Localized to delocalized spatial quantum correlation evolution in structured bright twin beams

TL;DR

This paper investigates how spatial quantum correlations in bright twin beams evolve from localized to delocalized states during propagation, combining theoretical models with experimental validation to enhance understanding for quantum imaging and information.

Contribution

It provides the first analytical description of the evolution of spatial quantum correlations in structured twin beams, supported by experimental measurements with different pump configurations.

Findings

Localized correlations in near field with Gaussian pump

Transition to delocalized correlations in far field with structured pump

Experimental validation of theoretical correlation evolution model

Abstract

Quantum correlations in the spatial domain hold great promise for applications in quantum imaging, quantum cryptography and quantum information processing, owing to the infinite dimensionality of the associated Hilbert space. Here, we present a theoretical investigation, complemented by experimental measurements, of the propagation dynamics of the spatial quantum correlations in bright structured twin beams generated via a four-wave mixing process in a double-$\Lambda$ configuration in atomic vapor. We derive an analytical expression describing the evolution of the spatial quantum correlation distribution from the near field to the far field. To qualitatively support the theoretical predictions, we perform experiments measuring intensity-difference noise between different spatial subregions of the twin beams as they propagate from the near field to the far field. The presence of quantum correlations is manifested as squeezing in the intensity difference noise measurement. With a Gaussian pump, we observe localized correlations in the near field and localized anti-correlations in the far field. In contrast, with a structured Laguerre-Gaussian pump, there is a transition from localized correlations in the near field to delocalized correlations in the far field. The present results offer valuable insights into the fundamental behavior of spatial quantum correlations and open possibilities for potential applications in quantum information, quantum imaging and sensing.