Quantum Interferometry with Photon-Subtracted Twin Beams

物理学依赖于对自然和宇宙的实验观察，并进行更精确的测量。 因此，提高物理测量的精度和灵敏度是推动科学进步的关键。 这个项目将探索一种新的方法来改善测量使用量子光学推进干涉测量的艺术。 干涉测量是最精确的测量方法之一，其中测量两个波之间的相位差，以获得有关导致这种相位差的物理定律的信息。 激光干涉仪引力波天文台（LIGO）是干涉测量力量的一个壮观的例证，它揭示了宇宙中黑洞合并引起的时空结构的微小涟漪，自2015年秋季以来观察到了三次这样的事件。干涉测量的其他流行例子包括微光刻中的高分辨率相位掩模，这对半导体芯片制造和计算机工业中的摩尔定律至关重要;显微镜的干涉测量技术，如生物学中的相位对比成像;以及用于精确原子钟的拉姆齐干涉测量。因此，该项目的结果可能会对许多关键技术领域产生重大影响。干涉仪（如LIGO和原子钟）的最终灵敏度取决于量子力学。事实上，任何干涉仪，例如光学干涉仪，都具有量子力学测量噪声基底，这是光的波动（电磁波）和微粒（光子）性质之间的量子对偶性的结果。经典的干涉仪，如LIGO和原子钟在其当前版本中，是散粒噪声有限的，这意味着它们的相位噪声基底是测量中使用的平均粒子数（光子或原子）的平方根的倒数。然而，这离最终的海森堡极限还很远，海森堡极限是平均粒子数的倒数。这个极限可以通过干涉仪中使用的光波的“量子工程”来达到。该项目提出了一种新型的海森堡限幅干涉仪，其中双光束，即光学参量放大器发射的光子相关光束，在它们被用作马赫-曾德尔干涉仪的输入之前，以不可分辨的方式从它们中减去一个光子。该项目在海森伯有限干涉测量的所有先前提案中是独一无二的，因为它具有海森伯有限噪声基底，强烈的直接干涉条纹信号，并且使用最先进的量子光学技术在实验上是可行的，该技术先前在弗吉尼亚大学的Pfister教授小组中得到了证明。如果成功，该项目可以带来相位衬度成像的多个数量级的测量灵敏度提高，这将允许通过应用量子光进行无损体内生物成像。

Physics relies on the experimental observation of Nature and the Universe, with ever more precise measurements. Improving the precision and sensitivity of physical measurement is therefore key to furthering the progress of science. This project will explore a novel method to improve measurements using quantum optics to advance the art of interferometry. Interferometric measurements, in which the phase difference between two waves is measured in order to gain information about the physical laws that cause such a phase difference, are among the most precise classes of measurements. A spectacular illustration of the power of interferometry is the Laser Interferometer Gravitational-wave Observatory (LIGO), which has revealed the minescule ripples of the fabric of space-time caused by the merging of black holes in the cosmos, with three such events observed since the fall of 2015. Other prevalent examples of interferometry include high-resolution phase masks in microlithography, crucial to semiconductor chip fabrication and Moore's law in the computer industry; interferometric techniques for microscopy, such as phase contrast imaging in biology; and Ramsey interferometry, used for precise atomic clocks. Thus the results of this project can have a significant impact in a number of critical areas of technology.The ultimate sensitivity of interferometers such as LIGO and atomic clocks is dictated by quantum mechanics. Indeed, any interferometer, for example an optical one, possesses intrisically quantum mechanical measurement noise floors which are consequences of the quantum duality between the undulatory (electromagnetic wave) and corpuscular (photon) nature of light. Classical interferometers, such as LIGO and atomic clocks in their current versions, are shot-noise limited, which means their phase noise floor is of the order of the reciprocal of the square root of the average particle number (photon or atom) used in a measurement. However, this is far from the ultimate, Heisenberg, limit, which is of the order of the reciprocal of the average particle number. This limit can be reached by "quantum engineering" the light waves used in the interferometer. This project puts forward a new type of Heisenberg-limited interferometer, in which twin optical beams, the photon-correlated beams emitted by a optical parametric amplifier, see one photon subtracted from them in an indistinguishable manner before they are used as input in a Mach-Zehnder interferometer. The project is unique among all previous proposals for Heisenberg-limited interferometry in that it features a Heisenberg-limited noise floor, a strong, direct interference fringe signal, and is experimentally feasible using state-of-the-art quantum optics technology that was previously demonstrated in the group of Prof. Pfister at the University of Virginia. If successful, this project could bring about multiple orders of magnitude measurement sensitivity improvement in phase-contrast imaging, which would allow nondestructive in vivo biological imaging by applying quantum light.