Experimental quantum key distribution certified by Bell's theorem
(2021)
Micromotion minimisation by synchronous detection of parametrically excited motion
(2021)
Benchmarking a high-fidelity mixed-species entangling gate
Physical Review Letters American Physical Society 125:8 (2020) 080504
Abstract:
We implement a two-qubit logic gate between a 43Ca+ hyperfine qubit and a 88Sr+ Zeeman qubit. For this pair of ion species, the S–P optical transitions are close enough that a single laser of wavelength 402 nm can be used to drive the gate but sufficiently well separated to give good spectral isolation and low photon scattering errors. We characterize the gate by full randomized benchmarking, gate set tomography, and Bell state analysis. The latter method gives a fidelity of 99.8(1)%, comparable to that of the best same-species gates and consistent with known sources of error.High-rate high-fidelity entanglement of qubits across an elementary quantum network
Physical Review Letters American Physical Society 124:11 (2020) 110501
Abstract:
We demonstrate remote entanglement of trapped-ion qubits via a quantum-optical fiber link with fidelity and rate approaching those of local operations. Two 88Sr+ qubits are entangled via the polarization degree of freedom of two spontaneously emitted 422 nm photons which are coupled by high-numerical-aperture lenses into single-mode optical fibers and interfere on a beam splitter. A novel geometry allows high-efficiency photon collection while maintaining unit fidelity for ion-photon entanglement. We generate heralded Bell pairs with fidelity 94% at an average rate 182 s−1 (success probability 2.18×10−4).