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: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=633020
• 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.

物质通过相变改变状态。在我们的共同经验中，这发生在温度通过阈值时，例如水在0 °C时变成冰。然而，更奇特的转变可以通过首先将材料冷却到接近绝对零度（−273 °C）的最低温度来实现。在那里，控制电子行为的量子力学定律占主导地位，量子效应而不是热效应驱动的跃迁发生。我的研究将针对这样的量子相变，这可以通过向材料施加磁场，改变其化学成分或通过压缩来实现。例如，一些绝缘材料在非常低的温度下具有磁性秩序，但当通过改变化学成分添加足够的移动的电荷载体时，它们变成金属并失去磁性。在这种绝缘体到金属的量子相变附近发生了一个不寻常的现象：系统变成了超导体，其中电子形成了无电阻的电子对。这种现象无法用超导的标准理论来解释，并且当材料被加热到绝对零度以上约100 °C时仍然很稳定。虽然其基本机制仍然没有得到很好的理解，但有证据表明，它与磁绝缘体和金属之间的“混乱”状态下系统的量子涨落有关。