Merklein is the independent PI within the Eggleton group most focused on the acoustic side of Brillouin physics: he demonstrated on-chip photon-phonon memory (coherently transferring an optical pulse into a long-lived acoustic excitation and back), and works on distributed Brillouin sensing in optical fibre and on the coherent control of travelling acoustic waves in waveguides. The distributed-sensing thread is a practical, sensitivity-limited measurement problem: recovering strain and temperature along kilometres of fibre from a very weak backscattered signal. Positioned against the established body of NV-ensemble quantum sensing work — DEER, nanoscale NMR and T1 relaxometry protocols operating at pT/sqrt(Hz) field sensitivity — phonon-mediated storage and readout is a complementary transduction channel to spin-based sensing, and the group is now pushing toward the quantum regime where the acoustic mode must be treated as a quantum object rather than a classical one. Early-career PI (DECRA) with genuine independence inside a large group.