Differential atom interferometry and velocity selection using the clock transition of strontium atoms for AION

The technology developed in this programme will enhance atom interferometry in both the Atom Interferometry Observatory Network (AION) and MAGIS-100 projects by developing and implementing clock-laser technology and test of the methodology for very long baseline instruments. The strong scientific motivation for developing a new generation of quantum sensors stems from detailed theoretical work that shows how these instruments will push searches for certain types of dark matter beyond current boundaries and pioneer a new approach to the detection of gravity waves in a different range of frequency from the existing experiments LIGO and Virgo (thus complementing existing approaches). The long-baseline atom interferometers around the world will be networked, and there are many possible synergies through joint observations. Although gravity-wave detection on Earth provides a wealth of new information, much higher sensitivity can be achieved in space and future projects such as the Atomic Experiment for Dark Matter and Gravity Exploration in Space (AEDGE), are already being discussed.
The AION instrument combines the advantages of state-of-the-art optical clocks based on Sr atoms with atom interferometry. Two clouds of atoms will be prepared at different heights along a long vertical vacuum pipe, and both clouds will be launched so that they travel upwards before coming to rest and falling back down under gravity. Such 'atomic fountains' allow a long measurement time but atoms must be cooled to temperatures less than 1 nanokelvin otherwise they spread out too much before falling back through the detection region. A vertical laser beam runs through both clouds of atoms, at different heights, so that there is common-mode rejection of noise by differential measurement.

Some aspects of the required technology are being developed. In this proposal, we shall develop the narrow bandwidth (few Hz) laser systems required for an interferometer using the narrowest single-photon transition in atomic strontium; the clock transition at (698nm) which is 1000 times narrower than the transition (at 689nm) originally planned for the initial demonstrator of differential interferometry. This electronic and optical technology will be developed as reliable modules for future deployment at the site of large baseline instruments. This represents an important stepping stone towards the AION-10 device. In addition, the narrowness of the clock transition allows extremely precise velocity selection of atoms from a distribution as required for high-contrast fringes from a long interferometer sequences. Furthermore this allows rapid interleaving of interferometry sequences by the sequential selection of different velocity classes from a single transported atom cloud, without repeating the laser cooling and transport processes. This work will be supported by comprehensive simulations using efficient numerical techniques being developed in AION.
The AION programme exploits synergies between STFC and EPSRC science and the strategic areas of quantum technology, computing and metrology. It brings together a consortium of experimental and theoretical particle physicists, as well as astrophysicists and instrumentation experts, quantum information scientists, experts in Sr based atomic-clock research, and atomic physicists drawn from the STFC and EPSRC communities. The quantum technologies of AION have potential applications in such varied areas as navigation and oil drilling. We will work closely with the UK Quantum Technologies Hub in sensors and metrology to develop these technologies and bring them to market.