Researchers at University of Warsaw’s physics faculty superposed two clockwise twisted beams of light. The results of the study were published in the popular journal „Optical.” The discovery is important for the study of light-matter interactions and is a step towards observing a strange phenomenon known as quantum introspection.
Imagine you are throwing a tennis ball. The ball starts moving forward with positive velocity. If the ball doesn’t hit an obstacle, you’re unlikely to expect it to suddenly change direction and come back to you like a boomerang. For example, when you spin such a ball clockwise, you expect it to keep spinning in the same direction.
Bohnishika Ghosh, PhD Student, Faculty of Physics, University of Warsaw
However, in quantum mechanics things get more complicated when dealing with particles rather than balls.
In classical mechanics, an object has a known state. Meanwhile, in quantum mechanics and optics, an object can be in a state called superposition, meaning that a given particle can be in two or more states at the same time.
Dr Radek Lapkiewicz, Head, Quantum Imaging Laboratory, Faculty of Physics, University of Warsaw
Quantum particles, such as the aforementioned tennis ball, have the ability to move backwards or spin in a different direction at periodic intervals.
Physicists call such a phenomenon regression.
Bohnishika Ghosh, PhD Student, University of Warsaw
Retrospective in optics
So far, reversibility in quantum systems has not been experimentally detected. Instead, it is effectively accomplished in classical optics by using light beams.
Connection between anomalous behavior of optical waves at local scales and regressivity in quantum mechanics Yakir Aharonov, Michael V. Theoretically explored by Perry and Sandu Popescu. Y. Eliezer and co-workers synthesized a complex wavefront for optical backscattering. Then, using simple interference of two beams, Dr. Anat Daniel et al. Dr. Radek Lapkiewicz and his group have shown this effect in one dimension.
Dr. Anat Daniel added.What I find fascinating about this work is that when you enter the realm of local scales you realize very easily how things become different.„
Researchers from the University of Warsaw’s Faculty of Physics have demonstrated the two-dimensional retrospection effect in a recent publication titled „Azimuthal Aftereffect in Light-Carrying Orbital Angular Momentum,” published in the esteemed journal Optical.
„In our study, we have superposed two clockwise twisted light beams and locally observed counterclockwise twists.” Dr. Lapkiewicz explained.
The researchers used a Shack-Hartmann wavefront sensor to monitor the phenomenon. For two-dimensional spatial measurements, the system provides excellent sensitivity. It consists of a microlens array positioned in front of a CMOS (complementary metal-oxide semiconductor) sensor.
„We investigated the superposition of two beams carrying only negative orbital angular momentum and observed, in the dark region of the interference pattern, positive local orbital angular momentum. It is an azimuthal regressionIn the Quantum Imaging Laboratory, added Bernard Gorzkowski, a doctoral student in the Faculty of Physics.
It is noteworthy that the first experimental generation of light beams carrying orbital angular momentum with azimuthal (rotational) phase dependence was achieved in 1993 by Marco Beijersbergen et al. Using cylindrical lenses. Since then, they have been used in a wide range of fields, including optical microscopy and optical tweezers, for which inventor Arthur Ashkin was awarded the 2018 Nobel Prize in Physics.
These tools enable detailed manipulation of micro- and nanoscale materials. Currently, optical tweezers are used to investigate the mechanical properties of DNA strands, cell membranes, and interactions between cancer and healthy cells.
When physicists play Beethoven
Scientists assert that super-oscillations in the phase may be the explanation for their current demonstration. The first description of the connection between waves and recoil in quantum mechanics was made in 2010 by University of Bristol physics professor Michael Berry.
A phenomenon known as superoscillation occurs when the local oscillation of a superposition is faster than its fastest Fourier component. Early predictions were made by Yakir Aharonov and Sandu Popescu in 1990, when they found that certain combinations of sine waves make composite wave zones move faster than either part.
In his publication “Faster than Fourier”, Michael Perry demonstrated the possibility of superoscillation by theoretically combining Beethoven’s Ninth Symphony with only sound waves with frequencies below 1 Hz. . However, due to the relatively small amplitude of the wave in the super-oscillatory regions, this is highly unlikely.
Bonishika Ghosh concluded, “The regression we presented is a manifestation of rapid changes in phase, which may be important in applications involving light-matter interactions, such as optical trapping or designing ultra-precise atomic clocks.„
Apart from this, the publication by the team from the Faculty of Physics of the University of Warsaw is a step towards observing quantum recoil in two dimensions, which is theoretically more elastic than one-dimensional recoil.
This study was supported by the Polish Foundation for Science under the FIRST TEAM project „Spatiotemporal Photon Correlation Measurements for Quantum Metrology and Super-Resolution Microscopy”, funded by the European Union under the European Regional Development Fund (POIR.04.04.00-00-3004/17-00). .
Ghosh, B., and many others. (2023) Azimuthal retrospection on light-carrying orbital angular momentum. Optical. doi:10.1364/OPTICA.495710.
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