Development of Levitated Quantum Optomechanical Sensors for Dark Matter Detection

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There is overwhelming evidence that 85\% of the mass of the universe is made of dark matter. Its effects can be observed on astrophysical and cosmological scales, but yet we do not know what it is. Direct detection is one of the highest priorities in science and its discovery will be of enormous scientific importance, providing perhaps the most important missing piece in our understanding of the universe and of fundamental physics. Astrophysical and cosmological bounds placed on the origin of dark matter can be explained by a very large number of potential candidates that span over 30 orders of magnitude in mass. This complicates experimental efforts to design a specific detector since we do not know which of the many possible interactions to use in its design. As there is no fixed mass or cross section to target in this search, there is now a huge international effort to expand the search and to develop new sensor technologies that can ideally cover large mass ranges with increased sensitivity. An important new direction in this international effort is the use of quantum sensors whose sensitivity is only limited by the laws of quantum mechanics. These are very different technologies to what has been previously used for dark matter searches and they promise to revolutionise discovery. In the research programme, we will utilize one of the newest quantum sensors. These consist of small masses isolated from the environment by levitating them with optical and electric fields in vacuum. These are ultra-cold quantum oscillators, which can be cooled to their ground state, making them exquisitely sensitive to small forces. This importantly includes those due to interactions with dark matter. Remarkably, their mass and thus their coupling to dark matter, can be tuned over nine orders of magnitude, while their frequency of oscillation can be tuned over at least five orders of magnitude.We will develop these sensors as dark matter detectors for at least two types of dark matter in which they appear to be very well suited. This includes extending an initial search for composite dark matter particles by expanding on the mass range by six orders of magnitude and on sensitivity by at least an order of magnitude. We also aim to use these systems to begin the first search for ultralight dark matter using arrays of these sensors and establishing the first limits based on this technology. Lastly, we expect that this work will not only have impact in dark matter physics, but also in other areas of fundamental physics where measurement of weak forces are required.