Squeezed Light

The basic idea of squeezing can be understood by considering the quantum harmonic oscillator, familiar from undergraduate quantum mechanics. Squeezing is best visualized by means of the Wigner function—the quantum analog of the phase-space probability density. This chapter discusses the photon number decomposition of the two-mode squeezed state. Most frequently, squeezing is obtained by nonlinear optical wave-mixing processes, in which pairs of photons are emitted into degenerate (single-mode squeezing) or non-degenerate (two-mode squeezing) modes. In order to mathematically describe nonlinear-optical squeezing, the chapter describes the equations for the propagation of classical electromagnetic fields through a nonlinear medium. Amplitude squeezing is then readily observed by measuring the intensity with a single high-efficiency detector and evaluating the variance of the photocurrent noise.