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.

根据我们的普遍经验，当温度达到阈值时，物质会发生相变，例如水在 0°C 时变成冰。但是，通过首先将材料冷却到 0°C，可以实现更奇特的转变。最低可达到的温度，接近绝对零（−273°C），在那里，控制电子行为的量子力学定律变得占主导地位，并且由量子效应而不是热效应驱动的转变发生，我的研究将针对这种量子相变。这可以通过施加磁场来实现例如，一些绝缘材料在非常低的温度下具有磁性，但当通过改变化学成分添加足够的移动电荷载体时，它们会变成金属并失去磁性。在绝缘体到金属的量子相变附近会发生一种非同寻常的现象：系统变成一个超导体，其中电子形成无阻力的电子对，这种现象无法用超导的标准理论来解释，并且在材料被加热时仍然保持稳定。至~比绝对零高 100 °C 尽管其基本机制尚不清楚，但有证据表明它与磁绝缘体和金属之间处于“混乱”状态的系统的量子涨落有关。 *我的小组的理论研究将揭示这种量子相变附近量子材料的物理性质，其中出现新的物质状态这是一个具有挑战性的计划，因为这些转变附近的竞争相之间的强烈波动导致。毁掉长寿电子的“跳舞”模式变得非常复杂，并纠缠着非常遥远的伙伴：一个没有长期激发的系统如何动态响应各种扰动？多体“舞蹈模式”，我们如何利用它们来改进量子材料的数值建模？我们的研究将利用量子多体理论的尖端工具，包括数值模拟。例如量子信息甚至弦理论。********就像关于冰融化等普通相变的知识对社会很重要一样，关于它们的量子杠杆的知识确实变得至关重要。事实上，对量子的理解也变得至关重要。相变有望解释尖端材料中复杂而引人注目的现象，例如高温导电性，这些材料的潜在应用范围从低成本电力传输到强大的量子计算机。