Abstract

This issue, the largest issue of Optics Express to date, focuses on some recent developments in the generation and application of novel quantum states of light, particularly those quantum states of light that manifest one or more of the following characteristics upon detection: quadrature squeezing, sub-Poissonian photon statistics, or nonclassical photon correlation. The interest in such quantum states of light stems not only from their fundamental importance, but also from their potential utility in practical applications. The sensitivity of many optical measurements that can be made with laser light can be enhanced by use of such light states.

© Optical Society of America

This issue, the largest issue of Optics Express to date, focuses on some recent developments in the generation and application of novel quantum states of light, particularly those quantum states of light that manifest one or more of the following characteristics upon detection: quadrature squeezing, sub-Poissonian photon statistics, or nonclassical photon correlation. The interest in such quantum states of light stems not only from their fundamental importance, but also from their potential utility in practical applications. The sensitivity of many optical measurements that can be made with laser light can be enhanced by use of such light states.

The authors of this focus issue were invited to report results from their recent accomplishments in either the methods of generation or the application of the novel light states. Several of the authors have exploited the multimedia features of electronic publishing to present their results.

The paper by Schneider, Lang, Mlynek, and Schiller describes a semi- monolithic degenerate optical parametric amplifier that produces a bright beam of squeezed light having a record 6.5 dB of amplitude squeezing. The authors emphasize the stability of this source which can maintain a high degree of squeezing over long periods of time. In the subsequent paper, Teja and Wong describe their measurements of quantum correlations on the twin beams emitted by a triply-resonant dual-cavity optical parametric oscillator. They are motivated by this system's ability to allow separation of all the three interacting fields; which will make measurements possible in future experiments under conditions of strong pump depletion.

The next two papers discuss the generation of squeezing in optical fibers. In the first, Margalit, Yu, Ippen, and Haus report the first observation of squeezing by means of the cross-phase modulation effect in a very short piece of fiber. This approach avoids the guided acoustic-wave Brillouin scattering limitation that usually plagues experiments based on the self-phase modulation effect. The second paper on squeezing in fibers uses the method of spectral filtering of optical solitons, which is interesting because squeezing is observable in direct detection---a much easier measurement than homodyne detection. Spaelter, Burk, Strossner, Sizmann, and Leuch describe their observation of unexpectedly large amount of photon-number squeezing under conditions of strong Raman scattering.

The content of the next four papers deals with the application of the novel quantum light states. Marable, Choi, and Kumar report on the measurement of quantum-noise correlations in parametric image amplification. Operation of a spatially broadband parametric amplifier is described that can be configured either as a low-pass or a band-pass amplifier for spatial frequencies. These experiments open the door to the application of squeezing for enhancing the sensitivity of faint images. In the next paper Hald, Sorensen, Leich, and Polzik present recent results and future perspectives on the interaction of nonclassical light with an ensemble of atomic spins. They describe an apparatus with which the spin orientation of the trapped atoms can be measured with a sensitivity exceeding the shot-noise limit. They further discuss how such an apparatus can be used to create spin-squeezed states of atoms. The paper by Lam, Ralph, Huntington, McClelland, and Bachor presents experimental results on noiseless signal amplification and processing by use of a positive electro-optic feed-forward device. The feed-forward approach avoids many of the stability problems inherent in previous feed-back configurations. Inclusion of the theoretical background and physical interpretation makes the paper quite comprehensive. In the last paper Li and Xiao describe the use of amplitude-squeezed light from a semiconductor diode laser in Doppler anemometry, achieving sensitivities that exceeded the shot-noise limit.

I would like to take this opportunity to thank all the authors of this focus issue for their excellent contributions, and for their willingness to experiment with this new medium of scientific publication.

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