Order from Chaos: Technion Researchers Discover Photon Swirling

Technion researchers and colleagues in China have discovered the emergence of photon “swirling” in disordered nanometric systems

The journal Nature Materials reports the discovery of “hidden order” in systems that are disordered in space and time. The breakthrough was achieved by Professor Erez Hasman from the Faculty of Mechanical Engineering and the Helen Diller Quantum Center at the Technion – Israel Institute of Technology, together with colleagues in China led by Professor Bo Wang, head of Spin Nanophotonics Group, at the School of Physics and Astronomy, Shanghai Jiao Tong University. Prof. Wang conducted his postdoctoral research in Prof. Hasman’s group and was part of the team behind the development of the spin laser made from two-dimensional materials.

In their paper, the researchers present a new physical phenomenon called “spin locking effect induced by Brownian motion,” which enables the detection of spin-order in a physically disordered system.

A brief explanation of two key concepts: Spin – one of the fundamental properties of elementary particles, describing their “rotation” or “twist.” This is a simplified and somewhat inaccurate metaphor, but it is the common way to describe spin. Brownian motion, also known as a “drunkard’s walk,” refers to the random movement of tiny particles (not necessarily atomic in size) suspended in or floating on a liquid. Einstein made this phenomenon famous when he published his findings in 1905.

Until now, it was believed that Brownian motion causes the scattering of photons off particles to be chaotic – that is, unpolarized and incoherent – and so too the spin of the scattered photons.

The researchers set out to test whether, under specific light–matter interaction conditions, spin order could emerge – and found that it can. When they shone laser light on nanometric particles suspended in a liquid at room temperature, they discovered that the photons scattered sideways, beyond the laser’s impact zone, became “locked” in their spin. They demonstrated that this spin locking arises precisely because of the particles’ random movement – their Brownian motion. This process also allowed the researchers to measure the size of the particles, since the spin-locking effect depends on both particle size and material type, thus revealing information about them.

According to Prof. Hasman: “Our discovery beautifully illustrates the importance of experimental physics. We have shown that it is precisely the most disordered systems – in both space and time – that hold the key to the emergence of deep order. The spin-locking effect in a system undergoing Brownian motion is a previously unknown phenomenon, and we hope and believe that its applications – from nanoparticle characterization to the development of new optical technologies – will make a significant contribution to science and industry in the future.”

The research was supported by the National Science Foundations of Israel and China.

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