Crystalline Waveguide for quantum sensors and memories at telecom wavelength – GOMMETTE

The GOMETTE project aims at the emergence of a new integrated photonics platform compatible with telecom wavelengths that will allow the improvement of quantum processors based on erbium (Er) doped crystals. These systems are currently widely studied for the development of quantum memories (QM) as well as for the spectral analysis of broadband and real-time radio frequency signals
(ASRF). However, despite remarkable proofs of principle, several limitations are delaying the emergence of a mature technology. The main limitations are the same for MQ and ASRF, since the too weak interaction of light with matter imposes to work with too high concentrations of Er ion (>10ppm). Indeed, Er ions have a large electron spin, which facilitates their interaction and favors
decoherence. The consequence is a significant degradation of the storage time of the QM and the spectral resolution of the ASRF. Note that this weak coupling of light and matter leads to other limitations regarding the multiplexing of the QMs and accessible bandwidth for the ASRF.

GOMETTE offers to solve this problem by developing single crystalline waveguides (GOM) that combine an effective light confinement, allowing an increase of the light-matter interaction, with the preservation of the exceptional homogeneous linewidths of Er ions. As of now, no GOM preserving the properties of Er ions in a bulk crystal has been demonstrated yet. Single crystal Er: Y2SiO5 (Er:YSO), which is currently the reference material for the applications mentioned above, will be used. In order to guarantee the conservation of the exceptional properties of Er:YSO, we will develop an original and low invasive structuring process. This process based on mechanical lapping, molecular bonding and dry etching techniques, is widely used in the electro-technical industry, which is an advantage for scalability and industrial scale-up. It will allow to obtain a hybrid heterostructure based
on the assembly of Er:YSO with a substrate of lower refractive index. This composite stack will then be structured into a waveguide using lithography and dry etching methods (ICP-RIE).

The aim of this project is therefore to exploit integration and functional potential of GOMs to significantly increase the interaction between light and matter, while reducing the decoherence processes induced by Er ion interactions. The final component, a highly scalable integrated photonics platform operating at telecom wavelengths, will enable the development of new quantum devices with extended functionalities. A broadband spectrum analyzer with unrivalled performance operating at telecom wavelengths will be demonstrated. A preliminary demonstration of frequency-division multiplexed optical storage will also be carried out to confirm the interest of this platform for QM.

This multidisciplinary project at the interface between materials chemistry, photonics and quantum physics will involve three academic partners and one industrial partner. The consortium presents a wide range of expertise that includes crystal growth, photonics, and quantum physics, and goes up to the development and validation of the final device.