The god of quantum regulation assists--

The detection efficiency of single photon detector in China is over 90%

Hou Shuwen reporter Wang Chun

Take the "life gate" in your own hands.

As an international strategic emerging 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 are an indispensable key component in quantum control, and have also been included in the international embargo.

"Photon is the smallest unit of light. A 10-watt bulb can emit about 1020 photons per second." Dr. You Lixing, a researcher at the Shanghai Institute of Microsystems and Information Technology of the Chinese Academy of Sciences (hereinafter referred to as the Shanghai Institute of Microsystems), introduced to a reporter from Science and Technology Daily that single-photon detection technology is a technology that detects a photon, representing the limit of optical signal detection capabilities.

How important is a single photon detector to the field of quantum information? Yu Lixing made an analogy: suppose a water droplet is the smallest unit of water, usually when the faucet is turned on the water spouted out, and quantum control is like using the faucet to control every drop of water down, the single photon detector is equivalent to detecting every drop of water down. "We are going to convert the detected single photon into an electrical signal. The current detection level is that if 100 photons are emitted, we can detect 90."

Cooperation between SNSPD Special Forces and Quantum Information National Team

You Lixing returned to China in 2007 to carry out research and development of low temperature superconducting nanowire single photon detector (SNSPD) technology at Shanghai Microsystem Institute. The technology uses the light-sensitive properties of superconducting nanomaterials to achieve the detection of a single photon.

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 the core technology of SNSPD has been mastered independently, the single photon detector used in quantum communication experiment in China has an efficiency of only 20% and a great noise, which is far from the highest international level. The lack of high-performance single-photon detectors has seriously affected the competition between Chinese scientists and foreign counterparts in the field of quantum information.

You Lixing said that the start and development of single photon detectors in my country is to find out the direction of scientific research from the needs of users. The first step is to realize the practicality and reliability of the device.

In cooperation with the team of Academician Pan Jianwei of the Microscale National Laboratory of the University of Science and Technology of China, the You Lixing team improved the stability and reliability of the system by developing a new circuit structure, and changed its application environment from the laboratory environment to adapt to the actual field environment. In 2012, SNSPD developed by China was successfully applied to the intercity quantum key distribution network for the first time. Pan Jianwei mentioned in the user report: "Compared with the same type of single photon detectors abroad, the SNSPD system developed by Shanghai Microsystems is based on mechanical refrigeration technology to achieve plug and play, which not only greatly improves user-friendly performance, but also significantly reduces the application cost, which has good promotion value."

Key Technology Breakthrough Promotes the Industrialization of SNSPD Scientific Research in China

While my country's SNSPD has grown from scratch and realized domestic autonomy and control, the international single-photon detector technology level has also developed by leaps and bounds. The rapid development of quantum information in China also puts forward higher requirements for SNSPD detection efficiency.

You Lixing introduced that in 2013, the detection efficiency of SNSPD developed by tungsten silicide (WSi) material in the United States was up to 93%, while that of SNSPD prepared by niobium nitride (NbN) material in China was only 4%. "Devices made of WSi materials require lower operating temperatures than NbN, so the cost of low-temperature refrigeration equipment will also increase exponentially." The Youlixing team insists on moving forward in the direction of using NbN materials to carry out SNSPD research and development. After about 4 years of research, in 2016, the team finally took the lead in the world to realize the detection efficiency of NbN SNSPD devices at the 1550 nanometer wavelength of optical fiber communication exceeding 90%, and continued to maintain the world record for the efficiency of NbN SNSPD devices.

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

"The new method greatly reduces the probability of killing normal cells. It is a targeted therapy to kill cancer cells." Youlixing this analogy. It is reported that the detection efficiency of the ultra-low dark count SNSPD system using this method can reach 80% under the condition of dark count of 1Hz, ranking the international leading level. At present, the technology has been granted patents in China, the United States and Japan.

In the process of continuous advancement of China's high-performance SNSPD device technology, Pan Jianwei's team has successively created a number of international leading achievements such as 404 kilometers of optical fiber quantum key distribution and quantum random number generator that can resist hacker attacks. Quantum key distribution achievements have also been selected as "Academicians of the Chinese Academy of Sciences and Chinese Academy of Sciences" in 2014 China's Top Ten Science and Technology Progress News ". In 2015, Pan Jianwei once again provided user proof: "The SNSPD system developed by Shanghai Microsystems has completely solved the problems of my country's high-performance SNSPD technology, and its performance indicators have reached the international advanced level, providing sustainable development in the field of quantum information in my country. Key technical support."

The absolute advantage of SNSPD in efficiency and other performance can promote its application in quantum communication, optical quantum computing, lidar, deep space communication and other fields. Encouraged by the Chinese Academy of Sciences's policy of "facing the main battlefield of the national economy" in the new era and the national "double innovation" policy, the Shanghai Microsystem Institute has incubated and established a small high-tech company to carry out the industrialization of SNSPD technology. You Lixing said that the purpose is to solve the country's application needs, realize high-tech self-survival and technological iteration through market-oriented methods, and build a bridge between scientific research and industry.