Observation of Decoherence Induced Exceptional Points in the Dynamics of a Dissipative Superconducting Qubit*

Exceptional point degeneracies have been extensively studied in many dissipative systems with energy or particle loss where the dynamics are governed by non-Hermitian Hamiltonians. This Hamiltonian formalism, however, cannot capture the effect of decoherence that plays an essential role in quantum systems. Recently, Liouvillian superoperators have been proposed to take account of both energy loss and decoherence. The degeneracies of the (generically non-Hermitian) Liouvillian are also exceptional points, which are associated with critical dynamics as a dissipative quantum system approaches steady state. Here, we study the dynamics of a dissipative superconducting qubit and observe two different types of Liouvillian exceptional points that arise from the interplay of energy loss and decoherence, or purely due to decoherence. Further, by dynamically tuning the Liouvillian superoperators in real time we observe non-Hermiticity-induced chiral state transfer. This study opens new avenues for exploring non-Hermitian physics in open quantum systems and may help harness non-Hermitian dynamics into quantum control.