Photonic quantum computing on thin-film lithium niobate: Part I Design of an efficient heralded single photon source co-integrated with superconducting detectors

Photonic quantum computers are currently one of the primary candidates for fault-tolerant quantum computation. At the heart of the photonic quantum computation lies the strict requirement for suitable quantum sources e.g. high purity, high brightness single photon sources. To build a practical quantum computer, thousands to millions of such sources are required. In this article, we theoretically propose a unique single-photon source design on a thin-film lithium niobate (TFLN) platform co-integrated with superconducting nanowire single-photon detectors. We show that with a judicial design of single photon source using thin film periodically poled lithium waveguides (PPLN), back-illuminated grating couplers (GCs) and directly bonded or integrated cavity coupled superconducting nanowire single-photon detectors (SNSPDs) can lead to a simple but practical high efficiency heralded single-photon source using the current fabrication technology. Such a device will eliminate the requirement of out coupling of the generated photons and can lead to a fully integrated solution. The proposed design can be useful for fusion-based quantum computation and for multiplexed single photon sources and also for efficient on-chip generation and detection of squeezed light.