Error-robust quantum logic optimization using a cloud quantum computer
  interface
We describe an experimental effort designing and deploying error-robust
single-qubit operations using a cloud-based quantum computer and analog-layer
programming access. We design numerically-optimized pulses that implement
target operations and exhibit robustness to various error processes including
dephasing noise, instabilities in control amplitudes, and crosstalk. Pulse
optimization is performed using a flexible optimization package incorporating a
device model and physically-relevant constraints (e.g. bandwidth limits on the
transmission lines of the dilution refrigerator housing IBM Quantum hardware).
We present techniques for conversion and calibration of physical Hamiltonian
definitions to pulse waveforms programmed via Qiskit Pulse and compare
performance against hardware default DRAG pulses on a five-qubit device.
Experimental measurements reveal default DRAG pulses exhibit coherent errors an
order of magnitude larger than tabulated randomized-benchmarking measurements;
solutions designed to be robust against these errors outperform
hardware-default pulses for all qubits across multiple metrics. Experimental
measurements demonstrate performance enhancements up to: $\sim10\times$
single-qubit gate coherent-error reduction; $\sim5\times$ average
coherent-error reduction across a five qubit system; $\sim10\times$ increase in
calibration window to one week of valid pulse calibration; $\sim12\times$
reduction gate-error variability across qubits and over time; and up to
$\sim9\times$ reduction in single-qubit gate error (including crosstalk) in the
presence of fully parallelized operations. Randomized benchmarking reveals
error rates for Clifford gates constructed from optimized pulses consistent
with tabulated $T_{1}$ limits, and demonstrates a narrowing of the distribution
of outcomes over randomizations associated with suppression of coherent-errors.
Andre R. R. Carvalho Harrison Ball Michael J. Biercuk Michael R. Hush Felix Thomsen