Falling through masses in superposition: quantum reference frames for indefinite metrics

Anne-Catherine de la Hamette, 2, ∗ Viktoria Kabel, 2, ∗ Esteban Castro-Ruiz, and Časlav Brukner 2 Vienna Center for Quantum Science and Technology (VCQ), Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria Institute for Quantum Optics and Quantum Information (IQOQI), Austrian Academy of Sciences, Boltzmanngasse 3, A-1090 Vienna, Austria Institute for Theoretical Physics, ETH Zurich, Switzerland (Dated: December 23, 2021)