Dilution refrigerator

今天的干涉引力波探测器已经受到量子噪声的限制，在很宽的探测频率范围内。一般量子光学的许多桌面实验也受到量子噪声的限制，特别是量子辐射压力噪声对测量精度造成了根本性的限制。在我们的“量子控制”小组中，我们正在研究减少量子辐射压力噪声的实验实现方法，这既可以用于未来的引力波探测器，也可以用于一般的量子光学应用（例如小力的测量）。我们小组正在研究的最突出的方法是“相干量子噪声消除”（CQNC），该方法正在我们的实验室中实现，作为一种全光学装置，使用微光机械振荡器作为光力学耦合测试质量。在这里，发生的量子辐射压力噪声（由光和质量的光力学耦合引起）通过定制的“抗噪声过程”（由分束器相互作用和参数下转换过程组成）的破坏性干涉来减少。为了在我们的CQNC实验中使用，所使用的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（<50 ng），共振频率在300 kHz至500 kHz范围内，具有中等的机械Q因子（约1000），以及高（光学）反射率（用于光学谐振器中的光机械耦合端镜）。为此，我们使用光子晶体膜。由于所述的边界条件，热噪声主导了振荡器在室温下的运动（位置不确定性），使得量子辐射压力噪声的测量成为不可能。因此，对于任何量子降噪方案（如CQNC），绝对有必要通过降低振子的温度来降低热噪声，从而使量子辐射压力噪声成为主导并因此可检测到。只有这样，我们的量子辐射降压降噪实验才能产生可测量的结果。必须达到的温度在50 mK以下（最好是10 mK）。这些超低温只有用稀释冰箱才能达到，就像我们在这里申请的那样。CQNC是关于光力学系统中量子降噪主题的一系列实验中的第一个，我们正在研究并计划在我们的小组中实验实现。对于所有的实验，都需要在超低温下操作，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.