Non-Hermitian quantum dynamics near exceptional points

The second quantum revolution, where quantum technologies are directly harnessed, will realize an unprecedented advance in computation, simulation, sensing, and communication. Currently, quantum applications suffer from the dissipation of quantum systems due to their interactions with the environment. The undesired dissipation can become a valuable resource through careful bath engineering and provide novel functionalities in state preparation, entanglement generation, and error correction. My research focuses on harnessing non-Hermiticity—a special kind of dissipation that leads to nonunitary but coherent evolution—for quantum techniques. Non-Hermitian systems, in general, have complex energies and nonorthogonal eigenstates. Their unique characteristics appear at or near the non-Hermitian degeneracies, also known as exceptional points (EPs). In this talk, I will present our recent work on non-Hermitian dynamics of a superconducting qubit and highlight two striking features of EPs. One is the Riemann topology of complex energies near an EP that enables a new method to transfer quantum states via encircling the EP. The second is the enhanced response of EPs to perturbations. On one hand, this property leads to enhanced decoherence for the non-Hermitian qubit, yet I will describe how this enhancement can be leveraged in speeding up entanglement generation by proximity to EPs.