Quantum Phase Measurement and Metrology using Four-Wave Mixing

精密光学测量在灵敏度和分辨率上受到用于测量的光的噪声的限制。在日常生活中，光的经典描述通常就足够了。然而，采用这种方法会导致对测量灵敏度的限制，这不是根本的限制。如果用量子力学来描述光，那么我们就可以设想“非经典”光场，这将导致比“经典”光更灵敏的测量。这种额外的灵敏度可用于国防应用中的超灵敏检测，并且在非常低的光照水平下特别有用。因此，在活体生物组织成像领域，人们希望避免对组织的损害，这是很有趣的。该项目将利用某些材料的非线性光学特性来创造非经典光，并研究在经典光的限制上可以实现多少优势。特别是，该团队展示了一种光学相位测量装置，它比使用激光源的“经典”干涉仪对长度变化具有更高的灵敏度。该小组将进一步研究不同的基于量子的相位测量设备的设计，并研究这些方法的哪些方面导致更好的测量。非经典光的噪声统计数据与经典光不同，这将使该团队能够以低于相干状态或其他“近经典”光场的噪声水平进行测量。在计量应用中使用固有量子态，例如干涉测量，将使该小组能够改进这些测量，而不仅仅是用经典光获得的测量结果。该团队研究如何利用量子态来降低噪声，并证明这些状态的有用性和/或局限性。本项目重点研究基于“有源介质”的相位测量装置，具有增益或受激损耗。该团队将研究种子版本，基于使用放大的种子光束进行相位测量，以及非种子版本，基于单独使用自发发射。他们计划将这些干涉仪作为相位测量工具，并作为研究这些设备内部量子态的一种手段。在量子态方面，他们将研究直接调制量子态的效果，特别是调制双模压缩态中的一个模。

Precision optical measurements are limited in sensitivity and resolution by the noise on the light used to make them. In everyday life a classical description of light usually suffices. However taking this approach leads to limitations on the sensitivity of measurements that are not fundamental. If one uses a quantum mechanical description of the light, then one can envision "non-classical" light fields that will lead to more sensitive measurements than with "classical" light. This extra sensitivity can be used for ultrasensitive detection in defense applications and is especially useful at very low light levels. Thus it is interesting in the field of imaging of live biological tissues where one would like to avoid damage to the tissue. This project will use the non-linear optical properties of certain materials to create non-classical light and investigate how much advantage over the limits for classical light can be achieved. In particular, this team has demonstrated an optical phase measurement device that has more sensitivity to length changes than a "classical" interferometer using a laser source. The group will further investigate the design of different quantum-based phase measurement devices and study what aspects of these approaches lead to better measurements. Non-classical light, which has different noise statistics than classical light, will allow this team to make measurements with noise levels that are below those obtainable with a coherent state or other "nearly classical" optical fields. The use of intrinsically quantum states in metrological applications, such as interferometry, will allow the group to improve such measurements beyond what can be obtained with classical light. This team studies how to take advantage of quantum states for noise reduction and demonstrate the usefulness and/or limitations of these states. In particular, this project is centered on studying phase-measurement devices based on "active-media", with gain or stimulated loss. The team will study seeded versions, based on phase measurements using an amplified seed beam, as well as unseeded versions, based on the use of spontaneous emission alone. They plan to both look at these interferometers as phase measurement tools, and as a means to study the quantum states that are internal to these devices. In terms of the quantum states, they will study the effect of directly modulating a quantum state, and in particular, modulating one mode of a two-mode squeezed state.