Lasers are no longer required to produce quantum entanglement, physicists say, after achieving the state using sunlight. In a laboratory experiment, an international team of researchers demonstrated that natural sunlight can produce quantum-entangled photon pairs.

The researchers recently published their quantum entanglement study in Optica, showing that lasers aren’t the only game in town. The work could herald a new energy-efficient approach to sustainable quantum technologies, both on Earth and in space.

Quantum Entanglement

Quantum technologies such as computing, communications, and sensing rely on the strange principles of quantum mechanics, which often defy explanations rooted in classical physics. Typically, quantum technologies use lasers to convert photons inside a nonlinear crystal into entangled pairs through a process called spontaneous parametric down-conversion (SPDC).

Prior to this work, using sunlight to produce quantum entanglement in photons was largely considered impractical. Researchers had assumed that SPDC depended heavily on phase-stable electromagnetic fields, requiring the high coherence of laser beams. Scientists also believed that the intense power of lasers was crucial to the nonlinear processes that produce entanglement. By contrast, sunlight’s relative weakness and incoherence left it largely overlooked as a viable source for generating entangled photons.

Reconsidering Coherence

Earlier work may have dismissed sunlight too readily because scientists had not fully considered the different dimensions of coherence. Across different parameters, sunlight can exhibit varying degrees of coherence. This means that while a beam of sunlight may be coherent in a particular property, such as polarization, it can still generate quantum entanglement along that parameter.

“As long as the pump beam is perfectly polarized, its spatial or temporal incoherence should not preclude the generation of polarization entanglement,” said lead author Cheng Li in a statement.

“The trick to harnessing sunlight is to keep different degrees of freedom of light from influencing each other during the process,” Li added. “This means that sunlight is perfectly capable of generating entangled photons, as long as one can concentrate enough sunlight into a nonlinear crystal to induce SPDC.”

Directing Sunlight

In a natural environment, sunlight spreads across a broad area rather than remaining tightly focused like a laser beam. Efficiently directing it through a nonlinear optical crystal, only a few millimeters wide, therefore presents a significant challenge.

To overcome this obstacle, the researchers constructed a sunlight concentration system that collects light across a 1.4-square-meter surface and focuses it down to approximately the width of a human hair. The specialized solar concentrator is conical rather than flat and is constructed from glass. As sunlight reflects repeatedly across the interior surface on its way toward the cone’s tip, it becomes progressively concentrated and intensified before traveling through a single optical fiber to drive the SPDC process that generates quantum entanglement.

Quantum Entanglement Results

In laboratory tests, the researchers found that their sunlight-driven SPDC system produced performance comparable to that of a laser, achieving 94% fidelity. The efficiency of the entanglement process was also similar to that achieved with laser-based systems. Together, these findings challenge previous assumptions that SPDC requires highly coherent laser light to operate effectively.

The approach also eliminates the need to first convert electrical energy into optical energy, potentially reducing system complexity, heat generation, and points of failure.

“Sunlight is an abundant and reliable resource in many environments, especially in space. Being able to generate quantum-entangled photons directly from sunlight could enable simpler and more resilient quantum systems for satellites and future deep-space missions,” said Hanieh Fattahi, the study’s co-author, in a statement.

“We believe this work can inspire much new research in nonlinear and quantum optics,” Fattahi said, adding that this research “may in turn make sunlight-driven quantum technology more practical.”

The paper, “Generating Quantum Entanglement from Sunlight,” appeared in Science Advances on August 5, 2026.

Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org.

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