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Description
Optical vortices are optical beams characterized by a helical phase structure around their axis, possessing unique properties associated with orbital angular momentum (OAM) and phase singularities. Their significance is growing in both quantum communication and quantum computation due to their ability to encode and process information in higher-dimensional state spaces, expanding beyond traditional binary qubit systems [1].
We have experimentally observed the correlated vortex generation in the presence of a coherent medium. This new field has been generated from an old field applied to the coherent atoms. The uniqueness of this generation is that the new field replicates the helical phase front, carrying the same amount of OAM.
Coherent atoms are generated with a spatially separated ring-shaped (annular) beam. Then those atoms are again exposed under the influence of another beam with photons carrying $+4\hslash$ of OAM, positioned at the center of the ring. According to our experimental condition, we have separated two interaction regions, leading to a spatial evolution of the coherence. This spatial evolution of coherent atoms is verified through Ramsey interferometry, confirming the phase coherence dynamics in the system. This spatial evolution is highly sensitive to the magnetic field environment, which determines the frequency of the oscillation of this coherence in the dark region (in between the outer ring beam and the central beam).
This coherent generation is a third-order nonlinear process that requires both high optical power and a higher atomic number density. To achieve the necessary conditions, we used a standard vapor cell, which was heated to increase the atomic density and enhance the interaction strength.
We have used the well-known tilted lens detection method [2] to verify the generation and transfer of the OAM of the generated light. We also did the intensity correlation measurements between the generated beam and the applied beam by means of two identical photo detectors. We also have analyzed the sensitivity of the generation against the phase of initial coherence.
[1] Y. Shen, et al., Light: Science & Applications 8, 90 (2019)
[2] P. Vaity, et al., Physics Letters A 377, 1154-1156 (2013)
