Guo Guangcan's team at CSU realizes synthetic nonlinear effects on integrated photonic chips
The team of academician Guangcan Guo at the University of Science and Technology of China has made important progress in the study of quantum devices on integrated photonic chips. The research group of Changling Zou and Ming Li proposed a general method for artificially synthesizing optical nonlinear processes, and experimentally observed high-efficiency synthetic higher-order nonlinear processes in an integrated microcavity on a chip, and demonstrated its potential application in cross-band quantum entanglement light sources. The results, titled "Synthetic five-wave mixing in an integrated microcavity for visible-telecom entanglement generation", were published online on October 20, 2012. The results were published online in the international academic journal Nature Communications.
Since the introduction of lasers, nonlinear optical effects have been widely used in optical imaging, optical sensing, frequency conversion, and precision spectroscopy. For the emerging quantum information processing, it is also a core element to realize quantum entangled light sources as well as quantum logic gate operations. However, limited by the intrinsic property that the material nonlinear polarization rate decays exponentially with order, the application of optical nonlinearity is mainly limited to second- and third-order processes, and higher-order processes involving multiple photons simultaneously are rarely studied. On the one hand, low-order processes limit the performance of traditional nonlinear and optical quantum devices, such as the scalability of quantum light sources; on the other hand, people are curious about the novel nonlinear and quantum physical phenomena embedded in higher-order nonlinear processes.
The nonlinear interactions between photons can be enhanced by using micro and nano optical structures on integrated photonic chips, which has become an international research hotspot in the direction of integrated and nonlinear optics. Ming Li and others in Changling Zou's research group have long been devoted to the research of quantum devices on integrated photonic chips, pioneering microcavity-enhanced nonlinear photonics, proposing and confirming the synergistic effects of multiple nonlinear processes in microcavities [PRL 126, 133601 (2021); PRA 98, 013854 (2018)], opening up a new way to quantum devices with few photons or even single photon levels at room temperature [PRL 129, 043601 (2022); PRApplied 13, 044013 (2020)].
At this stage, the group has been able to increase the decay rate of nonlinear interaction strength with order from 10-10 to 10-5. Even so, it is still challenging to experimentally observe efficient nonlinear effects of order greater than three on an integrated photonic chip.
To address this challenge, Ming Li et al. proposed a novel theory of nonlinear process synthesis, i.e., using the inherent strong second-order and third-order low-order effects of materials to realize arbitrary forms and arbitrary orders of photonic nonlinear interactions by artificially modulating the nonlinear optical networks formed by cascading multiple low-order processes. This approach avoids the need to modify the nonlinear response of materials at the atomic scale, and only requires control of the geometry of the micro and nano devices to achieve highly efficient and reconfigurable higher-order nonlinear processes.
Using an integrated aluminum nitride optical microcavity, the team experimentally manipulated both a second-order sum-frequency process and a third-order four-wave mixing process to synthesize a higher-order fourth-order nonlinear process. The synthetic process was experimentally shown to be more than 500 times stronger than the material's inherent fourth-order nonlinear effect. If the quality factor of the microcavity is further enhanced, this enhancement multiplier can be more than 10 million.
Figure 1. Schematic diagram of synthetic nonlinear five-wave mixing
The team applied the synthetic fourth-order nonlinearity to generate a quantum entangled light source across the visible-communication band. The coherence of the synthetic process was verified by measuring the time-energy entanglement between photons across the band. Compared with conventional methods of generating quantum entangled light sources across wavelengths, this work greatly reduces the difficulty of phase matching and requires only a single pump laser at communication wavelengths, demonstrating the advantages and application potential of the synthetic nonlinear process. The reviewer highly recognized the innovative nature of this work ("it should be published in Nature communication for its innovation qualities).
Jiaqi Wang and Yuanhao Yang, PhD students of the Key Laboratory of Quantum Information, Chinese Academy of Sciences, are the co-first authors of the paper, and Associate Researcher Ming Li and Professor Changling Zou are the corresponding authors. This research was supported by the Key Research and Development Program of the Ministry of Science and Technology of China, the National Natural Science Foundation of China, the Natural Science Foundation of Anhui Province, and the Basic Research Operation Funds of the Central Universities.
https://www.nature.com/articles/s41467-022-33914-5
