We investigate the most general mechanisms that lead to perfect synchronization of the quantum states of all subsystems of an open quantum system starting from an arbitrary initial state. We provide a necessary and sufficient condition for such “quantum-state synchronization,” prove tight lower bounds on the dimension of the ancilla's Hilbert space in two main classes of quantum-state synchronizers, and give an analytical solution for their construction. The functioning of the found quantum-state synchronizer of two qubits is demonstrated experimentally on an IBM quantum computer and we show that the remaining asynchronicity is a sensitive measure of the quantum computer's imperfection.

• Received 10 March 2021
• Accepted 17 June 2021

DOI:https://doi.org/10.1103/PhysRevA.104.012410