Photo by Yossi Zeliger/TPS on 9 September, 2023

Colliding Photons Create New Vortices as Israeli Scientists Make Quantum Discovery

Public By Pesach Benson • 9 June, 2024

Jerusalem, 9 June, 2024 (TPS) -- In a turn of events that could have implications for the development of quantum computing, Israeli scientists stumbled upon a new type of vortices formed when photons collide.

Vortices are a well-known physical phenomenon appearing in various contexts, such as the swirling motion of water draining from a bathtub, hurricanes, tornadoes, even galaxies. They typically form when an area of very fast movement encounters a region of slow movement, creating a circular flow around a stationary focus. This helps bridge the tension between differing flow velocities in adjacent areas.

A team of scientists from the Weizmann Institute in Rehovot seeking to devise a method for quantum information processing using photons chanced upon the novel vortices during their experiments.

Quantum computing is an advanced field of computing based on the principles of quantum mechanics, which is the branch of physics that deals with phenomena at very small scales, such as atoms and subatomic particles. Classical computers use “bits” to process information in the binary form of 0s and 1s, but quantum computers use quantum bits or “qubits,” which, due to their extremely small size, behave similar to waves and can exist as 0s and 1s simultaneously.

Because qubits can be in many states at once, a quantum computer can look at many possible solutions to a problem all at the same time. This gives quantum computers the ability to solve problems faster than conventional computers.

Photon interaction, a rarity in itself, occurs through the mediation of matter. In their experiment, the researchers created a unique environment by using a glass container, approximately 10 cm long, which was empty except for a dense cloud of rubidium atoms compressed into a millimeter-long gas cloud at the center. By firing photons into this compressed gas cloud and measuring their state post-interaction, the team sought signs of mutual influence between the photons.

Professor Ofer Furstenberg explained, “The photons entering the dense gas cloud excite a series of atoms into exotic states called Rydberg states. In these states, an electron in the atom orbits in a circle with a diameter a thousand times greater than the atom itself. This electron produces an electric field that affects surrounding atoms, creating a kind of imaginary ‘glass ball.’ This ‘glass ball’ effect means a second photon in the vicinity cannot ignore the changes induced by the first photon, altering its speed as if passing through glass.”

When photons pass close to each other, their speeds change due to this mutual influence. Ideally, the positions of the photons’ peaks and troughs would completely reverse, a phenomenon known as a 180-degree phase shift. However, the researchers observed that when the photons were at a certain distance from each other, a pair of vortices developed, each completing a full 360-degree phase change with almost no photons at their centers, similar to the dark focus observed in other vortices.

These photon eddies resemble the effect created when a plate is pushed through water, where fast-moving water meets slower surrounding water, forming visible eddies. In their final research stages, the scientists added a third photon to the experiment, revealing the vortices’ three-dimensional nature. The third photon demonstrated that the two vortices formed with two photons are actually part of a vortex ring, akin to the phenomenon seen in smoke rings, which consist of many vortices moving together through the air.

Despite the unexpected prominence of these vortices, the research team continues to pursue their original goal of quantum information processing. Future experiments will involve sending photons directly towards each other to measure the phase change of each photon individually. The intensity of this phase change could enable its use as a qubit.