State Readout of a Trapped Ion Qubit Using a Trap-Integrated Superconducting Photon Detector

TL;DR

This paper demonstrates high-fidelity qubit state readout in a trapped ion system using an integrated superconducting photon detector, achieving nearly perfect accuracy in a compact setup.

Contribution

It introduces a trap-integrated superconducting photon detector for ion qubit readout, enabling self-calibrated efficiency measurement without intervening optical elements.

Findings

Readout fidelity of 0.9991 achieved

Mean readout duration of 46 microseconds

Detector efficiency depends on photon angle and polarization

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 (SNSPD) fabricated into the trap structure. The average readout fidelity is 0.9991(1), with a mean readout duration of 46 $\mu$s, 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.