Abstract
Abstract 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 $$F=0.753 \pm 0.021$$ F = 0.753 ± 0.021 is demonstrated, and improvements of the setup are discussed.
Highlights
In recent years, there has been an increasing effort to realize and study quantum hybrid systems
The procedure to find the right compensation crystal relies on measuring polarization-sensitive coincidence counts as a function of the orientation of the half-wave plate θHWP in one arm
In order to do this, we changed the temperature of a 30 mm compensation crystal slab
Summary
There has been an increasing effort to realize and study quantum hybrid systems. These consist of two dissimilar systems—often at different wavelengths—which are in a joint quantum state. Entanglement of a stationary and flying qubit, i.e., an electronic state with a long coherence time and a photon, respectively, represents a coherent quantum interface. Such interfaces are mandatory components of a quantum repeater [1], where entanglement has to be established between distant nodes. The collinear alignment enables further integration and can be used in a monolithic design [12]
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