The goal of DISCRYS is to use controlled chemical disorder in crystals to suppress decoherence, i.e. processes that corrupt quantum states. This approach will be developed with high quality rare earth doped crystals where disorder will be induced by co-doping with specific impurities. Our main challenges are growing crystals with very low level of optical decoherence; quantitatively understanding the relation between material composition, disorder and decoherence; and ultimately demonstrating high performance storage of telecom wavelength photons in optimized samples. Quantum information science (QIS) uses specific properties of quantum systems to process, store and transmit data in ways that are impossible to achieve with classical systems. As it fundamentally requires superposition states that remain uncorrupted during the storage and processing of information, only systems with low decoherence are useful in QIS. In this field, quantum light-matter interfaces, called quantum memories are urgently needed for applications in quantum computing, metrology and single photon sources. In addition, quantum memories are essential to extend quantum cryptography, an already commercial technology for extremely secure communications, over long distances. Rare earth doped crystals have been recently identified as very promising systems in QIS but their performance is still limited by decoherence that affects their optical transitions. At low temperature, this decoherence is due to fluctuating nuclear and electronic spins in the rare earth environment. To address this issue, complex experimental setups and protocols have been put forward. In contrast, DISCRYS proposes to suppress decoherence by a solid-state chemistry approach. By inducing controlled disorder in high quality crystals, resonance between neighboring spin transition can be disrupted, which inhibits relaxation by simultaneous spin flips and finally eliminates decoherence. DISCRYS will combine single crystal growth, advanced optical spectroscopy and electron paramagnetic resonance, as well as modeling to reach a quantitative understanding of the relations between disorder and decoherence. We will further demonstrate the effectiveness of our material chemistry approach by building a quantum memory operating at the 1.5 µm telecom wavelength, ideally suited for fiber based long distance quantum cryptography. We expect optimized crystals to allow an improvement of three orders of magnitude in memory performance over existing systems. The results of DISCRYS will be directly useful to groups working on rare earth doped materials for applications in QIS, and more generally to the broad scientific community dealing with quantum coherence in semi-conductors, other impurities in solids or molecules for applications in QIS, sensing, biology etc.. DISCRYS also addresses a key material issue in the development of quantum memories for long-range quantum cryptography. Our project will enable quantum memories compatible with existing fiber telecom networks and therefore has a large potential impact on quantum cryptography technology. DISCRYS gathers world-leading teams in optical material growth and design, spectroscopy, modeling, and optical quantum information processing. Our international collaboration will combine expertise from solid-state chemistry to quantum physics, and will be essential to achieve major advances in materials for quantum information science.