Quantum mechanics

Detector

Trapped ion quantum computer

Quantum error correction

Atomic physics

Physical chemistry

Polarization (electrochemistry)

Photon

Physics

Hyperfine structure

Optics

Quantum

Ion trap

Qubit

Chemistry

Optoelectronics

Physical Review Letters

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 $^{9}{\mathrm{Be}}^{+}$ 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 $46\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$, 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.

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