Gravitational decoherence and recoherence of a composite particle: the interplay between gravitons and a classical Newtonian potential

Abstract

The fact that gravitational environments cannot be shielded (since gravity is universal) makes them of great theoretical interest to decoherence mechanisms and to the quantum-to-classical transition. While past results seemed to indicate that graviton-induced decoherence of spatial superpositions happens only for macroscopic systems, recently it was shown that this mechanism can be enhanced through the system's own dynamical internal structure. In this work, we extend this analysis by including the interaction with a classical Newtonian potential. We show that, although the graviton bath alone dominates the mechanism for short times compared to a timescale established by the size of the quantum spatial superposition, the interplay between the gravitons and the internal degrees of freedom of the system renders decoherence inevitable in the long-time limit, even for microscopic masses. We also show that this mechanism is slightly slowed down by the interplay with the classical Newtonian potential, which, for systems without dynamical internal degrees of freedom, can even lead to recoherence, at least in principle.

Figures (6)

• Figure 1: Two test masses $M$ and $m$, with $M\gg m$, and their geodesic deviation in Fermi normal coordinates, represented by the vector $\boldsymbol{\xi}$. The mass $m$ is also described by internal degrees of freedom, represented by the curly red lines.
• Figure 2: The two test masses $M$ and $m$ are in the vicinity of a much bigger and much more massive spherical mass $M_N$, with radius $R_N$, located at $\vb{R}\simeq R_N\vu{e}_3$ with respect to the mass $M$.
• Figure 3: Different contributions for the decoherence function considering the gravitons to be initially in the vacuum state.
• Figure 4: Different contributions for the decoherence function considering the gravitons to be initially in the thermal state.
• Figure 5: Different contributions for the decoherence function considering the gravitons to be initially in the coherent state.