Dynamically Generated Decoherence-Free Subspaces and Subsystems on
  Superconducting Qubits
Decoherence-free subspaces and subsystems (DFS) preserve quantum information
by encoding it into symmetry-protected states unaffected by decoherence. An
inherent DFS of a given experimental system may not exist; however, through the
use of dynamical decoupling (DD), one can induce symmetries that support DFSs.
Here, we provide the first experimental demonstration of DD-generated DFS
logical qubits. Utilizing IBM Quantum superconducting processors, we
investigate two and three-qubit DFS codes comprising up to six and seven
noninteracting logical qubits, respectively. Through a combination of DD and
error detection, we show that DFS logical qubits can achieve up to a 23%
improvement in state preservation fidelity over physical qubits subject to DD
alone. This constitutes a beyond-breakeven fidelity improvement for DFS-encoded
qubits. Our results showcase the potential utility of DFS codes as a pathway
toward enhanced computational accuracy via logical encoding on quantum
processors.
Gregory Quiroz Bibek Pokharel Joseph Boen Lina Tewala Vinay Tripathi Devon Williams Lian-Ao Wu Paraj Titum Kevin Schultz Daniel Lidar