Qiushi Liu, Yuxiang Yang (Mar 15 2024).
Abstract: We propose efficient tensor network algorithms for optimizing control-enhanced sequential strategies in estimating a large number of quantum channels, with no ancilla or bounded ancilla. Our first approach allows for applying $N-1$ arbitrary interleaved control operations between the $N$ channels to estimate, and the second approach restricts all control operations to be identical, which could further facilitate simpler experimental demonstration. The numerical experiments show that our algorithm has a good performance in optimizing the metrological protocol for $N=100$ single-qubit and two-qubit channels. In particular, our algorithm identifies a strategy that can outperform the asymptotically optimal quantum error correction protocol when $N$ is finite but large.