When scientists originally disagreed on the nature of light in the 17th
century, between Christiaan Huygens and Isaac Newton, they couldn't agree on
whether light should be seen as a particle or a wave, or maybe both at once
at the quantum level. Using a 350-year-old mechanical theorem—typically
applied to explain the motion of massive, physical objects like planets and
pendulums—researchers at Stevens Institute of Technology have now unveiled a
new relationship between the two viewpoints. This theorem explains some of
the most intricate behaviors of light waves.
The research, led by Stevens assistant professor of physics Xiaofeng Qian,
and published in the August 17 online edition of Physical Review Research,
also establishes for the first time a direct and complementary relationship
between the degree of polarization and non-quantum entanglement of a light
wave. The amount of polarization may be used to immediately determine the
level of entanglement, and vice versa, when one rises and the other lowers.
This implies that much easier-to-measure variables, like light intensity,
may be used to infer difficult-to-measure optical properties, such
amplitudes, phases, and correlations—possibly even those of quantum wave
systems.
It has been known for more than a century that light may act as a particle
or a wave, but bringing those two frames into harmony has proven to be quite
challenging, according to Qian. "Our work demonstrates that there are
significant connections between wave and particle concepts not only at the
quantum level but also at the level of classical light-waves and point-mass
systems, even though it doesn't solve that particular problem."
Qian's group employed a mechanical theory that describes how the energy
needed to spin an item increases with its mass and the axis it rotates.
Huygens first proposed this theorem in a 1673 book on pendulums. Qian said,
"This is a well-known mechanical theory that describes how physical devices
like clocks or prosthetic limbs operate. However, we were also able to
demonstrate that it can provide fresh perspectives on the nature of
light.
Since there is no mass to detect in light, how could this 350-year-old
theorem—which details correlations between masses and their rotating
momentum—be applied to light? Qian's group translated measurements of light
intensity into a coordinate system that could be understood by using
Huygens' mechanical theory, interpreting light intensity as the mass of a
physical object. "Basically, we figured out how to convert an optical system
into a mechanical system that we could see and then describe with standard
physical equations," said Qian.
New relationships between the wave's features, such as the obvious
relationship between polarization and entanglement, were evident as soon as
the researchers envisioned a light wave as a component of a mechanical
system.
"This had never been demonstrated before, but it becomes evident as soon as
you transfer the characteristics of light onto a mechanical system," Qian
added. What was previously abstract becomes concrete: you can practically
measure the distance between the "center of mass" and other mechanical sites
to illustrate the relationships between various aspects of light using
mechanical equations.
It might be possible to infer complex and difficult-to-measure features of
optical systems—or even quantum systems—from more straightforward and
reliable measurements of light intensity if these correlations are
clarified, according to Qian. More broadly, the results of the team's
research raise the prospect of simulating and comprehending the peculiar and
intricate behaviour of quantum wave systems through the use of mechanical
systems.
"We've demonstrated with this first study that it is possible to understand
optical systems in a completely new way by applying mechanical concepts, but
that still lies ahead of us," Qian added. "Ultimately, by enabling us to
identify the intrinsic underlying connections between seemingly unrelated
physical laws, this research is helping to simplify our understanding of the
world."
Provided by
Stevens Institute of Technology
