Mpemba effect and super-accelerated thermalization in the damped quantum harmonic oscillator

Stefano Longhi

Dipartimento di Fisica, Politecnico di Milano, Piazza L. da Vinci 32, I-20133 Milano, Italy & IFISC (UIB-CSIC), Instituto de Fisica Interdisciplinar y Sistemas Complejos - Palma de Mallorca, Spain

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Abstract

The behavior of systems far from equilibrium is often complex and unpredictable, challenging and sometimes overturning the physical intuition derived from equilibrium scenarios. One striking example of this is the Mpemba effect, which implies that non-equilibrium states can sometimes relax more rapidly when they are further from equilibrium. Despite a rich historical background, the precise conditions and mechanisms behind this phenomenon remain unclear. Recently, there has been growing interest in investigating accelerated relaxation and Mpemba-like effects within quantum systems. In this work, we explore a quantum manifestation of the Mpemba effect in a simple and paradigmatic model of open quantum systems: the damped quantum harmonic oscillator, which describes the relaxation of a bosonic mode in contact with a thermal bath at finite temperature $T$. By means of an exact analytical analysis of the relaxation dynamics based on the method of moments in both population and coherence subspaces, we demonstrate that any initial distribution of populations with the first $r$ moments exactly matching those of the equilibrium distribution shows a super-accelerated relaxation to equilibrium at a rate linearly increasing with $r$, leading to a pronounced Mpemba effect. In particular, one can find a broad class of far-from-equilibrium distributions that relax to equilibrium faster than any other initial thermal state with a temperature $T'$ arbitrarily close to $T$. The super-accelerated relaxation effect is shown to persist even for a broad class of initial states with non-vanishing coherences, and a general criterion for the observation of super-accelerated thermalization is presented.

In this work, we examine the quantum version of the Mpemba effect, where systems far from equilibrium can relax to equilibrium more quickly than those closer to it, driven by super-accelerated thermalization. Focusing on the damped quantum harmonic oscillator—a model describing a quantum system in contact with a thermal bath—we show that, under certain conditions, the system can reach equilibrium much faster than expected. These findings provide new insights into the rapid thermalization of quantum systems.

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[3] Ze-Zhou Zhang, Hong-Gang Luo, and Wei Wu, "Quantum Mpemba Effect Induced by Non-Markovian Exceptional Points", Physical Review Letters 136 21, 210402 (2026).

[4] Stefano Longhi, "Quantum Mpemba effect from initial system–reservoir entanglement", APL Quantum 2 2, 026133 (2025).

[5] Zijun Wei, Mingdi Xu, Xiang-Ping Jiang, Haiping Hu, and Lei Pan, "Quantum Mpemba effect in dissipative spin chains at criticality", Science China Physics, Mechanics & Astronomy 69 4, 240315 (2026).

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[7] Israel Klich and Marija Vucelja, "Mpemba effect on near-complete graphs with independence Metropolis–Hastings dynamics", Journal of Physics A: Mathematical and Theoretical 59 25, 255002 (2026).

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[14] Pitambar Bagui, Arijit Chatterjee, and Bijay Kumar Agarwalla, "Accelerated relaxation and Mpemba-like effect for operators in open quantum systems", Physical Review A 114 1, L010601 (2026).

[15] Filiberto Ares, Pasquale Calabrese, and Sara Murciano, "The quantum Mpemba effects", Nature Reviews Physics 7 8, 451 (2025).

[16] Gianluca Teza, John Bechhoefer, Antonio Lasanta, Oren Raz, and Marija Vucelja, "Speedups in nonequilibrium thermal relaxation: Mpemba and related effects", Physics Reports 1164, 1 (2026).

[17] Shion Yamashika and Filiberto Ares, "Quantum Mpemba Effect in Long-Range Spin Systems", Physical Review Letters 136 9, 090402 (2026).

[18] Asad Ali, Hamid Arian Zad, Muhammad Irtiza Hussain, Saif Al‐Kuwari, Hashir Kuniyil, Muhammad Talha Rahim, Michal Jaščur, and Saeed Haddadi, "Quantum Mpemba Effect in a Four‐Site Bose–Hubbard Model", Fortschritte der Physik 74 3, e70089 (2026).

[19] Mingdi Xu, Zijun Wei, Xiang-Ping Jiang, and Lei Pan, "Expedited thermalization dynamics in incommensurate systems", Physical Review A 112 4, 042210 (2025).

[20] Doruk Can Alyürük, Mahir H. Yeșiller, Vlatko Vedral, and Onur Pusuluk, "Thermodynamic limits of the Mpemba effect: A unified resource theory analysis of correlation-enabled mechanisms", arXiv:2502.00123, (2025).

[21] Stefano Longhi, "Laser Mpemba effect", Optics Letters 50 6, 2069 (2025).

[22] Mingdi Xu, Kaixiang Lu, Xiang-Ping Jiang, Haiping Hu, and Lei Pan, "Strong Quantum Mpemba Effect from Exact Slow-Mode Selection in Constrained Rydberg Chains", arXiv:2607.17975, (2026).

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