by Advancements in quantum research have opened up new possibilities for photonic quantum technologies, with researchers at the University of Stuttgart achieving an efficiency that exceeds the theoretical limit. Quantum entanglement, a property of quantum systems that allows for the sharing of information in ways not possible in classical physics, has been a topic of debate since the time of Albert Einstein and Niels Bohr. The disagreement surrounding quantum entanglement was experimentally resolved by physicist John Stewart Bell in the 1960s. Bell’s framework has since been used in experiments with photons, which led to groundbreaking works in the field of quantum technologies by Alain Aspect, John Clauser, and Anton Zeilinger, who received the Nobel Prize in Physics for their contributions.
Bell-state measurements, which determine the quantum states of entangled particles, are essential for quantum teleportation and other quantum communication and computation processes. However, experiments using conventional optical elements have limitations, as two of the four Bell states have identical experimental signatures and cannot be distinguished from each other, leading to an inherent success rate limit of 50 percent. The research conducted by the Barz group at the University of Stuttgart overcame this limitation by using two additional photons along with the entangled photon pair to achieve a success rate of 57.9 percent in Bell-state measurements.
The use of auxiliary photons in Bell-state measurements was theoretically known to increase the efficiency beyond 50 percent, but experimental realization was challenging due to the need for sophisticated detectors that can resolve the number of photons. The Barz group overcame this challenge by using 48 single-photon detectors operating in near-perfect synchrony to detect up to four photons arriving at the detector array. The team was able to detect distinct photon-number distributions for each Bell state, surpassing the 50-percent barrier.
While the increase in efficiency may seem modest, it is significant for scenarios where multiple sequential measurements need to be made, such as in long-distance quantum communication. The improved Bell-state measurement scheme offers advantages in terms of instrumental complexity and can be utilized in various quantum technologies. The research collaboration between the University of Stuttgart and the Johannes Gutenberg University in Mainz has produced promising results and is part of the larger effort to advance photonic quantum computing in Germany.
The advancements in achieving higher efficiency in quantum technologies have broader implications for the field and can open up new perspectives for the development of quantum computation, communication, and sensor devices. The findings from this research offer new opportunities for harnessing quantum entanglement in practical applications and contribute to the ongoing exploration of quantum technologies in Stuttgart and Baden-Württemberg.
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