Welcome to QMetro++ documentation!

QMetro++ is a Python package that provides a set of tools for identifying optimal estimation protocols that maximize quantum Fisher information (QFI). Optimization can be performed for arbitrary configurations of input states, parameter-encoding channels, noise correlations, control operations, and measurements. The use of tensor networks and an iterative see-saw algorithm allows for an efficient optimization even in the regime of a large number of channel uses (\(N \approx 100\)).

Additionally, the package includes implementations of the recently developed methods for computing fundamental upper bounds on QFI, which serve as benchmarks for assessing the optimality of numerical optimization results. All functionalities are wrapped up in a user-friendly interface which enables the definition of strategies at various levels of detail.

See detailed description in our article.

Installation

To install QMetro++:

pip install qmetro

First import may take a couple seconds (circa 1,86s) because QMetro++ loads CVXPY and numerical backends.

Contents:

• Theoretical background
  • Quantum channel estimation problem
  • Quantum Fisher Information
  • Minimization over purifications
  • Iterative see-saw
  • Upper bounds
• Basic package usage—optimization of standard strategies
  • Specifying the parameter-dependent channel
  • Single-channel QFI optimization
  • Parallel strategy optimization
  • Adaptive strategy optimization
  • Correlated noise models
• Advanced package usage—optimization of strategies with arbitrary structures
  • QMetro++ tensors
  • Collisional strategy
• Appendix
  • Choi-Jamiołkowski matrix and the link product
  • Tensor network formalism and tensor representation
  • Quantum channel models
• Documentation
  • bounds
  • iss_opt
  • param_channel
  • protocols
  • qmtensor
  • qtools
  • utils
• References

Contact

For more information please contact: p.dulian@cent.uw.edu.pl