Atomic Memory for Correlated Photon States

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Experimental details are available as supporting material on Science Online.

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In the case where optical fields have losses before detection, the level of twin-mode squeezing that can be observed is reduced (32). For our data, the anti-Stokes signal appears identical to the Stokes signal, except for an apparent attenuation by a factor of ∼5 and a time shift (Fig. 2C). In this case, twin-mode squeezing can still be investigated when the time shift is compensated and when the unbalanced attenuation is compensated by unbalanced linear amplification of the two signals. We have developed a method based on fast, high-accuracy sampling of the Raman signals followed by software compensation of the time shift and linear amplification. Accordingly, this procedure accounts for the rescaling of photon shot-noise and detector dark-noise levels. The resulting signals are subtracted for evaluation of the spectrum in Fig. 4 For further details, see (40).

The criterion for two modes of light to be photon number squeezed is that for a sequence of photon number measurements, n₁ and n₂, the variance in (n₁ – n₂) must be less than the sum of the averages (n̄₁ + n̄₂) (32). For measurements on two continuous photon flux signals, analyzed in the frequency domain, this corresponds to the fluctuation spectrum of the time-domain difference signal being less than such a fluctuation spectrum from two classical fields with the same average photon flux and classical intensity correlations, such as would be obtained by splitting a single light beam on a perfect beam splitter.

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Experimental work was carried out at the Harvard University Department of Physics. We thank T. P. Zibrova, J. MacArthur, M. Hohensee, S. B. Shenai, P. R. Hemmer, and A. Trifonov for useful discussions and experimental help. Supported by NSF grant PHY-0113844, the Defense Advanced Research Projects Agency, the David and Lucille Packard Foundation, the Alfred Sloan Foundation, the Office of Naval Research (DURIP program), the Smithsonian Institution, the MIT-Harvard Center for Ultracold Atoms, a fellowship through the Netherlands Organization for Scientific Research (C.H.v.d.W.), and a NSF Graduate Research Fellowship (M.D.E.).