Investigation of transport of superfluid 4He through 2D materials

研究超流体 4He 通过 2D 材料的输运

• 批准号: 2103425
• 负责人: Keith Schwab
• 金额: $ 43.61万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-03-01 至 2025-02-28
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2103425&HistoricalAwards=false
• 关键词: Investigation; transport; superfluid; 4He; through

Non-technical AbstractSuperfluid helium, which appears in liquid helium cooled below 2.17K (-455.8F), is an amazing example of a “quantum material” — a material who’s unusual and counter-intuitive properties require quantum physics to be understood. An example of a remarkable property of superfluid is the ability to move without friction, even through holes and channels which are near atomic size. During a series of recent experiments in which the research team studied the motion of superfluid helium through nanometer diameter holes in atomically thin sheets of carbon (graphene), they observed, unexpectedly, that when in the superfluid state, helium appears to be able to move through the carbon sheet even without holes. The current project probes this observation more thoroughly through a series of experiments. If they do validate the previous surprising outcome, their team expects this to lead to more advances in experiment and theory which may involve more exotic and as of yet undiscovered states of matter, such as super solids. More broadly this work is expected to lead to technologically useful quantum devices using this unique quantum material. This award will be enable the education of young scientists at all stages of education and professional development in the area of quantum devices and ultra-sensitive measurements, both which have been identified as areas of national importance.Technical AbstractQuantum devices based on superfluid helium-4 have not yet been thoroughly developed due to the absence of a low temperature Josephson junction structure. The difficulty is due to the mass of the helium atom which inhibits quantum tunneling even through atomically thin membranes, and the low temperature coherence length of 0.3 nm which requires atomically sized pores to attenuate the quantum order parameter. Recently, the Schwab research team performed experiments to probe the transport of superfluid helium through nanometer sized pores in a graphene sheet. These graphene sheets covered a 2 micron diameter aperture in a silicon nitride membrane. Surprisingly, after a series of measurements, it appeared that graphene sheets were transparent to helium in the superfluid state. This is contrary to the expectation that graphene should be extremely opaque to the transport of helium. The current seed project will resolve this question with a series of control experiments. If it is concluded that graphene is indeed transparent to superfluid helium this may indicate the formation of a super solid state on the first few layers of helium, a possibility which has been anticipated by a number of theorists, and a novel quantum state of matter which has not yet been observed. If it is concluded that graphene is opaque as was originally expected, the experiments here will inform experiments to create a low temperature Josephson junction for superfluid helium, which is expected to lead to realization of novel quantum devices. Superfluid quantum devices are expected to yield advances in ultra-sensitive navigation useful for submarines and for precision pointing of telescopes and lasers and yield novel devices for quantum information processing and precision quantum standards. Furthermore, this seed will provide funds to purchase a cryogen-free cryostat which will allow the research team to perform experiments without the cost of expensive consumable cryogenic liquids.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

超流氦出现在冷却至2.17K （-455.8 f）以下的液氦中，是“量子材料”的一个惊人例子——这种材料的不寻常和反直觉性质需要量子物理学来理解。超流体一个显著特性的一个例子是，它能够在没有摩擦的情况下移动，即使是通过接近原子大小的孔洞和通道。在最近的一系列实验中，研究小组研究了超流氦在原子薄的碳片（石墨烯）上通过纳米直径孔的运动，他们意外地观察到，当处于超流状态时，氦似乎能够在没有孔的碳片上移动。目前的项目通过一系列实验更彻底地探索了这一观察结果。如果他们确实证实了之前令人惊讶的结果，他们的团队希望这将导致实验和理论的更多进步，这可能涉及更多奇异的和尚未发现的物质状态，比如超固体。更广泛地说，这项工作有望利用这种独特的量子材料制造出技术上有用的量子器件。该奖项将使年轻科学家在量子器件和超灵敏测量领域的所有教育和专业发展阶段的教育成为可能，这两个领域都被确定为国家重要领域。技术摘要基于超流体氦-4的量子器件由于缺乏低温约瑟夫森结结构而尚未得到彻底的发展。由于氦原子的质量，即使通过原子薄的薄膜也会抑制量子隧穿，并且氦原子的低温相干长度为0.3 nm，需要原子大小的孔来衰减量子有序参数。最近，Schwab研究小组进行了实验，以探测超流氦通过石墨烯薄片上纳米大小的孔的传输。这些石墨烯片在氮化硅膜上覆盖了一个直径为2微米的孔。令人惊讶的是，经过一系列的测量，石墨烯片在超流体状态下似乎对氦是透明的。这与预期相反，石墨烯对氦的传输应该是极不透明的。目前的种子项目将通过一系列的对照实验来解决这个问题。如果得出石墨烯确实对超流氦透明的结论，这可能表明在氦的最初几层上形成了超固态，这是许多理论家所预测的一种可能性，也是一种尚未观察到的新的物质量子态。如果石墨烯像最初预期的那样是不透明的，那么这里的实验将为超流氦创建低温约瑟夫森结的实验提供信息，这有望导致新型量子器件的实现。超流体量子器件有望在超灵敏导航方面取得进展，对潜艇、望远镜和激光的精确指向有用，并为量子信息处理和精确量子标准产生新的设备。此外，该种子将提供资金购买无低温恒温器，这将使研究小组进行实验，而不需要昂贵的消耗性低温液体。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。