Emil Zeuthen works on theoretical quantum optomechanics and quantum transduction. Research focuses on (1) figures of merit and protocols for quantum transducers (mechanical interfaces between microwave and optical domains); (2) back-action-evading measurements using optomechanical systems; (3) quantum limits for gravitational wave detection with mechanical systems in a negative-mass spin reference frame. Key QUANTOP theory collaborator bridging optomechanics and quantum sensing.