Dilution refrigerator

今天的干涉式引力波探测器在很大的探测频率范围内已经受到量子噪声的限制。一般量子光学中的许多桌面实验也受到量子噪声的限制，其中特别是量子辐射压力噪声对测量精度构成了根本限制。在我们的“量子控制”小组中，我们致力于减少量子辐射压力噪声的方法的实验实现，这既是为了未来引力波探测器的潜在用途，也是为了在一般的量子光学中应用(例如，测量小力)。我们团队正在研究的最著名的方法称为相干量子噪声消除(CQNC)，我们的实验室正在实现一种全光学装置，使用微光机械振荡器作为光机耦合测试质量。在这里，发生的量子辐射压力噪声(由光和质量的光-机械耦合引起)通过破坏性干涉的方式被降低，该干涉具有量身定制的“抗噪声过程”(由分束器相互作用和参数下转换过程组成)。为了在我们的CQNC实验中使用，所用振荡器的规格必须在一个明确定义的参数范围内：我们需要非常小的质量(&lt；50 ng)，具有中等机械Q因子(约1000)的300 kHz到500 kHz范围内的共振频率，以及高(光学)反射率(用于光学谐振器中的光机耦合后镜)。为此，我们使用光子晶体薄膜。由于规定的边界条件，热噪声主导了振子在室温下的运动(位置不确定)，使得量子辐射压力噪声的测量变得不可能。因此，对于任何量子降噪方案(如CQNC)来说，通过降低振荡器的温度来降低热噪声是绝对必要的，使得量子辐射压力噪声成为主导，因此是可检测的。只有到那时，我们的量子辐射压力降噪实验才能产生可测量的结果。必须达到的温度在50MK以下(最好是10MK)。这些超低温只能通过稀释冰箱才能达到，就像我们在这里申请的那样。CQNC是我们正在研究并计划在我们的团队中实验实现的关于光学机械系统中量子噪声降低的一系列实验中的第一个。对于所有的实验，它们都必须在超低温下运行，因此，未来的所有工作都需要一个MK-低温恒温器。

Today's interferometric gravitational wave detectors are already limited by quantum noise over a wide range of detection frequencies. Many table-top experiments in general quantum optics are also limited by quantum noise, where in particular quantum radiation pressure noise poses a fundamental limitation to measurement accuracy. In our "Quantum Control" group we are working on experimental realisations of methods to reduce quantum radiation pressure noise, both for potential use in future gravitational wave detectors and for applications in quantum optics in general (e.g. measurement of small forces). The most prominent method under investigation in our group called "Coherent Quantum Noise Cancellation" (CQNC) is being realised in our laboratories as an all-optical setup using micro-optomechanical oscillators as optomechanically coupled test masses. Here, the occurring quantum radiation pressure noise (caused by the optomechanical coupling of light and masses) is reduced by means of destructive interference with a tailored "anti-noise process" (consisting of a beam splitter interaction and a process of parametric downconversion). For use in our CQNC experiment the specifications of the employed oscillators have to be in a clearly defined parameter range: We require a very small mass (<50 ng), resonance frequencies in the range of 300 kHz to 500 kHz with moderate mechanical Q factors (around 1000), and a high (optical) reflectivity (for use as optomechanically coupled endmirrors in optical resonators). To this end we use photonic crystal membranes. Due to the stated boundary conditions, thermal noise dominates the movement (position uncertainty) of the oscillators at room temperature, making a measurement of quantum radiation pressure noise impossible. For any quantum noise reduction scheme (such as CQNC) it is therefore absolutely necessary to reduce the thermal noise by reducing the temperature of the oscillators such that the quantum radiation pressure noise becomes dominant and hence detectable. Only then can our experiment for quantum radiation pressure noise reduction produce measurable results. The temperatures that have to be reached are in the range of below 50 mK (better: 10 mK). These ultra-low temperatures can only be reached with a dilution refrigerator, as we are applying for here.CQNC is the first in a range of experiments on the topic of quantum noise reduction in optomechanical systems that we are investigating and planning on experimentally realising in our group. For all experiments it will be necessary to operate them at ultra-low temperatures, hence a mK-cryostat is required for all future work.