The talk will consist of three parts.
First, I will address the challenge posed by gravity gradients in many high-precision measurements based on atom interferometry, such as testing the universality of free fall (UFF) or measuring the gravitational constant G. A very effective method for compensating the effects of gravity gradients and overcoming such difficulties will be presented. This technique, which has already been successfully employed in tests of UFF, can also be exploited to perform measurements of G that are competitive or even outperform the best measurements relying on macroscopic test masses.
In the second part, I will explain how aspects of optical atomic clocks and atom interferometry can be combined to measure relativistic effects with matter-wave interferometers. In particular, I will show how to perform quantum-clock interferometry experiments where single clocks are prepared in a delocalized superposition experiencing differences in gravitational time dilation that are revealed in the interference signal when the two components are recombined. Additionally, a proposal for using atom interferometers as freely falling clocks for time-dilation measurements will also be presented.
After briefly reviewing state-of-the-art ground-based facilities for long-baseline atom interferometry, in the third part I will give an overview of experiments with ultracold atoms in space and their application to atom interferometric measurements. Finally, I will present the ACES mission, involving a highly accurate clock on the ISS based on cold Cs atoms. This ESA mission, launched last year, is the first experiment in space performing high-precision measurements with cold atoms (and quantum sensors in general). Among other applications, it will enable an improvement on previous gravitational-redshift measurements by more than an order of magnitude.