Multifrequency sources of quantum correlated photon pairs on-chip: a path toward integrated Quantum Frequency Combs

*Corresponding Author: Lucia Caspani: Institut National de la Recherche Scientifique Énergie Matériaux et Télécommunications, Université du Québec, 1650 Boulevard Lionel-Boulet, Varennes, Québec, Canada J3X 1S2 and Institute of Photonics and Quantum Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK, E-mail: [email protected] *Corresponding Author: Roberto Morandotti: Institut National de la Recherche Scientifique Énergie Matériaux et Télécommunications, Université du Québec, 1650 Boulevard Lionel-Boulet, Varennes, Québec, Canada J3X 1S2 and Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu 610054, China, E-mail: [email protected] Christian Reimer, Michael Kues, Piotr Roztocki, Yoann Jestin, Luca Razzari: Institut National de la Recherche Scientifique Énergie Matériaux et Télécommunications, Université du Québec, 1650 Boulevard Lionel-Boulet, Varennes, Québec, Canada J3X 1S2 Matteo Clerici: Institut National de la Recherche Scientifique Énergie Matériaux et Télécommunications, Université du Québec, 1650 Boulevard Lionel-Boulet, Varennes, Québec, Canada J3X 1S2 and School of Engineering, University of Glasgow, Glasgow G12 8LT, UK Benjamin Wetzel, Marco Peccianti, Alessia Pasquazi: Institut National de la Recherche Scientifique Énergie Matériaux et Télécommunications, Université du Québec, 1650 Boulevard Lionel-Boulet, Varennes, Québec, Canada J3X 1S2 and Department of Physics and Astronomy, University of Sussex, Falmer, Brighton BN1 9RH, UK Marcello Ferrera: Institut National de la Recherche Scientifique Énergie Matériaux et Télécommunications, Université du Québec, 1650 Boulevard Lionel-Boulet, Varennes, Québec, Canada J3X 1S2 and Institute of Photonics and Quantum Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK Brent E. Little: State Key Laboratory of Transient Optics and Photonics, Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Science, Xi’an, China Sai T. Chu: Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Hong Kong, China David J. Moss: Centre for Microphotonics, Swinburne University of Technology, Hawthorn, VIC 3122, Australia Abstract: Recent developments in quantum photonics have initiated the process of bringing photonic-quantumbased systems out-of-the-lab and into real-world applications. As an example, devices to enable the exchange of a cryptographic key secured by the laws of quantum mechanics are already commercially available. In order to further boost this process, the next step is to transfer the results achieved by means of bulky and expensive setups intominiaturized and affordable devices. Integrated quantum photonics is exactly addressing this issue. In this paper, we briefly review themost recent advancements in the generation of quantum states of light on-chip. In particular, we focus on optical microcavities, as they can offer a solution to the problem of low efficiency that is characteristic of the materials typically used in integrated platforms. In addition, we show that specifically designed microcavities can also offer further advantages, such as compatibility with telecom standards (for exploiting existing fibre networks) and quantum memories (necessary to extend the communication distance), as well as giving a longitudinal multimode character for larger information transfer and processing. This last property (i.e., the increased dimensionality of the photon quantum state) is achieved through the ability to generate multiple photon pairs on a frequency comb, corresponding to themicrocavity resonances. Further achievements include the possibility of fully exploiting the polarization degree of freedom, even for integrated devices. These results pave the way for the generation of integrated quantum frequency combs that, in turn, may find important applications toward the realization of a compact quantum-computing platform.