Entangled atoms found to supercharge light emission

In light-matter systems, many emitters (e.g., atoms) share the same optical mode within a cavity. This mode represents a pattern of light confined between mirrors, enabling collective behaviors that isolated atoms cannot exhibit. A key example is superradiance, a quantum effect in which atoms emit light in perfect synchronization, creating a brightness far greater than the sum of their individual emissions.

Most earlier studies of superradiance assumed that light-matter coupling dominates, modeling the entire atomic group as one large "giant dipole" connected to the cavity's electromagnetic field. "Photons act as mediators that couple each emitter to all others inside the cavity," explains Dr. João Pedro Mendonça, the study's first author, who earned his PhD at the University of Warsaw and now conducts research at its Centre for New Technologies. In real materials, however, nearby atoms also interact through short-range dipole-dipole forces, which are often overlooked. The new study examines what happens when these intrinsic atom-atom interactions are considered. The findings show that such interactions can either compete with or reinforce the photon-mediated coupling responsible for superradiance. Understanding this balance is vital for interpreting experiments where light and matter strongly influence one another.

The Role of Entanglement in Light-Matter Interactions

At the heart of this behavior lies quantum entanglement, the deep connection between particles that share quantum states. Yet many common theoretical methods treat light and matter as separate entities, erasing this crucial link. "Semiclassical models greatly simplify the quantum problem but at the cost of losing crucial information; they effectively ignore possible entanglement between photons and atoms, and we found that in some cases this is not a good approximation," the authors note.

To address this, the team developed a computational method that keeps entanglement explicitly represented, allowing them to track correlations both within and between the atomic and photonic subsystems. Their results show that direct interactions between neighboring atoms can lower the threshold for superradiance and even reveal a previously unknown ordered phase that shares its key properties. Overall, the work demonstrates that including entanglement is essential for accurately describing the full range of light-matter behaviors.

Implications for Quantum Technologies

Beyond deepening fundamental understanding, this discovery has practical significance for future quantum technologies. Cavity-based light-matter systems are central to many emerging devices, including quantum batteries -- conceptual energy storage units that could charge and discharge much faster by exploiting collective quantum effects. Superradiance can speed up both processes, enhancing overall efficiency.

The new findings clarify how microscopic atomic interactions influence these processes. By adjusting the strength and nature of atom-atom interactions, scientists can tune the conditions needed for superradiance and control how energy moves through the system. "Once you keep light-matter entanglement in the model, you can predict when a device will charge quickly and when it won't. That turns a many-body effect into a practical design rule," said João Pedro Mendonça. Similar principles could also advance quantum communication networks and high-precision sensors.

The research grew from an international partnership that brought together expertise from several institutions. João Pedro Mendonça conducted multiple research stays in the United States, supported by the University of Warsaw's "Excellence Initiative -- Research University" (IDUB) program and the Polish National Agency for Academic Exchange (NAWA). The researchers emphasize that collaboration and mobility were key to their success. "This is a great example of how international mobility and collaboration can open the door to breakthroughs," the team concludes.