Quantum Many Body Control and Metrology with an Atom-Light Interface

技术的核心是设计和控制可以执行所需任务的物理系统（设备）。 设备越复杂，它由许多相互连接的部件组成的可能性就越大，例如计算机中的硬件。 物理学家早就知道，当整个网络（节点和互连）受量子力学定律支配时，互连系统的行为将发生根本性的变化，最近的工作表明，这可以大大提高计算机，通信网络和传感器的性能。 建造和操作这种量子设备仍然是现代科学的一个巨大挑战。 该项目将通过开发可以连接远程量子系统的量子接口做出贡献。主要目标是使用激光，首先连接和“纠缠”被限制在激光“陷阱”中的原子的量子态，然后对它们进行量子限制测量。 原子系综用于最精确的时间传感器（原子钟）、旋转和加速度传感器（惯性传感器）以及磁场传感器。 首席研究员和其他人已经证明，量子接口可以用来抑制测量的内在量子不确定性（一种被称为“挤压”的现象），从而提高这种原子传感器的精度，使其超过“标准”极限。该项目旨在通过最佳利用原子的内部结构来增加压缩量，目的是将测量灵敏度提高一个数量级。 第二个目标是探索原子-光量子界面的一个版本，其中光由光学晶体引导，并与被困在其表面附近的原子重叠。 这种几何结构更加紧凑，并且具有在基于光纤的网络中作为量子节点操作的潜力。从单个粒子到复杂的多体系统的所有尺度上的量子控制是量子力学第二个世纪的巨大挑战。在过去十年中，在实现这一目标方面取得了重大进展，包括在现实世界的技术能力方面取得了重大进展。因此，非平凡的量子控制已经成为从量子计量学到模拟量子模拟和基本数字量子计算的实验中的常规。该项目的目标是在量子多体控制和量子计量学领域贡献新的想法和能力。上下文是Cs原子系综，由磁场驱动并耦合到量子化光场，以产生纠缠并进行量子限制测量。两个不同的版本将被研究：一个“自由空间”的几何结构与偶极阱耦合到一个傍轴探测光束的原子，和一个“微”的几何结构与原子捕获和探测周围的光学微扰的倏逝场。首席研究员带来了复杂原子内部状态控制的专业知识，可以显着提高原子-光界面的纠缠能力。纠缠功率的一个常用度量是在测量集体原子自旋时由量子反作用产生的自旋压缩。 初步研究表明，通过对原子内态的优化控制，可以将压缩效应从约3dB提高到8dB，达到与腔增强实验相当的水平。该平台的开发程度较低，但缩短了衍射对自由空间中原子-光耦合的一些限制，并且有可能比腔增强装置更紧凑，更简单，更强大。

At its core, technology is concerned with the design and control of physical systems (devices) that can perform desired tasks. The more complex the device, the greater the likelihood that it will consist of many interconnected parts, as is the case, for example, with the hardware in a computer. Physicists have long known that the behavior of interconnected systems will change in fundamental ways when the entire network (nodes and interconnects) is governed by the laws of quantum mechanics, and more recent work has shown that this allows for dramatic improvements in the performance of computers, communication networks, and sensors. Building and operating quantum devices of this sort remains a grand challenge for modern science. This project will contribute by developing a quantum interface that can connect distant quantum systems. The main goal is to use laser light, first to connect and "entangle" the quantum states of atoms confined in a "trap" made of laser light, and subsequently to perform a quantum limited measurement on them. Ensembles of atoms are used in the most precise sensors of time (atomic clocks), of rotation and acceleration (inertial sensors), and of magnetic fields. The principal investigator and others have demonstrated that a quantum interface can be used to suppress the intrinsic quantum uncertainty of measurement (a phenomenon known as "squeezing"), and thus to improve the precision of such atomic sensors beyond the "standard" limit. This project seeks to increase the amount of squeezing that can be generated by making optimal use of the internal structure of the atoms, with the goal of boosting measurement sensitivity by an additional order of magnitude. A secondary goal is to explore a version of the atom-light quantum interface where the light is guided by an optical nanofiber and overlaps with atoms trapped close to its surface. This geometry is far more compact and has the potential to operate as a quantum node in an optical fiber based network.Quantum control on all scales, from single particles to complex many body systems, is a grand challenge for the second century of quantum mechanics. Over the past decade there has been substantial progress towards this goal, including significant advances in real-world technical capabilities. As a result, non-trivial quantum control has become routine in experiments ranging from quantum metrology to analog quantum simulation and rudimentary digital quantum computing. The goal of this project is to contribute new ideas and capabilities in the areas of quantum many body control and quantum metrology. The context is that of a Cs atomic ensemble, driven by magnetic fields and coupled to a quantized light field for the purpose of generating entanglement and performing quantum limited measurements. Two distinct versions will be studied: a "free-space" geometry with atoms in a dipole trap coupled to a paraxial probe beam, and a "nanofiber" geometry with atoms trapped and probed by evanescent fields around an optical nanofiber. The principal investigator brings expertise in internal state control of complex atoms that can significantly enhance the entangling power of the atom-light interface. A common measure of entangling power is the spin squeezing generated by quantum backaction when measuring the collective atomic spin. A preliminary exploration indicates that squeezing can be increased from a baseline of ~3dB to as much as 8dB through optimal control of the atomic internal state, reaching a level comparable to cavity enhanced experiments. The nanofiber platform is less developed, but short-circuits some of the limitations that diffraction imposes on atom-light coupling in free space, and has the potential to be more compact, less complex, and far more robust than cavity-enhanced setups.