Taking an X-ray image of Earth's Gravity

Sensing the difference of gravity in 1mm altitude change on Earth using an SXWG and 45Sc nuclear clock transition.

We collaborate with Prof. Sven Ahrens from Shanghai Normal University to design a novel structured X-ray waveguide (SXWG) capable of detecting gravitational differences caused by height changes as small as 1 millimeter on Earth. Based on an analogy between the propagation of X-rays through a waveguide and the behavior of quantum particles, we designed the SXWG under the guidance of the optical Schrödinger equation, sandwiching a periodic structure of 45Sc scandium-carbon interleaved layers between two platinum-coated layers. The 45Sc isotope has an extremely narrow nuclear clock transition, with a natural linewidth of about 2 Hz and a transition energy of approximately 12.4 keV. Such a narrow linewidth can be used to detect tiny interaction differences between 45Sc and resonant X-rays under a 1-millimeter height change. Thus, altering the height of the SXWG will change the coupling strength between two X-ray waveguide modes due to the gravitational redshift effect. Our calculations show that the X-ray output intensity distribution of the SXWG is affected by height changes. Therefore, by examining the changes in the light pattern, the height difference between the SXWG and the X-ray source can be determined. Using other isotopes, such as 229Th or 109Ag, can even achieve sensitivity at the micrometer level. Please check our publication [Phys. Rev. Research 7, 013158 (2025)]