Coherence thermometry using multipartite quantum systems

We investigate, how finite temperature influences quantum coherence in multipartite open systems by analyzing a tripartite spin boson model subjected to non-Markovian dephasing. Two distinct environmental configurations are considered viz. independent local reservoir and a common structured reservoir characterized by an Ohmic spectral density. In this framework, temperature enters explicitly through the time dependent dephasing rates, enabling a systematic exploration of thermal effects on coherence dynamics. Using the relative entropy of coherence, we examine representative pure states belonging to inequivalent entanglement classes along with physically relevant mixed states constructed from them. Under local non-Markovian dephasing, all states exhibit monotonic coherence decay, with temperature acting as a universal accelerator of decoherence. In contrast, the common reservoir scenario reveals a strikingly non-universal behaviour. While GHZ and Star type states undergo temperature enhanced degradation, W class states and certain Werner type mixtures display robust stationary coherence that remains largely insensitive to thermal fluctuations. These results demonstrate that the thermal susceptibility of coherence is governed not only by environmental configuration but also by the internal architecture of multipartite quantum states. The interplay between reservoir structure and state geometry leads to qualitatively distinct dynamical regimes ranging from rapid thermal fragility to temperature resilient coherence preservation. Our findings identify coherence dynamics as a sensitive probe of structured finite temperature environments and suggest a pathway toward coherence based quantum thermometry and nanoscale calorimetry using engineered multipartite states.