Quantum Entanglement and Photons: From Aspect to Cirac, the Researchers Who Defined the Field

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Today is Father's Day. And in the world of quantum photonics, there are at least two physicists celebrating it with daughters, international awards, and decades of experiments that redefined our understanding of light: Alain Aspect and Juan Ignacio Cirac. One French, one Spanish. Both fathers. Both, in different ways, responsible for quantum photonic computing existing as we know it today.

Alain Aspect: The Father Who Proved Einstein Was (Partly) Wrong

Alain Aspect is married and has two children and seven grandchildren. But in scientific terms, his family is far larger: an entire generation of European quantum physicists was shaped by his influence.

In 1981, he demonstrated quantum entanglement experimentally for the first time, entangling two photons at a distance of 12 meters. That experiment closed decades of debate between Einstein's and Bohr's views on quantum mechanics, and opened the door to what Aspect himself called the "second quantum revolution" — the era of quantum computing, photonic cryptography, and quantum networks.

In 2022 he received the Nobel Prize in Physics together with Anton Zeilinger and John Clauser for that foundational work with entangled photons. He is currently Distinguished Research Director Emeritus at CNRS and Professor at the Institut d'Optique Graduate School at Université Paris-Saclay.

What Technical Legacy Does He Leave?

Aspect's experiment established the standard experimental protocol for Bell test experiments with polarized photons. His results are the empirical foundation on which today's quantum key distribution (QKD) systems and secure quantum communication protocols are built.

Juan Ignacio Cirac: The Spanish Physicist Who Devised How to Build a Quantum Computer

Cirac met his wife in his final year of secondary school; they married in 1991 and had their first daughter, Alicia, shortly afterwards; their second daughter, Sofía, was born in 1995. Today, with both daughters now grown up, he remains one of the world’s most active and frequently cited researchers in the fields of computing and quantum optics.

Born in Manresa, he graduated with a degree in Physics from the Complutense University of Madrid and obtained his PhD in 1991 in the field of optics. The turning point in his career came in 1994, when, at a conference in Boulder (Colorado), he witnessed a demonstration that a quantum system could break any classical encryption. Together with his collaborator Peter Zoller, they devised at that moment how to build the first quantum computer. That work is now considered one of the seminal papers in the field.

Since 2001, he has headed the Theoretical Division of the Max Planck Institute for Quantum Optics in Garching (Germany), and in 2025 he received the CSIC Medal for Scientific Excellence for his contributions to quantum entanglement, quantum teleportation and projected states.

His Connection to Spain and the Photonic Ecosystem

Cirac has played an active role in the establishment of the Institute of Photonic Sciences (ICFO) in Barcelona, thereby consolidating Spain’s position in this strategic field. The ICFO is now one of the world’s leading centres for integrated quantum photonics, with research groups working on single-photon sources, quantum communication and silicon photonics. His influence on the Spanish photonics research ecosystem is direct and measurable.

Jian-Wei Pan: China's "Father of Quantum"

In 2017, Nature magazine included him in its annual list of the ten people who had the greatest impact on science, dubbing him the ‘Father of Quantum’. He is a professor at the University of Science and Technology of China (USTC) in Hefei, and is arguably the most influential active researcher in applied quantum photonics on a global scale.

Pan led the development of the world’s first quantum satellite, Micius, which in 2017 enabled a completely secure video conference between Vienna and Beijing thanks to encryption keys encoded in photons in a quantum state. Pan completed his PhD under the supervision of Anton Zeilinger in Vienna before returning to China to implement these technologies. The relationship between the two is one of the clearest examples of how quantum photonics is passed down from generation to generation, from laboratory to laboratory, crossing borders.

Relevance for Integrated Photonics

Pan’s work on multiphoton entanglement and quantum satellite communication has direct implications for the design of long-distance photonic networks. His experiments establish the coherence and fidelity requirements that any photonic chip architecture must meet in order to be integrated into a future global quantum network.

Anton Zeilinger: The Teacher Who Trained the Teachers

Anton Zeilinger, professor emeritus at the University of Vienna, was a pioneer in quantum mechanics through his theoretical and experimental work on entanglement, and in 1997 he demonstrated quantum teleportation for the first time.

His impact on the field extends beyond his own experiments: he supervised the doctoral thesis of Jian-Wei Pan, one of the world’s most influential researchers in quantum photonics. In 2022, he was awarded the Nobel Prize in Physics alongside Aspect and Clauser for their experiments with entangled photons that established the violation of Bell’s inequalities.

In terms of scientific legacy, Zeilinger is perhaps the figure who best embodies the idea of ‘intellectual paternity’ in this field: his students and collaborators now head the world’s leading laboratories in quantum photonics.

A Field Built on Legacies

Quantum photonics is, in part, a story of transmission. Zeilinger trained Pan. Aspect inspired a whole generation of French quantum physicists. Clauser’s experiments in 1972 paved the way for Aspect’s in 1981, which in turn made Pan’s experiments in 2017 possible.

On this Father’s Day, that chain of scientific inheritance is perhaps the best argument for understanding why quantum photonics is not just technology: it is also culture, transmission and time.