Integrated sources of photon quantum states based on nonlinear optics

The ability to generate complex optical photon states involving entanglement between multiple optical modes is not only critical to advancing our understanding of quantum mechanics but will play a key role in generating many applications in quantum technologies. These include quantum communications, computation, imaging, microscopy and many other novel technologies that are constantly being proposed. However, approaches to generating parallel multiple, customisable bi- and multi-entangled quantum bits (qubits) on a chip are still in the early stages of development. Here, we review recent advances in the realisation of integrated sources of photonic quantum states, focusing on approaches based on nonlinear optics that are compatible with contemporary optical fibre telecommunications and quantum memory platforms as well as with chip-scale semiconductor technology. These new and exciting platforms hold the promise of compact, low-cost, scalable and practical implementations of sources for the generation and manipulation of complex quantum optical states on a chip, which will play a major role in bringing quantum technologies out of the laboratory and into the real world. Several new platforms are promising for generating and manipulating complex quantum optical states on a chip. Chip-based sources of quantum states of light are needed to bring quantum technologies out of the lab and into the real world, but such sources are still immature. David Moss at Swinburne University of Technology, Australia, and an international team have reviewed progress in developing and characterizing such sources. Waveguide, cavity and ring resonator devices made from nonlinear materials such as silicon, silicon nitride, silicon oxynitride, Hydex and periodically poled lithium niobate offer scientists a rich variety of sources. Furthermore, many of these technologies can be integrated with silicon CMOS photonics, providing a path for building sophisticated, scalable optical integrated circuits for generating and manipulating quantum optical states for applications in quantum information processing and communications.