Photon-pair production and frequency translation using backward-wave spontaneous parametric downconversion

Abstract

Backward-wave three-wave mixing is a difficult χ(2) interaction to observe, because it requires ultrashort poling periods to achieve phasematching. Having realized sub-micrometer periods in periodically poled KTiOPO4 (PPKTP), we demonstrate for the first time first-order quasi-phasematched, backward-wave spontaneous parametric downconversion (BW SPDC). We pumped the PPKTP crystal at 800 nm and obtained a forward-wave signal at 1400 nm and a backward-wave idler at 1868 nm. We estimated an internal pair production rate of 4.0 × 104 pairs/s/mW. The backward-wave phasematching constraints lead to the unique tuning property that spectral features of the pump are transferred to the forward-wave signal photons, which makes BW SPDC an attractive source of spectrally shaped, heralded single photons. These spectrally shaped photons are useful for quantum computing and quantum interconnects. For the first time, we experimentally show this effect by observing frequency translation between a spectrally shaped pump beam and the BW SPDC signal photons. Due to their unique properties, BW-SPDC-based devices will be important building blocks for quantum information processing.