Quantum optical sensor tested in space
Bose-Einstein condensate based on rubidium atoms has been created on board of a sounding rocket
For 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 environments 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 conditions of microgravity, very long and precise measurements can be carried out to determine whether different types of atoms actually “fall equally fast” in the gravitational field of the Earth.
As part of a national consortium, Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik (FBH) and Humboldt-Universität 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-Kelvin 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 experiencing huge mechanical and thermal stress caused by the rocket launch. This groundbreaking 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 gravitation with the other fundamental interactions (strong, weak, and electro-magnetic force) in a single consistent theory.
Laser modules for space applications
For this mission, the FBH has developed hybrid micro-integrated semiconductor laser modules that are suitable for application in space. These laser modules, together with optical and spectroscopic units provided by third partners, have been integrated and qualified by HU to provide the laser subsystem of the scientific payload. The results of this mission coordinated by Leibniz Universität Hannover do not only prove that quantum optical experiments with ultra-cold atoms are possible in space, but also give FBH and HU the opportunity to test their miniaturized laser system technology under real operating conditions.
The MAIUS mission is supported by the German Space Agency (DLR) with funds provided by the Federal Ministry of Economic Affairs and Energy and tests all key technologies of a space-borne quantum optical sensor on a sounding rocket: vacuum chamber, laser system, electronics, and software. The compact and robust diode laser system for laser cooling and atom interferometry with ultra-cold rubidium atoms has been developed under the leadership of the Optical Metrology 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-oscillator 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.