We report on squeezed states of light generated via polarization self rotation effect, their unique properties (low frequency noise suppression, multi mode spatial structure) and application for atom assisted measurements.
Squeezed states of light, i.e., quantum states exhibiting reduced noise statistics, may be used to greatly enhance the sensitivity of light-based measurements. We study a squeezed vacuum field generated in hot Rb vapor via the polarization self-rotation effect. By propagating a strong pump beam through an atomic vapor cell, we were able to achieve a noise suppression of 2.7 dB below shot noise. Our previous work revealed that this amount of noise suppression may be limited by the excitement of higher order modes in the squeezed field during the atom-light interaction. Once incident on the homodyne detection scheme, these higher order modes may induce an imperfect mode match between the squeezed field and the local oscillator (LO). In this work, we used a liquid-crystal-based spatial light modulator to modify the spatial mode structure of the pump and LO beams. We demonstrate that optimization of the spatial modes can lead to higher detected noise suppression.
Squeezed states of light, with field fluctuations smaller than the coherent state fluctuations (or shot noise), are used for improving accuracy of quantum-noise limited measurements, like the detection of gravitational waves. They are also essential resources for quantum information transfer protocols. We studied a squeezed vacuum field generated in hot Rb vapor via the polarization self-rotation effect. We studied the mode structure of the squeezed field by spatially-masking the laser beam after its interaction with the Rb atomic vapor. From analysis of the data we developed a multi-mode theory to simulate the mode composition of the squeezed vacuum field. Our experiments showed that the amount of observed squeezing may be limited by the complex mode structure due to the excitement of higher order spatial modes during the nonlinear atom-light interaction. We demonstrated that optimization of the spatial profile of the beam led to higher detected squeezing. Our studies are useful for enhancing precision metrology and quantum memory applications.
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 multimode 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 is in a good qualitative agreement with the experimental measurements.