Struct DensityMatrix 

pub struct DensityMatrix {
    pub n_qubits: u8,
    pub d: usize,
    /* private fields */
}

A density matrix, row-major d × d over the same fixed point as the simulator.

Fields

n_qubits: u8

d: usize

d = 2^n_qubits.

Implementations

impl DensityMatrix

pub fn from_entries(m: Vec<Amp>) -> Option<DensityMatrix>

Build a density matrix from raw row-major entries. m.len() must be d² for a power-of-two d; nothing here checks that the result is a physical state, so callers that construct one by hand own that.

pub fn expect_pauli(&self, ops: &[(u8, Pauli)]) -> i64

Tr(ρ P) for a Pauli string — the mixed-state counterpart of expect_pauli, and what a tomographer actually measures.

pub fn get(&self, r: usize, c: usize) -> Amp

pub fn from_pure(sv: &StateVector) -> DensityMatrix

ρ = |ψ⟩⟨ψ| for a pure state.

pub fn mixture(parts: &[(i64, DensityMatrix)]) -> Option<DensityMatrix>

A classical mixture Σ wᵢ ρᵢ, weights in fixed point (they should sum to ONE; nothing here silently renormalises them).

pub fn trace(&self) -> Amp

Tr ρ, which is ONE for any state.

pub fn purity(&self) -> i64

Tr ρ² — one for a pure state, 1/d for the maximally mixed one. The cheapest honest answer to “how mixed is this?”, and unlike the entropy it needs no eigenvalues, so it stays exactly in the fixed point.

pub fn partial_trace(&self, keep: &[u8]) -> DensityMatrix

Trace out every qubit not in keep, leaving the reduced state of the rest.

This is the operation that makes mixed states unavoidable: the reduced state of half a Bell pair is maximally mixed, and no state vector can say that.

pub fn hash(&self) -> [u8; 32]

Portable identity of the mixture itself.

Trait Implementations

impl Clone for DensityMatrix

fn clone(&self) -> DensityMatrix

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for DensityMatrix

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for DensityMatrix

impl PartialEq for DensityMatrix

fn eq(&self, other: &DensityMatrix) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for DensityMatrix