Design of integrated sources of entangled photons

Introduction and challenges

Quantum photonics offers a versatile platform for a wide variety of technologies, including quantum communications. Photons possess numerous degrees of freedom, such as polarization and frequency, which can be used to encode and transmit information between two or more nodes in a communications network. Furthermore, photon generation and transmission are compatible with semiconductor devices and the infrastructure used for standard communications (e.g., optical fiber). A crucial phenomenon for quantum communications is entanglement, which enables information transmission between network nodes without requiring its propagation through a communication channel. Despite these advantages, the use of entangled photons for quantum communications is highly limited by fundamental and technological challenges, primarily related to losses and the relatively low emission rate of photon pairs.

Main Objectives

This project aims to study and develop integrated sources of entangled photons featuring low optical losses and a high generation rate. This is a first, yet crucial, step towards the use of entangled photons for quantum communications in optical fiber networks. The project will be based on a study of the properties of entangled photons, as well as of the devices and technologies that enable their generation and manipulation via on-chip and fiber-based architectures and components. The project lies at the interface between the fields of linear and nonlinear optics, quantum optics and photonics, as well as electrical engineering, since the integrated platforms to be developed will require electronic circuits and devices for their implementation.

Objectives, Methodology, and Expected Results

The photon sources targeted in this project are based on second- and third-order nonlinear effects such as spontaneous parametric down-conversion and spontaneous four-wave mixing. It will include an in-depth study of parameters such as the quality factor, the resonance, the free spectral range, the bus-ring gap, and the evanescent coupling, in order to optimize photon generation via third-order nonlinear media (e.g., silicon-based waveguides and resonators). In parallel, optical properties such as birefringence and ordinary and extraordinary axes of second-order nonlinear crystals will be investigated as photon sources and/or for frequency conversion.

This project comprises two main research axes and development strategies. The first focuses on device technology, while the second on the physics of entanglement.

The project aims to fabricate a waveguide-based integrated photon source. This will then be used to generate photon pairs, whose quantum properties will be verified through experiments designed to estimate quantities such as the coincidence-to-accidental ratios (the equivalent of signal-to-noise-ratio), visibility fringes, and the correlation function. This will require knowledge and familiarity with linear and nonlinear optics (e.g., lasers) and electronics (for optical signal manipulation). Therefore, preliminary classical nonlinear-optical tests will precede the quantum experiments.

The physical approach that will be used to increase loss resistance and the emission rate is based on entanglement between multiple degrees of freedom of the photons (hyperentanglement). The plan is to obtain hyperentangled photons in both time and frequency. This requires a study of the physics of entanglement, as well as the devices necessary for its manipulation. In this case, schemes based on interferometry will be targeted.

The project is well-suited for two students. Students participating in the project will have access to ÉTS's research infrastructure in microelectronics, quantum optics, and photonics. Professor Sciara is a member of the LACIME research unit, which houses cutting-edge scientific equipment and instruments, such as lasers, oscilloscopes, function generators, single-photon detectors, and spectrum analyzers. In addition, students will have access to the computing servers and cloud services of Calcul Québec (a member of the Canadian Alliance for Digital Research), as well as the online training offered by this organization.

This project can be combined with internships with companies interested in using entangled photon sources for quantum technologies.

This project is particularly suited to students pursuing a M.Sc.A or a PhD program, but it is also possible to integrate an internship during a bachelor's degree and/or a final-year project (PFE).