Local Quantum Friction Method Achieves Unitary Dynamics in Large Fermi Systems
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Dissipative dynamics, the study of how energy fades from complex systems, presents a significant challenge for modelling large collections of interacting particles. J. E. Alba-Arroyo, Daniel Pęcak from the Institute of Physics, Polish Academy of Sciences, and Michael McNeil Forbes from Washington State University, alongside Gabriel Wlazłowski, now present a new framework that efficiently describes energy loss in large Fermi systems while maintaining the fundamental principle of unitarity. Their method introduces localised forces that mimic friction, unlike existing approaches which struggle with computational demands as system size increases. This advancement allows researchers to accurately simulate the damping of particle movement and pairing behaviour, opening new avenues for understanding phenomena ranging from the behaviour of superfluids to the extreme conditions found within neutron stars, and provides a foundation for exploring the interplay between fluctuations and dissipation in strongly interacting systems. TDDFT Models Microscopic Nuclear System Dynamics Scientists employ time-dependent density functional theory (TDDFT) to model the dynamic behaviour of nuclear systems, gaining insights into phenomena like superfluidity and cooling.
This research focuses on extending these methods to understand neutron star matter and the complex processes occurring during neutron star mergers, bridging the gap between microscopic many-body physics and macroscopic observations. Researchers utilize TDDFT to simulate superfluidity in nuclear matter, investigating how neutrons cool and form a superfluid state, influencing the star’s properties, and explore quantum friction, crucial for understanding energy loss and angular momentum changes in neutron stars. Detailed simulations of neutron star mergers are performed, modelling the formation of hypermassive neutron stars and their eventual collapse into black holes, alongside the emission of gravitational waves and electromagnetic radiation. The methods are also applied to study nuclear reactions, such as neutron-induced fission, and to investigate the structure of atomic nuclei, with sophisticated computational tools developed and implemented to enhance performance.
The team has developed a TDDFT code capable of simulating complex nuclear systems with high accuracy, providing improved modelling of nuclear reactions and more accurate predictions of fission cross-sections.,. Unitary Dynamics for Dissipative Fermi Systems Scientists have developed a new computational framework for modelling dissipative quantum dynamics in large-scale Fermi systems, overcoming limitations of traditional methods. This innovative approach introduces local Hermitian operators that effectively emulate frictional forces while rigorously preserving the unitarity of time evolution, a crucial advantage for accurate simulations. Unlike methods relying on non-Hermitian dynamics, this formulation scales favourably with system size and integrates seamlessly into TDDFT frameworks, enabling studies of significantly larger systems. The core innovation lies in constructing a time-dependent Hermitian potential that explicitly lowers the energy of the system, while remaining diagonal in position space for efficient implementation, avoiding computational bottlenecks associated with reorthogonalization procedures. Researchers demonstrate that energy dissipation arises from the damping of both particle currents and pairing-field fluctuations, providing insights into the fundamental mechanisms governing these processes.
The team engineered a method where the evolution of single-particle wavefunctions is governed by an augmented Schrödinger equation, incorporating a dissipative term and Lagrange multipliers to maintain orthonormality, allowing for simulations of systems with a significantly larger number of degrees of freedom than previously possible.,.
Dissipative Fermi Systems and Microscopic Damping Mechanisms Scientists have developed a novel framework for modelling dissipative dynamics in large-scale Fermi systems, introducing a method that preserves the unitarity of time evolution while efficiently simulating frictional forces. This work introduces local Hermitian operators that emulate friction, offering a significant advantage over traditional approaches based on the Lindblad equation, which often struggle with computational scaling for complex systems. Experiments reveal that energy dissipation arises from the damping of both particle currents and fluctuations in the pairing field, demonstrating a direct link between microscopic dynamics and macroscopic energy loss.
The team further developed a variant of the scheme allowing for controlled manipulation of the particle number over time, enabling precise density scans and opening new avenues for exploring the equation of state of matter. This versatility is illustrated through applications to spin-imbalanced unitary Fermi gases and to the complex environment of nuclear matter found within neutron star crusts, reproducing known phenomena and enabling the preparation of complex configurations like nuclear pasta states. Measurements confirm that the framework can be extended to include stochastic noise, providing a powerful tool for studying fluctuation-dissipation dynamics and thermalization in strongly interacting Fermi superfluids.,.
Dissipative Fermi Systems and Pairing Damping Scientists have presented a new computational scheme, termed local-quantum-friction, for modelling dissipative dynamics in large Fermi systems, including superfluids. The method introduces a means of emulating frictional forces while rigorously maintaining the unitarity of time evolution, offering a computational advantage over traditional approaches.
Results demonstrate that energy dissipation arises not only from the damping of particle currents, but also significantly through the damping of pairing-field fluctuations, particularly in strongly paired systems. The researchers developed a variant of the scheme that allows for controlled variation of particle number during simulations, enabling efficient density scans and the mapping of multiple equilibrium configurations. This advancement provides a practical tool for systematically exploring the properties of these systems and opens avenues for future investigations into areas such as vortex dynamics and quantum turbulence.
The team acknowledges that the computational cost scales with the number of nodes used in parallel computing, but believes their approach offers a valuable tool for generating initial states for studying the stability of nuclear pasta structures. 👉 More information 🗞 Local Quantum Friction with Pairing: Unitary Dissipation in Large Fermi Systems 🧠 ArXiv: https://arxiv.org/abs/2512.12866 Tags: