Steady state coherence in a qubit is incompatible with a quantum map

We consider the issue of steady state coherences in a single qubit in the case of a composite system-bath interaction as proposed in \cite{Guarnieri18}. Based on a field theoretical approach we reanalyse the issue within a Redfield description. We find that the Redfield approach in accordance with \cite{Guarnieri18} yields steady state coherences but violating the properties of a quantum map also gives rise to negative populations. The issue is resolved by applying the Lindblad equation which is in accordance with a proper quantum map. The Lindblad equation, however, also implies the absence of steady state coherence. We conclude that steady state coherence in a a qubit is incompatible with a quantum map.

Source: arXiv:2602.15790v1 - http://arxiv.org/abs/2602.15790v1 PDF: https://arxiv.org/pdf/2602.15790v1 Original Link: http://arxiv.org/abs/2602.15790v1