  Rydberg atom arrays have emerged as a leading platform for quantum
information science. Reaching system sizes of hundreds of long-lived qubits,
these arrays are used for highly coherent analog quantum simulation, as well as
digital quantum computation. Advanced quantum protocols such as quantum error
correction, however, require midcircuit qubit operations, including the
replenishment, reset, and readout of a subset of qubits. A compelling strategy
to achieve these capabilities is a dual-species architecture in which a second
atomic species can be controlled without crosstalk, and entangled with the
first via Rydberg interactions. Here, we realize a dual-species Rydberg array
consisting of rubidium (Rb) and cesium (Cs) atoms, and explore new regimes of
interactions and dynamics not accessible in single-species architectures. We
achieve enhanced interspecies interactions by electrically tuning the Rydberg
states close to a Forster resonance. In this regime, we demonstrate
interspecies Rydberg blockade and implement quantum state transfer from one
species to another. We then generate a Bell state between Rb and Cs hyperfine
qubits via an interspecies controlled-phase gate. Finally, we combine
interspecies entanglement with native midcircuit readout to achieve quantum
non-demolition measurement of a Rb qubit using an auxiliary Cs qubit. The
techniques demonstrated here pave the way toward scalable measurement-based
protocols and real-time feedback control in large-scale quantum systems.
