Controlling the biphoton orbital angular momentum eigenmodes using asymmetric pump vortex beam

TL;DR

This paper demonstrates how adjusting the asymmetry of a pump vortex beam in spontaneous parametric down conversion can control and enhance the orbital angular momentum eigenmodes and dimensionality of biphoton states.

Contribution

It introduces a method to control biphoton OAM modes by manipulating pump vortex beam asymmetry, increasing the system's dimensionality.

Findings

Increased spiral bandwidth of biphotons observed.

Controlling pump vortex asymmetry tailors biphoton OAM spectrum.

Potential to further enhance entanglement dimensionality.

Abstract

We report on controlling the bi-photon orbital angular momentum (OAM) eigenmodes in the spontaneous parametric down conversion process by simply adjusting the asymmetry of the pump vortex beam. Adjusting the optic axis of the spiral phase plate (SPP) of phase winding corresponding to OAM mode, l, with respect to the beam propagation axis, we have transformed a Gaussian beam into an asymmetric vortex beam with OAM modes, l, l-1, l-2, 0 with different weightages. Pumping the nonlinear crystal with such asymmetric vortices and controlling their asymmetry we have tailored the spiral spectrum of the biphoton OAM eigenmodes. Calculating the Schmidt number of the biphotons we observe the increase in the spiral bandwidth of the OAM eigenmodes and hence the dimensionality of the system. Although we have restricted our study to show the increase in spiral bandwidth of the biphotons by simply controlling the asymmetry of the pump vortices, we can, in principle, further enhance the dimensionality of the entangled states by manipulating the pump beam size and crystal length.