Source: CCTV News Client

On July 9th, the journal "Nature" published online a new research result led by Professor Wang Xuehua and Liu Jin's team from the School of Physics, Sun Yat-sen University. The team proposed a novel cavity-induced spontaneous two-photon radiation scheme, which achieved for the first time in the world a spontaneous two-photon radiation with intensity comparable to that of single-photon radiation. They developed a new nanoscale quantum entangled photon source with a fidelity as high as 99.4%, which is on-demand triggered. This achievement provides key support for the development of next-generation quantum precision measurement technology and the construction of functionalized photonic quantum information processing chips.

△ Spontaneous two-photon radiation. (a) Conceptual diagram of two-photon entanglement; (b) spectrum of cavity-induced spontaneous two-photon radiation; (c) quantum correlation characteristics of spontaneous two-photon radiation.

In the quantum world, a pair of photons can be like telepathic twins — even if they are thousands of miles apart, measuring one instantly causes the other to "respond". This amazing quantum entanglement plays a crucial role in multiple fields such as quantum computing, quantum communication, and quantum precision measurement.

Compared to letting photons randomly "pair up", the Zhongda team chose to directly cultivate photon "twins", allowing them to have "quantum bonds" from their birth, thus achieving quantum entanglement.

"Some special materials, such as the 'artificial atoms' structure we use, have a probability of emitting two closely related photons at the same time. This phenomenon is called 'spontaneous two-photon radiation'," explained Liu Shunfa, the first author of the paper and associate professor at the School of Physics, Sun Yat-sen University.

Although researchers had already proposed related theoretical predictions in the 1960s, due to the fact that atoms tend to radiate only one photon at a time, the probability of producing "twins" photons is usually far lower than that of single photons, making it almost impossible to observe experimentally. For nearly 40 years, despite numerous experimental attempts by international research teams, this field has not yet achieved substantial breakthroughs.

△ Associate Professor Liu Shunfa conducting quantum optical measurement experiments

Now, breakthroughs in semiconductor material growth and device fabrication technology have provided key support for the experimental realization of spontaneous two-photon radiation. "We designed an ultra-high quality optical microcavity and precisely controlled the photon generation process at the nanoscale," said Liu Shunfa. This optical microcavity has established a dedicated channel for the production of "twins" photons, and in experiments, the two-photon radiation efficiency was increased from less than 0.1% to about 50%, making it possible to prepare controllable triggered entangled photon pairs.

"We are like building a factory for producing entangled photons at the nanoscale," said Liu Shunfa. Based on the nano-sized solid-state "artificial atom" structure, this study proposed a cavity-induced spontaneous two-photon radiation scheme, which achieved for the first time in the world a spontaneous two-photon radiation with intensity comparable to that of single-photon radiation. It broke the traditional concept that "the second-order quantum process of photon radiation is necessarily much weaker than the first-order process" and successfully prepared a new type of entangled photon pair source with a fidelity as high as 99.4%. "This index means our entangled photons have extremely strong 'telepathy', and also shows the great potential of this technology in improving the security of quantum communication, the reliability of quantum computing, and the accuracy of quantum metrology."

The reviewers of the journal "Nature" highly evaluated this achievement, calling it a "breakthrough in the field of two-photon research" and "achieving entangled photon pairs with record-breaking fidelity."

Liu Shunfa stated that in the next step, the team will continue to conduct research on quantum precision measurement and quantum communication applications using the high-fidelity entangled light source and high-purity two-photon source achieved in this study.

(Total station reporter Zheng Shu Zhao Jing)

Original article: https://www.toutiao.com/article/7525644752168026675/

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