University of Ottawa researchers made entangled photons skipping the laser

Scientists at the University of Ottawa, collaborating with researchers from the Max Planck Institute for the Science of Light and the Max Planck Center for Extreme and Quantum Photonics, have achieved quantum entanglement using sunlight for the first time.

The team challenges the decades-long assumption that lasers are essential for creating correlated photon pairs, a key resource for quantum technologies. “As long as the pump beam is perfectly polarized, its spatial or temporal incoherence should not preclude the generation of polarization entanglement,” explains Dr. Cheng Li, a PhD graduate from the University of Ottawa. This breakthrough demonstrates that even the lower intensity and incoherence of sunlight can efficiently drive the necessary nonlinear optical processes, potentially leading to more sustainable photonic quantum systems.

Sunlight Challenges Laser Dominance in SPDC Entanglement Achieving 94% fidelity, researchers have, for the first time, successfully generated quantum-entangled photons using only sunlight as a pump source, a result that challenges the decades-long reliance on lasers for this process. This breakthrough, detailed recently in Optica, demonstrates that the high optical coherence traditionally considered essential for spontaneous parametric down-conversion (SPDC) is not, in fact, indispensable, opening avenues for more sustainable quantum technologies. Previously, scientists believed that the intense, coherent beams produced by lasers were uniquely capable of driving the nonlinear optical processes necessary for efficient SPDC, where photons from the pump beam are converted into entangled pairs within a nonlinear crystal. However, the team’s work reveals that sunlight, despite being significantly less intense and inherently incoherent, can achieve comparable results when properly harnessed. The researchers focused on maintaining polarization while accommodating the inherent incoherence of sunlight in other degrees of freedom. To overcome the low intensity of sunlight, the team engineered a sophisticated sunlight concentration system. A 1.4 square meter collection area funneled light into a fiber optic cable only as thick as a human hair. The core of this system is a cone-shaped glass concentrator coupled with a large Fresnel lens mounted on a solar-tracking motor, ensuring maximum light capture and concentration. This concentrated sunlight was then directed into a nonlinear crystal to initiate SPDC, demonstrating that sufficient pump power could be achieved even with a diffuse light source. The resulting entangled photons not only exhibited high fidelity, reaching nearly 94%, but also demonstrated violations of Bell’s inequality, confirming their genuinely quantum nature and ruling out classical explanations for their correlations. When normalized for pump power and bandwidth, the efficiency of sunlight-driven entanglement generation proved to be on par with laser-driven methods. This finding suggests that the perceived advantages of lasers were not as fundamental as previously thought, and that practical, sunlight-powered quantum light sources are increasingly within reach with further technical refinements. The implications of this work extend beyond simply offering a sustainable alternative to lasers. “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.” Sunlight’s broad spectrum could also unlock access to entangled photons across a wider range of wavelengths, particularly in areas where laser sources are limited. Eliminating the need for electrical-to-optical conversion reduces waste heat and potential points of failure, making sunlight-driven systems particularly attractive for deployment in challenging environments. Robert Boyd, a professor at the University of Ottawa, emphasizes that this research represents a starting point for a broader exploration of sunlight-driven quantum technologies. “In addition to SPDC, there are many other nonlinear optical approaches to generate entangled photons—four-wave mixing is one example,” he says. “For each of these nonlinear interactions, there are ways to make it more efficient, and we believe this work can inspire much new research in nonlinear and quantum optics, potentially making sunlight-driven quantum technology more practical.” As long as the pump beam is perfectly polarized, its spatial or temporal incoherence should not preclude the generation of polarization entanglement. Dr. Cheng Li, PhD graduate from Prof. Robert Boyd’s group at the University of Ottawa Polarization Entanglement Achieved Despite Solar Incoherence Scientists theorized that phase-stable electromagnetic fields were necessary to generate the quantum correlations central to SPDC. However, the team demonstrated that while coherence in one degree of freedom can limit entanglement in that same degree, targeting entanglement in a different degree of freedom bypasses this limitation. “The trick to harnessing sunlight is to keep different degrees of freedom of light from influencing each other during the process.” This cone-shaped device, built in-house, collects light over 1.4 square meters and funnels it down into a fiber as thin as a human hair. This concentrated sunlight then drives the SPDC process within a nonlinear crystal, effectively mimicking the power density previously thought only achievable with lasers. The resulting entangled photon pairs exhibited a high degree of entanglement, achieving a fidelity of nearly 94 percent, comparable to laser-driven SPDC. Hanieh Fattahi, a research group leader at MPL, states that “Sunlight is an abundant and reliable resource in many environments, especially in space,” highlighting the potential for deploying these systems in challenging locations. Beyond sustainability, sunlight-driven quantum devices offer unique advantages over laser-based systems; a spacecraft in a Sun-synchronous orbit, for example, would have nearly continuous access to the necessary pump source. Boyd emphasizes that this work is not an endpoint, but rather a starting point. Sunlight is an abundant and reliable resource in many environments, especially in space. Source: https://mpl.mpg.de/news/article/quantum-entanglement-generated-by-sunlight-for-the-first-time Stay currentSee today’s quantum computing news on Quantum Zeitgeist for the latest breakthroughs in qubits, hardware, algorithms, and industry deals. Tags: