State Readout of a Trapped Ion Qubit Using a Trap-Integrated Superconducting Photon Detector
Susanna Todaro, Varun B. Verma, Katherine C. McCormick, D. T. C. Allcock, Richard P. Mirin, D. J. Wineland, Sae Woo Nam, A. C. Wilson, D. Leibfried, D. H. Slichter
Abstract
We report high-fidelity state readout of a trapped ion qubit using a trap-integrated photon detector. We determine the hyperfine qubit state of a single ^{9}Be^{+} ion held in a surface-electrode rf ion trap by counting state-dependent ion fluorescence photons with a superconducting nanowire single-photon detector fabricated into the trap structure. The average readout fidelity is 0.9991(1), with a mean readout duration of 46 μs, and is limited by the polarization impurity of the readout laser beam and by off-resonant optical pumping. Because there are no intervening optical elements between the ion and the detector, we can use the ion fluorescence as a self-calibrated photon source to determine the detector quantum efficiency and its dependence on photon incidence angle and polarization.