For quantum systems as well as for classical continuous systems energetic stability is defined. It is proved that stability, supplemented with a cluster property, characterizes equilibrium states.
We propose a unifying framework for characterizing pure and mixed state phases of matter across equilibrium, non equilibrium, and metastable regimes. We introduce the concept of locally stable states, defined by the operational property that any local operation (including post selection) can be reversed by a local channel. We prove that local stability is equivalent to a state being short range correlated, defined by the decay of both correlations and conditional mutual information. We demonstrate that these properties are invariant under locally reversible channels, thus defining locally stable phases. Furthermore, we prove that local stability implies both the decay of a family of nonlinear correlators, including the fidelity correlator, and the decay of correlations in the canonical purification, thus bridging the gap between mixed and pure states. Along the way, we establish two results which may be of independent interest: we show that post-selection on locally stable (short range correlated) states can be implemented via local channels and that quantum Markov chains can be characterized by the local computability of nonlinear observables.
Stability against perturbations is a defining property of quantum many-body phases of matter. However, most rigorous stabilities are only established for static perturbations; whether any system can remain stable against generic time-dependent perturbations is largely elusive. Here, we identify a universal phenomenon, where the evolving state driven by time-dependent q-local Hamiltonians can be exponentially localized in an energy window of instantaneous spectrum, and prove its survival under generic time-dependent perturbations. Applying such energy-space localization to classical and quantum LDPC codes whose codewords are separated by extensive energy barriers, we show that the system remains localized near the original codeword for an exponentially long time under generic time-dependent perturbations. For classical optimization problems with clustered solution spaces, the stability becomes an obstacle for quantum Hamiltonian-based algorithms to escape local minima. Our work provides a new lens for analyzing quantum non-equilibrium dynamics and tools for establishing stability and designing quantum algorithms.
In this paper we consider a nonlinear stochastic approach to the description of quantum systems. It is shown that a possibility to derive quantum properties - spectrum quantization, zero point positive energy and uncertainty relations, exists in frame of Zaslavsky phase liquid. This liquid is considered as a projection of continuous turbulent medium into a Hilbert phase space.It has isotropic minimal diffusion defined by Planck constant.Areas of probability condensation may produce clustering centers: quasi stable particles-attractors which preserve boundaries and scale-free fractal transport properties.The stability of particles has been shown in frame of the first order perturbation theory. Quantum peculiarities of considered systems have been strictly derived from markovian Fokker-Planck equation. It turned out that the positive zero point energy has volumetric properties and grows for higher time resolutions. We have shown that a quasi stable attractor may be applied as a satisfactory model of an elementary quantum system. The conditions of attractor stability are defined on the basis of Nonlinear Prigogine Theorem. Finally the integrity of classical and quantum approaches is recovered: existence of particles is derived in terms of Zaslavsky quantum fluid.