Non-Markovianity of a two-level system transversally coupled to multiple bosonic reservoirs
Zhong‐Xiao Man, Nguyen Ba An, Yun‐Jie Xia · Physical Review A · 2014
Dynamics of a two-level open system transversally coupled to a single zero-temperature bosonic reservoir may be Markovian or non-Markovian, depending on whether the system-reservoir coupling is weak or strong. In this paper, we show that when the system is simultaneously coupled to $N$ reservoirs its dynamics is always non-Markovian, provided that $N\ensuremath{\ge}{N}_{\mathrm{cr}},$ with ${N}_{\mathrm{cr}}$ a critical number depending on the reservoirs' parameters. Quantitatively, the non-Markovianity $\mathcal{N}$ is shown proportional to the number of contributed reservoirs. We explain our results in terms of the pseudomode theory, finding out that when $N\ensuremath{\ge}{N}_{\mathrm{cr}}$ the pseudomodes of all the reservoirs can always partially return information back to the system, no matter how strong the couplings between the system and each individual reservoir.