Continuous parity measurement and error correction

In a multi-qubit system, performing continuous measurements of joint properties such as parity permits the study the quantum dynamics of multipartite state evolution and collapse. By performing simultaneous parity measurements in a three qubit system, we can also observe a single qubit flip in real time, providing the basis for quantum error correction. The parity of two superconducting transmons may be directly measured without qubit ancilla by coupling them to a single readout resonator, using identical dispersive couplings much larger than the resonator bandwidth. Using a chip with three qubits and connecting each pair of two to a parity readout resonator, we implement the two parity measurements needed to perform the conventional three-qubit bit-flip code. We control the qubits from a field programmable gate array while continuously monitoring the parity, allowing for low latency correction pulses to be applied when a qubit flip occurs.