Tim Rosenband Abstract

Till Rosenband
NIST - Boulder

" Coherent and incoherent comparisons of Al+ quantum-logic clocks"

Abstract: The 1S0-3P0 clock-resonance frequencies of two Al+ ions are compared by two methods. In the first, two separate optical clocks are constructed with accuracies of 2.3 × 10^−17 and 8.6 × 10^−18. The ions in these clocks share no quantum coherence, and their resonance frequencies are compared with a statistical uncertainty of 7.0×10−18 after 165,000 s of averaging (2.8 × 10−15 s/τ instability). Stability is limited by laser decoherence, which constrains the clocks’ probe-times to 150 ms. The clocks are applied to measure a height change of 37 ± 15 cm via the gravitational red-shift. In the second method, two Al+ ions in one trap are excited by a single laser beam, and clock-state superpositions evolve coherently for up to 5 s. Small frequency differences are measured with a fractional stability of 3.7 × 10^−16 s/τ , and 1.4 × 10^−16 s/τ may be attainable. The technique does not improve time-keeping stability, but speeds-up the measurement of small frequency-shifting effects by several orders of magnitude. Quality factors of 6.7 × 10^15 are observed. Recent developments allow state-detection without photon scattering, making the quantum-logic spectroscopy technique of the Al+ applicable to a wider variety of ions.