International first! CSU achieves detection-loophole-free test of high-dimensional Bell inequalities
The team of academician Guangcan Guo at the Chinese University of Science and Technology (CSU) has made important progress in the study of quantum nonlocality. The research group of Chuanfeng Li and Biheng Liu has improved the overall detection efficiency of high-dimensional entangled photons to 71.7%, thus achieving a high-dimensional Bell inequality test without detection loopholes. The result was published on August 3 in the internationally recognized journal Physical Review Letters.
Compared with two-dimensional quantum entanglement, high-dimensional quantum entanglement has obvious advantages in terms of channel capacity, security and noise immunity, so the realization of loophole-free high-dimensional Bell inequality test and the implementation of device-independent high-dimensional quantum information tasks based on this is an important direction that needs to be developed urgently in quantum information. In recent years, Chuanfeng Li and Biheng Liou's research group has devoted itself to the experimental study of high-dimensional quantum networks and has made a series of progresses to solve the difficulties of preparation, transmission and measurement of high-dimensional quantum entanglement, which lay a solid foundation for the realization of high-dimensional quantum networks.
In this experiment, the research group has made a breakthrough in the detection efficiency of high-dimensional entangled photons, and achieved a high-dimensional Bell inequality test without detection loopholes. The research group used laser-pumped beamlike cut nonlinear crystals with a wavelength of 775 nm to obtain entangled photons with a wavelength of 1550 nm, which can effectively increase the collection efficiency of entangled photons, and used a filter with 99% transmittance and a superconducting single-photon detector with 90% detection efficiency. The optical glass with extremely low absorption was used for all the optical elements, resulting in a four-dimensional entangled photon state with an overall detection efficiency of 71.7%, which is much higher than the threshold of 61.8% needed to close the four-dimensional Bell inequality detection loophole, and the fidelity of the four-dimensional entangled photon state reached 99.5%. Through reasonable choice of parameters, the research group has achieved the first high-dimensional Bell inequality test without detection loophole in the world. The results lay an important foundation for further realization of the high-dimensional Bell inequality test with simultaneous closure of detection loophole and non-local loophole and device-independent high-dimensional quantum communication process.
The first authors of the article are Dr. Xiaomin Hu, an associate researcher at the Key Laboratory of Quantum Information, Chinese Academy of Sciences, and Chao Zhang, a PhD student. This research was supported by the Ministry of Science and Technology, the State Foundation of China, the Chinese Academy of Sciences, and the Hefei National Laboratory. Researcher Biheng Liu is a Chung-Ying Young Scholar at the University of Science and Technology of China.
Figure 1: Diagram of the experimental setup.
Figure 2: Comparison of the detection efficiency required to achieve a Bell inequality test without detection holes. At a fidelity of 99.5% for both, the detection efficiency requirement for the four-dimensional entangled state is significantly lower than that for the two-dimensional entangled state.
Link to article:
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.060402
