Energy-ordered occupation is deeply embedded in quantum physics, from the Aufbau principle governing the filling of electronic states in atoms and molecules to the emergence of low-energy configurations in quantum many-body systems. However, the dynamical mechanism by which a generic quantum state develops such an energy hierarchy remains a fundamental question. Here we show that such an energy hierarchy can emerge dynamically from nonlinear quantum dissipation. Rather than being imposed as a principle or generated through coupling to a thermal reservoir, an Aufbau-like ordering of energy levels emerges intrinsically under quantum Landau-Lifshitz-Gilbert dynamics from a generic initial mixed state. This convergence is a nontrivial consequence of Lyapunov monotonicity and instability of disordered population configurations. The resulting dynamics establish an intrinsic nonlinear mechanism for organizing density-matrix populations and provides a route toward selective preparation of low-energy subspaces. Numerical simulations confirm analytical predictions and illustrate convergence toward low-energy sectors.
Energy-ordered occupation is deeply embedded in quantum physics, from the Aufbau principle governing the filling of electronic states in atoms and molecules to the emergence of low-energy configurations in quantum many-body systems. However, the dynamical mechanism by which a generic quantum state develops such an energy hierarchy remains a fundamental question. Here we show that such an energy hierarchy can emerge dynamically from nonlinear quantum dissipation. Rather than being imposed as a principle or generated through coupling to a thermal reservoir, an Aufbau-like ordering of energy levels emerges intrinsically under quantum Landau-Lifshitz-Gilbert dynamics from a generic initial mixed state. This convergence is a nontrivial consequence of Lyapunov monotonicity and instability of disordered population configurations. The resulting dynamics establish an intrinsic nonlinear mechanism for organizing density-matrix populations and provides a route toward selective preparation of low-energy subspaces. Numerical simulations confirm analytical predictions and illustrate convergence toward low-energy sectors.
Ground-state preparation of quantum many-body systems is a fundamental challenge across quantum science, with implications for quantum simulation, quantum computing, and the study of complex quantum matter. The exponential growth of Hilbert space and the complexity of entangled eigenstates motivate the development of new approaches that go beyond conventional strategies based on adiabatic evolution, variational optimization, imaginary-time methods, and engineered dissipative processes. Here, we demonstrate that the recently proposed quantum Landau-Lifshitz-Gilbert (QLLG) dynamics [Phys. Rev. Lett. {\bf 133}, 266704 (2024)] provides an intrinsic nonlinear dissipative mechanism for real-time ground-state preparation. Unlike engineered dissipative schemes, QLLG encodes relaxation directly into the quantum equation of motion while preserving the underlying quantum structure of the evolution. The QLLG evolution selectively suppresses excited-state contributions, driving the system toward the lowest-energy eigenstate within the accessible symmetry sector. We show that the dynamics admits a monotonic energy functional and a stable ground-state fixed point, and that for generic initial states in an N-qubit Hilbert space the characteristic convergence time scales linearly with N and inversely with the spectral gap. Numerical simulations of an interacting spin chain confirm our analytical predictions. These results establish nonlinear dissipative QLLG dynamics as a new avenue for quantum state preparation, opening a new route for quantum simulation, computation, and state engineering.
We show that current noisy quantum computers are ideal platforms for the simulation of quantum many-body dynamics in generic open systems.We demonstrate this using the IBM Quantum Computer as an experimental platform for confirming the theoretical prediction from Wang et al., [Phys. Rev. Lett. 124, 100604 (2020)] of an emergent hierarchy of relaxation timescales of many-body observables involving different numbers of qubits.Using different protocols, we leverage the intrinsic dissipation of the machine responsible for gate errors, to implement a quantum simulation of generic (i.e., structureless) local dissipative interactions.
