Particle physics in a humble glass chip: how quantum optics illuminates the nature of the quark

Scientists from the University of Rostock in Germany have been able to recreate fundamental physical properties from the field of elementary particle physics in a photonic system. The results are published in Natural Physics.

In their fundamental research, experimental physicists routinely use gigantic but complex machines: huge particle accelerators smash microscopic particles at speeds close to the speed of light, releasing unimaginable amounts of energy. In the remains of these collisions, scientists search for signatures of the fundamental forces of the universe.

Since the 1970s, a veritable zoo of particles has been discovered and organized in the Standard Model of particle physics. Among them are quarks, the elementary building blocks of protons and neutrons. These unusual particles have specific, rather idiosyncratic properties that distinguish them from any other form of matter. For example, while there is only one type of electric charge, which can be positive or negative, the behavior of quarks obeys completely different physical laws.

Professor Stefan Scheel, head of the Quantum Optics of Macroscopic Systems research group at the University of Rostock, explains: “In addition to their electric charge, quarks come with their own color charge: red, green or blue. This, of course, has nothing to do with the colors found in a rainbow.”

It is because of this peculiar behavior that individual quarks stubbornly escape direct observation. Recently, the group of German scientists succeeded in studying the fundamental symmetries of quarks by preparing light in an analogous configuration.

Professor Alexander Szameit, head of the experimental solid-state optics research group at the University of Rostock, describes the experimental approach: “Using high-intensity laser pulses, we inscribe circuits for light in a humble piece of glass. In such photonic chips, complex phenomena can be modeled, the color charge of quarks being only one of them.”

In order to simulate this charge, the Rostock scientists had to exploit the exotic properties of quantum light. Light particles (called photons) can not only exist in multiple places at the same time, but an arbitrary number of them can also exist in exactly the same place.

“In this way, so-called holonomies can be designed as photons propagate through photonic circuits. These abstract objects are usually the playground of mathematicians. But, it turns out, they also describe possible symmetries of a quantum system and have some very interesting properties. For example, they do not depend on the passage of time, a rarity in physics”, explains Vera Neef, one of the principal authors of the work, while she is doctoral student revolves around the new field of holonomic quantum optics.

The second lead author, Julien Pinske, who in his Ph.D. studies holonomy from the point of view of theoretical physics, specifies: “In order to simulate the three charges of different colors, it was necessary to design a three-dimensional holonomy. Until now, only photons did the trick, and that goes beyond our everyday intuition of nature. .”

Awaiting their first experimental realization of this effect, the group of scientists anticipate deeper insights into the fascinating physics of the quark. Beyond the study of this fundamental physics, the reported results could prove useful in the design of future quantum technologies, including quantum computers. There, holonomies could prove to be the crucial ingredient upon which the quantum can be made tough enough for commercial use.