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Conference on Lasers and Electro-Optics

Narrowband PPKTP Source for Polarization Entangled Photons

Siddarth Koduru Joshi, Felix Anger, Antı́a Lamas-Linares, Christian Kurtsiefer

Published May 22, 2011• 0 citations
OpenAlex

Abstract

We present a highly efficient (25%) PPKTP based source of narrowband (82 GHz) Entangled Photon Pairs whose wavelength can be temperature tuned. We use a Sagnac geometry that decouples the pump and the downconverted beams.

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We present our efforts to create a narrow-bandwidth source of entangled photons with a high spectral brightness to facilitate their interaction with single trapped atoms. A pump beam with 1=405 nm, focused into a type II PPKTP crystal, is down-converted to obtain signal and idler beams; their frequency can be tuned via the temperature of the crystal. By changing the beam waist inside the crystal, we determine the optimal focusing parameters for our source. We observe that weak focusing results in large pair to single ratio (efficiency).
We demonstrate a wavelength-tunable, fiber-coupled source of polarization-entangled photons with extremely high spectral brightness and quality of entanglement. Using a 25 mm PPKTP crystal inside a polarization Sagnac interferometer we detect a spectral brightness of 273000 pairs/(s mW nm), a factor of 28 better than comparable previous sources while state tomography showed the two-photon state to have a tangle of T=0.987. This improvement was achieved by use of a long crystal, careful selection of focusing parameters and single-mode fiber coupling. We demonstrate that, due to the particular geometry of the setup, the signal and idler wavelengths can be tuned over a wide range without loss of entanglement.
We demonstrate a wavelength-tunable, fiber-coupled source of polarization- entangled photons with extremely high spectral brightness and quality of entanglement. Using a 25 mm PPKTP crystal inside a polarization Sagnac interferometer we detect a spectral brightness of 273000 pairs (s mW nm)(-1), a factor of 28 better than comparable previous sources while state tomography showed the two-photon state to have a tangle of T = 0.987. This improvement was achieved by use of a long crystal, careful selection of focusing parameters and single-mode fiber coupling. We demonstrate that, due to the particular geometry of the setup, the signal and idler wavelengths can be tuned over a wide range without loss of entanglement.
We demonstrate a compact and stable source of polarization-entangled pairs of photons, one at 810 nm wavelength for high detection efficiency and the other at 1550 nm for long-distance fiber communication networks. Due to a novel Sagnac-based design of the interferometer no active stabilization is needed. Using only one 30 mm ppKTP bulk crystal the source produces photons with a spectral brightness of 1.13 x 10(6) pairs/s/mW/THz with an entanglement fidelity of 98.2%. Both photons are single-mode fiber coupled and ready to be used in quantum key distribution (QKD) or transmission of photonic quantum states over large distances.