Atom interferometers are versatile instruments, working as quantum sensors in the field and probing the laws of physics at the deepest level in the lab. We will discuss two examples, testing the standard model by measuring the fine-structure constant and searching for quantum aspects of the gravitational field, such as superposition and entanglement.
In typical atom interferometers, the freely-falling motion of the atoms limits the free evolution to a few seconds. We will show that atoms trapped in optical lattices allow free evolution times as long as 70 seconds, during which small effects can generate large, measurable phase shifts. We use a system of signal inversions to suppress systematics caused by the trapping potential. This enables measuring the attractive force from a small tungsten mass with a precision that is five times improved over a previous measurement with freely falling atoms. In the future, this may yield insights into the coherence of the gravitational field itself. The long-lasting coherence lends itself well to measuring the dynamic interactions between the atoms and a coherent mechanical system, such as a torsion pendulum. A setup that is intended to take the first step is under construction.
Our measurement of the fine-structure constant uses atoms in free fall. This isolates them strongly from environmental influences and minimizes systematic effects. It is favorable in applications that require long-term stability or absolute accuracy. Minimizing the leading systematic effects requires clean and well characterized laser wavefronts. This is hoped to improve the accuracy beyond current limitations and clarify the issues raised by the current, discrepant, measurements.