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 3s_1/2 → 3p_3/2 → 3d_5/2 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