qig

Quantum information geometry primitives.

Install

[dependencies]
qig = "0.1"

Example

use qig::fidelity;

let rho = [0.9, 0.1]; // Diagonal of density matrix
let sigma = [0.1, 0.9];

// Classical fidelity (Bhattacharyya coefficient)
let f = fidelity(&rho, &sigma);
assert!(f > 0.0 && f < 1.0);

Examples

Runnable examples live in examples/. These are mathematical demonstrations: each verifies a geometric identity that motivates the library, not a production workload.

• bures_manifold parameterizes the Bures manifold via the Bloch sphere (qig + skel), the natural geometry for comparing single-qubit states.
• bures_wasserstein shows the Bures distance between density matrices equals the L2-Wasserstein distance between the corresponding Gaussians, the bridge from quantum fidelity to optimal transport.
• classical_quantum_divergences relates classical and quantum divergences for diagonal states (logp + infogeom + qig), showing the classical case as a special case of the quantum one.
• flow_on_states runs flow matching between quantum states on the Bloch sphere (qig + flowmatch), generative modeling applied to state preparation.
• random_density_matrices samples random density matrices and reports the random-matrix-theory eigenvalue statistics used to reason about entanglement and typicality.

License

MIT OR Apache-2.0