Dr David Nadlinger

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.

Abstract:

Robust qubit memory is essential for quantum computing, both for near-term devices operating without error correction, and for the long-term goal of a fault-tolerant processor. We directly measure the memory error ε_m for a ⁴³Ca⁺ trapped-ion qubit in the small-error regime and find ε_m<10⁻⁴ for storage times t ≲ 50  ms. This exceeds gate or measurement times by three orders of magnitude. Using randomized benchmarking, at t = 1  ms we measure ε_m=1.2(7)×10⁻⁶, around ten times smaller than that extrapolated from the T^∗₂ time, and limited by instability of the atomic clock reference used to benchmark the qubit.

Abstract:

We directly observe the quantum interference between two well-separated trapped-ion mechanical oscillator wave packets. The superposed state is created from a spin-motion entangled state using a heralded measurement. Wave packet interference is observed through the energy eigenstate populations. We reconstruct the Wigner function of these states by introducing probe Hamiltonians which measure Fock state populations in displaced and squeezed bases. Squeezed-basis measurements with 8 dB squeezing allow the measurement of interference for Δα=15.6, corresponding to a distance of 240 nm between the two superposed wave packets.