Quantum Cavity Optomechanics of Levitated Nanoparticles: from Foundations to Technologies

微观世界中的过程可以用量子理论很好地描述，但对于宏观尺度上向经典世界的过渡却知之甚少。例如，像病毒这样的宏观物体能否被置于量子叠加态，如果不能，在这些长度和质量尺度上是什么过程阻止了这一点？这些类型的问题不仅对我们对世界的基本理解很重要，而且还将影响未来工程宏观量子系统的发展。直到最近，这些问题仍然主要是理论上的追求，因为在存在环境噪声的情况下制备和保持精细量子态所需的实验方法还不存在。这是因为即使是量子系统与其环境之间的弱相互作用也可以迅速摧毁它们。因此，这些系统必须在良好控制的隔离下制备，并且通常，这通常需要冷却至非常低的温度。新的实验技术为宏观量子力学的实验室测试提供了前景。这个领域，统称为量子腔光学力学，使用光与纳米级和微米级振荡器的机械运动的受控相互作用，以相干地控制它们的运动。到目前为止，量子基态冷却只在少数这些固态设备中得到了证明，但宏观叠加，甚至非经典运动，还没有被观察到。UCL小组最近研制了一种新的悬浮在真空中的光机械振荡器系统。它使用了一种新颖的电场和光场配置，以实现与环境的极好隔离。通过采用一种称为腔冷却的技术，首次实现了从室温到毫开尔文温度的冷却，量子基态冷却现在已经触手可及。我们在这项研究计划中的目标是通过使用混合技术来创建一个良好控制的，低耗散的宏观振荡器，可以在其绝对基态下制备，从而建立在这一初步成功的基础上。该系统将允许我们通过准备和测量其非经典运动来探索宏观量子力学。我们将首次对宏观波函数坍缩的理论模型进行实验室测试。即使系统不处于基态，这也是可能的。该振荡器系统的极低噪声和高机械Q值也为传感应用提供了重要的前景。因此，作为这项研究计划的一部分，我们将开始探索这些更经典的应用，其中包括开发一种新型的阱内光谱仪，能够测量纳米粒子的质量，电荷和形状，而另一条链将寻求使用悬浮粒子之间的可调相互作用来控制，切换和存储光场。

Processes in the microscopic world are extremely well described by quantum theory, but yet little is known about the transition to the classical world at macroscopic scales. For example, can a macroscopic object such as a virus be put into a quantum superposition, and if not, what are the processes at these length and mass scales that prevent this? These types of questions are not only important for our fundamental understanding of the world but they will also impact on the development of future engineered macroscopic quantum systems. Until very recently these questions remained a primarily theoretical pursuit because the experimental methods required to prepare and maintain the delicate quantum states in the presence of environmental noise did not exist. This is because even weak interactions between a quantum system and its environment can rapidly destroy them. As such, these systems must be prepared in well controlled isolation, and typically, this often requires cooling to very low temperatures. New experimental techniques now offer the prospect for laboratory tests of macroscopic quantum mechanics. This field, collectively known as quantum cavity optomechanics, uses the controlled interaction of light with the mechanical motion of nanoscale and microscale oscillators, to coherently control their motion. To date quantum ground state cooling has been demonstrated in only a handful of these solid-state devices but a macroscopic superposition, and even non-classical motion, has yet to be observed. A new optomechanical oscillator system that is levitated in vacuum has recently been developed by the UCL group. It uses a novel configuration of electric and optical fields to achieve extremely good isolation from the environment. Cooling from room temperatures down to milliKelvin temperatures has been achieved for the first time, by employing a technique called cavity cooling, with quantum ground state cooling now within reach. Our aim in this research programme is to build on this initial success by using the hybrid technologies to create a well controlled, low dissipation macroscopic oscillator, that can be prepared in its absolute ground state. This system will allow us to explore macroscopic quantum mechanics by preparing and measuring its nonclassical motion. For the first time, we will undertake laboratory tests of theoretical models for macroscopic wavefunction collapse. This will be possible even when the system is not in the ground state. The very low noise and high mechanical Q of this oscillator system also offers significant promise for sensing applications. Therefore as part of this research programme we will begin to explore these more classical applications which includes the development of a new type of in-trap spectrometer capable of measuring mass, charge and shape of nanoparticles, while another strand will seek to use the tunable interactions between the levitated particle for controlling, switching and storing light fields.