Researchers Create Anti-Clockwise Twists in Light Beams, Paving the Way for Quantum Backflow

University of Warsaw physicists achieve a breakthrough in optics, superposing light beams to observe counterintuitive phenomena.

In a groundbreaking study published in the prestigious journal “Optica,” researchers at the University of Warsaw’s Faculty of Physics have successfully superposed two light beams twisted in the clockwise direction, resulting in the creation of anti-clockwise twists in the dark regions of the superposition. This discovery holds significant implications for the study of light-matter interactions and represents a crucial step towards the observation of a peculiar phenomenon known as quantum backflow.

The Nature of Quantum Backflow:

Quantum mechanics introduces a level of complexity when dealing with particles. Unlike classical mechanics, where objects have known positions, quantum particles can exist in multiple positions simultaneously, a state known as superposition. This superposition allows quantum particles to exhibit peculiar behaviors, including the possibility of moving backward or spinning in the opposite direction during certain time periods. This phenomenon, known as backflow, has long fascinated physicists.

Backflow in Classical Optics:

While backflow in quantum systems has not been directly observed, researchers have successfully achieved it in classical optics using beams of light. Theoretical works by Yakir Aharonov, Michael V. Berry, and Sandu Popescu explored the connection between backflow in quantum mechanics and the anomalous behavior of optical waves on a local scale. Optical backflow was first observed by Y. Eliezer et al. through the synthesis of a complex wavefront. Building upon this work, Dr. Anat Daniel et al. from Dr. Radek Lapkiewicz’s group demonstrated this phenomenon in one dimension using the interference of two beams.

The Study: Azimuthal Backflow in Light:

In their latest publication, “Azimuthal backflow in light carrying orbital angular momentum,” the researchers from the University of Warsaw’s Faculty of Physics showcased the backflow effect in two dimensions. By superposing two beams of light twisted in a clockwise direction, they observed counterclockwise twists in the dark regions of the interference pattern. To observe this phenomenon, the researchers utilized a Shack-Hartman wavefront sensor, a system that provides high sensitivity for two-dimensional spatial measurements.

Applications and Implications:

The discovery of backflow in light has significant implications for various fields, including optical trapping, ultra-precise atomic clocks, and the design of super-resolution microscopy techniques. Light beams with azimuthal phase dependence, carrying orbital angular momentum, have already found applications in optical microscopy and optical tweezers, a tool that allows the manipulation of objects at the micro- and nanoscale. This breakthrough paves the way for further exploration of light-matter interactions and the potential development of advanced technologies.

Superoscillations and Playing Beethoven:

The researchers also noted that their demonstration can be interpreted as superoscillations in phase. Superoscillation refers to situations where the local oscillation of a superposition is faster than its fastest Fourier component. This phenomenon was first predicted by Yakir Aharonov and Sandu Popescu in 1990. Professor Michael Berry later illustrated the power of superoscillation by showing that it is theoretically possible to play Beethoven’s Ninth Symphony using only sound waves with frequencies below 1 Hertz. However, the amplitude of waves in the super-oscillatory regions is extremely small, making this application highly impractical.


The University of Warsaw’s Faculty of Physics has achieved a significant milestone in the field of optics with the observation of azimuthal backflow in light. By superposing twisted light beams, the researchers have demonstrated a counterintuitive phenomenon that could revolutionize our understanding of light-matter interactions. This breakthrough opens doors to new applications in optical trapping, atomic clocks, and super-resolution microscopy. Furthermore, the study provides valuable insights into the intriguing connection between backflow in quantum mechanics and superoscillations in waves. As researchers continue to unravel the mysteries of light, the possibilities for technological advancements and scientific discoveries are boundless.