Researchers have used a 350-year-old mechanical theorem commonly applied to tangible objects to reveal new insights into the nature of light. By interpreting the intensity of light as equivalent to physical mass, they mapped light onto a system to which established mechanical equations could be applied. This approach reveals a direct correlation between the degree of non-quantum entanglement of light waves and their degree of polarization. These findings could simplify the understanding of complex optical and quantum properties through more direct measurements of light intensity.
Researchers at Stevens Institute of Technology have applied a 350-year-old theorem originally used to describe the behavior of pendulums and planets to reveal new properties of light waves.
Ever since Isaac Newton and Christiaan Huygens debated the nature of light in the 17th century, the scientific community has grappled with the question: Is light a wave or a particle—or, at the quantum level, a wave or a particle? Now, researchers at the Stevens Institute of Technology have revealed a new connection between the two ideas, using a 350-year-old mechanical theorem - often used to describe the motion of large physical objects such as pendulums and planets - to explain some of the most complex behaviors of light waves.
Revealing connections between light properties
This research work, led by Qian Xiaofeng, assistant professor of physics at Stevens University, was published in the journal Physical Review Research published online on August 17. It also proved for the first time that there is a direct complementary relationship between the degree of non-quantum entanglement of light waves and their degree of polarization. As one goes up, the other goes down, so the degree of entanglement can be inferred directly from the degree of polarization, and vice versa. This means that hard-to-measure optical properties such as amplitude, phase and correlation, and even properties of quantum wave systems, can be derived from something much easier to measure: light intensity.
Physicists at Stevens Institute of Technology have revealed new properties of light waves by using a 350-year-old theorem to explain how pendulums and planets work. Image source: Stevens Institute of Technology
"For more than a century, we have known that light sometimes behaves like a wave and sometimes behaves like a particle, but reconciling these two frameworks has proven extremely difficult, and our work does not solve the problem -- but it does show that there are deep 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," said Qian Yongjian.
Applying Huygens' mechanical theorems to light
The team used a mechanical theorem originally proposed by Huygens in a 1673 book on pendulums, which explains how the energy required to rotate an object varies with the object's mass and axis of rotation. "This is a well-established mechanical theorem that explains how physical systems such as clocks or prosthetics work. But we were able to show that it can also provide new insights into how light works."
This 350-year-old theorem describes the relationship between masses and their rotational momentum, so how can it be applied to light when there is no mass to measure? Qian's team interpreted the intensity of light as equivalent to the mass of a physical object and then mapped these measurements onto a coordinate system that could be explained using Huygens' mechanical theorems. Basically, they found a way to transform an optical system so that it could be visualized as a mechanical system and then described using full-fledged physics equations.
Once the team visualized the light waves as part of a mechanical system, new connections between their properties immediately became apparent - including a clear relationship between entanglement and polarization.
Qian Yongjian said: "This has never been demonstrated before, but once the properties of light are mapped to a mechanical system, it becomes very clear. What was once abstract becomes concrete: using mechanical equations, the distance between the 'center of mass' and other mechanical points can be measured realistically, thus showing the relationship between different properties of light."
Clarifying these relationships could have important practical implications, allowing subtle and difficult-to-measure properties of optical systems - even quantum systems - to be deduced from simpler, more reliable measurements of light intensity. More speculatively, the team's findings suggest that it may be possible to use mechanical systems to simulate and better understand the strange and complex behavior of quantum wave systems.
"This is still before us, but with this first study, we have clearly shown that it is possible to understand optical systems in a completely new way by applying mechanical concepts. Ultimately, this research helps simplify the way we understand the world, allowing us to recognize the intrinsic connections between seemingly unrelated physical laws," Qian Yongjian said.