No probing vulnerabilities Govi Bell inequality test is implemented

The team of academician Guo Guangcan of the University of Science and Technology of China has made new progress in quantum non-local research, and the research team of Li Chuanfeng and Liu Biheng has increased the overall detection efficiency of high-dimensional entangled photons to 71.7%, thus realizing the high-dimensional Bell inequality test without detection vulnerabilities. The results of the research were published in the Physical Review Letters.


Experimental apparatus diagram Courtesy of The University of Science and Technology of China

Non-locality is an important foundation for quantum mechanics and quantum information science. With the advent of Bell’s inequality, it is possible to experimentally test quantum non-locality. Due to the imperfection of the experimental device, the vast majority of experiments have loopholes, including widely concerned vulnerabilities such as probe vulnerabilities and local vulnerabilities. In 2015, scientists closed both detection vulnerabilities and local vulnerabilities in a two-dimensional entanglement system for the first time, and developed various device-independent quantum information tasks based on this.

Compared with two-dimensional quantum entanglement, high-dimensional quantum entanglement has obvious advantages in channel capacity, safety and noise immunity, so realizing the flawless high-dimensional Bell inequality test and realizing the device-independent high-dimensional quantum information task on this basis is an important direction that needs to be developed urgently in the field of quantum information.

In this experiment, the research team used a laser with a wavelength of 775 nanometers to pump beamlike-cut nonlinear crystals to obtain entangled photons with a wavelength of 1550 nanometers. This cutting method can effectively increase the collection efficiency of entangled photons, and the use of filtering devices with a transmittance of 99% and a superconducting single-photon detector with a detection efficiency of 90%, and the substrates of all optical components use optical glass with a very low absorption rate of 1550 nanometers, thus finally achieving a four-dimensional entangled photon state with an overall detection efficiency of 71.7%, which is much higher than the threshold of 61.8% required to close the detection loophole of the four-dimensional Bell inequality. At the same time, the fidelity of the four-dimensional entangled photon state reached 99.5%. Through the rational selection of parameters, the research team has achieved the High Vibel inequality test without detection vulnerabilities for the first time in the world.

This achievement lays an important foundation for further realizing the high-dimensional Bell inequality test and device-independent high-dimensional quantum communication process that closes both detection vulnerabilities and non-local vulnerabilities. (Source: China Science Daily Wang Min)

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