New Technique: Generalized Quantum Subspace Expansion

[purva-thakre]

Generalized QSE (GSE) introduced in https://arxiv.org/abs/2107.02611

Expands the 'search' subspace compared to what's used in QSE. Shown to be robust in the presence of imperfect control and is an error-agnostic QEM. Requires measurements that scale quadratically.

Dual GSE introduced in https://arxiv.org/abs/2309.14171

A better version of GSE that's resource-efficient in terms of required measurements. Relies on dual-state purification.