Gravitational Waves (GWs) were observed for the first time in 2015, one century after Einstein predicted their existence. There is now growing interest to extend the detection bandwidth to low frequency. The scientific potential of multi-frequency GW astronomy is enormous as it would enable to obtain a more complete picture of cosmic events and mechanisms. This is a unique and entirely new opportunity for the future of astronomy, the success of which depends upon the decisions being made on existing and new infrastructures. The prospect of combining observations from the future space-based instrument LISA together with third generation ground based detectors will open the way towards multi-band GW astronomy, but will leave the infrasound (0.1 Hz to 10 Hz) band uncovered. GW detectors based on matter wave interferometry promise to fill such a sensitivity gap. We propose the European Laboratory for Gravitation and Atom-interferometric Research (ELGAR), an underground infrastructure based on the latest progress in atomic physics, to study space-time and gravitation with the primary goal of detecting GWs in the infrasound band. ELGAR will directly inherit from large research facilities now being built in Europe for the study of large scale atom interferometry and will drive new pan-European synergies from top research centers developing quantum sensors. ELGAR will measure GW radiation in the infrasound band with a peak strain sensitivity of 3.3×10-22/√Hz at 1.7 Hz. The antenna will have an impact on diverse fundamental and applied research fields beyond GW astronomy, including gravitation, general relativity, and geology.
In matterwave interferometry, atoms are put into a superposition of two different momentum states. They are then made to travel in two different paths (yes, during part of the interferometry sequence every individual atom is at two distinct places at the same time) before being recombined. Depending on the phase accumulated in the two different paths the atoms end up in two different distinguishable states. The accumulated phase is extremely sensitive to minute entry differences between the two paths travelled, making ultra-sensitive measurements of gravitation, acceleration, or rotation possible. Atoms, however, have the tendency to fall under the influence of earth’s gravitation. This means, that in order to measure at the highest precision, the apparatus has to be very large (some reaching tens or even one hundred of meters in height). The ideal solution would be to contain the atoms in waveguides (much like the optical fibres in optical gyroscopes). Until recently, this has not been possible, because even the smallest roughness in these guides destroys the coherence of the travelling matterwaves.
Our recent contributions
In a recent paper (published in Nature), we have demonstrated for the first time coherent guiding of matterwaves over macroscopic distances. This will make possible, for the first time ever, to perform guided matter-wave spectroscopy over macroscopic distances and in non-trivial geometries. This will greatly enhance the interaction time of the atoms and thus the sensitivity of matterwave interferometers.
The new PhD student will work together with our current Giannis Drougakis on the first guided matterwave interferometry. En route to this he/she will explore the limits on the roughness of waveguides, thus providing invaluable input to the design of any guided matterwave interferometer. The student(s) will work under the supervision of Wolf von Klitzing and Dimitris Papazoglou and be enrolled in the University of Crete
Vinay has joined us in March 2020 after some difficulty in bringing him from India to Greece (due to COVID 19 restrictions). He will work on Cavity enhanced Microscopy (CEMIC). He received his Master of Science in Physical Sciences from the Indian Institute of Science Education and Research, Kolkata (India) in Jun 2019.
Our paper AEDGE: Atomic Experiment for Dark Matter and Gravity Exploration in Space has just been accepted in EJP!
We propose in this White Paper a concept for a space experiment using cold atoms to search for ultra-light dark matter, and to detect gravitational waves in the frequency range between the most sensitive ranges of LISA and the terrestrial LIGO/Virgo/KAGRA/INDIGO experiments. This interdisciplinary experiment, called Atomic Experiment for Dark Matter and Gravity Exploration (AEDGE), will also complement other planned searches for dark matter, and exploit synergies with other gravitational wave detectors. We give examples of the extended range of sensitivity to ultra-light dark matter offered by AEDGE, and how its gravitational-wave measurements could explore the assembly of super-massive black holes, first-order phase transitions in the early universe and cosmic strings. AEDGE will be based upon technologies now being developed for terrestrial experiments using cold atoms, and will benefit from the space experience obtained with, e.g., LISA and cold atom experiments in microgravity.
Our ELGAR proposal to build a ground-based detector for Gravitational Waves has been featured in PhysicsWorld.com: “Physicists from across Europe have revealed plans for a huge underground gravitational-wave observatory that, if funded, could be operational by the mid-2030s. The European Laboratory for Gravitational and Atom-interferometric Research (ELGAR) could be located in either France or Italy and would cost around €200m to build. Those involved in the project have now applied for European funding to carry out a detailed design and costing for the facility.”
We have just published on https://arxiv.org/abs/1908.11785 a white paper on the scientific motivation for future space tests of the equivalence principle, to explore some of the big questions in physics (e.g. Equivalence Principle, Dark Matter and Gravitational Waves) using matter-wave interferometry, especially in space.
We discuss two possible mission scenarios, one based on quantum technologies, the other on electrostatic accelerometers, that could reach that goal are briefly discussed. We propose experiments to test the universality of free fall, at the level of 10−17 or better.