Quantum Superposition States of a Mirror

量子力学是基于对系统的波力学描述和冯·诺伊曼假设(1920年代)，即量子测量导致不确定的结果。波-力学描述允许一个系统的叠加状态(例如，一个物体同时在两个地方)，而冯·诺依曼假设意味着人们不能直接检测到这样的叠加。环境诱导退相干的模型确实解释了为什么量子叠加在日常生活中没有被观察到，然而测量结果的不确定性仍然是许多争论的主题。这个研究方案的目的是创建一个包含10^14个原子的量子叠加态。这种量子叠加态的质量将比迄今观察到的任何量子叠加态的质量大十个数量级，因此将在新的方案中提供量子力学的基本测试。该实验包含一个微小的镜子(直径小于人类头发的厚度)，它是光学腔的一部分，它构成了干涉仪的一只手臂。这种镜子安装在一个微小的硅棒上，可以通过光子的多次反射而移位。单个光子被送入干涉仪，并将演变为与微小反射镜在光学腔内的叠加，从而使其轻微移位，并处于干涉仪的另一臂中，使反射镜保持静止。因此，单个光子的叠加被转移到镜面的叠加，或者更准确地说，镜面与光子纠缠。通过观察离开干涉仪的光子的干涉，人们可以研究涉及镜面的叠加的产生和消相干。初步实验得到了美国国家科学基金会为期一年的探索性研究拨款的支持，并取得了显著的初步进展；利用聚焦离子束制造了直径20微米的高质量布拉格反射镜，并将其放置在硅悬臂上[原子力显微镜(AFM)的尖端]。悬臂梁/反射镜系统已经被压电地定位为光学腔的端镜。在空气中的测量表明，最初的空腔精确度为1000。该精密测量系统的各个组件将在许多其他领域的应用中产生兴趣，并产生直接的社会效益。预计的副产品项目是超高速可切换反射镜(用于光通信)、超高分辨率AFM读出和微机械振荡器的光学冷却(用于位置测量)。该项目将提供出色的培训，因为它将基础研究兴趣与尖端技术结合在一起。由于该项目涉及不同的子项目，计划每年夏天有几名本科生研究人员协助该项目，以及一名高中生参加UCSB暑期科学教育计划。

Quantum Mechanics is based on a wave-mechanical description of a system and on the von Neumann postulate (1920s) that a quantum measurement results in an indeterministic outcome. The wave-mechanical description allows for superposition states of a system (e.g. an object being in two places at the same time), and the von Neumann postulate implies that one cannot directly detect such a superposition. Models of environmental induced decoherence do give an explanation of why quantum superpositions are not observed in everyday life, however the indeterministic nature of the measurement outcome is still the topic of many debates. The aim of this research proposal is to create a quantum superposition states involving of order 10^14 atoms. Such quantum superposition states will be ten orders of magnitude more massive than any quantum superposition observed to date and will therefore provide a fundamental test of quantum mechanics in a new regime.The experiment contains a tiny mirror (smaller in diameter than the thickness of a human hair) that is part of an optical cavity, which forms one arm of an interferometer. The mirror is mounted on a tiny Silicon rod and can be displaced by the multiple reflections of a photon. A single photon is sent into the interferometer and will evolve into a superposition of being inside the optical cavity with the tiny mirror, thereby slightly displacing it, and being in the other arm of the interferometer, leaving the mirror at rest. The superposition of a single photon is therefore transferred to a superposition of the mirror, or more precise, the mirror becomes entangled with the photon. By observing the interference of the photon leaving the interferometer one can study the creation and decoherence of superpositions involving the mirror. Preliminary experiments have been supported by a one-year NSF exploratory-research grant and led to remarkable initial progress; a high-quality Bragg mirror of diameter 20 microns has been fabricated using a focussed ion beam and has been positioned onto a Silicon cantilever [tip of an atomic force microscope (AFM)]. The cantilever/mirror system has been piezo-positioned to be the end mirror of an optical cavity. Measurements in air showed an initial cavity finesse of 1000.The individual components of the precision measurement system will be of interest for applications in many other fields with direct benefits to society. Anticipated spin-off projects are ultra-fast switchable mirrors (for optical communication), ultra-high resolution AFM readout, and optical cooling of micro-mechanical oscillators (for position measurements). The project will provide excellent training since it combines fundamental research interests with cutting-edge technologies. Since the project involves different subprojects, it is the intention to have several undergraduate researchers assisting the project each summer, as well a high-school students participating in the UCSB summer science education program.