Experimental Realization of a Quantum Measurement for Intensity Difference Fluctuation Using a Beam Splitter

Abstract

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, T s 1 T m 1.31 and V s͞m 22.1 dB. [S0031-9007(99)08445-8] PACS numbers: 42.50.Dv, 03.65.Bz Quantum nondemolition (QND) measurements have attracted extensive interest [1]. Since 1986, a variety of QND-type measurements have been successfully demonstrated in optical experiments [2][3][4][5][6][7][8][9]. In most experiments measurements of the quadrature phases of the probe field were involved to provide the information of signal observables. In a recent paper Harrison et al. [10] have proposed a QND scheme, in which the signal and probe observables are the intensity difference between twin beams on the left and right hand sides of a double ended nondegenerate optical parametric oscillator; therefore, only the field intensities need to be measured rather than the quadrature phases [10]. So far there is no published experimental realization of this QND-type measurement.It is well known that a beam splitter is the simplest optical coupling device [11]. Recently Bruckmeier et al. [9] have realized a quantum measurement satisfying the quantum nondemolition criteria by injection of a 3.7 dB quadrature squeezed wave into the usual vacuum port of a beam splitter. The good results of signal transfer T s 1 T m 1.29 and the conditional variance V s͞m 21.3 dB were obtained. On the other hand great reductions of quantum fluctuations in the intensity difference between twin beams produced by a nondegenerate parametric oscillator were achieved in several groups [12][13][14]. The above-mentioned successful experiments motivated us to design a quantum measurement scheme using a beam splitter, the dark port of which is filled by quantum correlated twin beams instead of a quadrature squeezed wave as in Ref. [9]. When the twin beams with quantum noise reduction in the intensity difference of 76% below the standard quantum limit (SQL) are injected into the vacuum port of a beam splitter, the measurement of intensity difference fluctuation in the quantum domain is experimentally realized. The measured T s 1 T m 1.31 and V s͞m 22.1 dB fulfill the QND criteria introduced by Holland et al. [15] and Poizat et al. [16].At first we simply present the measurement principle of the proposed scheme. S in and M in are, respectively, the signal and meter input waves incident upon the beam splitter (BS) from opposite sides with small angles of incidence; S out and M out are, respectively, the output signal and meter waves. Both S in and M in consist of two orthogonal polarized modes (S polarization and P polarization) of equal mean intensit...

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