204520348600212100001503698700002303713700002403736700001903760700001903779700002503798700002503823700001803848700002103866700002403887856006003911 2018 eng d00aDark state optical lattice with sub-wavelength spatial structure0 aDark state optical lattice with subwavelength spatial structure c2018/02/20 a0836010 v1203 aWe report on the experimental realization of a conservative optical lattice for cold atoms with a subwavelength spatial structure. The potential is based on the nonlinear optical response of three-level atoms in laser-dressed dark states, which is not constrained by the diffraction limit of the light generating the potential. The lattice consists of a one-dimensional array of ultranarrow barriers with widths less than 10 nm, well below the wavelength of the lattice light, physically realizing a Kronig-Penney potential. We study the band structure and dissipation of this lattice and find good agreement with theoretical predictions. Even on resonance, the observed lifetimes of atoms trapped in the lattice are as long as 44 ms, nearly 105times the excited state lifetime, and could be further improved with more laser intensity. The potential is readily generalizable to higher dimensions and different geometries, allowing, for example, nearly perfect box traps, narrow tunnel junctions for atomtronics applications, and dynamically generated lattices with subwavelength spacings.

1 aWang, Yang1 aSubhankar, Sarthak1 aBienias, Przemyslaw1 aLacki, Mateusz1 aTsui, Tsz-Chun1 aBaranov, Mikhail, A.1 aGorshkov, Alexey, V.1 aZoller, Peter1 aPorto, James, V.1 aRolston, Steven, L. uhttps://link.aps.org/doi/10.1103/PhysRevLett.120.08360103349nas a2200217 4500008004100000245008400041210006900125260001500194300001100209490000700220520266700227100002202894700002002916700001702936700003102953700002102984700002403005700002103029700002503050856005603075 2018 eng d00aDissipation induced dipole blockade and anti-blockade in driven Rydberg systems0 aDissipation induced dipole blockade and antiblockade in driven R c2018/02/28 a0234240 v973 aWe study theoretically and experimentally the competing blockade and antiblockade effects induced by spontaneously generated contaminant Rydberg atoms in driven Rydberg systems. These contaminant atoms provide a source of strong dipole-dipole interactions and play a crucial role in the system's behavior. We study this problem theoretically using two different approaches. The first is a cumulant expansion approximation, in which we ignore third-order and higher connected correlations. Using this approach for the case of resonant drive, a many-body blockade radius picture arises, and we find qualitative agreement with previous experimental results. We further predict that as the atomic density is increased, the Rydberg population's dependence on Rabi frequency will transition from quadratic to linear dependence at lower Rabi frequencies. We study this behavior experimentally by observing this crossover at two different atomic densities. We confirm that the larger density system has a smaller crossover Rabi frequency than the smaller density system. The second theoretical approach is a set of phenomenological inhomogeneous rate equations. We compare the results of our rate-equation model to the experimental observations [E. A. Goldschmidt *et al.*, Phys. Rev. Lett. 116, 113001 (2016)] and find that these rate equations provide quantitatively good scaling behavior of the steady-state Rydberg population for both resonant and off-resonant drives.