Probing Gravitational Cat States in Canonical Quantum Theory vs Objective Collapse Theories

Abstract: Using as a testbed the recently proposed "gravcat" experimental scheme in [1], we compare the properties of gravitational cat states in three descriptions: (1) canonical quantum theory (CQT) combined with the Newtonian limit of GR, (2) objective collapse theories (OCTs) extended to the regime of semiclassical Newtonian gravity, and (3) OCTs extended to incorporate quantized Newtonian gravity. For the CQT approach, we follow the treatment of Hu and Anastopoulos in [2]. For the OCTs, we consider the GRW, CSL, DP, and Karolyhazy theories, based on the semiclassical approaches of Derakhshani [3] and Tilloy-Diosi [4], respectively, and we consider the most straightforward extension of the aforementioned OCTs to the regime of quantized Newtonian gravity. We show that the gravitational cat scheme can, in principle, experimentally discriminate the quantum jumps in gravitational cat states predicted by the CQT approach and the quantized-gravity OCTs (which we show make effectively the same predictions as each other), from the predictions of the semiclassical-gravitational OCTs. We also show that the GRW and Karolyhazy versions of semiclassical gravity (based on Derakhshani's approach) make distinctly different predictions from the CSL and DP versions of semiclassical gravity (based either on Derakhshani's approach or the Tilloy-Diosi approach).