Quantum Sensors: Novel directional dark matter detectors

Quantum Sensors

Efforts to detect galactic dark matter directly have thus far been primarily focused on candidates such as WIMPs or axions; these are theoretically well motivated candidates that can provide solutions to the missing mass problem in the universe. However, astrophysical and cosmological bounds are satisfied by a vast number of different candidates beyond these, spanning over 30 orders of magnitude in mass; some of the candidates and indicative mass scales are illustrated below. Most of the available parameter space where such candidates may be detected has to-date been largely inaccessible and is yet to be explored. Dark matter detection may come from anywhere and it is important to leave no stone unturned in the quest for discovery.

DM Detection — *Illustation of the broad range of some of the theorised candidates that may constituent the dark matter in the Universe.*

The use of levitated quantum optomechanics as a novel technique is only beginning to be explored as a method to test fundamental physics. Nanospheres, levitated utilising the trapping potential provided by either an optical tweezer or Paul trap setup, coupled with quantum ground state cooling, act as highly sensitive accelerometers. The ability to measure interactions on the scale of atto-Newtons, and the isolation afforded by levitation in vacuum, allows for extremely sensitive measurements of weak forces at both short and long range. At UCL, we have pioneered the world’s first levitated nonsphere quantum sensor experiment designed for direct dark matter detection. Our team has demonstrated the ability to detect and reconstruct momentum transfers from potential dark matter interactions with impeccable precision, marking a major milestone in the use of quantum optomechanics for rare event searches. We are continuing to develop this technique for deployment in searches for very light dark matter, complementing the relatively higher mass searches with LZ and XLZD operating large xenon targets in deep underground laboratories.

Particles and Trap — Left: a) SEM image of silica nanoparticles. b) Illustration of the optically levitated nanoparticle confined in the optical tweezer trapping potential, surrounded by electrodes used to cool the motion of the particle in all three directions. Right: photograph of a levitated nanoparticle held by optical tweezers setup.

Paul Trapped Nanosphere — *Photograph of a linear Paul trap levitated nanoparticle.*

This quantum sensor platform opens exciting possibilities beyond dark matter. Its extreme sensitivity to tiny forces makes it a powerful tool for testing fundamental physics: from probing self-interacting dark matter models to exploring signatures of dark energy, extra dimensions, or deviations from Newtonian gravity. The technology is scalable, cost-effective, and environmentally low impact—ideal for next-generation physics experiments. In addition to superb sensitivity to very light dark matter particles, this technique can provide unique directional information about the signal to discriminate against terrestrial backgrounds and deliver robust evidence for galactic dark matter.

QS detection methods — Cartoon depictions of how UCL's Levitated Nanosphere quantum sensor setup can detect potential rare astrophysical signals. In the steady state, one can look for 'wave-like' signals like axions or dark energy through their harmonic signature on the Power Spectral Density, and one can also detect directional dark matter signals using a cross-correlational approach (i.e. the relative size of nanosphere oscillations in one direction versus another). There are also transient signals that arise from 'kicks' or momentary energy depositions from particle scatters.

The experiment, being developed by the UCL dark matter group in collaboration with colleagues in the AMOPP Group, is located in UCL's low noise Quantum Measurement Laboratory. Our next steps include reducing experimental noise levels to enhance our sensitivity to a wider energy range, refining statistical analyses in order to begin testing dark matter hypotheses. With these further developments, these sensors are expected to deliver world leading sensitivity to uncharted parameter space. In UCL's Quantum Sensor Programme, we will build on our early success, extending the experimental reach of our dark matter group as well as developing novel probes of BSM physics.