Macroscopic quantum coherence in solids, such as in superfluids, superconductors, and condensates, is generally limited to low temperatures because order forms within a fixed excitation spectrum whose competing states become thermally populated as temperature rises. Here, we show that strong coupling between electronic excitations and a deformable lattice enables a different route. Above a critical density, this coupling nucleates self generated confining potentials that trap the very excitations generating them. Unlike rigid external traps, these potentials can translate through the host lattice without changing their internal structure, defining a translational zero mode. Coupling to this zero mode provides a shared dynamical coordinate that lowers and isolates a single collective many body configuration, opening a density dependent gap that suppresses thermal occupation of competing states and supports off diagonal long range order at elevated temperatures. As a concrete realization, we identify high-temperature superfluorescence in lead halide perovskites as the radiative instability of this zero mode dressed ordered excitonic state. More broadly, this establishes a general route to macroscopic quantum order: not cooling within a fixed spectrum, nor pairing instabilities, but a self generated mobile confining structure whose translational zero mode reconstructs the many-body spectrum to protect coherence.
The use of dissipation for the controlled creation of nontrivial quantum many-body correlated states is of much fundamental and practical interest. What is the result of imposing number conservation, which, in closed system, gives rise to diffusive spreading? We investigate this question for a paradigmatic model of a two-band system, with dissipative dynamics aiming to empty one band and to populate the other, which had been introduced before for the dissipative stabilization of topological states. Going beyond the mean-field treatment of the dissipative dynamics, we demonstrate the emergence of a diffusive regime for the particle and hole density modes at intermediate length- and timescales, which, interestingly, can only be excited in nonlinear response to external fields. We also identify processes that limit the diffusive behavior of this mode at the longest length- and timescales. Strikingly, we find that these processes lead to a reaction-diffusion dynamics governed by the Fisher-Kolmogorov-Petrovsky-Piskunov equation, making the designed dark state unstable towards a state with a finite particle and hole density.
Understanding the dynamics of open quantum systems is intrinsically important to control and utilize quantum hardware in various applications. The generic behavior of purely dissipative open quantum many-body systems with k-local, normal dissipation processes can be investigated using random matrix theory, revealing different decay timescales of observables determined by their complexity, as shown by Wang et al. [K. Wang et al., Phys. Rev. Lett. 124, 100604 (2020)]. The time evolution of an open quantum system is entirely described by the eigenvalue spectrum of the Lindbladian, in which the hierarchy of decay timescales is reflected in the formation of well-separated eigenvalue clusters. Here, we extend the analysis of this spectrum to the presence of unitary dynamics using a random matrix model. In the case of strong dissipation, the unitary dynamics can be treated perturbatively and the k locality of the Hamiltonian determines how susceptible the spectrum is to such a perturbation. For the physically most relevant case of (dissipative) two-body interactions, the correction in the first order of the perturbation vanishes, leading to the relative robustness of the spectral features, which in turn implies the same robustness of the corresponding separation of decay timescales. We find the perturbative approach for the spectrum to yield an excellent agreement with exact-diagonalization results. For weak dissipation, the spectrum flows into clusters except for outlier eigenmodes, which we identify to be the local symmetries of the Hamiltonian. We support our analytic findings by numerical simulations and show that our generic model applies to a nonrandom Heisenberg chain.
The Landau-Lifshitz-Gilbert (LLG) equation provides the fundamental description of dissipative magnetization dynamics. A recently proposed quantum analog, the quantum Landau-Lifshitz-Gilbert (QLLG) equation, extends this framework to quantum spin systems. However, whether the QLLG equation recovers the LLG equation in the classical large-spin limit for interacting spin systems remains an open question. Here, we demonstrate this connection by deriving the LLG equation as the classical large-spin limit of the QLLG equation. We establish this correspondence analytically and verify it numerically for an interacting spin system. These results provide a quantum-to-classical description of dissipative spin dynamics, offering a microscopic foundation for the LLG equation. From numerical calculations provided here, we also conclude that quantum effects become much less noticeable for systems with larger number of spins in the Hamiltonian.