Adiabaticity in non-Hermitian dynamics of a superconducting qubit*

In general, a quantum system subject to slow parameter variation will closely follow its instantaneous eigenstates. This well-known adiabatic theorem, however, has been shown to break down in recent studies of open systems with gain or loss. Such systems are effectively described by non-Hermitian Hamiltonians and thus possess complex eigenvalues and nonorthogonal eigenstates. In this talk, I will present our study of adiabaticity in non-Hermitian dynamics of a single dissipative superconducting qubit, where we tune the frequency and amplitude of microwave drives to vary the system Hamiltonian. The resulting dynamics is determined by the nonadiabatic coupling between eigenstates as well as their complex-eigenvalue-induced growth or decay. Our understanding of adiabaticity in the presence of complex eigenvalues will be important in harnessing non-Hermiticities for quantum sensing and control.