Continuous Error Correction with Parity Measurements*

In a multi-qubit system, performing continuous measurements of joint properties such as parity allows us to study the collapse dynamics of multipartite states. Simultaneous parity measurements in a three-qubit system also act as continuous stabilizer detection for a quantum error correction code, allowing us to observe a single qubit flip in real time. The parity of two superconducting transmons may be directly measured without qubit ancilla by coupling them to a single readout resonator, using identical dispersive coupling chis much larger than the resonator bandwidth kappa. Using a chip with three qubits and connecting each of two pairs 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 board which also continuously monitors the parity, allowing for low latency correction pulses to be applied when a qubit flip occurs. Using this method, we extend the lifetime of an excited logical state past the lifetime of an excited bare qubit.