Coupling a single atomic quantum bit to a high finesse optical cavity

The quadrupole S$_{1/2}$ -- D$_{5/2}$ optical transition of a single trapped Ca$^+$ ion, well suited for encoding a quantum bit of information, is coherently coupled to the standing wave field of a high finesse cavity. The coupling is verified by observing the ion's response to both spatial and temporal variations of the intracavity field. We also achieve deterministic coupling of the cavity mode to the ion's vibrational state by selectively exciting vibrational state-changing transitions and by controlling the position of the ion in the standing wave field with nanometer-precision

Raman spectroscopy of a single ion coupled to a high-finesse cavity

We describe an ion-based cavity-QED system in which the internal dynamics of an atom is coupled to the modes of an optical cavity by vacuum-stimulated Raman transitions. We observe Raman spectra for different excitation polarizations and find quantitative agreement with theoretical simulations. Residual motion of the ion introduces motional sidebands in the Raman spectrum and leads to ion delocalization. The system offers prospects for cavity-assisted resolved-sideband ground-state cooling and coherent manipulation of ions and photons.Comment: 8 pages, 6 figure

Using Administrative Data to Explore the Effect of Survey Nonresponse in the UK Employment Retention and Advancement Demonstration

Background: Even a well-designed randomized control trial (RCT) study can produce ambiguous results. This paper highlights a case in which full-sample results from a large-scale RCT in the United Kingdom (UK) differ from results for a sub-sample of survey respondents. Objectives: Our objective is to ascertain the source of the discrepancy in inferences across data sources and, in doing so, to highlight important threats to the reliability of the causal conclusions derived from even the strongest research designs. Research design: The study analyzes administrative data to shed light on the source of the differences between the estimates. We explore the extent to which heterogeneous treatment impacts and survey non-response might explain these differences. We suggest checks which assess the external validity of survey measured impacts, which in turn provides an opportunity to test the effectiveness of different weighting schemes to remove bias. The Subjects included 6,787 individuals who participated in a large-scale social policy experiment. Results: Our results were not definitive but suggest non-response bias is the main source of the inconsistent findings. Conclusions. The results caution against overconfidence in drawing conclusions from RCTs and highlight the need for great care to be taken in data collection and analysis. Particularly, given the modest size of impacts expected in most RCTs, small discrepancies in data sources can alter the results. Survey data remain important as a source of information on outcomes not recorded in administrative data. However, linking survey and administrative data is strongly recommended whenever possible

Prognosis and longitudinal changes of physical activity in idiopathic pulmonary fibrosis

Background: Physical activity (PA) is associated with disease severity in idiopathic pulmonary fibrosis (IPF), but longitudinal studies evaluating its prognostic value and changes over time are lacking. Methods: We measured PA (steps per day, SPD) in a cohort of 46 IPF-patients (mean age, 67 years; mean FVC, 76.1%pred.) by accelerometry at baseline, recorded survival status during 3 years follow-up and repeated measurements in survivors. We compared the prognostic value of PA to established mortality predictors including lung function (FVC, DLCO) and 6-min walking-distance (6MWD). Results: During follow-up (median 34 months) 20 patients (43%) died. SPD and FVC best identified non-survivors (AUROC-curve 0.79, p < 0.01). After adjustment for confounders (sex, age, therapy), a standardized increase (i.e. one SD) in SPD, FVC%pred. or DLCO%pred. was associated with a more than halved risk of death (HR < 0.50; p < 0.01). Compared to baseline, SPD, FVC, and 6MWD annually declined in survivors by 973 SPD, 130 ml and 9 m, resulting in relative declines of 48.3% (p < 0.001), 13.3% (p < 0.001) and 7.8% (p = 0.055), respectively. Conclusion: While PA predicts mortality of IPF patients similar to established functional measures, longitudinal decline of PA seems to be disproportionally large. Our data suggest that the clinical impact of disease progression could be underestimated by established functional measures

Trapped ions in optical lattices for probing oscillator chain models

We show that a chain of trapped ions embedded in microtraps generated by an optical lattice can be used to study oscillator models related to dry friction and energy transport. Numerical calculations with realistic experimental parameters demonstrate that both static and dynamic properties of the ion chain change significantly as the optical lattice power is varied. Finally, we lay out an experimental scheme to use the spin degree of freedom to probe the phase space structure and quantum critical behavior of the ion chain

Coherence of qubits based on single Ca+^+ ions

Two-level ionic systems, where quantum information is encoded in long lived states (qubits), are discussed extensively for quantum information processing. We present a collection of measurements which characterize the stability of a qubit based on the $S_{1/2}$--$D_{5/2}$ transition of single $^{40}$Ca$^+$ ions in a linear Paul trap. We find coherence times of $\simeq$1 ms, discuss the main technical limitations and outline possible improvements.Comment: Proceedings of "Trapped charged particles and fundamental interactions" submitted to Journal of Physics B (IoP