  Parameterized circuit instantiation is a common technique encountered in the
generation of circuits for a large class of hybrid quantum-classical
algorithms. Despite being supported by popular quantum compilation
infrastructures such as IBM Qiskit and Google Cirq, instantiation has not been
extensively considered in the context of circuit compilation and optimization
pipelines. In this work, we describe algorithms to apply instantiation during
two common compilation steps: circuit optimization and gate-set transpilation.
When placed in a compilation workflow, our circuit optimization algorithm
produces circuits with an average of 13% fewer gates than other optimizing
compilers. Our gate-set transpilation algorithm can target any gate-set, even
sets with multiple two-qubit gates, and produces circuits with an average of
12% fewer two-qubit gates than other compilers. Overall, we show how
instantiation can be incorporated into a compiler workflow to improve circuit
quality and enhance portability, all while maintaining a reasonably low compile
time overhead.
