Injection locking of two frequency-doubled lasers with 3.2 GHz offset for driving Raman transitions with low photon scattering in 43^{43}Ca+^+

We describe the injection locking of two infrared (794 nm) laser diodes which are each part of a frequency-doubled laser system. An acousto-optic modulator (AOM) in the injection path gives an offset of 1.6 GHz between the lasers for driving Raman transitions between states in the hyperfine split (by 3.2 GHz) ground level of $^{43}$Ca$^+$. The offset can be disabled for use in $^{40}$Ca$^+$. We measure the relative linewidth of the frequency-doubled beams to be 42 mHz in an optical heterodyne measurement. The use of both injection locking and frequency doubling combines spectral purity with high optical power. Our scheme is applicable for providing Raman beams across other ion species and neutral atoms where coherent optical manipulation is required.Comment: 3 pages, 3 figure

High-rate, high-fidelity entanglement of qubits across an elementary quantum network

We demonstrate remote entanglement of trapped-ion qubits via a quantum-optical fiber link with fidelity and rate approaching those of local operations. Two ${}^{88}$Sr${}^{+}$ qubits are entangled via the polarization degree of freedom of two photons which are coupled by high-numerical-aperture lenses into single-mode optical fibers and interfere on a beamsplitter. A novel geometry allows high-efficiency photon collection while maintaining unit fidelity for ion-photon entanglement. We generate remote Bell pairs with fidelity $F=0.940(5)$ at an average rate $182\,\mathrm{s}^{-1}$ (success probability $2.18\times10^{-4}$).Comment: v2 updated to include responses to reviewers, as published in PR

Dielectronic recombination of W^20+ (4d^10 4f^8): addressing the half-open f-shell

A recent measurement of the dielectronic recombination (DR) of W^20+ [Schippers et al Phys. Rev. A83, 012711 (2011)] found an exceptionally large contribution from near threshold resonances (<1eV). This still affected the Maxwellian rate coefficient at much higher temperatures. The experimental result was found to be a factor 4 or more than that currently in use in the 100-300eV range which is of relevance for modeling magnetic fusion plasmas. We have carried-out DR calculations with AUTOSTRUCTURE which include all significant single electron promotions. Our intermediate coupling (IC) results are more than a factor of 4 larger than our LS-coupling ones at 1eV but still lie a factor 3 below experiment here. If we assume complete (chaotic) mixing of near-threshold autoionizing states then our results come into agreement (to within 20%) with experiment below about 2eV. Our total IC Maxwellian rate coefficients are 50-30% smaller than those based-on experiment over 100-300eV.Comment: 10 pages, 8 figures, submitted to Phys.Rev.

A STUDY OF CRYOPUMP CONFIGURATIONS IN FREE MOLECULAR FLOW REGIONS

Monte carlo computer technique applied to focusing of cryopump configurations in free molecular flow regio

Non-Equilibrium Modeling of the Fe XVII 3C/3D ratio for an Intense X-ray Free Electron Laser

We present a review of two methods used to model recent LCLS experimental results for the 3C/3D line intensity ratio of Fe XVII (Bernitt et al. 2012), the time-dependent collisional-radiative method and the density-matrix approach. These are described and applied to a two-level atomic system excited by an X-ray free electron laser. A range of pulse parameters is explored and the effects on the predicted Fe XVII 3C and 3D line intensity ratio are calculated. In order to investigate the behavior of the predicted line intensity ratio, a particular pair of A-values for the 3C and 3D transitions was chosen (2.22 $\times$ 10$^{13}$ s$^{-1}$ and 6.02 $\times$ 10$^{12}$ s$^{-1}$ for the 3C and 3D, respectively), but our conclusions are independent of the precise values. We also reaffirm the conclusions from Oreshkina et al.(2014, 2015): the non-linear effects in the density matrix are important and the reduction in the Fe XVII 3C/3D line intensity ratio is sensitive to the laser pulse parameters, namely pulse duration, pulse intensity, and laser bandwidth. It is also shown that for both models the lowering of the 3C/3D line intensity ratio below the expected time-independent oscillator strength ratio has a significant contribution due to the emission from the plasma after the laser pulse has left the plasma volume. Laser intensities above $\sim 1\times 10^{12}$ W/cm$^{2}$ are required for a reduction in the 3C/3D line intensity ratio below the expected time independent oscillator strength ratio

Probing Qubit Memory Errors at the Part-per-Million Level

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 $\epsilon_m$ for a $^{43}$Ca$^+$ trapped-ion qubit in the small-error regime and find $\epsilon_m<10^{-4}$ for storage times t\lesssim50\,\mbox{ms}. This exceeds gate or measurement times by three orders of magnitude. Using randomized benchmarking, at t=1\,\mbox{ms} we measure $\epsilon_m=1.2(7)\times10^{-6}$, around ten times smaller than that extrapolated from the $T_{2}^{\ast}$ time, and limited by instability of the atomic clock reference used to benchmark the qubit.Comment: 8 pages, 5 figure