Topological energy transfer in an optomechanical system with exceptional points

Topological operations have the merit of achieving certain goals without requiring accurate control over local operational details. To date, topological operations have been used to control geometric phases, and have been proposed as a means for controlling the state of certain systems within their degenerate subspaces[1-8]. More recently, it was predicted that topological operations can be extended to transfer energy between normal modes, provided that the system possesses a specific type of degeneracy known as an exceptional point (EP)[9-11]. Here we demonstrate the transfer of energy between two modes of a cryogenic optomechanical device by topological operations. We show that this transfer arises from the presence of an EP in the device's spectrum. We also show that this transfer is non-reciprocal[12-14]. These results open new directions in system control; they also open the possibility of exploring other dynamical effects related to EPs[15,16], as well as the behavior of thermal and quantum fluctuations in the vicinity of EPs.