Physicists develop a linear response theory for open systems having exceptional points
The linear response theory developed in this work provides a full characterization of the relation between output and input signals (indicated by green and yellow arrows, respectively) in terms of the eigenmodes and the canonical states of the underlying non-Hermitian Hamiltonian. Credit: Ramy El-Ganainy Linear analysis plays a central role in science and engineering. Even when dealing with nonlinear systems, understanding the linear response is often crucial for gaining insight into the underlying complex dynamics. In recent years, there has been a great interest in studying open systems that exchange energy with a surrounding reservoir. In particular, it has been demonstrated that open systems whose spectra exhibit non-Hermitian singularities called exceptional points can demonstrate a host of intriguing effects with potential applications in building new lasers and sensors. At an exceptional point, two or modes become exactly identical. To better understand this, let us consid...