When light becomes a crystal: The quantum revolution of supersolid light

Pallab Bhattacharyya

(Pallab Bhattacharyya is a former director-general of police, Special Branch and erstwhile Chairman, APSC. Views expressed by him is personal. He can be reached at pallab1959@hotmail.com)

Light is a form of electromagnetic radiation that is visible to the human eye and is essential to life on Earth. It travels in waves and has both particle-like and wave-like properties, a concept known as wave-particle duality. Light plays a crucial role in natural processes such as photosynthesis and vision, and it also enables modern technologies like fibre-optic communication and laser systems. It moves at a speed of approximately 299,792 kilometres per second in a vacuum, making it the fastest thing in the universe. Beyond visible light, the electromagnetic spectrum includes other types of waves such as ultraviolet, infrared, X-rays, and radio waves. This is what I learnt during my postgraduation in 1982. But lo and behold, how time has changed! 

In March 2025, a historic experiment in quantum physics reshaped our understanding of light. For the first time, scientists succeeded in transforming light into a supersolid—a paradoxical state of matter that combines the structural rigidity of a solid with the frictionless flow of a superfluid. This achievement was more than a scientific curiosity; it was a quantum leap, marking a turning point in the way we perceive light and opening the door to transformative innovations in science and technology.

This revolutionary breakthrough defied well-held convention till the other day. The epoch-making experiment was conducted by a team of Italian physicists led by Dimitrios Trypogeorgos and Daniele Sanvitto from Italy’s National Research Council (CNR) and the University of Pavia. By using a gallium arsenide semiconductor platform engineered with nanometric ridges, they were able to manipulate light at an unprecedented level. When laser light interacted with this structure, it formed polaritons—quasiparticles that are hybrids of photons and excitons (electron-hole pairs).

These polaritons didn’t just bounce around randomly; they arranged themselves into a supersolid phase, combining ordered crystalline patterns with fluid-like, resistance-free movement. This duality was astonishing. Light, long considered the quintessential ephemeral entity, now demonstrated properties typically reserved for exotic phases of atomic matter. As Trypogeorgos put it, “This is not simply a photonic analogy of atomic systems, but a fundamentally new approach to achieve supersolidity.”

Supersolids are among the rarest and most mysterious states of matter. They simultaneously exhibit:

• Crystalline order, like a conventional solid.

• Frictionless flow, like a superfluid.

Imagine a lattice of atoms that can slide through itself with no internal resistance. Now imagine that instead of atoms, you have light behaving in that way. That’s what these Italian researchers have managed to achieve. If one is looking for a metaphor, think of a crystal made of honey—structured, yet flowing effortlessly. This is the duality that defines a supersolid and makes it so counterintuitive.

The success of this experiment was built on a foundation of collaboration between Italy’s top research institutions: CNR-INO, CNR-Nanotec, and the University of Pavia. Key contributors included Antonio Gianfrate, Davide Nigro, Dario Gerace, Iacopo Carusotto, and many others. Each brought specialised knowledge in fields ranging from photonics to condensed matter physics, embodying the multidisciplinary spirit necessary for breakthroughs of this magnitude.

The transformation of light into a supersolid is more than a marvel of quantum mechanics; it is a gateway to a new era of scientific discovery and technological innovation.

1. Quantum Computing: Supersolid light offers a tantalising promise for quantum information processing. Its inherent stability and coherence make it an ideal candidate for storing and manipulating qubits. Unlike conventional light or matter, supersolid light can maintain quantum coherence over longer durations, a key requirement for scalable quantum computers.

Dario Gerace suggests that this fluid of light could be harnessed to develop quantum simulators capable of exploring the behaviour of complex quantum systems, accelerating both fundamental research and technological application.

2. Photonics and Optical Processing: Supersolid light could revolutionise the field of optical computing by enabling ultra-efficient, low-loss photonic circuits. These systems could outperform traditional electronics in both speed and energy efficiency, thanks to the frictionless movement of polaritons.

Additionally, light-based logic gates using supersolid behaviour might eventually lead to fully photonic processors, minimising the need for electricity-based semiconductors.

3. High-Precision Sensing: One of the defining features of supersolids is their sensitivity to external perturbations. This makes them exceptional candidates for next-generation sensors, particularly in applications requiring high precision, such as:

• Gravitational wave detection

• Magnetic field mapping

• Medical imaging

These sensors could operate in extreme environments and detect fluctuations at scales previously considered impossible.

4. Energy Transmission and Materials Science

Supersolidity hints at the potential to create lossless energy transfer systems, much like superconductors but based on light. Such materials could significantly reduce energy waste in everything from power grids to transportation. Moreover, new metamaterials inspired by supersolid principles might offer custom-designed optical and mechanical properties for use in aerospace, defence, and energy storage.

A Glimpse Into the Future: The creation of supersolid light is not the conclusion—it’s the beginning of a rich and expansive field of study. Future research will aim to:

• Stabilise supersolid light under varying environmental conditions.

• Explore new materials that better support the formation of polaritons.

• Harness this state for real-world applications, from quantum communication to novel light-emitting devices.

As Daniele Sanvitto noted, this is a “new and controlled way” to explore exotic states of matter, and it could finally bridge the divide between quantum theory and practical technology.

The philosophical and scientific significance of this experiment can be gauged from the fact that the idea that light—a symbol of intangibility and speed—can behave like a solid structure shatters our long-held assumptions about the nature of energy and matter. It underscores a fundamental lesson from modern physics: what we perceive as separate domains of reality may in fact be deeply interconnected. This achievement invites us to reconsider the very foundations of how the universe works. It is a reminder that even in the 21st century, the natural world continues to surprise us with its complexity and elegance.

The transformation of light into a supersolid stands as a monumental achievement in quantum science. It represents a convergence of theoretical brilliance and experimental finesse, and its implications will ripple across multiple domains of science and technology for years to come. It challenges what we know, expands what is possible, and exemplifies the very spirit of scientific progress: to venture into the unknown, guided by curiosity and a relentless pursuit of truth. As we contemplate this quantum leap, it is fitting to close with the words of one of history’s greatest minds:

“The universe is not only stranger than we think; it is stranger than we can think.” — Albert Einstein

Indeed, the creation of supersolid light proves that the frontier of discovery is far from over. If anything, it has only just begun. The International Day of Light, being celebrated on the 16th of May every year, is a cause for celebration for all for the likely impact of light on humanity as a whole in the days to come.