Emergence of nonequilibrium steady states in periodically driven closed composite quantum systems

周期性驱动的封闭复合量子系统中非平衡稳态的出现

• 批准号: 397122187
• 负责人: Professor Dr. Martin Holthaus
• 金额: --
• 依托单位: Institut für Physik (IFP)
• 依托单位国家: 德国
• 项目类别: Research Units
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/397122187?language=en
• 关键词: Emergence; nonequilibrium; steady; states; periodically

Within the previous first funding period of FOR 2692 we have contributed to the area of ``periodic thermodynamics'', and have determined the probability distributions which govern the Floquetstate occupation probabilities for periodically driven open quantum systems of theoretical and experimental interest. In particular, we have demonstrated that the nonequilibrium magnetization of a periodically driven paramagnetic material is strongly affected by details concerning the spins' coupling to their environment, and have established the novel concept of ``Floquet-state cooling'', demonstrating that a Floquet state emerging from the ground state of a quantum system can carry even significantly higher population in the presence of a strong driving force than that ground state in thermal equilibrium. These results still rest on an approach which is equivalent to the usual Born-Markov approximation, disregarding potential complications due to the denseness of the quasienergy spectrum. In the second funding period we will therefore extend the above findings beyond the scope of that proposition, moving towards environments which actually ``feel'' the time-periodic driving force. To this end, we will study particular periodically driven quantum systems coupled to N bath oscillators which can be solved analytically for an N by means of a generalized Husimi transformation, and explore how the limit of infinitely large N is approached. On the other hand, we will numerically investigate models of periodically driven bosonic Josephson junctions occupied by two particle species, one representing a periodically driven system, the other a bath. In this way, predictions implied by the Born-Markov-like formulation of periodic thermodynamics can be put to a hard test. In addition, two strands of development arising out of the work accomplished in the first project period will be continued, namely, the task of selectively populating certain ``resonant'' Floquet states by means of suitably designed system-bath couplings and bath densities of states, and the variational computation of Floquet states of large systems which may not be amenable to the presently used standard numerical methods. As a long-term goal linking several of these subtopics we also consider the feasibility of Floquet condensates of weakly interacting atomic Bose gases in time-periodically modulated trapping potentials, which may exhibit some fairly unusual features.

在之前的 FOR 2692 的第一个资助期内，我们对“周期性热力学”领域做出了贡献，并确定了控制具有理论和实验兴趣的周期性驱动开放量子系统的 Floquetstate 占据概率的概率分布。特别是，我们证明了周期性驱动的顺磁材料的非平衡磁化强度受到自旋与其环境耦合细节的强烈影响，并建立了“Floquet态冷却”的新概念，证明从量子系统基态出现的Floquet态在存在强驱动力的情况下可以携带比热中基态更高的布居数。 平衡。这些结果仍然基于相当于通常的玻恩-马尔可夫近似的方法，忽略了由于准能谱的致密性而导致的潜在复杂性。因此，在第二个资助期，我们将把上述发现扩展到该命题的范围之外，转向真正“感受到”时间周期驱动力的环境。为此，我们将研究与 N 浴振荡器耦合的特定周期性驱动量子系统，该系统可以通过广义 Husimi 变换解析求解 N，并探索如何接近无限大 N 的极限。另一方面，我们将在数值上研究由两种粒子种类占据的周期性驱动的玻色约瑟夫森结模型，一种代表周期性驱动系统，另一种代表浴。通过这种方式，周期性热力学的类玻恩-马尔可夫公式所隐含的预测就可以接受严格的测试。此外，第一个项目期间完成的工作中产生的两条发展路线将继续下去，即通过适当设计的系统浴耦合和状态浴密度选择性地填充某些“共振”Floquet状态的任务，以及可能不适合目前使用的标准数值方法的大型系统的Floquet状态的变分计算。作为连接其中几个子主题的长期目标，我们还考虑了弱相互作用原子玻色气体的 Floquet 凝聚体在时间周期调制捕获势中的可行性，这可能表现出一些相当不寻常的特征。