Measuring the effect of gravity on antimatter is a longstanding problem in physics that has significant implications for our understanding of the fundamental nature of the universe. Here, we present a technique to measure the gravitational mass of atoms, motivated by a recent measurement of antimatter atoms at CERN [Nature (London) 621, 716 (2023)]. We demonstrate our technique on cold atoms by measuring the fraction of atoms that survive in the trap after gradually softening a quadrupole magnetic trap in a gravitational potential. We compare our measurements with a Monte Carlo simulation to extract the value of the gravitational acceleration. The difference between the accepted value for
g, the local acceleration due to gravity, and the measured value is $(\ensuremath{-}1.9\ifmmode\pm\else\textpm\fi{}{12}^{\text{stat}}\ifmmode\pm\else\textpm\fi{}{40}^{\text{syst}})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}g$. We demonstrate the importance of various design parameters in the experiment setup and estimate their contribution to the achievable accuracy in future experiments. Our method demonstrates simplicity, precision, and reliability, facilitating future precision studies of the gravitational force on antimatter. It can also be used to precisely calibrate atom traps based on the known gravitational attraction of ordinary matter to Earth.
Atoms from an otherwise unconfined 87Rb condensate are shown to be suspended against gravity using repeated reflections from a pulsed optical standing wave. Reflection efficiency was optimized using a triple-pulse sequence that, theoretically, provides accuracies better than 99.9%. Experimentally, up to 100 reflections are observed, leading to dynamical suspension for over 100 ms. The velocity sensitivity of the reflections can be used to determine the local gravitational acceleration. Further, a gravitationally sensitive atom interferometer was implemented using the suspended atoms, with packet coherence maintained for a similar time. These techniques could be useful for the precise measurement of gravity when it is impractical to allow atoms to fall freely over a large distance.