Error Mitigation and Classical Support for Variational Quantum Algorithms
ABSTRACT :
Variational Quantum Algorithms (VQA) are among the promising candidates for near-term quantum advantage due to their inherent robustness to quantum device noise. However, noise is still a significant detriment to VQAs target estimations on today s quantum machines and, therefore, improving their execution through error mitigation and classical support is critical.
First, I will discuss VAQEM, a Variational Approach to Quantum Error Mitigation, which dynamically tailors existing error mitigation techniques to the actual, dynamic noisy execution characteristics of VQAs on a target quantum machine. This is done by tuning specific features of these mitigation techniques similar to VQAs traditional rotation angle parameters. In this work, 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.
Second, I will discuss finding a good ansatz initialization for VQAs through CAFQA, a Clifford Ansatz For Quantum Accuracy. The CAFQA ansatz is a hardware-efficient circuit built with only Clifford gates, wherein the good Clifford gates are found through classical execution and search. CAFQA produced stabilizer states always equal or outperform state-of-the-art initialization and enable high-accuracy VQA estimations. CAFQA is well-suited to classical computation because a) Clifford-only quantum circuits can be exactly simulated classically in polynomial time, and b) the discrete Clifford space is searched efficiently via Bayesian Optimization.
Finally, if time permits, I will briefly highlight some other recent work targeting VQAs, error mitigation and quantum error correction.