Investigation of transport of superfluid 4He through 2D materials

超流氦，出现在冷却到2.17K（-455.8F）以下的液氦中，是“量子材料”的一个惊人的例子-这种材料的不寻常和违反直觉的特性需要量子物理学来理解。 超流体的一个显著特性是能够无摩擦地移动，甚至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级薄片碳（石墨烯）中纳米直径孔的运动，他们意外地观察到，当处于超流状态时，氦似乎能够即使没有孔也能穿过碳片。 目前的项目通过一系列实验更彻底地探索这一观察。 如果他们确实验证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，这可能涉及更多奇异的和尚未发现的物质状态，例如超级固体。 更广泛地说，这项工作预计将导致使用这种独特的量子材料的技术上有用的量子设备。 该奖项将使教育和专业发展的各个阶段的年轻科学家在量子器件和超灵敏测量领域，这两个已被确定为国家重要领域的教育。技术摘要基于超流氦-4量子器件尚未得到彻底发展，由于缺乏低温约瑟夫森结结构。 困难是由于氦原子的质量，其抑制量子隧穿，甚至通过原子级薄膜，和0.3 nm的低温相干长度，其需要原子级大小的孔来衰减量子序参数。 最近，Schwab研究小组进行了实验，以探测超流氦通过石墨烯片中纳米尺寸的孔的运输。 这些石墨烯片覆盖氮化硅膜中的2微米直径的孔。令人惊讶的是，经过一系列的测量，石墨烯片似乎对超流体状态下的氦是透明的。 这与石墨烯对氦的传输应该是极不透明的预期相反。 目前的种子项目将通过一系列控制实验来解决这个问题。 如果得出结论，石墨烯确实对超流氦是透明的，这可能表明在氦的前几层上形成了超固态，这是许多理论家预期的可能性，以及尚未观察到的新的物质量子态。 如果得出结论，石墨烯是不透明的，正如最初预期的那样，这里的实验将为实验提供信息，为超流氦创造低温约瑟夫森结，这有望导致实现新型量子器件。 超流体量子器件有望在超灵敏导航方面取得进展，可用于潜艇以及望远镜和激光器的精确指向，并产生用于量子信息处理和精确量子标准的新型器件。 此外，该种子将提供资金购买无冷冻剂的低温恒温器，这将使研究团队能够在不使用昂贵的消耗性低温液体的情况下进行实验。该奖项反映了NSF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。

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.