Centre for Quantum Information & Quantum Control and Institute for Optical Sciences, Department of Physics, University of Toronto, 60 Saint George Street, Toronto, Ontario M5S 1A7, Canada.
Centre for Quantum Information & Quantum Control and Institute for Optical Sciences, Department of Physics, University of Toronto, 60 Saint George Street, Toronto, Ontario M5S 1A7, Canada and Research Institute for Electronic Science, Hokkaido University, Kita-ku, Sapporo 060-0812, Japan and The Institute of Scientific and Industrial Research, Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan.
Phys Rev Lett. 2014 Jun 6;112(22):223602. doi: 10.1103/PhysRevLett.112.223602. Epub 2014 Jun 2.
N00N states-maximally path-entangled states of N photons-exhibit spatial interference patterns sharper than any classical interference pattern. This is known as superresolution. However, even given perfectly efficient number-resolving detectors, the detection efficiency of all previous measurements of such interference would decrease exponentially with the number of photons in the N00N state, often leading to the conclusion that N00N states are unsuitable for spatial measurements. A technique known as the "optical centroid measurement" has been proposed to solve this and has been experimentally verified for photon pairs; here we present the first extension beyond two photons, measuring the superresolution fringes of two-, three-, and four-photon N00N states. Moreover, we compare the N00N-state interference to the corresponding classical superresolution interference. Although both provide the same increase in spatial frequency, the visibility of the classical fringes decreases exponentially with the number of detected photons. Our work represents an essential step forward for quantum-enhanced measurements, overcoming what was believed to be a fundamental challenge to quantum metrology.
N00N 态——即 N 个光子的最大路径纠缠态——表现出比任何经典干涉图样都更清晰的空间干涉图案。这被称为超分辨率。然而，即使使用效率完美的数分辨探测器，以前对这种干涉的所有测量的探测效率都会随着 N00N 态中光子数量的指数级增加而降低，这通常导致 N00N 态不适合空间测量的结论。一种称为“光学质心测量”的技术已被提出以解决此问题，并已在光子对的实验中得到验证；在这里，我们首次将其扩展到两个光子之外，测量了两个、三个和四个光子 N00N 态的超分辨率条纹。此外，我们将 N00N 态干涉与相应的经典超分辨率干涉进行了比较。尽管两者都提供了相同的空间频率增加，但经典条纹的可见度会随着探测到的光子数量的指数级增加而降低。我们的工作代表了量子增强测量的重要一步，克服了被认为是量子计量学的一个基本挑战。
