Bath-induced collective phenomena on superconducting qubits: synchronization, subradiance, and entanglement generation.

A common environment acting on a pair of qubits gives rise to a plethora of different phenomena, such as the generation of qubit-qubit entanglement, quantum synchronization and subradiance. Here we define time-independent figures of merit for entanglement generation, quantum synchronization and subradiance, and perform an extensive analytical and numerical study of their dependence on model parameters. We also address a recently proposed measure of the collectiveness of the dynamics driven by the bath, and find that it almost perfectly witnesses the behavior of entanglement generation. Our results show that synchronization and subradiance can be employed as reliable local signatures of an entangling common-bath in a general scenario. Finally, we propose an experimental implementation of the model based on two transmon qubits capacitively coupled to a common resistor, which provides a versatile quantum simulation platform of the open system in any regime.