Counting photons from Bragg-reflection waveguides

In order to make optical quantum technologies more practicable, we want to create compact, small-scale few photon emitters with controllable photon-number properties. Such sources are often based on photon splitting, which is a non-linear optical process for producing photons in pairs. For this purpose, semiconductor waveguides provide a promising technology because they offer possibilities for the integration with standard embedded platforms and provide brighter sources than bulk optics. In our project Counting photons from Bragg-reflection waveguides we will use such semiconductor waveguides as photonic sources for producing multi-photon pairs and investigate the photon-number content of theses states with highly efficient photon-number resolving superconducting photo-detectors. Our goal is to prepare specific classes of multi-photon states with good quality and resolve fine features in their photon-number statistics.

Each light source can be classied by its specic photon-number distribution, which is an important tool in quantum optical state characterization. Recently, the development of non- commercial, true photon-number resolving detectors based on superconductors have enabled a direct experimental access in it. In this project we measured the photon-number content of novel semiconductor light emitters at the single- and few photon level and classied their characteristics. Especially, we investigated radiation emitted via a non-linear optical process in Bragg-reection waveguides, in which a pump photon in the near infrared wavelength is splitted to two photons in the telecommunication wavelengths. By detecting one of the created photons with our photon counter we prepared nonclassical heralded states. However, due to the inevitable optical losses the verication of their non-classicality is challenging. We showed that by controlling the parameters involved in the state preparation and manipulation we can accurately predict the properties of the heralded states. Further, we experimentally applied a new method for the reconstruction of the photon-number parity from loss-degraded measurements excluding the need of sophisticated loss-inversion algorithms used earlier. Being the difference between the weights of the even and odd photon-number contributions, the photon-number parity is a key gure of merit when characterizing quantum light sources. Keeping in mind that until today there exists no direct measurement of photon- number parity for light traveling in free space, such alternative experimental methods as the our one are pivotal for probing it accurately.