Guo Guangcan's team achieves low-temperature integrated quantum entanglement light source

The team of academician Guangcan Guo at the Chinese University of Science and Technology (CSU) has made important progress in the research of integrated quantum light source preparation. The team's research group, Ren Xifeng, demonstrated the preparation of integrated quantum entangled light sources under low-temperature conditions based on a low-temperature integrated spontaneous four-wave mixing process, and the related results were published in Optica, a leading academic journal of optics, on June 2.

"Entanglement generation using cryogenic integrated four-wave mixing"

Optical quantum integrated chips, with their extremely high phase stability and reconfigurability, are gradually developing into an ideal platform for demonstrating novel quantum applications and developing new quantum devices.

Currently, most optical quantum integrated devices focus on the function at room temperature conditions, but many quantum components (such as superconducting nanowire single photon detectors) and semiconductor and superconducting quantum computing systems, need to operate at low temperature conditions. In order to realize the full on-chip integration of optical quantum systems and optical interconnection of different quantum computing systems to build quantum networks, the study of low-temperature nonlinear processes is indispensable.

In this time, the research group placed the integrated micro-nano silicon waveguide in a low-temperature cavity and studied the spontaneous four-wave mixing process in the silicon waveguide at 4 K-294K temperature and realized the preparation of low-temperature integrated quantum entanglement light source based on this process.

Experimental system of low-temperature integrated quantum light source

A photon pair source with frequency multiplexing generated by a silicon photonics chip at low temperature and room temperature.

Energy-time entanglement interference measurement.

Low-temperature cooling suppresses noise and enables a high-quality quantum photon source. The results successfully extend quantum light sources based on spontaneous four-wave mixing processes to low-temperature conditions, laying the foundation for full on-chip integration of optical quantum devices and further applications of nonlinear optics at low temperatures.

In combination with the low-temperature integrated photonic modulator, various optical quantum applications are possible using quantum photonic integrated circuits (QPICs) under low-temperature operating conditions. In particular, SNSPDs with excellent performance can be operated at similar temperatures. Integrated photonic devices containing all core functions, such as photonic source generation, quantum state modulation and single photon detection, will greatly reduce chip input and chip output losses, thus facilitating photonic quantum applications in daily life. For fully integrated operation, pump filtering at low temperature is also very important and verifying its functionality will be the next step. In addition to quantum photon pair sources, this work will also facilitate other low-temperature nonlinear applications such as all-optical modulation, wavelength conversion, and parametric amplification of silicon photonic circuits.

In summary, the team demonstrated the preparation of quantum photon pair sources with integrated silicon photonic circuits at low temperatures. SFWM in silicon waveguides has proven to remain an effective method for generating quantum photon sources at such low temperatures. The bandwidth of the photon pair was experimentally verified to be ∼2 THz , and energy-time entangled states with frequency multiplexing were generated. The observed near-single interference visibility indicates that this low-temperature multichannel entangled photon source is of high quality and can be used for further quantum information applications.

The reviewers gave high praise to the work: "This paper provides useful insight into the study of integrated quantum optics in cryogenic environments This paper provides useful insight into the study of integrated quantum optics in cryogenic environments".

Professor Ren Xifeng of CAS Key Laboratory of Quantum Information is the corresponding author of the paper, and Lantian Feng, a special associate researcher of CAS Key Laboratory of Quantum Information, and Yujie Cheng, a PhD student, are the co-first authors of the paper. In addition, Prof. Zhiyuan Zhou from Key Laboratory of Quantum Information, CAS, Dr. Xiaozhuo Qi from Tianjin University of Technology, and Prof. Daoxin Dai and Assistant Researcher Ming Zhang from Zhejiang University provided technical support for the work. This work was supported by grants from the Ministry of Science and Technology, the State Foundation of China, the Chinese Academy of Sciences, Anhui Province, and the University of Science and Technology of China.