On March 11, 2016, magazine Science published the research paper titled “Generation of multiphoton entangled quantum states by means of integrated frequency combs” jointly by our foreign expert thousand-program research fellow Brent E. Little and the National Institute of Research, Quebec University, Canada, UK University of Sussex and City University of Hong Kong, etc. That same day, Science published a review titled “The time is right for multiphoton entangled states – A chip-based microresonator enables time-bin entanglement”, giving high evaluation on the on-chip multi-photon entangled quantum frequency combs. The result is another important progress of XIOPM in research of photon-integrated on-chip quantum optics after on-chip Heraled single photon source (Optics Express, 22, 6536, 2014) and on-chip crossing polarized entangled photon pair (Nature Communications, 6, 8236, 2015).
Multi-photon entangled state is the cornerstone for quantum communication, quantum computing and beyond-classic-limit ultrahigh resolution sensing and imaging technology, and has extremely important application in exploring basic issues of quantum physics. Particularly, large-scale integrated on-chip entangled photon source has become a pressing demand for development of quantum application technology. Brent E. Little, etc., taking advantages of the spontaneous Four Wave Mixing (FMW) effect in micro-ring resonator, with time domain separated, phase adjustable light pulse as pumping source, has gained entangled photon pair crossing over S-C-L three communication bands and with frequency space of 200GHz — the entangled photon source is the quantum frequency comb with the widest bandwidth by far, and its quantum interference fringe visibility reaches 93.2%. By extracting two pairs of photon at two different resonance wavelengths, the four-photon entangled state is obtained, with quantum interference fringe visibility reaching 89%. The research opens the times of on-chip generation and control of complicated quantum state and provides a light quantum information processing platform with ability of scale integration.
Doctor Brent E. Little, with more than 20 years’ research in integrated optics field, an internationally famous photon integration expert, joined XIOPM as a full member to pursue research of photon integration related technology in 2013. He is one of early pioneers of micro-ring resonator theory and experimental research, and his article of micro-ring up-down channel wave filer has been cited for more than 1300 times. Meanwhile, he has scored many achievements in on-chip non-linear effect aspect, and has published more than 10 of papers of OPO, mode-locked laser and multi-channel entangled photon pair generation, etc. in Nature Photonics, Nature Communication and other periodicals.
Paper download linkage: http://science.sciencemag.org/content/351/6278/1176
Review download linkage: http://science.sciencemag.org/content/351/6278/1152
Fig. 1 Experimental Device
Fig. 2 Four-photon Entangled State
In addition, Doctor Zhang Wenfu topic group with China-UK Micro Nano Photonics Joint Research Center of XIOPM Laboratory for Transient Optics and Photon Technology also made series important progresses in photon-integration on-chip optical frequency combs recently. Optical frequency comb（OFC for short） is the optical frequency scale with fixed optical frequency comb teeth space and frequency, and its invention is a work of milestone important significance in laser technology and metering science in the 21st century. Benefited from generation of broadband fine spectrum, optical frequency combs have important applications in ultra-precision optical clock, physical constant precise measurement, terrestrial celestial body/galaxy-beyond life detecting, attosecond measurement of electron movement, ultra-fine spectrum measurement, and light communication multi-wavelength light source, etc. By far, generation of most optical frequency combs has been based on solid and optical fiber mode-locked laser. Limited to component size and resonator length, the recurrence frequency is generally lower than 10GHz generally. In recent years, a new microresonator-based Kerr optical frequency comb was proposed and reported important progress. Due to its small size and high recurrence frequency characteristics, it is hopeful to have important applications in future astronomical observation, integrated microwave photon source, RF arbitrary wave front generation, light communication, and small optical clock fields, etc. Over the past 10 years, a series of major breakthroughs have been made internationally in research of Kerr microresonator optical frequency combs. Limited by conditions of process and technology, China has not made major progress in the orientation.
Doctor Zhang Wenfu topic group, after more than 3 years of theory and process tackling, firstly realized visible-light optical frequency comb within Si3N4 micro-ring internationally, namely in single integrated micro-ring component, with Four Wave Mixing (FWM) and third-order frequency mixing effect, generating infrared and green optical frequency combs at the same time, and the infrared optical frequency combs triggered simultaneously has the frequency range (1,300-2,100nm) with width up to 2/3 times; the green optical frequency comb bandwidth and power are current world records (502-580nm, 80THz,0.1mW), and conversion efficiency is -35dB, solving the problem that optical frequency comb cannot be generated in visible light band due to in-micro-ring strong Rayleigh scattering and strong material dispersion. Meanwhile, based on high-Q value (>2*106) up/down channel micro-ring resonator (Add-Drop Filter), the group firstly realized OPO-based micro-ring optical frequency comb in China, with pumping power of 50mW, frequency space of 50GHz and bandwidth more than 200nm, and achieved generation of high-quality microwave signal. The research built double-pumping self-locking mode-locked laser resonator system, firstly realized frequency space tuning and generated 300GHz, 400GHz, 1THz and 2.3THz ultra-high recurrence frequency stable optical frequency combs with outer-resonator regulating technology internationally. Main contributors to relevant achievements also include Doctor Wang Leiran and Doctor Wang Weiqiang within Doctor Cheng Dong Topic Group of the Information Photon Component and Photon Integration Research Center. The series achievements will be published in succession in the near future.
Fig. 3 OPO-based Broadband Kerr Optical Frequency Bombs
Fig. 4 Simultaneous Generation of Green Light and Infrared Optical Frequency Combs
Doctor Zhang Wenfu graduated from CAS XIOPM and received the doctorate of optics engineering in Jan. 2012; went to Canadian Mcmaster University for visiting research in Oct. 2009 - Nov. 2011; established (China-UK) Micro Nano Photonics Joint Research Center in 2014 through cooperation with UK University of South Wales, as the standing vice director of the Center. He won CAS Daheng Excellent Award for Optics in 2009, CAS President Excellent Award in 2012 and Shaanxi Excellent Doctor Dissertation in 2015, and was chosen as a youth sci-tech star of Shaanxi in 2015. He is a member of the Professional Committee of Fiber Optics and Photon Integration, the Chinese Optical Society and a member of the Subcommittee on Optical System of the National Technical Committee on Optics and Photonics of Standardization Administration of China. Doctor Zhang Wenfu is mainly devoted to relevant theoretical research and application development of micro nano photon component and photon integration, with research orientation covering micro nano wave guide theory and making, plane wave guide functional component, wave guide non-linear optics, micro nano sensor, surface plasma and meta-material and ultra-high-speed photon integrated chip, etc.