We report an experimental generation of polarization-entangled photon pairs in a cold atomic ensemble. A single Stokes photon and one spin-wave excitation are simultaneously created via spontaneous Raman scattering. T...We report an experimental generation of polarization-entangled photon pairs in a cold atomic ensemble. A single Stokes photon and one spin-wave excitation are simultaneously created via spontaneous Raman scattering. The spin-wave excitation is then converted into an anti-Stokes photon via an electromagnetic-induced-transparency reading process. The measured cross-correlation functions between the Stokes and anti-Stokes photons for two orthogonal polarizations are -75 and 74, respectively, at a generation rate of the photon pair of -60/s. Based on such correlations, we obtain polarization-entangled photon pairs, whose Bell parameter is S = 2.77 4- 0.01, violating Bell-CHSH inequality by -77 standard deviations. The presented polarization-entangled photon source has high entanglement degree and fast generation rate, which will promise us to apply it in future quantum repeater.展开更多
Quantum measurement is a fundamental problem in quantum control theory and experiments.It can obtain unknown information of quantum systems,and can also change state of the systems inevitably.Both the outcome and back...Quantum measurement is a fundamental problem in quantum control theory and experiments.It can obtain unknown information of quantum systems,and can also change state of the systems inevitably.Both the outcome and back action could be used to control quantum systems.This paper presents recent research progress about optimal control of state transformation in finite-dimensional quantum systems by back action of non-selective quantum measurement,and optimal control of signal and background of CARS (coherent anti-Stokes Raman spectroscopy) by phase shaping technique.In measurement sequence control of finite-dimensional quantum systems,the necessary condition for critical points of the underlying state transformation objective is found to be a highly symmetric form as a chain of equalities,and analytical and numerical solutions in several cases are explored.In the CARS control,it is found that the maximal resonant signal and minimal background at a specific frequency can be achieved by shaping the probe pulse only while keeping pump and Stokes pulses in transform limited forms (TLFs).An arctan-type phase function is obtained for the probe pulse to simultaneously enhance the resonant signal and suppress the background.For broadband background elimination,we find that the optimal phase shaping scheme of probe pulse is quasi-time-delay while keeping the pump and Stokes pulses in TLFs.These conclusions could help design control strategies of quantum devices.展开更多
Terahertz(THz) generation by periodically-poled RbTiOPO_4(PPRTP) with a quasi-phase-matching scheme based on cascaded difference frequency generation(DFG) processes is theoretically analyzed. The cascaded Stokes and a...Terahertz(THz) generation by periodically-poled RbTiOPO_4(PPRTP) with a quasi-phase-matching scheme based on cascaded difference frequency generation(DFG) processes is theoretically analyzed. The cascaded Stokes and anti-Stokes interaction processes are investigated from coupled wave equations. The THz intensities and quantum conversion efficiency are calculated. Compared with that of non-cascaded DFG processes, the THz intensity in 7-order cascaded DFG processes is increased to 2.95 times. The quantum conversion efficiency of 149.9% in cascaded processes can be realized, which exceeds the Manley-Rowe limit.展开更多
基金the National Basic Research Program of China (2010CB923103)the National Natural Science Foundation of China (11475109, 11274211 and 60821004)
文摘We report an experimental generation of polarization-entangled photon pairs in a cold atomic ensemble. A single Stokes photon and one spin-wave excitation are simultaneously created via spontaneous Raman scattering. The spin-wave excitation is then converted into an anti-Stokes photon via an electromagnetic-induced-transparency reading process. The measured cross-correlation functions between the Stokes and anti-Stokes photons for two orthogonal polarizations are -75 and 74, respectively, at a generation rate of the photon pair of -60/s. Based on such correlations, we obtain polarization-entangled photon pairs, whose Bell parameter is S = 2.77 4- 0.01, violating Bell-CHSH inequality by -77 standard deviations. The presented polarization-entangled photon source has high entanglement degree and fast generation rate, which will promise us to apply it in future quantum repeater.
基金Gao was supported by Open Foundation of State Key Laboratory of Robotics(RLO201011)Shuang would acknowledge the support from the National Natural Science Foundation of China(61074052and61072032)+1 种基金Foundation of the President of Hefei Institutes of Physical Science CASOpen Foundation of State Key Laboratory of Precision Spectroscopy
文摘Quantum measurement is a fundamental problem in quantum control theory and experiments.It can obtain unknown information of quantum systems,and can also change state of the systems inevitably.Both the outcome and back action could be used to control quantum systems.This paper presents recent research progress about optimal control of state transformation in finite-dimensional quantum systems by back action of non-selective quantum measurement,and optimal control of signal and background of CARS (coherent anti-Stokes Raman spectroscopy) by phase shaping technique.In measurement sequence control of finite-dimensional quantum systems,the necessary condition for critical points of the underlying state transformation objective is found to be a highly symmetric form as a chain of equalities,and analytical and numerical solutions in several cases are explored.In the CARS control,it is found that the maximal resonant signal and minimal background at a specific frequency can be achieved by shaping the probe pulse only while keeping pump and Stokes pulses in transform limited forms (TLFs).An arctan-type phase function is obtained for the probe pulse to simultaneously enhance the resonant signal and suppress the background.For broadband background elimination,we find that the optimal phase shaping scheme of probe pulse is quasi-time-delay while keeping the pump and Stokes pulses in TLFs.These conclusions could help design control strategies of quantum devices.
基金supported by the National Natural Science Foundation of China(Nos.61201101,61601183 and 61205003)the Young Backbone Teachers in University of Henan Province(No.2014GGJS-065)+1 种基金the Foundation and Advanced Technology Research Program of Henan Province(No.162300410269)the Program for Innovative Research Team(in Science and Technology)in University of Henan Province(No.16IRTSTHN017)
文摘Terahertz(THz) generation by periodically-poled RbTiOPO_4(PPRTP) with a quasi-phase-matching scheme based on cascaded difference frequency generation(DFG) processes is theoretically analyzed. The cascaded Stokes and anti-Stokes interaction processes are investigated from coupled wave equations. The THz intensities and quantum conversion efficiency are calculated. Compared with that of non-cascaded DFG processes, the THz intensity in 7-order cascaded DFG processes is increased to 2.95 times. The quantum conversion efficiency of 149.9% in cascaded processes can be realized, which exceeds the Manley-Rowe limit.
