Rapid cavity based mid-circuit measurement and feed-forward in a neutral atom array

Mid-circuit measurement is a state-projection readout on a subset of a quantum system without disturbing the remaining bystander qubits. This capability is essential for a broad range of quantum applications, including quantum error correction, measurement-based quantum computing, and quantum-enhanced metrology. Previous implementations of mid-circuit measurement in neutral atom systems have relied on shuttling atomic qubits to a dedicated readout zone, which fundamentally limits the operation speed. In this work, we demonstrate selective mid-circuit readout in an array of atomic qubits placed in a high finesse optical cavity. By optically selecting a single atomic qubit to emit photons into the cavity, we achieve a measurement infidelity below 0.8% using 30 us detection windows and 20 us time intervals for switching between individual qubit readouts. To show that the measurement does not affect the quantum evolution, we did a Ramsey type experiment and showed that the normalized contrast is above 97%. We further employ a measurement–feedforward loop with a Red Pitaya device programmed with FPGA to adaptively correct for unwanted z-axis rotations on bystander qubits induced by cavity photons. The residual decoherence on bystander qubits from each measurement is below 0.2%