Modern quantum technologies rely on low temperatures for large-scale quantum computation , quantum simulation , for integrated quantum circuits , or quantum transducers . In particular the latter ones are of great interest, as they vow to bridge the gap between different quantum systems coherently. A robust and highly integratable system to transfer quantum information between terahertz to gigahertz photons are spin waves, and their single quanta magnons . To interconnect with individual quantum systems, such as photons , phonons  or fluxons , and to remove thermally excited magnons, these magnons also have to operate at ultralow temperatures. A system of choice is Yttrium-Iron-Garnet (YIG), with its remarkable properties, such as a low damping at room-temperature. In this work I will present our latest results on spin-wave propagation at ultralow temperatures. An example is given in Fig.1. Here we show a measured propagating spin-wave signal (|S12|) through a 70x2mm (thickness: 5.65#m) YIG sample on a 500#m thick Gadolinium-Gallium-Garnet substrate, at a temperature of 30mK in the Damon-Echbach configuration. Further, my presentation will directly lead to the future perspectives of hybrid Opto-Magnonic Quantum Systems. References 1. J.M. Hornibrook et al., PRA. 3, 024010 (2015). 5. 2. G. Pagano et al., Q. Sci. Technol. 4, 014004 (2019). 6. 3. M. Kiczynski et al., Nat. 606, 7915 (2022). 7. 4. R.W. Andrews et al., Nat. Phys. 10, 4 (2014). 8. A.V. Chumak et al., IEEE Transactions on Magnetics 31, 49664 (2022). D. Lachance-Quirion et al., APE 12, 070101 (2019). Y. Li et al., JAP. 128, 130902 (2020). O.V. Dobrovolskiy et al., Nat. Phys. 15, 477 (2019).