Stuttgart 2012 – wissenschaftliches Programm
Q 24.6: Vortrag
Dienstag, 13. März 2012, 12:00–12:15, V7.02
Efficient, Narrowband PPKTP Source for Polarization Entangled Photons — •Siddarth.K. Joshi1, Chen Ming Chia1, Felix Anger3, and Christian Kurtsifer1,2 — 1Center for Quantum Technologies, Singapore — 2Physics Dept., National University of Singapore, Singapore — 3Ludwig-Maximilians-Universität, München
The underlying protocols behind many applications often require a complete detection of almost all entangled photons to outperform their classical counterparts. While photodetectors have come close to unit detection efficiency (>95%) , photon pair sources seem to be the current bottleneck in applications requiring a high efficiency.
We present a high efficiency photon pair source which addresses this issue. A pump laser (λ= 405 nm) is focused into a type II PPKTP crystal, where it undergoes spontaneous parametric down-conversion into signal and idler modes collinear with the pump mode, maximizing the mode overlap between the target modes. To obtain polarization entangled photons, we pump the crystal from both directions and interferometrically combine the two downconverted paths in a Sagnac interferometer. We experimentally optimized the focusing parameters for a maximal efficiency and we observe uncorrected efficiencies > 35%. This efficiency is the value obtained from uncorrected count rates from Silicon Avalanche Photo Diodes (Si APDs) of 49.7% ± 2% and 48.1% ±2% connected directly to the single mode fibers supporting the downconverted photons. No corrections are applied. Our source efficiency ( 71%) thus starts to reach the threshold for a loophole free Bell test.
 A.E. Lita, A.J. Miller, S.W. Nam,Opt. Express 16, 3032 (2008)