Quantum interference of integrated high purity lithium niobate on insulator spontaneous parametric down-conversion heralded photon sources

Integrated photonics is a promising candidate for quantum information processing applications, however, there are some essential requirements a material needs to fulfil to be able to provide a fully integrated platform, among those is the ability of creating and interfering single photons.

Given its second-order non-linearity lithium niobate on insulator (LNOI) stands out among the contenders in integrated quantum photonics since it enables spontaneous parametric down-conversion (SPDC) as a process of creating pairs of single photons and allows for fast electro-optical tunability of integrated interferometric networks.

We engineer the dispersion relations inside integrated periodically poled LNOI waveguides to enable Type 2 SPDC phase-matching at telecom wavelengths, which creates pairs of orthogonally polarized photons with minimally correlated spectra.

By measuring the phase-matching function and joint spectral intensity of two different integrated SPDC sources we estimate heralded purities of over 95% for both. After pumping them with a pulsed laser and separating the photon pairs, we herald one photon from each source and, without the need for filters, observe quantum interference of the remaining photons at an integrated beam splitter.

The ability to interfere sources of indistinguishable, pure, single photons is a crucial requirement for linear optical quantum computing, which underlines the importance of the development of integrated high purity SPDC sources.