Atom gravimeters and gravitational redshift

Arising from: H. Müller, A. Peters & S. Chu 463, 926–929 (2010); Müller & Chu replyIn ref. 1 the authors present a re-interpretation of atom interferometry experiments published a decade ago. They now consider the atom interferometry experiments as a measurement of the gravitational redshift on the quantum clock operating at the Compton frequency ωC = mc2/ ≈ 2π × 3.0 × 1025 Hz, where m is the caesium (Cs) atom rest mass. They then argue that this redshift measurement compares favourably with existing as well as projected clock tests. Here we show that this interpretation is incorrect.