PRIMUS - precision interferometry with matter waves in zero gravity

(Präzisionsinterferometrie mit Materiewellen unter Schwerelosigkeit)

Motivation and Objectives

Atom interferometers constitute the matter wave analogon to optical interferometers. They often use ultra-cold atoms as a source of coherent matter waves and laser pulses to further control and manipulate the atoms. Matter wave interferometers have been used for extremely sensitive measurements of inertial forces such as accelerations or rotations in many laboratory experiments already. They have also been used in precision experiments of fundamental physics that have determined e.g. the local gravitational acceleration g, Newton´s gravitational constant G or the fine structure constant.

The general approach to further enhance their sensitivity is to increase the area enclosed between the interferometer paths. Since high-precision measurements do not permit the use of levitating or guiding potentials they also require freely falling matter waves, and thus the enclosed area is often limited by the available free fall time. This makes zero gravity an ideal environment to push matter wave interferometry to much increased sensitivity. The PRIMUS project aims to demonstrate this potential using the extended free fall time of several seconds available in the drop tower.

To that end PRIMUS builds on the technology developments of the QUANTUS project. The ultimate goal is to realize a dual species matter wave interferometer that allows to compare the free fall of two different species of atoms. Such a comparison constitutes a test of the so called Universality of Free Fall, also known as the Weak Equivalence Principle, which is a fundamental postulate underlying General Relativity.

The PRIMUS project will ultimately serve as a pathfinder project for a future space based precision test of the UFF. Due to the limited number of measurements per day permitted by the drop tower, it will be restricted to a relative sensitivity not competitive with the best earth-bound tests so far. Rather the experiment shall provide the opportunity to study the systematic effects and limitations inherent to long matter wave evolution times in a microgravity environment.

Also, a test of the UFF using matter waves could also provide an interesting new complement to these existing already very sensitive tests with macroscopic test masses. They operate with quantum degenerate ensembles and have test masses freely falling in a quantum superposition of momentum states, which provides a window to probe for violations different from classical tests.

Metrology tools

The dual interferometer will operate with beam splitter lasers at different wavelengths of 780 nm and 767 nm. A common frequency reference will be established by means of a femtosecond frequency comb. To that end we have acquired a drop tower compatible frequency comb from Menlo Systems. As a further part of the PRIMUS project we also set up a highly stable optical frequency reference, based on a high finesse cavity.

Funding

The PRIMUS project is supported by the German Space agency DLR with funds provided by the Federal Ministry of economics and energy (BMWi) under grant number 50WM1142.

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