Spatial multimode structure of atom-generated squeezed light

Abstract

We investigated the spatial distribution of quantum fluctuations in a squeezed vacuum field, generated via polarization self-rotation (PSR) interaction of an ensemble of Rb atoms and a strong near-resonant linearly polarized laser field. We found that the noise suppression is greatly effected by the transverse profile of a spatial mask, placed in both the squeezed field and the local oscillator, as well as its position along the focused beam near the focal point. These observations indicate the spatial multi-mode structure of the squeezed vacuum field. We have developed a theoretical model that describes the generation of higher-order Laguerre-Gauss modes as a result of PSR light-atom interaction. The prediction of this model are in a good qualitative agreement with the experimental measurements.

Why a hole is like a beam splitter: A general diffraction theory for multimode quantum states of light

“…V, we will consider three examples of applying our formalism to describe propagation of various quantum input optical fields through an iris mask. The first one uses two single-mode squeezed vacuums as input, which has been tested experimentally [27], and our predictions agree well with the experimental observations. The other examples study the cases of a single photon, and two-photon inputs, in which case our calculations predict the generation of a photon-number entanglement and a Hong-Ou-Mandel-like effect, implying that an opaque spatial mask displays characteristics of a regular but lossy optical beam splitter.…”

“…Indeed, if the squeezed states generated in different Gaussian modes have different squeezing angles, then the interaction among the states in the various modes can worsen rather than improving the overall squeezing. Recent work further confirms the deficiency of using plane waves to analyze quantum states of light, and motivates us to investigate the quantum behavior of Gaussian beams [27][28][29].…”

“…The y-polarized field is coherent vacuum. The nonlinear interaction between the atoms and the strong field generates a squeezed-vacuum field in the y-polarized direction, which is in a multi-mode structure, and it is the lower two p modes that contribute the most to the squeezing, and states in nonzero l modes are vacuum because of conservation of angular momentum [27]. Amplified by the strong field, the noise in this squeezed field will be then detected in a homodyne detection scheme.…”

“…To verify our theory, we now realize this model in our experiment [27], which has the following setup, shown in Fig. 5.…”

“…Let us consider the following model of our recent experiment [27]. In the two signal LG modes of (l = 0, p = 0) and (l = 0, p = 1), we input two squeezed-vacuum quantum states, which are defined asŜ(ξ 0 ) |0 l=0,p=0 and S(ξ 1 ) |0 l=0,p=1 , respectively, while in every other LG mode we input vaccum states.…”