Heralded Bell State of Dissipative Qubits Using Classical Light

Maximally entangled two-qubit states (Bell states) are one of the most exotic states in the quantum world and have important applications from testing quantum foundations to quantum information processing. Here we show that a Bell state can be generated using classical light by coupling two qubits to a one-dimensional (1d) waveguide. Even though the steady state of the qubits is a trivial product state with no coherence or entanglement, continuous monitoring unravels the steady state nontrivially such that a Bell state is generated in its trajectories and heralded by a reflected photon. This provides a particularly sharp illustration that information gained by measuring an open quantum system can affect its physical state and lead to surprising and useful results. Further, the specific role of information in our system is explored by including imperfect photon detection as a source of information loss.