Entanglement-enhanced atom interferometry

Interferometers based on ultracold atoms enable absolute measurements of inertial forces with unprecedented precision. However, their resolution is fundamentally limited by quantum fluctuations, and surpassing this limit requires the use of entangled atomic quantum states. In our experiments, entanglement is generated via spin-changing collisions in Bose–Einstein condensates. I will present a characterization of the resulting quantum states with single-particle counting resolution, revealing Hong–Ou–Mandel correlations, genuine multi-particle entanglement, and Heisenberg-limited interferometric sensitivity. We apply these quantum states to demonstrate the operation of an atomic gravimeter that surpasses the quantum limit by −1.7(−0.5+0.4) dB. This demonstration is enabled by Bose–Einstein condensates whose expansion is further reduced through delta-kick collimation. The concept is compatible with state-of-the-art atom interferometers and provides a pathway to enhancing the performance of current and future very-long-baseline atom interferometers.