Quantum Sensing Using Cold Atoms and Molecules for Nuclear and Particle Physics

Abstract: Technologies for manipulating single atoms and molecules have advanced drastically in the past decades. Due to their excellent controllability of internal states, atoms and molecules serves as one of the ideal platforms as quantum systems. One major research direction in atomic systems is the precise determination of energy differences between two energy levels in atoms. This field, known as precision measurement, is symbolized by the remarkable fractional uncertainty of $10^{-18}$ or lower achieved in the state-of-the-art atomic clocks. Two-level systems in atoms are sensitive to various external fields and can therefore be function as quantum sensors. The effect of these fields manifests as energy shifts in the two-level system. Traditionally, such shifts are induced by electric or magnetic fields, as recognized even before the advent of the precision spectroscopy with lasers. However, with high-precision measurements, energy shifts can also be caused by hypothetical fields weakly coupled to ordinary matter, or by small effects mediated by massive particles, which are conventionally dealt with in the field of nuclear and particle physics. In most cases, the atomic systems as quantum sensors have not been sensitive enough to detect such effects. Instead, experiments searching for these interactions have placed constraints on coupling constants, except in a few cases where effects are predicted by the Standard Model of particle physics. Nonetheless, measurements and searches for these effects in atomic systems have led to the emergence of a new field of physics. In some cases, they open new parameter spaces to explore in conventionally investigated topics, e.g., dark matter, fifth force, CP-violation, and other physics beyond the Standard Model.