Investigation of transport of superfluid 4He through 2D materials

非技术摘要超流氦出现在2.17K(-455.8华氏度)以下冷却的液氦中，是“量子材料”的一个令人惊叹的例子--一种需要理解量子物理的不寻常和反直觉的材料。超流体显著特性的一个例子是能够在没有摩擦的情况下移动，即使通过接近原子大小的孔和通道。在最近的一系列实验中，研究小组研究了超流氦通过原子薄层碳片(石墨烯)中纳米直径孔的运动，他们出人意料地观察到，当处于超流状态时，氦似乎能够通过碳片，即使没有孔。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。如果他们真的证实了之前令人惊讶的结果，他们的团队预计这将导致实验和理论的更多进步，可能涉及更奇异的和尚未发现的物质状态，如超固体。更广泛地说，这项工作有望导致使用这种独特的量子材料的技术上有用的量子设备。该奖项将使年轻科学家能够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接受教育，这两个领域都已被确定为国家重要领域。技术摘要由于缺乏低温约瑟夫森结结构，基于超流氦-4的量子器件尚未得到彻底开发。困难是由于氦原子的质量，即使在原子薄的薄膜中也抑制了量子隧道，以及0.3 nm的低温相干长度，这需要原子大小的孔来衰减量子序参数。最近，施瓦布研究小组进行了实验，以探索超流氦通过石墨烯薄片中纳米大小的孔的传输。这些石墨烯薄片覆盖了氮化硅薄膜上直径2微米的孔。令人惊讶的是，经过一系列测量后，似乎石墨烯薄片在超流状态下对氦是透明的。这与人们的预期相反，即石墨烯应该对氦的运输极其不透明。目前的SEED项目将通过一系列对照实验来解决这个问题。如果得出结论，石墨烯对超流氦确实是透明的，这可能表明在氦的头几层上形成了超固态，这是一种可能性，许多理论家已经预测到了这种可能性，以及一种尚未被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，这里的实验将为实验创造超流氦的低温约瑟夫森结提供依据，这有望导致新型量子器件的实现。超流体量子设备有望在超灵敏导航方面取得进展，用于潜艇和望远镜和激光的精确指向，并产生用于量子信息处理和精确量子标准的新型设备。此外，该种子将提供资金购买无冷冻剂低温恒温器，使研究团队能够在没有昂贵的消耗性低温液体成本的情况下进行实验。这一奖励反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.