Atom interferometry with Bose-Einstein condensates
Naceur Gaaloul
QUEST, Institute of Quantum Optics - Leibniz University, Hanover, Germany
A central goal of modern physics is to test fundamental principles of nature with ever increasing precision. Atomic quantum sensors are a key-technology for the ultra-precise monitoring of accelerations and rotations. These sensors evolved to a new kind of optics based on matter waves rather than light waves. Matter wave optics is still a young, but rapidly progressing science which recently generated sensational Nobel-prize awarded inventions. It allows for example to compare the free fall of two atomic clouds of different species, thus testing the weak equivalence principle in the quantum domain. In a weightless environment the precision of such sensors can be considerably increased by increasing the free propagation time of the atoms in the interferometer.
In this talk, we present three projects where atom interferometers are realized in compact and autonomous apparatus suited to operate in µ-gravity environments. At the heart of the three experiments, atom chips are the key ingredient that allows for an unprecedented miniaturization of BEC machines. Atom chips have proven to be excellent sources for the fast production of ultra-cold gases due to their outstanding performance in fast evaporative cooling. The first generation of experiments consists in a Bragg-type interferometer on a chip operated with 87Rb atoms in the thermal or Bose-Einstein condensed regime [1]. With the help of delta-kick cooling [2,3], implemented via the atom chip, we can further slow the expansion of the atoms down. With this toolbox we could extend the observation of a BEC of only 104 atoms up to two seconds. Benefiting from the extended free fall in the ZARM drop-tower in Bremen, we could operate an asymmetric Mach-Zehnder interferometer over hundreds of milliseconds (over 700 ms) to study the coherence and to analyze the delta-kick cooling with the help of the observed interference fringes [4]. A novel generation of atom chips allows improving the performance of these flexible devices. We have developed a novel loading scheme that allowed us to produce Bose-Einstein condensates of a few 105 87Rb atoms every two seconds. The apparatus is also designed to be operated in microgravity at the drop tower in Bremen, where even higher numbers of atoms can be achieved in the absence of any gravitational sag. Using the drop tower’s catapult mode, our setup will perform atom interferometry during nine seconds in free fall.
As a next step towards the transfer of such a system in space, either on board the ISS or as a dedicated satellite mission, a chip-based atom interferometer operating on a sounding rocket is currently being built. The success of this project would mark a major advancement towards a precise measurement of the equivalence principle with a space-born atom interferometer.
References:
[1] T. van Zoest et al., Science 328, 1540 (2010).
[2] S. Chu, J. E. Bjorkholm, A. Ashkin, J. P. Gordon, and L.W. Hollberg, Opt. Lett. 11, 73 (1986).
[3] H. Amman and N. Christensen, Phys. Rev. Lett. 78, 2088 (1997).
[4] H. Müntinga et al., Phys. Rev. Lett. 110, 093602 (2013).