Scientists spin liquid light into never-before-seen optical vortex cluster

15 Aug 2022

Illustration of the optical vortex cluster, featured on the cover of Physical Review Letters. Image: Physical Review Letters

Researchers said these optical vortices could help overcome bandwidth limitations in fibre optic communication, or enhance the optical tweezers that can manipulate atoms.

Researchers have created an odd entity in the realm of quantum physics: a cluster of optical vortices of liquid light that have periodic speed changes.

An optical vortex is when light is twisted into a spiral around its axis, which appears as a ring with a dark spot in the middle when projected on a flat surface.

The study of these vortices could have benefits for areas such as optical microscopy, quantum cryptography, enhanced-bandwidth communication and analog computation.

In a new study published in Physical Review Letters and featured on the issue cover, scientists managed to induce four optical vortices as a cluster.

These vortices have a topological charge, which is basically a number that shows how fast the vortex is spinning and in which direction. The researchers detected that the charges in their liquid light cluster varied in a regular manner, switching with a period of one-fifth of a nanosecond.

While optical vortex clusters have been observed before, the study claims this is the first time such a fast charge variation has been detected.

The researchers hope that optical vortices such as these could help overcome bandwidth limitations in fibre optic communication lines. The study could also benefit optical tweezers, which are specially prepared laser beams for holding or manipulating microscopic objects such as atoms or cells.

“Our work opens new perspectives on creating structured free-evolving light, and singular optics in the strong light-matter coupling regime,” the researchers said in their study.

The vortices in the study were generated in a system known as microcavity exciton-polaritons. The researchers used a semiconductor microcavity structure, which consisted of two highly reflecting, closely spaced mirrors with quantum wells sandwiched between.

Quantum wells are nanometer-thin layers that can confine particles such as electrons in the dimension perpendicular to the layer surface.

The experiments were conducted by researchers from Russia’s Skoltech university, the University of Iceland and the University of Southampton. Skoltech’s Prof Pavlos Lagoudakis, who led the study, said the “catch” was to make sure each vortex was random to begin with.

“This means the system would spontaneously self-arrange its vortices, implying emergent behaviour,” Lagoudakis said. “So we couldn’t just imprint a vortex lattice into our system with a laser, because that would create vortices with known charges and remove any spontaneity.”

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Leigh Mc Gowran is a journalist with Silicon Republic