We consider the impact of a weakly coupled environment comprising a light scalar field on the open dynamics of a quantum test mass, resulting in a master equation for the test mass that features corrections to the coherent dynamics, as well as decoherence and momentum diffusion. The light scalar is assumed to couple to matter either through a non-minimal coupling to gravity or, equivalently, through a Higgs portal. Motivated by applications to experiments such as atom interferometry, we assume that the test mass can be initialized, by means of external driving, in a state that is not an eigenstate of the light scalar field-matter system, and we derive the master equation for single-particle matrix elements of the reduced density operator of a toy model. We comment on the possibilities for experimental detection and the related challenges, and highlight possible pathways for further improvements. This derivation of the master equation requires techniques of non-equilibrium quantum field theory, including the Feynman-Vernon influence functional and thermo field dynamics, used to motivate a method of LSZ-like reduction. In order to obtain cutoff-independent results for the test-mass dynamics, we find that it is necessary to use a time-dependent renormalization procedure. Specifically, we show that non-Markovian effects following a quench, namely the violation of time-translational invariance due to finite-time effects, lead to a time-dependent modulation of the usual vacuum counterterms.
Burrage, C., Käding, C., Millington, P., & Minár, J. (2019). Open quantum dynamics induced by light scalar fields. Physical Review D, 100(7), https://doi.org/10.1103/PhysRevD.100.076003