Quantum Superposition States of a Mirror

量子力学基于对系统的波动力学描述和冯·诺伊曼假设（1920年），即量子测量的结果是不确定的。波动力学描述允许系统的叠加状态（例如，一个物体同时在两个地方），而冯·诺伊曼假设意味着人们不能直接检测到这种叠加状态。环境诱导退相干模型确实解释了为什么在日常生活中不能观察到量子叠加态，但是测量结果的不确定性仍然是许多争论的主题。这项研究计划的目的是创造一个涉及10^14阶原子的量子叠加态。这样的量子叠加态将比迄今为止观测到的任何量子叠加态都要大10个数量级，因此将为量子力学在新体制下的基本测试提供依据。这个实验包含了一个微小的镜子（直径比人类头发的厚度还小），它是光学腔的一部分，形成了干涉仪的一个臂。镜子安装在一个微小的硅棒上，可以通过光子的多次反射来移动。一个光子被送入干涉仪，并将演变成一个叠加在光学腔内的微小反射镜，从而略微取代它，并在干涉仪的另一个臂上，使反射镜静止。因此，单个光子的叠加态被转移到镜子的叠加态，或者更准确地说，镜子与光子纠缠在一起。通过观察离开干涉仪的光子的干涉，可以研究涉及镜面的叠加的产生和退相干。初步实验得到了为期一年的国家科学基金会探索性研究基金的支持，并取得了显著的初步进展；一个高质量的直径为20微米的布拉格反射镜已经用聚焦离子束制造出来，并被放置在硅悬臂上[原子力显微镜（AFM）的尖端]。悬臂/镜系统已被压电定位为光学腔的端镜。在空气中的测量显示，初始空腔精细度为1000。精密测量系统的各个组成部分将在许多其他领域的应用中引起人们的兴趣，对社会有直接的好处。预期的衍生项目包括超高速可切换镜（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）。该项目将基础研究兴趣与尖端技术相结合，将提供优秀的培训。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员协助该项目，以及一名高中生参加UCSB夏季科学教育计划。

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.