VAQEM: A Variational Approach to Quantum Error Mitigation
Variational Quantum Algorithms (VQAs) are relatively robust to noise, but
errors are still a significant detriment to VQAs on near-term quantum machines.
It is imperative to employ error mitigation techniques to improve VQA fidelity.
While existing error mitigation techniques built from theory provide
substantial gains, the disconnect between theory and real machine execution
limits their benefits. Thus, it is critical to optimize mitigation techniques
to explicitly suit the target application as well as the noise characteristics
of the target machine.
  We propose VAQEM, which dynamically tailors existing error mitigation
techniques to the actual, dynamic noisy execution characteristics of VQAs on a
target quantum machine. We do so by tuning specific features of these
mitigation techniques similar to the traditional rotation angle parameters - by
targeting improvements towards a specific objective function which represents
the VQA problem at hand. In this paper, we target two types of error mitigation
techniques which are suited to idle times in quantum circuits: single qubit
gate scheduling and the insertion of dynamical decoupling sequences. We gain
substantial improvements to VQA objective measurements - a mean of over 3x
across a variety of VQA applications, run on IBM Quantum machines.
  More importantly, the proposed variational approach is general and can be
extended to many other error mitigation techniques whose specific
configurations are hard to select a priori. Integrating more mitigation
techniques into the VAQEM framework can lead to potentially realizing
practically useful VQA benefits on today's noisy quantum machines.
Gokul Subramanian Ravi Kaitlin N. Smith Pranav Gokhale Andrea Mari Nathan Earnest Ali Javadi-Abhari Frederic T. Chong