Precision Measurement of Gravity with Cold Atoms in an Optical Lattice and Comparison with a Classical Gravimeter

We report on a precision measurement of gravitational acceleration using ultracold strontium atoms confined in an amplitude-modulated vertical optical lattice. An uncertainty $\Delta g/g\approx {10}^{-7}$ is reached by measuring at the 5th harmonic of the Bloch frequency. The value obtained with this microscopic quantum system is consistent with the one measured with a classical gravimeter. Using lattice modulation to prepare the atomic sample, we also achieve high visibility of Bloch oscillations for $\sim 20\mathrm{s}$. These results can be of relevance for testing gravitational redshift and Newtonian law at micrometer scale.

Figure 1

Experimental setup for the measurement of gravity with ${}^{88}\mathrm{Sr}$ atoms trapped in a vertical optical lattice and the comparison with a classical absolute gravimeter (FG5). AM: amplitude-modulation signal; AOM: acousto-optical modulator; FCC: falling corner cube; ID: interference detector; PD: photodiode; PMF: polarization-maintaining fiber; RCC: reference corner cube.

Figure 2

Spectrum recorded by modulation of the lattice depth at the 5th harmonic of the Bloch frequency for 10.4 s with a modulation depth of 8%. The red line is a fit of experimental data with a sinc function.

Figure 3

Measurements of $g$ using the amplitude-modulation technique. Each experimental point is corrected for the systematic effects presented in Table . The red dashed line represents the weighted mean of the 21 measurements. The blue solid line is the value obtained with the classical absolute FG5 gravimeter.

Figure 4

Long-lived Bloch oscillations for Sr atoms in the vertical lattice under the influence of gravity. Each picture shows one Bloch cycle in successive time-of-flight absorption images giving the momentum distribution at the time of release from the lattice. Displayed are the first (a), the 2900th (b), the 7500th (c), and the 9800th (d) Bloch cycles.