The Nature of Multimode Generation when Quasi-equilibrium is Disturbed

Vladimir S. Mashkevich, M. S. Soskin

O. A. Chichigina

The decrease in entropy when passing from an equilibrium thermodynamic system to a slightly nonequilibrium system is investigated. A quasi-equilibrium Boltzmann distribution is used to prove the conservation of free energy during this passage. Results are obtained for a Brownian particle in a potential well with a low escape probability. The escape is interpreted as a measurement. It is shown that because of the measurement itself, the distribution function is narrower than that for a system undisturbed by measurement, i.e., an equilibrium system. In this case, the entropy difference between the equilibrium and measurement-disturbed systems is equal to the amount of information entered into the system.

Xiaofan Luo, Yaoting Zhou, Z. S. Xu +1 more

Abstract Discrete time quasi-crystals are non-equilibrium phenomena with quasi-periodic order in time domain, an extension of the discrete time-crystal phase. As a natural platform to explore the non-equilibrium phases, Rydberg atomic arrays have demonstrated the quantum simulation of the discrete-time crystal phase, associated with quantum many-body scar state. However, the existence of discrete time quasi-crystal in this platform has yet to be conceived. Here, we propose a method to generate the discrete time quasi-crystal behavior by coupling two discrete time-crystals, where two external driving frequencies have the maximum incommensurability. Upon the characterization of the phase diagram and the robustness, we explore the entanglement entropy between two subsystems. We find that the emergence of the aperiodic response appears at an appropriate driving frequency, which could be well interpreted by the model with two coupled oscillators. Our method thus offers the possibilities to explore the phases of matters in the quantum simulator.

J. Scott Rodgers

Krzysztof Gawryluk, Mirosław Brewczyk

Abstract We theoretically study the sound propagation in a two-dimensional weakly interacting uniform Bose gas. Using the classical fields approximation we analyze in detail the properties of density waves generated both in a weak and strong perturbation regimes. While in the former case density excitations can be described in terms of hydrodynamic or collisionless sound, the strong disturbance of the system results in a qualitatively different response. Within this regime we identify observed structures as quasisolitons and uncover their internal complexity. Quasisolitons break into vortex pairs as time progresses, eventually reaching an equilibrium state. We find this state, characterized by only fluctuating in time averaged number of pairs of opposite charge vortices and by appearance of a quasi-long-range order, as the Berezinskii-Kosterlitz-Thouless (BKT) phase.