Reducing the impact of intrinsic dissipation in a superconducting circuit by quantum error detection

A fundamental challenge for quantum information processing is reducing the impact of environmentally-induced errors. Quantum error detection and rejection (QEDR) provides one approach to handling such errors, in which errors are rejected when they are detected. Here we demonstrate a QEDR protocol based on the idea of quantum un-collapsing, using this protocol to suppress energy relaxation due to the environment in a three-qubit superconducting circuit. We encode quantum information in a target qubit, and use the other two qubits to detect and reject errors caused by energy relaxation. This protocol improves the storage time of a quantum state by a factor of roughly three, at the cost of a reduced probability of success. This constitutes the first demonstration of the extension of the effective lifetime of a quantum state using a quantum protocol. Using a similar protocol and a four-qubit superconducting circuit, we further demonstrate the protection of Bell-state entanglement against energy relaxation.