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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Characterization of nonclassical light and new methods for its production

G. S. Agarwal

Published Oct 28, 1992• 0 citations
Publisher

Abstract

In this lecture I consider the question of characterization of nonclassical light in terms of measurable quantities. I show that there are many situations where the usual methods based on the Q and S parameters fail and which call for new measures of the nonclassical light. I also present newer methods of producing nonclassical states of quantum systems.

DOI
10.1117/12.140325

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In this lecture I consider the question of characterization of nonclassical light in terms of measurable quantities. I show that there are many situations where the usual methods based on the Q and S parameters fail and which call for new measures of the nonclassical light. I also present newer methods of producing nonclassical states of quantum systems.
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A great deal of research in optics concentrates on developing quantum methods ranging from precision measurement to optical telecommunication, and from quantum information processing to fundamental tests of nature. To this aim, engineering and characterization of quantum states of light becomes extremally important. Nonclassical sources are based on various underlying physical phenomena, from parametric downconversion and four-wave mixing to solid state and atomic single emitters to ensembles of atoms or ions. I will discuss recent efforts in engineering and characterization of nonclassical light states applicable to a broad range of sources, predominantly based on tunable narrow-band filtering.
Nonclassical states of light are necessary resources for quantum technologies such as cryptography, computation and the definition of metrological standards. Distinguishing nonclassical states from those that can be described without invoking quantum mechanics is both a necessary practical task and of fundamental interest. In general, signatures of nonclassicality arise from apparently pathological behaviour of the quasi-probability distributions used to describe the states. While tomographic reconstruction of the state is therefore sufficient to show nonclassicality, it is often more convenient to probe photon-counting statistics of on-off detectors directly. This is formalised by the Mandel Q-parameter QM= 〈Δn〉 / 〈n〉 - 1, which is negative for sub-Poissonian statistics arising from nonclassical states. However, the Mandel Q-parameter can fail when using a multiplexed array of on-off detectors to measure states with several photons; splitting in this manner can corrupt its original statistics. A new parameter, QB= N 〈(Δ c) 2 〉 / 〈 c 〉 (N - 〈 c 〉) can be used to witness nonclassicality directly from such click statistics. For QB<; 0, such statistics are thus deemed sub-binomial and therefore arise from a nonclassical state.