  Executing quantum applications with quantum error correction (QEC) faces the
gate non-universality problem imposed by the Eastin-Knill theorem. As one
resource-time-efficient solution, code switching changes the encoding of
logical qubits to implement universal logical gates. Unfortunately, it is still
unclear how to perform full-stack fault-tolerant quantum computing (FTQC) based
on the changeable logical qubit. Specifically, three critical problems remain
unsolved: a) how to implement the dynamic logical qubit on hardware; b) how to
determine the appropriate timing for logical qubit varying; c) how to improve
the overall system performance for programs of different features. To overcome
those design problems, We propose CECQ, to explore the large design space for
FTQC based on changeable logical qubits. Experiments on various quantum
programs demonstrate the effectiveness of CECQ.
