  Quantum computing is on the cusp of reality with Noisy Intermediate-Scale
Quantum (NISQ) machines currently under development and testing. Some of the
most promising algorithms for these machines are variational algorithms that
employ classical optimization coupled with quantum hardware to evaluate the
quality of each candidate solution. Recent work used GRadient Descent Pulse
Engineering (GRAPE) to translate quantum programs into highly optimized machine
control pulses, resulting in a significant reduction in the execution time of
programs. This is critical, as quantum machines can barely support the
execution of short programs before failing.
  However, GRAPE suffers from high compilation latency, which is untenable in
variational algorithms since compilation is interleaved with computation. We
propose two strategies for partial compilation, exploiting the structure of
variational circuits to pre-compile optimal pulses for specific blocks of
gates. Our results indicate significant pulse speedups ranging from 1.5x-3x in
typical benchmarks, with only a small fraction of the compilation latency of
GRAPE.
