Quantum clock interferometry and violations of the equivalence principle*

Atom interferometers and atomic cocks are both based on the interference of different degrees of freedom: the atom's motion or their internal state. A combination of the two gives rise to quantum clock interferometry. While clocks are naturally susceptible to violations of the gravitational redshift, atom interferometers constitute a sensor for violations of the universality of free fall. However, quantum clock interferometry has been shown to only test the redshift in specific configurations. In our contribution, we explore the origin of a sensitivity to gravitational redshift violations in both interference experiments and characterize their underlying limitations: The action of trapping potential leads to such a sensitivity of atomic clocks. Due to the linear nature of momentum kicks, Bragg-based interferometers on the other hand are insensitive. However, modified light-pulse configurations can mimic such tests. Internal transitions during the interferometer sequence provide an additional lever to generate redshift-sensitive quantum sensors.