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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - A Ps-Pulse Laser for Ultrafast Entanglement Generation at 42.66 Ghz Repetition Rate
摘要： Entangled-photon sources are a key element for most quantum-information applications, ranging from quantum communication systems to quantum simulators and full photonic quantum computers. Spontaneous parametric downconversion (SPDC), requiring a pump laser and a nonlinear medium, is up-to-date still the preferred technique to generate such photonic entanglement. To scale the transmission rates or gate operations of the aforementioned applications, high clock rates of the pump lasers are needed. Moreover, photonic quantum-processing algorithms require photons with not only high entanglement visibility but also high spectral indistinguishability and purity. This can either be achieved by narrow spectral filtering, costly in rate, or by suitable choice of the pump pulse length (typically in the ps range). Attempts have been made to increase the rate of conventional fs-lasers by adding multiple spatial-paths [1] but this method cannot be used to go beyond GHz repetition rates. This results in the quest to produce pump lasers with very high repetition rate, ps-pulse width and high enough power to drive the weak SPDC process. We report here on an implementation of a compact and fast ps-pump laser setup which can generate entangled photon pairs at repetition rates up to 42.66 GHz. Our entangled-photon source can be operated at these high generation rates and is basically only limited by the jitter of the detectors. In addition, we achieve a high spectral purity without narrow bandpass-filtering by mutually matching the length of the PDC crystal and the pump laser‘s pulse length [2], yielding polarisation-entangled photon pairs with minimal spectral correlations. The pump laser consists of a monolithically integrated mode locked DBR laser emitting pulses with a fixed repetition rate of 42.66 GHz at 1554 nm with 1.8 ps length. A pulse picker, made of an intensity modulator and driven by the same controller as the pump laser, allows adjusting the repetition rate used in the experiment, as depicted in Fig. 1. The power of the laser pulses is boosted with a series of optical amplifiers to 25 dBm. Conversion to the proper wavelength for the PDC process takes place in a second-harmonic-generation module, which finally generates output pulses of (cid:79)=777 nm to pump the entangled-photon source. Our entanglement source is based on a Sagnac-interferometer, where a ppKTP crystal is pumped by two pulsed laser beams from opposed directions. The generated photon pair at 1554 nm is split into different spatial modes by a polarizing beamsplitter, collected in optical fibers and detected with InGaAs detectors (10% efficiency). An experimental analysis of the entangled polarisation state yields an average visibility of 0.95 ± 0.01, corresponding to a CHSH parameter of S=2.685 which is in good agreement with theoretical calculations. Two-photon interference based on the Hong-Ou-Mandel effect also shows a high degree of purity.
关键词： ppKTP crystal,quantum-information applications,high clock rates,Sagnac-interferometer,InGaAs detectors,entangled-photon sources,ps-pump laser,spectral purity,spontaneous parametric downconversion
更新于2025-09-11 14:15:04
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Spatial and temporal resolution in entangled ghost imaging
摘要： We show that, when the integration time of the single photon detectors is longer than the correlation time of the biphoton, the attainable spatial resolution in ghost imaging with entangled signal-idler pairs generated in type II spontaneous parametric down conversion is limited by the angular spread of single-frequency-signal-idler pairs. If, however, the detector integration time is shorter than the biphoton correlation time, the transverse k-vectors of different spectral components combine coherently in the image, improving the spatial resolution.
关键词： ghost imaging,spontaneous parametric downconversion,entangled photons,nonclassical correlation,single photon,phase matching
更新于2025-09-11 14:15:04