Abstract
We demonstrate an efficient generation of frequency anti-correlated entangled photon pairs at telecom wavelength. The fundamental laser is a continuous-wave high-power fiber laser at 1560 nm, through an extracavity frequency doubling system, a 780-nm pump with a power as high as 742 mW is realized. After single passing through a periodically poled KTiOPO4 (PPKTP) crystal, degenerate down-converted photon pairs are generated. With an overall detection efficiency of 14.8 %, the count rates of the single photons and coincidence of the photon pairs are measured to be 370 kHz and 22 kHz, respectively. The spectra of the signal and idler photons are centered at 1560.23 and 1560.04 nm, while their 3-dB bandwidths being 3.22 nm both. The joint spectrum of the photon pair is observed to be frequency anti correlated and have a spectral bandwidth of 0.52 nm. According to the ratio of the single photon spectral bandwidth to the joint spectral bandwidth of the photon pairs, the degree of frequency entanglement is quantified to be 6.19. Based on a Hong Ou Mandel interferometric coincidence measurement, a frequency indistinguishability of 95 % is demonstrated. The good agreements with the theoretical estimations show that the inherent extra intensity noise in fiber lasers has little influence on frequency entanglement of the generated photon pairs.
Highlights
Entangled photon pairs based on spontaneous parametric down-conversion (SPDC) process [1] are at the heart of the most fundamental tests of quantum mechanics [2, 3] and essential resources for quantum information processing (QIP) [4]
Several experiments on generation of frequency-correlated photon pairs at telecom wavelength have been reported [28,29,30,31] since pulse pumped SPDC can be generated and detected much more efficiently
At an incident fundamental power of 1.41 W, a power as high as 742 mW of 780-nm laser is generated and the corresponding second harmonic generation efficiency reaches 52.6 %
Summary
Entangled photon pairs based on spontaneous parametric down-conversion (SPDC) process [1] are at the heart of the most fundamental tests of quantum mechanics [2, 3] and essential resources for quantum information processing (QIP) [4]. In a fiber-based quantum information network, frequencyentangled photon pair source at telecom wavelength is required for minimum absorption. Several experiments on generation of frequency-correlated photon pairs at telecom wavelength have been reported [28,29,30,31] since pulse pumped SPDC can be generated and detected much more efficiently. In application to the entanglementbased quantum communication, their broad spectral width of the photon pairs limits the fiber transmission distance. Frequency anti-correlated photon pairs have unprecedented advantage of dispersion cancelation in quantum synchronization [6, 11, 14]. The generation of frequency anti-correlated entangled photon pairs in the telecom wavelength regime and with a high brightness is required for the long-distance quantum communication
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