In a pioneering achievement that blurs the line between light and matter, an international team of physicists has engineered a novel state of matter by coaxing hybrid light-matter particles into the ordered yet non-repeating pattern of a quasicrystal. The resulting entity, a type of quantum fluid, demonstrated a unique form of long-range order and collective behavior never before observed, establishing a new platform for exploring the fundamental properties of matter in exotic, aperiodic environments.
The breakthrough lies in the creation of a reconfigurable two-dimensional quasicrystal made of quasiparticles called polaritons. These constructs, which are part light and part matter, were arranged in a lattice that has order but lacks the endlessly repeating structure of a conventional crystal. Within this special arrangement, the polaritons settled into a macroscopic coherent state, acting in unison and synchronizing in a complex phase pattern dictated by the underlying aperiodic geometry. This opens new avenues for investigating complex quantum phenomena, such as superfluidity and supersolids, in systems that exist outside the predictable confines of traditional crystalline structures.
An Unconventional Crystalline World
Typical crystals, from snowflakes to table salt, are defined by their periodic structure—a grid-like arrangement of atoms that repeats identically in all directions. Quasicrystals are a fascinating exception to this rule. First identified in the 1980s in a Nobel Prize-winning discovery by Dan Shechtman, these materials possess a paradoxical nature: they have definite long-range order, but their atomic patterns never perfectly repeat. This aperiodicity grants them unique symmetries forbidden in ordinary crystals, such as five-fold rotational symmetry, similar to that seen in a pentagon.
This unusual atomic arrangement gives quasicrystals remarkable properties that have found uses in a range of real-world applications. Their hardness and low friction have led to their use in creating durable non-stick coatings for cookware and long-lasting razor blades. Other potential applications include advanced thermal insulation and more efficient LED lighting, making them a subject of intense interest in both fundamental physics and materials science. However, their behavior in non-equilibrium, laser-driven quantum systems remained largely unexplored until this recent breakthrough.
Crafting Matter by Painting with Light
The new form of matter was realized by a collaborative team from the Skolkovo Institute of Science and Technology (Skoltech), the University of Iceland, the University of Warsaw, and the Institute of Spectroscopy of the Russian Academy of Sciences. Their success depended on combining a sophisticated experimental technique with a strange form of quasiparticle.
The Hybrid Ingredients
The core components of the system are exciton-polaritons. These are not fundamental particles but rather hybrid quasiparticles that emerge inside a semiconductor. They are formed from the strong coupling of a photon (a particle of light) with an exciton (a bound state of an electron and an electron-hole). This intimate blend gives polaritons unique characteristics; they are extremely lightweight due to their light component but can still interact with each other because of their matter component. This interactivity allows them to behave as a quantum fluid and form condensates, which are macroscopic quantum states akin to a Bose-Einstein condensate.
The Experimental Blueprint
The researchers’ method was described as “painting with light.” They used a device called a spatial light modulator to precisely shape a laser beam. The beam was sculpted into a complex pattern known as a Penrose tiling—a well-known quasicrystal pattern with five-fold symmetry constructed from two different shapes of rhombuses. This patterned laser light was then projected onto a semiconductor microcavity, a structure designed to trap light and facilitate the creation of polaritons. The laser did not create the polaritons directly but instead established a potential energy landscape—an invisible terrain of energy peaks and valleys—that mirrored the Penrose tiling.
Emergence of a Synchronized Collective
As the researchers increased the power of the imprinted laser pattern, exciton-polaritons generated by a separate, uniform laser beam began to gather and cool at the energy peaks, forming individual condensates at each node of the quasicrystal lattice. These condensates, being a quantum fluid, were not confined to their spots but could flow across the sample, interacting and interfering with each other. This interaction led to two remarkable observations that defined the new state of matter.
Macroscopic Quantum Coherence
The team found that despite being located at dozens of different, non-periodically arranged points, the individual polariton condensates began to behave as a single, unified entity. This spontaneous formation of macroscopic coherence extended across the entire structure, over distances up to 100 times larger than any single condensate. The definitive proof came from measuring the momentum of the light emitted by the polaritons, which showed sharp diffraction peaks corresponding to the five-fold symmetry of the Penrose pattern—a clear signature of long-range quasicrystalline order.
A Novel Phase Locking
Using sensitive interferometry techniques, the scientists mapped the phase relationships between the different condensates. In a regular crystal, condensates typically synchronize in a simple pattern, either perfectly in-phase or perfectly out-of-phase with their neighbors. In the quasicrystal, however, the team discovered a far more complex and unusual synchronization pattern. This “nontrivial phase locking” was a direct consequence of the intricate, aperiodic geometry of the Penrose tiling, forcing the condensates into a frustrated, complex configuration that reflects the underlying structure.
Implications for Future Physics and Technology
The ability to create and control a polariton quasicrystal in the lab provides physicists with a highly configurable testbed for studying the behavior of quantum matter in aperiodic systems. By adjusting the laser power, the number of nodes, and their spacing, researchers can now directly probe how quantum fluids behave in an environment that is ordered but not repetitive. This could provide crucial insights into exotic states of matter, such as supersolids, which simultaneously exhibit the properties of a solid and a frictionless fluid.
The work also establishes a powerful new methodology for creating arbitrary potential landscapes for quantum fluids of light, going beyond the limits of naturally occurring crystals. The team suggests that this optical approach could be adapted to realize even more complex designs, including the recently discovered aperiodic “einstein” monotile—a single shape that can tile a plane without repetition. Sergey Aliatkin, the lead author of the study published in Science Advances, captured the aesthetic and scientific richness of the finding. “The results are literally beautiful,” Aliatkin stated. “We observed a complex interference pattern as polaritons from different nodes propagated and interacted across the micro cavity.”
