Abstract
A precise measurement of a quantity X in a quantum mechanical system perturbs the conjugated variable Y(ΔX·ΔY ≥ h/2). In a repeated measurement of the quantity X the results usually fluctuate due to 'backaction' of the variable Y on the time-evolution of X. When the measurement scheme is, however, designed in such a way that the noise remains only on the nonmeasured quadrature component, the experiment is called a quantum-nondemolition (QND) experiment. A QND measurement of the intensity fluctuations of a pump beam can be achieved by coupling the intensity of the pump beam to a probe beam using the crossed Kerr effect.1 Recently, experiments using the two-photon 3s1/2 → 3p3/2 → 3d5/2 transition in a sodium atomic beam gave promising results.2,3 The efficiency of the measurement was, however, limited by fluctuations of the number of atoms in the beam and by Doppler broadening. Measurements in a sample of trapped atoms could overcome these problems.
© 1994 IEEE
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