In a New Quantum Simulator, Light Behaves Like a Magnet

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LAUSANNE, Switzerland, March 26, 2019 — When following the laws of quantum mechanics, systems made of many interacting particles can display behavior so complex that they cannot be quantitatively described by even the most powerful computers. In 1981, visionary physicist Richard Feynman argued that such complex behavior could be simulated using a “quantum simulator” — an artificial device governed by the same quantum laws as the system being studied.

Physicists at École Polytechnique Fédérale de Lausanne (EPFL) have proposed a new quantum simulator — a laser-based device that could be used to study a range of quantum systems. The simulator could help scientists better understand the properties of complex materials under extreme conditions.

Riccardo Rota and Vincenzo Savona, the two EPFL physicists leading the study, working on the design of their quantum simulator. Courtesy of R. Ravasio/EPFL.
Riccardo Rota and Vincenzo Savona, the two EPFL physicists leading the study, working on the design of their quantum simulator. Courtesy of R. Ravasio/EPFL.

The researchers built their simulator using superconducting circuits coupled to laser fields to cause an effective interaction among photons. They modeled the behavior of their simulator using traditional computer simulations.

One example of a complex quantum system that could be studied using such a quantum simulator are magnets placed at extremely low temperatures. At near-absolute zero (−273.15 °C), magnetic materials can undergo a quantum phase transition. Like a conventional phase transition, the system still switches between two states; however, when near the transition point, the system manifests quantum entanglement. Studying this phenomenon in real materials would be an extremely challenging task, the researchers said.

The EPFL simulator could address this problem, according to the team. “The simulator is a simple photonic device that can easily be built and run with current experimental techniques,” said researcher Riccardo Rota. “But more importantly, it can simulate the complex behavior of real, interacting magnets at very low temperatures. 

“When we studied the simulator, we found that the photons behaved in the same way as magnetic dipoles across the quantum phase transition in real materials,” Rota said. “In short, we can now use photons to run a virtual experiment on quantum magnets instead of having to set up the experiment itself.”

“Our findings prove that the quantum simulator we propose is viable, and we are now in talks with experimental groups who would like to actually build and use it,” said professor Vincenzo Savona.

Rota believes that the simulator could be applied to a broad class of quantum systems, allowing it to be used to study several complex quantum phenomena.

The research was published in Physical Review Letters (

Published: March 2019
The term quantum refers to the fundamental unit or discrete amount of a physical quantity involved in interactions at the atomic and subatomic scales. It originates from quantum theory, a branch of physics that emerged in the early 20th century to explain phenomena observed on very small scales, where classical physics fails to provide accurate explanations. In the context of quantum theory, several key concepts are associated with the term quantum: Quantum mechanics: This is the branch of...
quantum entanglement
Quantum entanglement is a phenomenon in quantum mechanics where two or more particles become correlated to such an extent that the state of one particle instantly influences the state of the other(s), regardless of the distance separating them. This means that the properties of each particle, such as position, momentum, spin, or polarization, are interdependent in a way that classical physics cannot explain. When particles become entangled, their individual quantum states become inseparable,...
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