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Nonlinear Optics: Materials, Fundamentals, and Applications. Technical Digest. Postconference Edition. TOPS Vol.46 (IEEE Cat. No.00CH37174)

Quantum jumps in backaction evasion measurements of a light field component

Holger Friedrich Hofmann, Toshiki Kobayashi, Akira Furusawa

Published Nov 7, 2002• 0 citations
Publisher

Abstract

Backaction evasion measurements of a quadrature component of the light field vacuum necessarily induce quantum jumps in the photon number. The correlation between measurement results and quantum jump events reveals fundamental nonclassical aspects of quantization.
DOI
10.1109/nlo.2000.883646

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It is shown that the quantum jumps in the photon number https://www.w3.org/1998/Math/MathML" display="inline"> n ^ from zero to one or more photons induced by backaction evasion quantum nondemolition (QND) measurements of a quadrature component https://www.w3.org/1998/Math/MathML" display="inline"> x ^ of the vacuum light field state are strongly correlated with the quadrature component measurement results. This correlation corresponds to the operator expectation value https://www.w3.org/1998/Math/MathML" display="inline"> x ^ n ^ x ^ , which is equal to one-fourth for the vacuum even though the photon number eigenvalue is zero. QND measurements of a quadrature component can thus provide experimental evidence of the nonclassical operator ordering dependence of the correlations between photon number and field components in the vacuum state.
It is shown that the quantum jumps in the photon number $\mathrm{n\ifmmode \hat{}\else \^{}\fi{}}$ from zero to one or more photons induced by backaction evasion quantum nondemolition measurements of a quadrature component ◯◯◯ of the vacuum light field state are strongly correlated with the quadrature component measurement results. This correlation corresponds to the operator expectation value $〈◯\mathrm{n\ifmmode \hat{}\else \^{}\fi{}}◯〉$ which is equal to one-fourth for the vacuum even though the photon number eigenvalue is zero. Quantum nondemolition measurements of a quadrature component can thus provide experimental evidence of the nonclassical operator ordering dependence of the correlations between photon number and field components in the vacuum state.
Finite resolution quantum nondemolition (QND) measurements allow a determination of light field properties while preserving some of the original quantum coherence of the input state. It is thus possible to measure correlations between the photon number and a quadrature component of the same light field mode. Nonclassical features emerge as photon number quantization is resolved. In particular, a strong anti-correlation of quantization and coherence is observable in QND measurements of photon number, and a correlation between measurement induced quantum jumps and quadrature component measurement results is obtained in QND measurements of quadrature fluctuations in the photon vacuum. Such nonclassical correlations represent fundamental quantum properties of the light field and may provide new insights into the nature of quantization itself.