RESUMO
This corrects the article DOI: 10.1103/PhysRevLett.123.033201.
RESUMO
We describe an optical atomic clock based on quantum-logic spectroscopy of the ^{1}S_{0}â^{3}P_{0} transition in ^{27}Al^{+} with a systematic uncertainty of 9.4×10^{-19} and a frequency stability of 1.2×10^{-15}/sqrt[τ]. A ^{25}Mg^{+} ion is simultaneously trapped with the ^{27}Al^{+} ion and used for sympathetic cooling and state readout. Improvements in a new trap have led to reduced secular motion heating, compared to previous ^{27}Al^{+} clocks, enabling clock operation with ion secular motion near the three-dimensional ground state. Operating the clock with a lower trap drive frequency has reduced excess micromotion compared to previous ^{27}Al^{+} clocks. Both of these improvements have led to a reduced time-dilation shift uncertainty. Other systematic uncertainties including those due to blackbody radiation and the second-order Zeeman effect have also been reduced.
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We observe matter wave interference of a single cesium atom in free fall. The interferometer is an absolute sensor of acceleration and we show that this technique is sensitive to forces at the level of 3.2×10(-27) N with a spatial resolution at the micron scale. We observe the build up of the interference pattern one atom at a time in a free-space interferometer where the mean path separation extends far beyond the coherence length of the atom. Using the coherence length of the atom wave packet as a metric, we directly probe the velocity distribution and measure the temperature of a single atom in free fall.
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We describe a framework for calculating the frequency shift and uncertainty of trapped-ion optical atomic clocks caused by background-gas collisions, and apply this framework to an 27Al+ clock to enable a total fractional systematic uncertainty below 10-18. For this clock, with 38(19) nPa of room-temperature H2 background gas, we find that collisional heating generates a non-thermal distribution of motional states with a mean time-dilation shift of order 10-16 at the end of a 150 ms probe, which is not detected by sideband thermometry energy measurements. However, the contribution of collisional heating to the spectroscopy signal is highly suppressed and we calculate the BGC shift to be -0.6(2.4) × 10-19, where the shift is due to collisional heating time dilation and the uncertainty is dominated by the worst case ±π/2 bound used for collisional phase shift of the 27Al+ superposition state. We experimentally validate the framework and determine the background-gas pressure in situ using measurements of the rate of collisions that cause reordering of mixed-species ion pairs.