文摘
We demonstrate a two-color entangled photon pair source which can be adapted easily to a wide range of wavelength combinations. A Fresnel rhomb as a geometrical quarter-wave plate and a versatile combination of compensation crystals are key components of the source. Entanglement of two photons at the Cs D1 line (894.3 nm) and at the telecom O-band (1313.1 nm) with a fidelity of \(F=0.753 \pm 0.021\) is demonstrated, and improvements of the setup are discussed. This paper is part of the topical collection “Quantum Repeaters: From Components to Strategies” guest edited by Manfred Bayer, Christoph Becher and Peter van Loock.