Ancillary Gaussian modes activate the potential to witness non-Markovianity

We study how the number of employed modes impacts the ability to witness non-Markovian evolutions via correlation backflows in continuous-variable quantum dynamics. We first prove the existence of non-Markovian Gaussian evolutions that do not show any revivals in the correlations between the mode evolving through the dynamics and a single ancillary mode. We then demonstrate how this scenario radically changes when two ancillary modes are considered. Indeed, we show that the same evolutions can show correlation backflows along a specific bipartition when three-mode states are employed, and where only one mode is subjected to the evolution. These results can be interpreted as a form of activation phenomenon in non-Markovianity detection and are proven for two types of correlations, entanglement and steering, and two classes of Gaussian evolutions, a classical noise model and the quantum Brownian motion model.

Automated summary

We study the influence of the number of employed modes on the ability to witness non-Markovian evolutions in continuous-variable quantum dynamics. We find that the presence of multiple ancillary modes can cause correlation backflows in non-Markovian Gaussian evolutions, unlike the case with a single ancillary mode. This activation phenomenon occurs when three-mode states are employed, with only one mode undergoing the evolution, and is observed in both entanglement and steering correlations under two different Gaussian evolution models.