Protecting logical qubits with dynamical decoupling

Demonstrating that logical qubits outperform their physical counterparts represents a milestone in achieving reliable quantum computation. Here, we propose to protect logical qubits with a dynamical decoupling scheme that implements i gates on nearest-neighbor physical qubits, and we experimentally demonstrate this scheme on superconducting transmon qubits. In our scheme, each logical qubit requires only 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 357% compared to the better-performing physical qubit. Moreover, we demonstrate—to the best of our knowledge, for the first time—that multiple logical qubits can outperform their physical superconducting counterparts. 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.