Dynamics and entanglement near quantum phase transitions

量子相变附近的动力学和纠缠

• 批准号: RGPIN-2016-06667
• 负责人: WitczakKrempa, William
• 金额: $ 2.33万
• 依托单位: Université de Montréal
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=668741
• 关键词: Dynamics; entanglement; near; quantum; phase

Matter changes states by undergoing phase transitions. In our common experience, this occurs as the temperature goes through a threshold, such as water turning into ice at 0 °C. However, more exotic transitions can be realized by first cooling a material down to the lowest accessible temperatures, near absolute zero (−273 °C). There the laws of quantum mechanics governing the behavior of the electrons become dominant, and transitions driven by quantum effects instead of thermal ones occur. My research will target such quantum phase transitions, which can be realized by applying a magnetic field to the material, changing its chemical composition, or by compressing it. For example, some insulating materials possess magnetic order at very low temperatures but when enough mobile charge carriers are added by varying the chemical composition, they become metallic and loose their magnetism. An extraordinary phenomenon occurs near this insulator-to-metal quantum phase transition: the system becomes a superconductor in which the electrons form pairs that travel without resistance. This phenomenon cannot be explained with the standard theory of superconductivity, and remains robust as the material is heated up to ~ 100 °C above absolute zero. Although the underlying mechanism is still not well-understood, evidence suggests that it is connected to the quantum fluctuations of the system in its “confused” state between a magnetic insulator and a metal. ******The theoretical research of my group will shed light on the physical properties of quantum materials in the vicinity of such quantum phase transitions, where novel states of matter emerge. This is a challenging program because the strong fluctuations between the competing phases near these transitions lead to the destruction of long-lived excitations. The “dancing” patterns of the electrons become highly intricate and entangle very distant partners. We will aim to answer the consequential questions: How does a system without long-lived excitations dynamically respond to various perturbations? What are the essential features of its many-body “dancing patterns”, and how can we exploit them to improve numerical modeling of quantum materials? Our research will make use of cutting edge tools in quantum many-body theory, including numerical simulations. We will borrow pertinent insights other disciplines such as quantum information and even string theory.******In the same way that knowledge about ordinary phase transitions like the melting of ice is important to society, knowledge about their quantum counterparts is becoming crucial. Indeed, the understanding of quantum phase transitions holds the promise to explain complex and striking phenomena in cutting edge materials, such as high temperature conductivity. Potential applications of these materials range from the low cost transport of electricity, to robust quantum computers.

物质通过进行相转换来改变状态。在我们的共同经验中，这是随着温度经过阈值而发生的，例如在0°C下变成冰的水。但是，可以通过将材料冷却到最低的可接近温度（-273°C）的最低温度来实现更多的外来过渡。在那里，管理电子行为的量子力学定律成为主导，而量子效应而不是热效应的过渡。我的研究将针对此类量子相变，可以通过将磁场应用于材料，更改其化学成分或通过压缩来实现。例如，某些绝缘材料在非常低的温度下具有磁性顺序，但是当通过改变化学成分来增加足够的移动荷载载流子时，它们就会变成金属并松散其磁性。在这种绝缘体到金属量子相变附近发生了非凡现象：系统变成了一个超导体，其中电子形成没有电阻的行驶的电子产品对。这种现象不能用超导性的标准理论来解释，并且随着材料的加热高达〜100°C以高于绝对零。尽管基本机制仍然没有得到充分理解，但有证据表明，它与磁绝缘体和金属之间的“混淆”状态的系统的量子波动相连。 *****我小组的理论研究将阐明在这种量子相变的附近量子材料的物理特性，其中新颖的物质状态出现。这是一个挑战计划，因为这些过渡附近的竞争阶段之间的强烈波动导致了长寿兴奋的破坏。电子的“舞蹈”模式变得高度复杂和纠缠，我们的目标是回答相关性问题：没有长期兴奋的系统如何动态地对各种扰动做出反应？其多体“舞蹈模式”的基本特征是什么，我们如何探索它们以改善量子材料的数值建模？我们的研究将利用量子多体理论（包括数值模拟）中的尖端工具。我们将借用相关的见解其他学科，例如量子信息，甚至是字符串理论。****以相同的方式了解普通的相位过渡（例如冰的融化对社会很重要），对其量子对应物的知识也变得至关重要。实际上，对量子相变的理解有望解释尖端材料（例如高温电导率）中复杂和引人注目的现象。这些材料的潜在应用范围从低成本运输到稳健的量子计算机。