<p>We study particle and energy transport in an open quantum system consisting of a three-harmonic oscillator chain coupled to thermal baths at different temperatures placed at the ends of the chain. We consider the exact dynamics of the open chain and its so-called local and global Markovian approximations. By comparing them, we show that, while all three yield a divergence-like continuity equation for the probability flow, the energy flow exhibits instead a distinct behavior. The exact dynamics and the local one preserve a standard divergence form for the energy transport, whereas the global open dynamics, due to the rotating wave approximation (RWA), introduces non-divergence sink/source terms. These terms also affect the continuity equation in the case of a master equation obtained through a time-coarse-graining method whereby RWA is avoided through a time-zoom parameter <InlineEquation ID="IEq1"> <EquationSource Format="TEX">$\Delta t$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="normal">Δ</mi> <mi>t</mi> </mrow> </math></EquationSource> </InlineEquation>. In such a scenario, sink and source contributions are always present for each <InlineEquation ID="IEq2"> <EquationSource Format="TEX">$\Delta t>0$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="normal">Δ</mi> <mi>t</mi> <mo>></mo> <mn>0</mn> </mrow> </math></EquationSource> </InlineEquation>. While in the limit <InlineEquation ID="IEq3"> <EquationSource Format="TEX">$\Delta t\rightarrow +\infty $</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="normal">Δ</mi> <mi>t</mi> <mo stretchy="false">→</mo> <mo>+</mo> <mi>∞</mi> </mrow> </math></EquationSource> </InlineEquation> one recovers the global dissipative dynamics, sink and source terms instead vanish when <InlineEquation ID="IEq4"> <EquationSource Format="TEX">$\Delta t\rightarrow 0$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="normal">Δ</mi> <mi>t</mi> <mo stretchy="false">→</mo> <mn>0</mn> </mrow> </math></EquationSource> </InlineEquation>, restoring the divergence structure of the exact dynamics. Our results underscore how the choice of the dissipative Markovian approximation to an open system dynamics critically influences the energy transport descriptions, with implications for discriminating among them and thus, ultimately, for the correct modeling of the time-evolution of open quantum many-body systems.</p>

Open harmonic chain without secular approximation

期刊论文
发表日期：

2026年1月3日

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Melika Babakan,
Fabio Benatti,
Laleh Memarzadeh

摘要

We study particle and energy transport in an open quantum system consisting of a three-harmonic oscillator chain coupled to thermal baths at different temperatures placed at the ends of the chain. We consider the exact dynamics of the open chain and its so-called local and global Markovian approximations. By comparing them, we show that, while all three yield a divergence-like continuity equation for the probability flow, the energy flow exhibits instead a distinct behavior. The exact dynamics and the local one preserve a standard divergence form for the energy transport, whereas the global open dynamics, due to the rotating wave approximation (RWA), introduces non-divergence sink/source terms. These terms also affect the continuity equation in the case of a master equation obtained through a time-coarse-graining method whereby RWA is avoided through a time-zoom parameter $\Delta t$ $Δ t$ . In such a scenario, sink and source contributions are always present for each $\Delta t>0$ $Δ t > 0$ . While in the limit $\Delta t\rightarrow +\infty $ $Δ t \to + \infty$ one recovers the global dissipative dynamics, sink and source terms instead vanish when $\Delta t\rightarrow 0$ $Δ t \to 0$ , restoring the divergence structure of the exact dynamics. Our results underscore how the choice of the dissipative Markovian approximation to an open system dynamics critically influences the energy transport descriptions, with implications for discriminating among them and thus, ultimately, for the correct modeling of the time-evolution of open quantum many-body systems.