Realization of a continuous time crystal based on photonic metamaterial

A time crystal, as originally proposed in 2012, is a new state of matter in which particles are in a continuous oscillatory motion. Time crystals break the symmetry of time translation. Discrete time crystals do this by oscillating under the action of a periodic external parametric force, and this type of time crystal has been demonstrated in ions, atoms, and spin-entrapped systems.

Continuous time crystals are more interesting and arguably more important, as they exhibit continuous symmetry in time translation but can spontaneously enter a regime of periodic motion, due to a small vanishing perturbation. It is now understood that this state is only possible in an open system, and a continuous quantum crystal state has recently been observed in a quantum system of very cold atoms inside a photocavity illuminated by light.

In a paper published in nature physicsresearchers at the University of Southampton in the United Kingdom have shown that the nanostructure of a classical metamaterial can be forced into a state that exhibits the same key properties of a continuous time crystal.

“We have been studying the interactions of photonic matter with nanomechanical metamaterials for several years,” Nikolai I. Zeludov, one of the researchers who conducted the study, told Phys.org. “We recently realized that this was an ideal platform for demonstrating the crystal state of time,”

As part of their latest study, Zheludev and colleagues set out to realize a time-continuous crystal state using photonic metamaterial. The system they used is a two-dimensional array of plasmonic metamolecules (i.e., artificial structures that facilitate interaction with light at the nanoscale) supported by flexible nanowires.

The authors show that continuously and coherently illuminating this photonic metamaterial with light that resonates with the plasmonic position of the meta-particles within causes a spontaneous phase transition into a state that possesses the key properties of a continuous time crystal. This state is characterized by continuous oscillations caused by many-body interactions between metamolecules.

“We found that the photonic metamaterial, which is an array of nanowires decorated with plasmonic nanoparticles, can be driven into a state of coherent oscillations of the nanowires by the light-induced interaction between the particles,” explained Zelodev. “These oscillations appear spontaneously when a threshold of light exposure is reached. Such behavior constitutes a continuous time crystal, a new state of matter.”

The latest study by this team of researchers could open up new avenues of investigation into time crystals and the dynamical classical states of many objects in the tightly coupled system. In the future, the unique system achieved by Zheludev and colleagues could also pave the way toward the development of new optical and photonic devices.

“We have demonstrated a continuous time-shell state crystal, a new state of matter on a simple classical platform, which is a huge step towards applications of continuous temporal-shell state in photonics devices,” added Zelodev. “The reported observation is only the beginning, and we will continue to explore the fundamental properties of time-continuous crystals of photomechanical nanomaterial and their applications.”