Optical foundations illuminated with quantum light

Optics, the science of light, is one of the oldest areas of physics and keeps surprising researchers. Although the classical description of light as a wave phenomenon is rarely questioned, the physical origins of some optical effects are. A team of researchers from the University of Tampere has taken the discussion about a fundamental wave effect, the debate about the anomalous behavior of focused light waves, to the quantum domain.

The researchers were able to show that quantum waves behave significantly differently than their classic counterparts and can be used to increase the accuracy of distance measurements. Their results also add to the discussion about the physical origin of the anomalous focusing behavior. The results are now published in nature photonics.

“Interestingly, we started with an idea based on our previous results and set about structuring quantum light for improved measurement precision. But then we realized that the underlying physics of this application also contributes to the long debate about the origins of the Gouy phase anomaly of focused light fields,” explains Robert Fickler, group leader of the Experimental Quantum Optics group at the University of Tampere.

Quantum waves behave differently but point to the same origin

In the last few decades, methods for structuring light fields down to the level of individual photons have matured and led to a large number of new findings. In addition, an improvement in the fundamentals of optics was achieved. However, the physical origin of why light behaves so unexpectedly when passing through a focus, the so-called Gouy phase anomaly, is still often debated. This is true despite its widespread use and importance in optical systems. What is new about the current study is that it transfers the effect to the quantum domain.

“In developing the theory to describe our experimental results, we found (after much debate) that the Gouy phase for quantum light is not only different from the standard phase, but that its origin can also be linked to a different quantum effect, which is what.” speculated in an earlier work,” adds PhD student Markus Hiekkamäki, lead author of the study.

In the quantum domain, the anomalous behavior is accelerated compared to classical light. Since Gouy phase behavior can be used to determine the distance a light beam has traveled, speeding up the quantum Gouy phase could allow for an improvement in distance measurement accuracy.

With this new understanding, the researchers plan to develop novel techniques to improve their measurement capabilities so that it will be possible to measure more complex beams of structured photons. The team expects this will help them advance the application of the observed effect and potentially unearth more differences between quantum and classical light fields.

Provided by the University of Tampere