权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Robust many-body Quantum phenomena through Driving and Dissipation

通过驱动和耗散实现鲁棒多体量子现象

基本信息

批准号：
MR/T040947/2
负责人：
Curt Von Keyserlingk
金额：
$ 99.06万
依托单位：
King's College London
依托单位国家：
英国
项目类别：
Fellowship
财政年份：
2022
资助国家：
英国
起止时间：
2022 至无数据
项目状态：
未结题

来源：
https://gtr.ukri.org/projects?ref=MR%2FT040947%2F2
关键词：
Robust many body Quantum phenomena

项目摘要

Schoolchildren learn of three phases of matter: Liquid, solid and gas. This list is glaringly incomplete at low temperatures where quantum mechanical principles more markedly determine material properties, leading to a plethora of new states including superconductors and topological phases, many of which have profound practical applications. The theoretical search for phases has implicitly assumed that all such systems come to thermodynamic equilibrium. This seemingly solid assumption underlies all thermodynamics, of which Einstein once said: "It is the only physical theory of universal content, which I am convinced...will never be overthrown". Two important questions arise: 1) is the assumption valid, i.e., do all systems tend to equilibrium and 2) when they do, how do they get there? "No" is the shocking answer to the first question: some systems do not equilibrate, and a host of new non-equilibrium phases exist beyond the standard thermodynamic paradigm. The realisation was sparked by the discovery of many-body localised (MBL) phases, for which strong disorder prevents the equilibration of, e.g., charge and energy, contrary to the standard assumptions of thermodynamics. As revolutionary as MBL systems are, they do settle in the following sense: left undisturbed, observables settle (are static) at late times. Astonishingly, through a combination of both periodic driving and disorder, one can realise systems that robustly both fail to equilibrate and settle! Many-body localised time crystals (TCs) are a prominent example: for almost any initial state, their local observables eventually oscillate with a period that is an integer multiple (e.g., 2T) of the underlying driving period T, hence the system spontaneously breaks time translation symmetry. A prominent open question is whether the effect can be robust in an open quantum system, i.e., one subject to environmental dissipation. The second question concerns how strongly correlated systems that do settle generate the dissipation that drives them towards a steady state, as well as quantitative questions of how bulk transport coefficients (conductivity, etc.) depend on the underlying microscopic parameters, how systems respond to external dissipation, and what features of transport are universal and robust. This field has a long history, few controlled results, and is of great practical importance: further progress will aid in the search for new materials with specified transport properties, and clarify existing experimental questions (below). Our increased understanding of novel quantum phases revolutionised the material world. This project aims to continue the revolution, extending our understanding of the non-equilibrium frontier, searching for new robust---and hence potentially useful---quantum phenomena. Our primary focus will be on a poorly understood class of many-body systems, namely those subject to both environmental dissipation and periodic driving. We will explore various phenomena in this setting, most prominently aiming to: 1) develop the theory behind a new notion of time crystal stable in the presence of dissipation, 2) formulate a theory of quantum information/entanglement spreading and 3) expand our cachet of solvable models with dissipation. We will 4) use our theoretical results in 2) to develop new numerical techniques able to probe the experimentally relevant late time regimes in many-body systems. Finally, we will 6) transform our theoretical progress into experimental proposals pertaining to, amongst other possibilities: a) the exciting prospect that dissipation---rather than being an impediment---can be used to enhance the stability, and hence practical utility, of time crystals; b) exotic transport in interacting systems, e.g., anomalous spin diffusion in 1D quantum magnets; c) a careful assessment of claimed sightings of time crystals in experiments, particularly in Nitrogen vacancy centre platforms.

小学生学习物质的三个阶段：液体、固体和气体。这份清单在低温下显然是不完整的，因为在低温下，量子力学原理更明显地决定了材料的性质，导致了包括超导体和拓扑相在内的大量新状态，其中许多具有深刻的实际应用。对相的理论探索隐含地假定所有这样的体系都达到热力学平衡。这一看似可靠的假设是所有热力学的基础，爱因斯坦曾说过：“这是宇宙内容的唯一物理理论，我相信它……永远不会被推翻”。出现了两个重要的问题：1)假设是有效的，即，所有系统都趋向于平衡吗？2)当它们趋于平衡时，它们是如何达到平衡的？对于第一个问题，“不”是令人震惊的答案：一些系统不平衡，许多新的非平衡相存在于标准热力学范式之外。这种认识是由多体定域(MBL)相的发现引发的，对于多体定域(MBL)相，强烈的无序阻止了例如电荷和能量的平衡，这与热力学的标准假设相反。尽管MBL系统是革命性的，但它们确实在以下意义上得到了解决：不受干扰，可观测对象在后期稳定(是静态的)。令人惊讶的是，通过周期性驾驶和无序的结合，一个人可以实现既不平衡又不稳定的系统！多体定域时间晶体(TCS)就是一个突出的例子：对于几乎任何初始状态，它们的局域可观测值最终都会以驱动周期T的整数倍(例如2T)的周期振荡，因此系统自发地打破了时间平移对称性。一个突出的悬而未决的问题是，在一个开放的量子系统中，即一个受环境耗散影响的系统中，这种效应是否可以保持稳健。第二个问题涉及强关联系统如何产生驱使它们进入稳定状态的耗散，以及体积输运系数(电导率等)如何的定量问题。取决于基本的微观参数，系统如何对外部耗散做出反应，以及交通的哪些特征是普遍和健壮的。这一领域历史悠久，可控结果很少，具有重要的现实意义：进一步的进展将有助于寻找具有特定输运性质的新材料，并澄清现有的实验问题(见下文)。我们对新的量子相的理解的增加使物质世界发生了革命性的变化。这个项目的目的是继续这场革命，扩大我们对非平衡前沿的理解，寻找新的强健的-因此可能有用的--量子现象。我们的主要关注点将放在一类知之甚少的多体系统上，即那些既受环境耗散又受周期性驾驶影响的系统。我们将在这个背景下探索各种现象，最突出的目的是：1)发展耗散存在下时间晶体稳定的新概念背后的理论，2)建立量子信息/纠缠扩散理论，3)扩大我们的耗散可解模型的威望。我们将使用我们在2)中的理论结果来开发新的数值技术，能够探索多体系统中实验上相关的晚时间区域。最后，我们将把我们的理论进展转化为与其他可能性有关的实验建议：a)耗散--而不是阻碍--可以用来增强时间晶体的稳定性，从而增强其实用价值的令人兴奋的前景；b)相互作用系统中的奇异输运，例如，一维量子磁铁中的反常自旋扩散；c)对声称在实验中观察到时间晶体的仔细评估，特别是在氮空位中心平台上。