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The detection efficiency of China's single photon detector exceeds 90 percent

Hou Shuwen, our reporter Wang Chun

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As an emerging international strategic technology, the field of quantum information is facing fierce international competition, and its core component technology is affected by the international embargo. High-performance single-photon detectors, an indispensable core component of quantum regulation, were also under an international embargo.

"Photons are the smallest unit of light, and a 10-watt light bulb can emit about 1020 photons a second." Dr. You Lixing, a researcher at the Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, told Science and Technology Daily that single-photon detection is a technology to detect one photon, which represents the limit of the detection ability of optical signals.

Just how important are single-photon detectors to the field of quantum information? For example, if a water drop is the smallest unit of water, normally the tap is turned on and the water splatters out. However, quantum regulation is just like the tap controlling every drop of water, and a single photon detector is equivalent to detecting every drop of water. "We have to turn a single photon that we detect into an electrical signal, and the current level of detection is that if we emit 100 photons, we can detect 90."

SNSPD special forces and quantum information national team cooperation

Lixing You returned to China in 2007 to conduct research and development of low-temperature superconducting nanowire single photon detector (SNSPD) technology at the Shanghai Institute of Microsystems. This technology utilizes the light sensitive property of superconducting nanomaterials to detect single photons.

The research and development of single photon detector is a very complex system engineering, from material production, processing to system integration must be explored from scratch. Before we have not independently mastered the core technology of SNSPD, the efficiency of the single photon detector used in quantum communication experiments in China is only 20%, and the noise is very high, which is far from the highest international level. The lack of high performance single photon detector has seriously affected the competition between Chinese quantum information scientists and foreign counterparts.

China's single photon detector started and developed from the needs of users to explore the direction of scientific research, the first step is to achieve the practicability and reliability of the device, You Lixin said.

In collaboration with Pan Jianwei, a member of USTC National Laboratory of Microbiology, You Lixing's team has developed a new circuit structure to improve the stability and reliability of the system, and to adapt the application environment from the laboratory environment to the actual field environment. In 2012, China's self-developed SNSPD was successfully applied to intercity quantum key distribution network for the first time. Pan Jianwei mentioned in the user report: "Compared with the same type of foreign single photon detector, the SNSPD system developed by Shanghai Microsystems realizes plug-and-play based on the mechanical cooling technology, which not only greatly improves the user-friendly performance, but also significantly reduces the application cost, and has a good promotion value."

Key technological breakthroughs promote the industrialization of SNSPD research in China

In China, SNSPD from scratch, to achieve domestic independent control at the same time, the international level of single photon detector technology also has a rapid development. The rapid development of quantum information in China also puts forward higher requirements for the detection efficiency of SNSPD.

According to You Lixing, in 2013, the detection efficiency of SNSPD developed by tungsten silicide (WSI) in the United States was up to 93%, while the detection efficiency of SNSPD prepared by niobium nitRIDE (NBN) in China was only 4%. "Devices made from WSI require lower operating temperatures than NBN, so the cost of cryogenic equipment increases exponentially." The Unistar team keeps moving forward in the research and development of SNSPD using NBN materials. After about 4 years of research, in 2016, the team finally achieved the first detection efficiency of NBN SNSPD device at the wavelength of 1550 nm in the world, and kept the world record for the efficiency of NBN SNSPD device.

"Background dark count suppression is the key to reduce the noise of the detection system." The so-called dark count is noise, and the lower the noise, the higher the system signal-to-noise ratio, You said. At that time, there were some foreign methods to reduce the noise, but these methods also weakened the signal. "It's like chemotherapy kills healthy cells as well as the cancer cells." After investigating the origin of the noise, the team found that the black body radiation from the optical fiber connected to the chip was the main source of background noise. On this basis, they developed two key technologies of dark counting suppression, the on-chip integrated cryogenic filter and the fiber end face cryogenic filter.

"The new method greatly reduces the chance of killing normal cells. It only kills the 'cancer cells'. It is a targeted treatment." You Lixing spoke this way. It is reported that the detection efficiency of the ultra-low dark counting SNSPD system using this method can reach 80% under the condition of dark counting 1 Hz, which ranks the leading level in the world. At present, the technology has been authorized by China, the United States and Japan.

High-performance SNSPD device technology in our country in the process of advancing, jian-wei pan team has created a 404 km against hacker attacks fiber quantum key distribution, the random number generator and so on many international leading, quantum key distribution results are to be included in the "member of both houses of the selection in 2014 China's top ten scientific and technological progress news". In 2015, Pan Jianwei provided user certificate again: "The SNSPD system developed by Shanghai Microsystems thoroughly solves the problem of China's high-performance SNSPD technology, and its performance index reaches the international advanced level, providing key technical support for the sustainable development of China's quantum information field."

The absolute advantage of SNSPD in efficiency and other performance can promote its application in many fields such as quantum communication, optical quantum computing, laser radar, deep space communication and so on. Under the guideline of "facing the main battlefield of national economy" of Chinese Academy of Sciences in the new period and the encouragement of the national policy of "mass entrepreneurship", Shanghai Institute of Microsystems has incubated and established a small high-tech company to carry out the industrialization operation of SNSPD technology. The aim is to meet the country's application needs, realize the self-survival and technological iteration of high technology through a market-oriented approach, and build a bridge between scientific research and industry, You said.