High-NOON States by Mixing Quantum and Classical Light

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Science  14 May 2010:
Vol. 328, Issue 5980, pp. 879-881
DOI: 10.1126/science.1188172

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All and Nothing

Entanglement, where a system can be in a superposition of a number of distinct states simultaneously, is a principle at the foundation of quantum mechanics (recall Schrödinger's cat, which is both dead and alive). It can also be used in many applications—imaging, communication, patterning, and metrology—with the effect being amplified by entangling larger systems. However, the systematic generation of “large” entangled systems is challenging. Afek et al. (p. 879; see the Perspective by Wildfeuer) present a technique for generating many-photon entanglement in so-called NOON states, where there are two possible paths and N photons in one path and 0 in the other—the system being a superposition of “all and nothing” states. Mixing of entangled pairs with classical light at a beam splitter formed up to five photon-entangled states. The technique should be generally applicable to generate higher-order entangled states.


Precision measurements can be brought to their ultimate limit by harnessing the principles of quantum mechanics. In optics, multiphoton entangled states, known as NOON states, can be used to obtain high-precision phase measurements, becoming more and more advantageous as the number of photons grows. We generated “high-NOON” states (N = 5) by multiphoton interference of quantum down-converted light with a classical coherent state in an approach that is inherently scalable. Super-resolving phase measurements with up to five entangled photons were produced with a visibility higher than that obtainable using classical light only.

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