# Time-invariant Discord: High Temperature Limit and Initial Environmental Correlations

## TL;DR

This paper investigates the robustness of quantum discord in two-qubit systems under realistic environmental effects, revealing the persistence of time-invariant discord at high temperatures and initial reservoir correlations.

## Contribution

It demonstrates the existence of high-temperature time-invariant quantum discord and analyzes the impact of initial reservoir correlations on its dynamics.

## Key findings

- Time-invariant discord persists at high temperatures in the weak coupling regime.
- Initial correlations between reservoirs modify the behavior of frozen discord.
- Thermal photons influence the dynamical stability of quantum discord.

## Abstract

We present a thorough investigation of the phenomena of frozen and time-invariant quantum discord for two-qubit systems independently interacting with local reservoirs. Our work takes into account several significant effects present in decoherence models, which have not been yet explored in the context of time-invariant quantum discord, but which in fact must be typically considered in almost all realistic models. Firstly, we study the combined influence of dephasing, dissipation and heating reservoirs at finite temperature. Contrarily to previous claims in the literature, we show the existence of time-invariant discord at high temperature limit in the weak coupling regime, and also examine the effect of thermal photons on the dynamical behaviour of frozen discord. Secondly, we explore the consequences of having initial correlations between the dephasing reservoirs. We demonstrate in detail how the time-invariant discord is modified depending on the relevant system parameters such as the strength of the initial amount of entanglement between the reservoirs.