LASER 2017

••• 11 ••• Innovationen F or the first time ever, a cloud of ultra-cold atoms has been successfully created in space on board of a sounding rocket. The MAIUS mission demonstrates that quantum optical sensors can be operated even in harsh environ- ments like space – a prerequisite for finding answers to challenging questions of fundamental physics. According to Albert Einstein’s Equivalence Principle, all bodies are accelerated at the same rate by the Earth’s gravity, regardless of their properties. Under condi- tions of microgravity, very long and precise measurements can be carried out to determine whether different types of atoms actually “fall equally fast” in the gravita- tional field of the Earth. As part of a national consortium, Ferdinand-Braun-Institut, Leibniz- Institut für Höchstfrequenztech- nik (FBH) and Humboldt-Univer- sität zu Berlin (HU) now made a historical step towards testing the Equivalence Principle in the microcosm of quantum objects. In the MAIUS mission launched on 23 January 2017 a cloud of nano-Kel- vin cold rubidium atoms has been generated in space for the first time ever. This cloud was cooled down with laser light and radio frequency electrical fields so that the atoms finally formed a single quantum object, a Bose-Einstein condensate (BEC). Today’s quantum optical sensor is as small as a freezer and remains fully operational even after ex- periencing huge mechanical and thermal stress caused by the rocket launch. This groundbreak- ing mission is a pathfinder for applications of quantum sensors in space. In the future, scientists expect to use quantum sensor technology to cope with one of the biggest challenges of modern physics: the unification of gravita- tion with the other fundamental interactions (strong, weak, and electro-magnetic force) in a single consistent theory. Lasermodules for space applications For this mission, the FBH has de- veloped hybrid micro-integrated semiconductor laser modules that are suitable for application in space. These laser modules, together with optical and spec- troscopic units provided by third partners, have been integrated and qualified by HU to provide the laser subsystem of the scien- tific payload. The results of this mission coordinated by Leibniz Universität Hannover do not only prove that quantum optical ex- periments with ultra-cold atoms are possible in space, but also give FBH and HU the opportunity to test their miniaturized laser sys- tem technology under real oper- ating conditions. The MAIUS mission is supported by the German Space Agency (DLR) with funds provided by the Federal Ministry of Economic Af- fairs and Energy and tests all key technologies of a space-borne quantum optical sensor on a sounding rocket: vacuum cham- ber, laser system, electronics, and software. The compact and ro- bust diode laser system for laser cooling and atom interferometry with ultra-cold rubidium atoms has been developed under the leadership of the Optical Metrol- ogy Group at HU. This system is required for the operation of the MAIUS experiment and consists of four diode laser modules that have been developed by FBH as hybrid-integrated master-oscilla- tor power-amplifier (MOPA) laser modules. The master laser is a monolithic distributed feedback (DFB) laser which is frequency- stabilized to the frequency of an optical transition in rubidium. Quantum optical sensor tested in space Bose-Einstein condensate based on rubidium atoms has been created on board of a sounding rocket Hybrid-integrated master-oscillator power-amplifier (MOPA) laser module for rubidium precision spectroscopy in space Photo: FBH / schurian.com