Ultra-light Dark Matter Searches with Atom Interferometers
Lead Research Organisation:
King's College London
Department Name: Physics
Abstract
Ultra-light dark matter consists of a class of light bosonic candidates that can be treated as classical waves owing to their large phase space density. Such dark matter candidates can cause extremely small time-dependent effects in matter. These fluctuations, which oscillate at a frequency set by the dark matter mass and have amplitude determined by the local dark matter density, could be detected using quantum sensors. This report reviews some basics of ULDM and introduces the salient points of ULDM detection with atom interferometers, one of the best examples of a large scale experiment employing quantum sensors. We present preliminary studies of refined searches of scalar ULDM at compact atom interferometers like the 10m AION experiment. Subsequently, we present detailed calculations of a DM-induced signal that could be used in atom interferometry experiments to disentangle a DM signal from potential backgrounds or other non-DM physics signals.
Organisations
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| ST/T506199/1 | 01/10/2019 | 30/09/2023 | |||
| 2282160 | Studentship | ST/T506199/1 | 01/10/2019 | 31/07/2023 | Leonardo Badurina |
| Description | Despite overwhelming astrophysical and cosmological evidence for its existence through gravitational interactions, dark matter (DM) has yet to be understood at a fundamental level. Assuming that a single species saturates the inferred DM energy density, the DM could range from particles as light as 1e-22 eV to asteroid-mass primordial black holes. Until recently, the possibility of charting the strikingly diverse and vast phenomenological landscape of DM models beyond conventional GeV-mass candidates seemed like a remote possibility. Now, thanks to extraordinary advancements in a wealth of cutting-edge technologies with ever-increasing sensitivity to minute effects, it is expected that large regions of DM model space will be within the reach of the next generation of DM direct detection experiments. Following this research philosophy, in this project I explored the potential of atom interferometers as novel dark matter detectors, arguing that these large-scale quantum sensors, which consist of long-lived spatially delocalised quantum superpositions of atom clouds, could shed light on DM model space in the ultralight (i.e. ~1e-20 eV to 1e-15 eV) and light (~10 eV to 1 MeV) mass ranges. We first showed how two spatially-separated atom interferometers that are referenced by the same laser sources (i.e. an atom gradiometer) can probe linearly-coupled ultralight scalar dark matter through the oscillation of optical transition frequencies. In particular, we generalised the treatment of the time-dependent phase shift induced by a scalar ULDM candidate for vertical atom gradiometers of any length and found correction factors that especially impact the ULDM signal in short-baseline gradiometer configurations. Using these results, we refined the sensitivity estimates in the limit where shot noise dominates for AION-10, a compact 10 m gradiometer that will be operated in Oxford, and discussed optimal experimental parameters that enhance the reach of searches for linearly-coupled scalar ULDM. We will also discussed the DM mass range that can be probed by these experiments. Specifically, we will show how high-frequency aliasing could extend the DM range by several orders of magnitude beyond the Nyquist frequency associated with the experiment's sampling time, by making use of the features associated with the expected DM speed distribution, which would be imprinted onto the DM signal. We also showed how the reach of long-baseline experiments in the sub-Hz regime is limited by gravity gradient noise (GGN), which arises as a result of mass fluctuations around the experiment. In particular, we modeled the GGN as surface Rayleigh waves and constructed a likelihood-based analysis that consistently folds GGN into the sensitivity estimates of vertical atom gradiometers in the frequency window between 1 mHz and 1 Hz. We showed that in certain geological settings GGN can be significantly mitigated when operating a multi-gradiometer configuration, which consists of three or more atom interferometers in the same baseline. Finally, we argued that atom interferometers can be used to search for particle-like DM in the sub-MeV range through phase-shifts and loss of contrast effects arising from DM-atom collisions. In particular, we first focused on DM-nucleon spin-independent interactions giving rise to collisional decoherence, and we showed how precise velocity selection of atoms through atom-light interactions largely limits an experiment's sensitivity reach. Then, we showed how scattering in the forward regime can be used to set competitive bounds in the sub-keV mass range. |
| Exploitation Route | Through this work, we have paved the way for a systematic study of different atom interferometer configurations that maximise the science potential of DM searches using this innovative large-scale quantum technology. |
| Sectors | Other |