Quantum Imaging

成像是许多学科中的重要技术工具，例如生物医学研究、纳米技术和基础物理研究。然而，由于光的波动性质，在经典成像技术中可以实现的分辨率和对比度存在限制。另一方面，量子纠缠可以提供对这些经典限制的改进，从而导致量子成像的主题。最著名的量子成像协议是双光子显微镜和光谱学，量子全息术，量子光刻术和量子照明。理解经典成像和量子成像之间的精确区别有两个原因。首先，它将有助于确定改进成像的新方法，可能导致新技术。其次，它将揭示物理学的一个基本方面，这一点迄今为止仍然难以捉摸，即是什么使量子光学在成像方面比经典光学更强大。这个问题的答案显而易见，即，量子纠缠，在某种程度上已经被证明是错误的。虽然纠缠可能是必要的，但它肯定是不够的。这让人想起了量子计算，在量子计算中，纠缠是必要的，但不足以获得承诺的指数加速超过经典计算。当我们试图理解经典成像和量子成像之间的差异时，我们遇到的第一个问题是缺乏成像质量的可操作定量测量。因此，我们需要一个定量的措施，为实际的成像协议，提供了一个明确的阈值之间的经典和量子制度。其次，纠缠在量子成像中究竟扮演什么角色？此外，是否有可能推导出量子成像的成像质量测量的基本界限？第三，一旦发现了客观成像测量的基本极限，一个明显的问题是什么程序使这个界限饱和。

Imaging is an important technological tool in many disciplines, such as biomedical research, nanotechnology, and basic physics research. However, due to the wave nature of light there are limits in resolution and contrast that can be achieved in classical imaging techniques. On the other hand, quantum entanglement may offer an improvement over these classical limits, leading to the subject of quantum imaging. The best known quantum imaging protocols are two-photon microscopy and spectroscopy, quantum holography, quantum lithography, and quantum illumination. There are two reasons why it is important to understand the precise distinction between classical and quantum imaging. First, it will help identify new methods for improved imaging, potentially leading to new technology. Second, it will reveal a fundamental aspect of physics that has hitherto remained elusive, namely what makes quantum optics more powerful in imaging than classical optics. The obvious answer to this question, i.e., quantum entanglement, has already been proved false to some extent. While entanglement is probably necessary, it is certainly not sufficient. This is reminiscent of quantum computing, where it was shown that entanglement is necessary but not sufficient for obtaining the promised exponential speed-up over classical computing.The first problem we encounter when we try to understand the difference between classical and quantum imaging is the lack of an operational quantitative measure of the imaging quality. We therefore need a quantitative measure for practical imaging protocols that provides a well-defined threshold between the classical and the quantum regime. Secondly, what exactly is the role of entanglement in quantum imaging? Furthermore, is it possible to derive fundamental bounds on quantum imaging with respect to the imaging quality measure? Thirdly, once a fundamental limit on the objective imaging measure has been found, an obvious question is what procedures saturate this bound.