"What we really want is to do quantum mechanics with patterns of
light," Andrew Forbes, physicist at the University of the Witwatersrand
in South Africa, said in a news release. "By this, we mean that light
comes in a variety of patterns that can be made unique -- like our
faces."
Forbes is the first of author of a paper -- published Tuesday
in the journal AVS Quantum Science -- detailing the technological progress being made in the field of structured light.
Light can be structured to produce different images or patterns.
Because each light pattern is distinguishable from the others,
structured light can be used like an alphabet.
"The cool thing is that there are, in principle at least, an infinite
set of patterns, so an infinite alphabet is available," Forbes said.
Most quantum systems use polarization to distinguish light photons.
Polarization only offers two values, limiting the amount of information
that can be embedded in each photon. Using a patterned light alphabet
allows for information to be carried at greater densities, according to
the new research paper.
"Patterns of light are a route to what we term high-dimensional
states," Forbes said. "They're high dimensional, because many patterns
are involved in the quantum process. Unfortunately, the toolkit to
manage these patterns is still underdeveloped and requires a lot of
work."
Despite the potential of encoding alphabets based on patterns of
light, "progress in harnessing high dimensional spatial mode
entanglement remains in its infancy," according to the newly published
review.
Still, researchers are making advances. For example, scientists have
demonstrated entanglement swapping using spatial modes of light, quantum
states confined to spatially separated waveguides. Scientists have also
improved the resolution of ghost imaging, allowing them to more
precisely measure entangled photons. But hurdles remain.
"We know how to create and detect photons entangled in patterns,"
said Forbes. "But we don't really have good control on getting them from
one point to another, because they distort in the atmosphere and in
optical fiber. And we don't really know how to efficiently extract
information from them. It requires too many measurements at the moment."
Forbes and his colleagues suggest further advances can be made using
simpler tools to yield more complex quantum states. According to the
paper, physicists can move beyond the strictures of two dimensions by
combining the advantages of polarization and patterns to produce hybrid
light states.
"Rather than two dimensions of patterns, hybrid states allow access
to multidimensional states, for example, an infinite set of
two-dimensional systems," Forbes said. "This looks like a promising way
forward to truly realize a quantum network based on patterns of light."
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