Quantum phenomena in rotating solid helium

固体氦-4是量子晶体的一个例子，因为存在大的量子涨落（零点运动）。它为研究晶体物质的量子行为和结构缺陷（如位错（晶体线缺陷））提供了理想的测试平台。Kim和Chan的实验表明，固体氦的一小部分似乎与他们的容器（扭转振荡器）的振荡运动解耦，这引发了关于所谓的超固体（即固体的矛盾超流体流动）是否在固体氦中发生的巨大争议。最近的研究指出，这种效应很大程度上是由于位错运动引起的固体氦的异常量子塑性，以及由于氦-3杂质在极低温度下的钉住而导致的随后的冻结。然而，最近有几个涉及四个不同研究小组的其他观察结果表明，稳定的直流旋转可能与弹性的变化无关，而是由于一些奇异的量子行为和可能的超固体性。对这些实验的正确解释是不明确和有争议的。此外，Hallock小组还观察到直接直流质量流通过固体氦，这被解释为由于沿位错核心的超流。因此，需要新的实验来寻找固体氦中量子相干性（如超固体性）的明确证据。在许多不同的实验中，旋转已经成功地用于探测氦超流体，也许最引人注目的是在证明持续的质量流（由于没有耗散的流动）-超流体的“确凿证据”。当固体氦被旋转时，我们将使用我们新的旋转稀释冰箱来寻找新的量子现象。首先，我们将寻找由于扭转振荡器中固体氦盘的稳定旋转而产生的影响，这些影响与弹性效应无关，弹性效应将同时使用剪切板进行测量。其次，我们将通过使用高灵敏度陀螺仪测量环形通道中旋转产生的流动角动量，直接搜索固体氦中的持续质量流。对持续电流的观察将构成超固体行为的直接证据。由于机械搅拌引起的塑性效应和松弛，如旋转的快速变化也将被研究。

Solid helium-4 is an example of a quantum crystal due to the presence of large quantum fluctuations (zero point motion). It provides an ideal testbed for investigating the quantum behaviour of crystalline matter and structural defects such as dislocations (crystallographic line defects). Experiments by Kim and Chan, showed that a small component of solid helium appeared to decouple from the oscillatory motion of their container (a torsional oscillator), sparking a huge amount of controversy regarding whether so-called supersolidity (i.e. the paradoxical superfluid flow of a solid) occurs in solid helium. The most recent research points towards the effect been largely due to the anomalous quantum plasticity of solid helium due to the motion of dislocations and their subsequent freezing due to pinning by helium-3 impurities at very low temperatures.However, there have been several other very recent observations involving four different research groups of an effect due to steady DC rotation that may be independent of the changes in elasticity and instead due to some exotic quantum behaviour and perhaps supersolidity. The correct interpretation of these experiments is unclear and controversial. In addition, the group of Hallock has observed direct DC mass flow through solid helium which has been interpreted as being due to superflow along the cores of dislocations. There is thus a need for new experiments to search for unambiguous evidence of quantum coherence (such as supersolidity) in solid helium. Rotation has been successfully used to probe the helium superfluids in many different experiments, perhaps most remarkably in the demonstration of persistent mass currents (due to flow with no dissipation) - the "smoking gun" of superfluidity. We will use our new rotating dilution refrigerator to search for novel quantum phenomena when solid helium is rotated. Firstly, we will look for effects due to steady rotation on a disk of solid helium housed in a torsional oscillator that are independent of elastic effects, which will be measured simultaneously using shear plates. Secondly, we will conduct a direct search for persistent mass currents in solid helium by measuring the angular momentum of flow generated by rotation in an annular channel using a high-sensitivity gyroscope. Observation of persistent currents would constitute direct evidence of supersolid behaviour. Plastic effects and relaxation due to mechanical agitation, such as rapid changes in rotation will also be investigated.