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IT Home reported on August 13 that the University of Science and Technology of China published a blog post on August 7:Announced that its research team has achieved a flawless Hardy paradox test for the first time.

Introduction to Hardy's Paradox

In the 1990s, physicist Lucien Hardy proposed a new way to test local reality:Hardy's Violation。

The paradox is that two observers make random measurements on the particles they receive and record the results. When the probability of an event occurring when three Hardy conditions are met is zero, quantum mechanics predicts that the probability of a fourth Hardy event occurring is greater than zero. This contradicts local realism's prediction that the probability of the fourth Hardy event is zero.

Hardy's paradox reveals the contradiction between the non-locality of quantum mechanics and local realism with simple logic and minimal resources.

Although there have been many experiments to test the Hardy paradox, these works all have locality loopholes and detection efficiency loopholes similar to those in Bell's inequality test: if the observer's measurement choices and results can influence each other (locality loophole), or there is high optical loss (detection efficiency loophole), the classical local hidden variable theory can explain the Hardy paradox.

At the same time, since the probability of the fourth Hardy event occurring is very low according to the predictions of quantum mechanics, in order to experimentally confirm that the occurrence of this event is not an error caused by noise, extremely high requirements are placed on the fidelity and efficiency of the entanglement source.

Therefore, achieving a flawless Hardy paradox test has always been a theoretical and experimental challenge.

Introduction to my country's scientific research team

A research team consisting of Pan Jianwei, Zhang Qiang, Chen Kai and others from the University of Science and Technology of China, in collaboration with Chen Jingling and others from Nankai University, successfully achieved a demonstration of Hardy nonlocality that closed the detection efficiency loophole and locality loophole by developing a high-efficiency and high-fidelity optical quantum entangled state preparation and measurement system.

The relevant research results were published in the international academic journal Physical Review Letters under the title "Loophole-Free Test of Local Realism via Hardy's Violation" and received the "editor's suggestion".

Zhao Siran and Dong Haihao, doctoral students at the University of Science and Technology of China, and Zhao Shuai, a young teacher at Hangzhou Dianzi University, are the co-first authors of the paper. Academician Pan Jianwei, Professor Zhang Qiang, Professor Chen Kai at the University of Science and Technology of China, and Professor Chen Jingling at Nankai University are the co-corresponding authors of the paper.

In this study, the research team further theoretically developed the Hardy-constrained Eberhard inequality, which allows Hardy's paradox test to be performed when the detection efficiency loophole is closed and in the presence of noise.

Results

By optimizing the parameters of the spatial optical path, the research team produced entangled photon pairs with a predictable detection efficiency of 82% and a fidelity of 99.1%, successfully closing the detection efficiency loophole.

A diagram of the experimental setup for testing the Hardy paradox without any loopholes. Source: the paper

In addition, the research team ensured the generation of entangled photon pairs and the observer's measurement choice through carefully designed space-time configuration. Both the measurement event and the observer's measurement choice were in space-like intervals, thus closing the locality loophole and realizing a loophole-free Hardy's paradox test for the first time.

Project Significance

This research is not only of great significance to the basic research of quantum physics, but also has an important impact on the development of quantum information technology such as quantum key distribution and quantum random number authentication. The reviewers highly praised this work and believed that "The experimental results, along with the quantified evidence against local realism, are impressive.” and “Editor's Recommendations" published in the form of

IT Home attaches the reference address