Chinese Scientists Develop 100-Channel Single-Photon Detector to Advance Quantum Internet Technology

The Shanghai Institute of Microsystem and Information Technology (SIMIT) in China has developed a 100-channel single-photon detector, paving the way for the country's development of broadband quantum networks. A prototype network tested using this detector demonstrated a communication fidelity exceeding 90%. As advancements in quantum computing and sensing technologies progress, the demand for quantum information networks is expected to grow. While various network schemes are currently being tested, those similar to existing fiber optic networks are seen as more promising due to their ease of transition. Single-photon detectors (SPDs) are critical components of such networks, as they can measure photons or individual light particles, which are then used for storing quantum information.

SPDs can assist in deploying fiber or space links for quantum data transmission, while also aiding in quantum entanglement or instantaneous transfer by transmitting quantum states to photons.

Challenges and Demands of SPDs

The challenge with using SPDs lies in the need to develop higher-capacity SPDs to facilitate the growth and expansion of quantum technologies. Currently, there are two main types of SPDs used in quantum research. Superconducting nanowire single-photon detectors (SNSPDs) are high-end optoelectronic devices with extremely high detection precision but require operation at ultra-low temperatures. In contrast, single-photon avalanche diodes (SPADs) can operate at room temperature but have lower accuracy, making SNSPDs more favored. However, the ultra-low temperature requirement of SNSPDs presents additional challenges.

During the readout process, SNSPDs must be connected to instruments maintained at room temperature. This is typically achieved through relatively thick coaxial cables made of thermally conductive metals, which allow room temperature heat to enter the low-temperature chamber of the SNSPD, a phenomenon known as thermal load. As the number of detection channels within the SNSPD increases, the number of required readout cables also rises, thereby increasing the thermal load.

Application and Effects of New Materials

To overcome this issue, researchers at SIMIT conducted a comprehensive redesign of the SNSPD and replaced the coaxial cables with a special flexible material known as high-density multi-core microstrip lines. These microstrip lines are not only ultra-thin but also possess good thermal insulation properties, resulting in very limited heat transfer to the low-temperature chamber. According to the SIMIT team, the heat entering the system is only one twenty-first of that from traditional cables. This allows them to increase the number of independent channels without significantly enlarging the SNSPD's size.

To test their design, the researchers conducted a continuous operation for seven days, finding that the temperature of the low-temperature chamber remained below 2.1K, close to absolute zero at 0K (-273.15 degrees Celsius). During the testing period, the detection efficiency of the channels reached 80%, while the reported false positive rate was extremely low, the researchers noted in a paper.

Testing of Quantum Entanglement Distribution Networks

To conduct a comparison closer to real-world scenarios, the research team established a five-user quantum entanglement distribution network with 10 bidirectional quantum links. Each user received photons through the newly developed SPD channels and found that the communication fidelity, or preservation of quantum information, exceeded 90%. The research results have been published in the journal Laser & Photonics Reviews.