The realm of quantum physics is currently undergoing its second major revolution, which is set to significantly advance fields such as computing, the internet, telecommunications, cybersecurity, and biomedicine. There is a growing interest among students in learning about complex concepts from the subatomic domain, including quantum entanglement and quantum superposition, as they seek to harness the groundbreaking possibilities of quantum science. In fact, grasping the peculiar characteristics of quantum technologies and understanding their implications for technological advancement is expected to be one of the key challenges in 2025, which UNESCO has declared as the International Year of Quantum Science and Technology.
The realm of quantum physics is currently undergoing its second major revolution, which is set to significantly advance fields such as computing, the internet, telecommunications, cybersecurity, and biomedicine. There is a growing interest among students in learning about complex concepts from the subatomic domain, including quantum entanglement and quantum superposition, as they seek to harness the groundbreaking possibilities of quantum science. In fact, grasping the peculiar characteristics of quantum technologies and understanding their implications for technological advancement is expected to be one of the key challenges in 2025, which UNESCO has declared as the International Year of Quantum Science and Technology.
A research team from the Faculty of Physics at the University of Barcelona has created new experimental tools that allow students to engage with more intricate aspects of quantum physics. Their setup, which is versatile, affordable, and can be applied in various classroom settings, is already in use at the Advanced Quantum Laboratory of the Faculty of Physics at UB, and has the potential for use in less specialized institutions as well.
This development is highlighted in a paper published in the journal EPJ Quantum Technology, resulting from the collaboration of professors Bruno Juliá from the Department of Quantum Physics and Astrophysics as well as the UB Institute of Cosmos Sciences (ICCUB); Martà Duocastella from the Department of Applied Physics and the UB Institute of Nanoscience and Nanotechnology (IN2UB); and José M. Gómez from the Department of Electronic and Biomedical Engineering. This work is based on Raúl Lahoz’s master’s final project, and included contributions from experts Lidia Lozano and Adrià Brú.
Exploring Unique Quantum Mechanics Phenomena Quantum mechanics allows for the creation of entangled systems, like pairs of particles or photons, which exhibit non-intuitive behavior. In 1964, physicist John S. Bell experimentally validated that quantum mechanics predictions were fundamentally at odds with classical physics descriptions, a notion proposed by Albert Einstein, thus affirming the probabilistic nature inherent to quantum mechanics. In 2022, the Nobel Prize in Physics was awarded to scientists Alain Aspect, John F. Clauser, and Anton Zeilinger for their groundbreaking experiments involving quantum information and entangled photons, along with the experimental confirmation of violations of Bell’s inequalities.
Currently, quantum entanglement is a crucial resource for advancing quantum technologies, including quantum computing and data encryption. “Studying Bell inequalities—particularly observing their violations—is essential for characterizing quantum entangled systems. It’s vital to conduct these experiments in a teaching lab to grasp Bell’s inequalities and the probabilistic nature of quantum mechanics,” emphasizes Bruno Juliá.
Martà Duocastella notes in the article, “We have developed new experimental equipment that enables students to perform direct measurements of quantum entanglement. We believe that allowing students to take these measurements will significantly enhance their grasp of this unintuitive phenomenon.”
Equipping Students with Advanced Tools The system designed by the UB team not only allows for the study of Bell inequalities but also enables complete two-photon state tomography. It can prepare various quantum entangled states with uncomplicated operations. Compared to previous designs, “the new equipment enhances the process of capturing photons: it incorporates detectors attached to optical fibers, a key innovation that simplifies the experiment, aids system alignment, and boosts detection efficiency. Consequently, complete measurements of Bell inequalities can be conducted during a practical lab session lasting one to two hours,” assert Juliá and Duocastella.
The results indicate successful control of the quantum state of photons, achieving high-fidelity entangled states and significant violations of Bell inequalities. Additionally, since the components of this system are prevalent in current quantum technologies, they provide students with exposure to cutting-edge instrumentation.
This innovation, which has already been implemented in both bachelor’s and master’s courses, has received outstanding feedback from students. In the undergraduate Physics program, it supports experimental demonstrations that complement the curriculum in Classical and Quantum Information Theory as well as Quantum Mechanics. In the master’s program, it forms part of four experiments in the Advanced Quantum Laboratory for the Master’s in Quantum Science and Technologies.
This research has received funding from the Spanish Ministry of Science, Innovation, and Universities, as well as the European Union’s Next Generation EU funds.
