Silicon photonics for quantum optics & communication – SITQOM

SITQOM is geared towards realizing and optimizing dense photonic quantum circuits on silicon, showing increased complexity in terms of number of photon sources and routing channels, as well as regarding the flexibility of quantum properties manipulation. Its main objective lies in the integration of photon pair sources and optical functions, ranging from directional couplers to arrays of coupled waveguides, for demonstrating on-chip photonic quantum state preparation and advanced manipulation, with unprecedented scalability and stability features.

The groups at C2N-SILICON and at INPHYNI have jointly developed a photon-pair source based on Si. The performances of this source have permitted to validate the foundations of this project, namely the exploitation of the silicon platform as a novel and promising tool for on-chip quantum photonics. Thanks to the demonstration of entanglement qualities that go beyond the state-of-the-art, the consortium is now very well positioned, i.e. among the best actors in the field, at the international level. Moreover, sub-wavelength structure engineering mastered by the C2N-SILICON has permitted to design and fabricate novel integrated Bragg filters showing high rejection capabilities. Up to now the refractive index difference between silicon and silica was requiring to etch silicon with high precision (~10nm). The original geometries that we have studied, based on a double grating periodicity (instead of one usually), permit to adjust the filter performances in terms of both rejection central wavelength and wavelength band. or the first time in the field, total on-chip rejection of the residual laser pump intensity can be considered. Within the framework of a close collaboration between C2N-SILICON and C2N-PHOTONICS, a record coupling efficiency has been demonstrated in silicon waveguide arrays comprising 100 waveguides, separated by 1.2 µm over 700 µm, with a coupling constant of 37 mm-1.

The envisioned applications span from advanced and heralded entanglement demonstrators, to the exploitation of arrays of coupled waveguides for large-scale entangled states, as well as high bit rate quantum cryptosystems based on multiplexed wavelength bins. Due to the degree of difficulties, none of those applications have ever been demonstrated so far. We however strongly believe that further successes in this field highly depends on the exploitation of novel and disruptive key technologies, among which silicon photonics stands as one of the most promising approaches. For example, demonstrating efficient heralded entanglement out of a single chip would pave the pave towards synchronized quantum communication networks with signal- to-noise ratio unreachable with current systems. In this perspective, the related technological developments carried out in the project should lead in practice to state-of-the-art quantum devices, for which flexibility and reconfigurability stand as key features, as well as novel prospects in quantum optics.

[MAZ16] F Mazeas, M Traetta, M Bentivegna, F Kaiser, D Aktas, W Zhang, C.A Ramos, L.A. Ngah, T. Lunghi, É Picholle, N Belabas-Plougonven, X. Le Roux, É Cassan, D Marris-Morini, L Vivien, G Sauder, L. Labonté, S Tanzilli, « High-quality photonic entanglement for wavelength-multiplexed quantum communication based on a silicon chip », Optics Express 24(25) 28731-28738 (2016). [RAM17] D Pérez-Galacho, Diego, C.A Ramos, F Mazeas, X Le Roux, D Oser, W Zhang, D Marris-Morini, L Labonté, S Tanzilli, E Cassan, L Vivien, « Optical pump-rejection filter based on silicon sub-wavelength engineered photonic structures », Optics Letters 42(8) 1468-1471 (2017).

Quantum information science has established a new benchmark in communication and processing of information, thanks to protocols allowing augmented security in data exchange and increased processing capabilities. Despite numerous proofs-of-principle, next generation applications are currently envisioned, such as quantum simulators, real-world cryptosystems, and efficient sensors. In this perspective, where device scalability and reliability appear to be mandatory, integrated optical circuits showing high density of functionality and configurable features are destined to play a major role. Integrated quantum photonics has already proven its suitability for high-performance photon-pair source realizations and basic quantum state simulation. In this framework, SITQOM is geared towards fully developing a novel, silicon based, integrated quantum photonics platform showing gradually augmented and beyond state-of-the-art capabilities. Our ambition lies in the dense integration of both linear and non-linear optical functionalities enabling, on single substrates, the generation, the routing, the advanced manipulation, as well as the detection, of photonic quantum states. The addressed challenges are multiple and have not been tackled so far on chip: i) achievement of standard and heralded two- photon entanglement demonstrators, ii) simulation of quantum operators based on arrays of coupled waveguides, and iii) development of high bit-rate quantum cryptography protocols based on multi-frequency coding.
Silicon photonics stands as a one of the most promising platform for exploiting dense functionality integration. Notably, integrated ring cavities already enable producing entangled photons thanks to enhanced third-order nonlinear processes. In the short term perspective, such cavities, as well as Bragg reflectors, will be employed for demonstrating stand-alone photon-pair generators, i.e., featuring on-chip filtering stages, such as wavelength splitters and pump laser rejecters. In the mid term perspective, electro-optical switches and single photon detectors will be addressed towards achieving heralded two-photon states based on active photon routing. Thanks to incomparable fabrication reproducibility, silicon photonics makes it possible to design and realize arrays of coupled waveguides. Thanks to pre-engineered or configurable mutual coupling constants, such circuits will permit routing single photons in a “quantum bus” fashion. They also stand as compact, flexible, and multiport tools for quantum propagation control and quantum manipulation of light in a scalable and integrated manner. Induced photonic lattices are suitable hosts for implementing quantum processes, such as quantum logic gates and optical simulator analogues of the quantum properties of condensed matter systems. Furthermore, by merging, on a single chip, a high-brightness photon pair sources and dedicated filtering and routing stages, we aim at developing novel large-scale quantum cryptosystems. By pumping an integrated ring cavity using a frequency-comb high repetition rate laser, multi-frequency bin coded photon-pairs will be exploited in standard telecommunication channels towards achieving unprecedented secret key rates over long distances.
The SITQOM program represents a unique opportunity to gather recognized French experts in quantum optics and information, namely the LPMC, the IEF, and the LPN, to enter the worldwide competition on silicon quantum photonics at its earliest stage. Thanks to this competitive and complementary consortium, both silicon photonics device developments and their exploitation in advanced quantum information applications will be addressed. The expected compactness and integration levels, solely offered by our platform, promise significant advances in quantum-enabling technologies and novel perspectives in quantum optics.