  Rapidly improving gate fidelities for coherent operations mean that errors in
state preparation and measurement (SPAM) may become a dominant source of error
for fault-tolerant operation of quantum computers. This is particularly acute
in superconducting systems, where tradeoffs in measurement fidelity and qubit
lifetimes have limited overall performance. Fortunately, the essentially
classical nature of preparation and measurement enables a wide variety of
techniques for improving quality using auxiliary qubits combined with classical
control and post-selection. In practice, however, post-selection greatly
complicates the scheduling of processes such as syndrome extraction. Here we
present a family of quantum circuits that prepare high-quality |0> states
without post-selection, instead using CNOT and Toffoli gates to non-linearly
permute the computational basis. We find meaningful performance enhancements
when two-qubit gate fidelities errors go below 0.2%, and even better
performance when native Toffoli gates are available.
