Prof. Wei Zhang Electronic Engineering Department, Tsinghua University
时间： 2015-06-17 10:30-2015-06-17 11:30
1.5 μm correlated/entangled photon pairs have important applications in quantum communication, quantum information processing and quantum metrology. Traditionally, photon pairs were generated by spontaneous parametric down conversion (SPDC) in nonlinear crystals, which has been widely used in researches of quantum optics. In recent years, to realize correlated/entangled photon pair generation in optical communication band, several new schemes have been proposed and investigated, such as SPDC in periodically poled lithium niobate (PPLN) waveguides and spontaneous four wave mixing (SFWM) in optical fibers and silicon devices, such as silicon waveguides and micro-ring cavities. In this talk, I will introduce our recent works about 1.5 mm quantum light sources based on optical fibers and silicon devices.
In the researches of optical fiber based quantum light sources, we realized high performance 1.5mm correlated photon pair generation with a generation rate as high as several tens megahertz utilizing commercial optical components used in optical communications. Then various quantum light sources are developed based on it. We realized a heralded single photon source with a preparation efficiency of 80% under g(2)(0)=0.06 . Then, we proposed three schemes for polarization entanglement generation in optical fibers, based on the polarization walk-off effect in birefringent fibers, group birefringence in microstructure fibers and modified polarization maintaining fiber loop, respectively . By introducing interferences of two photon states generated in optical fibers, we proposed and demonstrated different schemes for telecom band frequency entanglement , path entanglement, energy-time entanglement  and hyper entanglement on difference freedoms , respectively, realizing a complete solution for various telecom band photon pair sources based on optical fibers. On the other hand, aiming at the requirement of quantum engineering, we developed techniques for the practical telecom band quantum light sources based on optical fibers and realized prototypes of quantum light source equipment .
In the researches of quantum light sources based on silicon devices, recently we focused our work on correlated and entangled photon pair generation in micro-ring cavities. Utilizing a silicon micro-ring cavity with a Q of 105, 1.5 mm correlated photon pair generation was realized with a maximum CAR close to 250 under a coincidence time bin width of 5ns. Based on it, we investigated the impact of the nonlinear loss in the silicon micro-ring cavity on the correlated photon pair generation, showing that the nonlinear loss reduces the Q value of the cavity under high pump level and the photon pair generation rate is in proportion to Q7 . On the other hand, we realized the non-degenerate SFWM process in the silicon micro-ring cavity firstly, and demonstrated the quantum interference of the generated degenerate-frequency two-photon state in an unbalanced Mach-Zehnder interferometers . Recently, by setting the silicon micro-ring cavity in a modified polarization maintaining fiber loop, we realized the hyper-entanglement generation in the freedoms of polarization and energy-time , showing that silicon micro-ring cavities have great potential on integrated quantum light sources for various two-photon state generation.
Dr. Wei Zhang was born in Luoyang, Henan province, China in 1974. He received his Bachelor’s degree from Electronic Engineering Department, Tsinghua University, China in 1998 and won the excellent graduate award of Tsinghua University. He received his Doctor’s degree on physical electronics from Institute of Information Optoelectronics, Electronic Engineering Department, Tsinghua University, China in 2003 and won the excellent Ph.D student award in Tsinghua University. His dissertation for the Ph. D concentrated on crucial technologies for fiber transmission systems with Raman amplification, which won the excellent dissertation award of Tsinghua Univeristy. In 2003, he joined Institute of Information Optoelectronics, Electronic Engineering Department, Tsinghua University as an instructor. He was promoted to associate professor in 2007 and got the qualification of Ph. D. supervisor in 2011. Now he is the vice director of the Institute of Information Optoelectronics, Electronic Engineering Department, Tsinghua University. He is the member of Chinese opticalsociety and Optical society of America.
His research interest is on the fields of micro/nano-structured optoelectronic materials and opto-quantum devices. In recent years, his work focused on quantum light sources based on the third order nonlinear waveguides and their applications.