  Demonstrating that logical qubits outperform their physical counterparts is a
milestone for achieving reliable quantum computation. Here, we propose to
protect logical qubits with a novel dynamical decoupling scheme that implements
iSWAP gates on nearest-neighbor physical qubits, and experimentally demonstrate
the scheme on superconducting transmon qubits. In our scheme, each logical
qubit only requires two physical qubits. A universal set of quantum gates on
the logical qubits can be achieved such that each logical gate comprises only
one or two physical gates. Our experiments reveal that the coherence time of a
logical qubit is extended by up to 366% when compared to the better-performing
physical qubit. Moreover, to the best of our knowledge, we demonstrate for the
first time that multiple logical qubits outperform their physical counterparts
in superconducting qubits. We illustrate a set of universal gates through a
logical Ramsey experiment and the creation of a logical Bell state. Given its
scalable nature, our scheme holds promise as a component for future reliable
quantum computation.
