Highly efficient entanglement swapping at telecom wavelength

Rui‐Bo Jin, Masahiro Takeoka, Utako Takagi +2 more

Entanglement swapping at telecom wavelengths is at the heart of quantum networking in optical fiber infrastructures. Although entanglement swapping has been demonstrated experimentally so far using various types of entangled photon sources both in near-infrared and telecom wavelength regions, the rate of swapping operation has been too low to be applied to practical quantum protocols, due to limited efficiency of entangled photon sources and photon detectors. Here we demonstrate drastic improvement of the efficiency at telecom wavelength by using two ultra-bright entangled photon sources and four highly efficient superconducting nanowire single photon detectors. We have attained a four-fold coincidence count rate of 108 counts per second, which is three orders higher than the previous experiments at telecom wavelengths. A raw (net) visibility in a Hong-Ou-Mandel interference between the two independent entangled sources was 73.3 ± 1.0% (85.1 ± 0.8%). We performed the teleportation and entanglement swapping, and obtained a fidelity of 76.3% in the swapping test. Our results on the coincidence count rates are comparable with the ones ever recorded in teleportation/swapping and multi-photon entanglement generation experiments at around 800 nm wavelengths. Our setup opens the way to practical implementation of device-independent quantum key distribution and its distance extension by the entanglement swapping as well as multi-photon entangled state generation in telecom band infrastructures with both space and fiber links.

홍정식

Akio Yoshizawa, Yinghong Xue, Han Chuen Lim +1 more

Our research work related to quantum entanglement in the 1550-nm telecom wavelength band is reviewed. We developed a very stable source of high-quality polarization-entangled photon-pairs, which we used to demonstrate both long-distance and broadband fiber-optic entanglement distribution. Polarization-based entanglement swapping experiment was also performed.

S. N. Molotkov, S. S. Nazin

吉朗 逵本

Anthony Martin, Florian Kaiser, Olivier Alibart +2 more

Periodically poled lithium niobate waveguides (PPLN/W) are considered to be one of the most useful toolboxes for quantum communication experiments. Thanks to the high optical confinement over longer lengths than in bulk configurations (a few cm in our case), such structures provide highly efficient non-linear interactions, both in down- and up-conversion regimes. Within the framework of long-distance quantum communication at telecom wavelengths, PPLN/Ws have therefore been proved to be a key ingredient for building ultra-bright sources of energy-time, time-bin, as well as polarization entangled pairs of photons, up-conversion based detectors for telecom photon detection, photonic quantum interfaces for coherent wavelength conversion, and also for quantum relays in the entanglement swapping configuration.