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Acta Physica Sinica

EXPERIMENTAL REALIZATION OF QUANTUM NONDEMOLITION MEASUREMENT BY SERIES-COUPLED LIGHT EMITTER DIODES

J Zhang, Van E

Published Jan 1, 2000• 0 citations
OpenAlex

Abstract

By means of series\|amplified of two Light emilter diodes and face\|to\|face coupling with high efficiency photodetectors,we demonstrated the quantum nondemolition measurement of modulated optical signal at room temperature for the first time to our knowledge.The quantum transfer coefficient of T=T \-s+ T \-m=1 8 and conditional variance of V \-\{s/m\}=0 92 have been experimentally obtained.

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By means of series|amplified of two Light emilter diodes and face|to|face coupling with high efficiency photodetectors,we demonstrated the quantum nondemolition measurement of modulated optical signal at room temperature for the first time to our knowledge.The quantum transfer coefficient of T=T -s+ T -m=1 8 and conditional variance of V -{s/m}=0 92 have been experimentally obtained.
A new quantum measurement scheme of intensity difference fluctuation between two light beams of equal mean intensity is presented. In this system a beam splitter is used as the coupling device and the twin beams with high quantum correlation are injected into its dark port as the input meter wave instead of the usual vacuum field. A measurement satisfying all the quantum nondemolition criteria is experimentally achieved. The measured sum of the transfer coefficients and the conditional variance are, respectively, Ts+Tm=1.31{T}_{s}{+T}_{m}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.31Ts​+Tm​=1.31 and ${V}_{s/m}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}2.1\mathrm{dB}$.
Optical quantum nondemolition measurements are performed using a beamsplitter with a nonclassical meter input and a electro-optic feedforward loop. The nonclassical meter input is provided by a stable 4.5 dB amplitude squeezed source generated by an optical parametric amplifier. We show that the implementation of a feedforward loop gives a substantial improvement in the signal transfer efficiency. With a 92% reflective beamsplitter we measure a transfer coefficient of Ts+m = 1.81. The quantum state preparation ability of our system is evaluated using two-dimensional correlation plots. This technique allows the direct visualization of the quantum correlations between the outputs of the QND system.
Methods for the enhancement of optical quantum nondemolition (QND) measurements are discussed. We review the use of meter squeezing as a QND enhancement tool and present a method of QND enhancement using an electro-optic feed-forward amplifier. By applying a linearized theory it is shown that these techniques work very well together. The combined effect of these enhancement methods is modeled for two QND systems, a squeezed light beam splitter and an optical parametric amplifier. We also discuss the conflict between the normal QND criteria and QND systems that involve noiseless amplification. We use an additional parameter to quantify the problem. A method for correcting the effects of noiseless amplification is discussed and modeled. We also discuss a special case of QND that eliminates the optical interaction between the meter and signal input beams. This system is shown to be a very effective QND device.