Project B01: Entangled neutral atoms for interferometry beyond the standard quantum limit

Introduction

Atom interferometers belong to today’s most precise sensors with broad applications for navigation, geodesy, time keeping as well as fundamental research. Typically, they are operated with uncorrelated particles, resulting in a fundamental limitation of the achievable sensitivity – the standard quantum limit (SQL). While the SQL allows improving the sensitivity by increasing the particle number, we have shown in the second funding period in collaboration with B07 (delocalised states) that quantum density fluctuations place a limit to this improvement, leading to an optimal atom number and a corresponding sensitivity limit, the density quantum limit (DQL). Both sensitivity limits can only be overcome by employing entangled particles as an input for new types of non-classical interferometers. However, up to now, only few proof-of-principle experiments have actually succeeded to exploit entangled sources of atoms for interferometric measurements. In this project, we advance our method from demonstration experiments to a valuable source for a future generation of highest-sensitivity atomic sensors.

Within the third funding period, we will combine these developments. The novel single-particle resolving detection scheme will allow demonstrating a metrological sensitivity close to the Heisenberg limit, which has so far only been reached with a small number of trapped ions or photons. We will further employ squeezed states to scale up the particle number in entanglement-enhanced interferometry and experimentally probe and surpass the DQL as a fundamental sensitivity limit.

The Raman laser system from project A02 will be implemented to extend the investigations towards inertially sensitive interferometers, including gravimetric measurements. The dynamically shapeable potentials enable us to generate multiple BECs and squeeze them simultaneously. This will be exploited for further enhancing the data rate by more than an order of magnitude, allowing for high-precision tomography of many-particle entangled states. The technique will be further employed to spatially resolved interferometry, where the multiple ensembles act as individual probes. This work will be pursued in close collaboration with project B07.

We will further increase the sensitivity of our squeezing-enhanced atom interferometers by the implementation of multi-photon beam splitters. We will apply the Raman laser system to transfer multiple momenta during the beam splitting process in order to achieve larger spatial splittings and a corresponding boost of the sensitivity, while maintaining the squeezing enhancement offered by the atomic source. We will provide further theoretical insight on the dynamics of our spin-1 BECs.