Abstract
Quantum entanglements between integer-order and fractional-order orbital angular momentums (OAMs) have been previously discussed. However, the entangled nature of arbitrary rational-order OAM has long been considered a myth due to the absence of an effective strategy for generating arbitrary rational-order OAM beams. Therefore, we report a single metadevice comprising a bilaterally symmetric grating with an aperture, creating optical beams with dynamically controllable OAM values that are continuously varying over a rational range. Due to its encoded spiniform phase, this novel metagrating enables the production of an average OAM that can be increased without a theoretical limit by embracing distributed singularities, which differs significantly from the classic method of stacking phase singularities using fork gratings. This new method makes it possible to probe the unexplored niche of quantum entanglement between arbitrarily defined OAMs in light, which could lead to the complex manipulation of microparticles, high-dimensional quantum entanglement and optical communication. We show that quantum coincidence based on rational-order OAM-superposition states could give rise to low cross-talks between two different states that have no significant overlap in their spiral spectra. Additionally, future applications in quantum communication and optical micromanipulation may be found.
Highlights
Light has many different properties that are described by its electromagnetic field
We show that quantum coincidence based on rational-order orbital angular momentum (OAM)-superposition states could give rise to low cross-talks between two different states that have no significant overlap in their spiral spectra
At q = 1, an elliptical transverse profile is formed with a single phase singularity, which splits into a two-lobed shape from q = 2 onwards due to the spatial mismatch of the singularities
Summary
Light has many different properties that are described by its electromagnetic field. One of the most interesting properties of light is its ability to carry orbital angular momentum (OAM), which manifests itself as a helical wavefront with a phase singularity on the beam axis. An OAM carrying beam has a helical phase eilφ (where l and φ are the winding numbers of the helical phase and angular coordinate, respectively)[1], giving rise to an intensity annulus (i.e., doughnut) that is uniform for the integer l, while for fractional l, the intensity annulus is discontinuous with a phase step along φ = 0 This smoothness leads to a similar influence on the design of the kinoform for generating the diffractive optical component, for example, fork gratings have smoothly varying fringes for integer l and cutoff fringes with a discontinuity along φ = 0 for fractional l35,36. Digital devices such as spatial light modulators (SLMs)[41] and digital micromirror devices (DMDs)[42] have been used to generate different
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