Spectral properties of the squeeze operator

Xin Ma, William Rhodes

Vladislav Sukharnikov, Olga V. Tikhonova

A theoretical approach has been developed in the Schmidt mode formalism and photon operators in these modes to describe the spectral properties of the light generated in the nonlinear process of sum-frequency generation. A special regime at which the frequency correlations of photons in the output beams are suppressed has been described in detail. The control of the mode composition and spectral properties of the nonclassical squeezed light used to illuminate the signal channel with the possibility of generating a squeezed vacuum at the sum-frequency mode has been demonstrated at this regime.

Stefano Zippilli, Giovanni Di Giuseppe, David Vitali

Spectral components of continuous squeezed fields are entangled. In this article we review and clarify this phenomenon by analyzing systematically the relations between the correlations of modes filtered from stationary continuous fields and the cross-power spectrum between the operators of the corresponding spectral components. Moreover, we study the specific spectral components that are filtered in homodyne or heterodyne detections and their entanglement properties. In particular, we establish the equivalence between two-mode squeezing variance and logarithmic negativity for the spectral components of continuous stationary fields, thereby demonstrating that the measurement of the homodyne or heterodyne spectrum is, in fact, a direct measurement of the logarithmic negativity between specific spectral modes. As an illustrative example, we apply these concepts to the analysis of entanglement in ponderomotive squeezing.

Felipe Araújo de Oliveira, I. A. Pedrosa, B. Baseia

Z. Y. Ou, C. K. Hong, L. Mandeļ

Certain two-time correlation functions of squeezed optical fields and their Fourier conjugates are investigated. These functions are related to the autocorrelation function and the spectral density of the photoelectric current that appears in measurements made of the squeezed light by a homodyne technique. Because the field is often assumed to contain a monochromatic carrier, it is only quasi-stationary, and modified quantum correlation functions, specially constructed to be time independent, are used to describe its properties. The symmetries of the corresponding conjugate spectral functions, which are not always spectral densities, are investigated. The concepts of homogeneous squeezing, inhomogeneous squeezing, and spectral component squeezing are introduced, and it is shown that the condition for cross-spectral purity, when satisfied, leads to homogeneous squeezing. A frequency-dependent parameter called the degree of squeezing, which lies between 0 and −1 for a squeezed state and is simply related to photoelectric measurements, is introduced. These ideas are then applied to the squeezing produced in resonance fluorescence, in parametric downconversion, and in four-wave mixing, and the degrees of squeezing under different conditions are compared.

Luigi Accardi, Alexander Bach