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//! Noise model types and Kraus operator implementations
use crate::error::QuantRS2Result;
use scirs2_core::ndarray::Array2;
use scirs2_core::Complex64 as Complex;
/// Noise model types for quantum systems
#[derive(Debug, Clone, Copy, PartialEq)]
pub enum NoiseModel {
/// Depolarizing channel: ρ → (1-p)ρ + p(I/d)
Depolarizing { probability: f64 },
/// Amplitude damping: models energy dissipation
AmplitudeDamping { gamma: f64 },
/// Phase damping: models loss of quantum coherence
PhaseDamping { lambda: f64 },
/// Bit flip channel: X error with probability p
BitFlip { probability: f64 },
/// Phase flip channel: Z error with probability p
PhaseFlip { probability: f64 },
/// Bit-phase flip channel: Y error with probability p
BitPhaseFlip { probability: f64 },
/// Pauli channel: general combination of X, Y, Z errors
Pauli { p_x: f64, p_y: f64, p_z: f64 },
/// Thermal relaxation (T1 and T2 processes)
ThermalRelaxation { t1: f64, t2: f64, time: f64 },
}
impl NoiseModel {
/// Get Kraus operators for this noise model
pub fn kraus_operators(&self) -> Vec<Array2<Complex>> {
match self {
Self::Depolarizing { probability } => {
let p = *probability;
let sqrt_p = p.sqrt();
let sqrt_1_p = (1.0 - p).sqrt();
vec![
Array2::from_shape_vec(
(2, 2),
vec![
Complex::new(sqrt_1_p, 0.0),
Complex::new(0.0, 0.0),
Complex::new(0.0, 0.0),
Complex::new(sqrt_1_p, 0.0),
],
)
.expect("2x2 matrix creation"),
Array2::from_shape_vec(
(2, 2),
vec![
Complex::new(0.0, 0.0),
Complex::new(sqrt_p / 3.0_f64.sqrt(), 0.0),
Complex::new(sqrt_p / 3.0_f64.sqrt(), 0.0),
Complex::new(0.0, 0.0),
],
)
.expect("2x2 matrix creation"),
Array2::from_shape_vec(
(2, 2),
vec![
Complex::new(0.0, 0.0),
Complex::new(0.0, -sqrt_p / 3.0_f64.sqrt()),
Complex::new(0.0, sqrt_p / 3.0_f64.sqrt()),
Complex::new(0.0, 0.0),
],
)
.expect("2x2 matrix creation"),
Array2::from_shape_vec(
(2, 2),
vec![
Complex::new(sqrt_p / 3.0_f64.sqrt(), 0.0),
Complex::new(0.0, 0.0),
Complex::new(0.0, 0.0),
Complex::new(-sqrt_p / 3.0_f64.sqrt(), 0.0),
],
)
.expect("2x2 matrix creation"),
]
}
Self::AmplitudeDamping { gamma } => {
let g = *gamma;
vec![
Array2::from_shape_vec(
(2, 2),
vec![
Complex::new(1.0, 0.0),
Complex::new(0.0, 0.0),
Complex::new(0.0, 0.0),
Complex::new((1.0 - g).sqrt(), 0.0),
],
)
.expect("2x2 matrix creation"),
Array2::from_shape_vec(
(2, 2),
vec![
Complex::new(0.0, 0.0),
Complex::new(g.sqrt(), 0.0),
Complex::new(0.0, 0.0),
Complex::new(0.0, 0.0),
],
)
.expect("2x2 matrix creation"),
]
}
Self::PhaseDamping { lambda } => {
let l = *lambda;
vec![
Array2::from_shape_vec(
(2, 2),
vec![
Complex::new(1.0, 0.0),
Complex::new(0.0, 0.0),
Complex::new(0.0, 0.0),
Complex::new((1.0 - l).sqrt(), 0.0),
],
)
.expect("2x2 matrix creation"),
Array2::from_shape_vec(
(2, 2),
vec![
Complex::new(0.0, 0.0),
Complex::new(0.0, 0.0),
Complex::new(0.0, 0.0),
Complex::new(l.sqrt(), 0.0),
],
)
.expect("2x2 matrix creation"),
]
}
Self::BitFlip { probability } => {
let p = *probability;
vec![
Array2::from_shape_vec(
(2, 2),
vec![
Complex::new((1.0 - p).sqrt(), 0.0),
Complex::new(0.0, 0.0),
Complex::new(0.0, 0.0),
Complex::new((1.0 - p).sqrt(), 0.0),
],
)
.expect("2x2 matrix creation"),
Array2::from_shape_vec(
(2, 2),
vec![
Complex::new(0.0, 0.0),
Complex::new(p.sqrt(), 0.0),
Complex::new(p.sqrt(), 0.0),
Complex::new(0.0, 0.0),
],
)
.expect("2x2 matrix creation"),
]
}
Self::PhaseFlip { probability } => {
let p = *probability;
vec![
Array2::from_shape_vec(
(2, 2),
vec![
Complex::new((1.0 - p).sqrt(), 0.0),
Complex::new(0.0, 0.0),
Complex::new(0.0, 0.0),
Complex::new((1.0 - p).sqrt(), 0.0),
],
)
.expect("2x2 matrix creation"),
Array2::from_shape_vec(
(2, 2),
vec![
Complex::new(p.sqrt(), 0.0),
Complex::new(0.0, 0.0),
Complex::new(0.0, 0.0),
Complex::new(-p.sqrt(), 0.0),
],
)
.expect("2x2 matrix creation"),
]
}
Self::BitPhaseFlip { probability } => {
let p = *probability;
vec![
Array2::from_shape_vec(
(2, 2),
vec![
Complex::new((1.0 - p).sqrt(), 0.0),
Complex::new(0.0, 0.0),
Complex::new(0.0, 0.0),
Complex::new((1.0 - p).sqrt(), 0.0),
],
)
.expect("2x2 matrix creation"),
Array2::from_shape_vec(
(2, 2),
vec![
Complex::new(0.0, 0.0),
Complex::new(0.0, -p.sqrt()),
Complex::new(0.0, p.sqrt()),
Complex::new(0.0, 0.0),
],
)
.expect("2x2 matrix creation"),
]
}
Self::Pauli { p_x, p_y, p_z } => {
let p_i = 1.0 - p_x - p_y - p_z;
vec![
Array2::from_shape_vec(
(2, 2),
vec![
Complex::new(p_i.sqrt(), 0.0),
Complex::new(0.0, 0.0),
Complex::new(0.0, 0.0),
Complex::new(p_i.sqrt(), 0.0),
],
)
.expect("2x2 matrix creation"),
Array2::from_shape_vec(
(2, 2),
vec![
Complex::new(0.0, 0.0),
Complex::new(p_x.sqrt(), 0.0),
Complex::new(p_x.sqrt(), 0.0),
Complex::new(0.0, 0.0),
],
)
.expect("2x2 matrix creation"),
Array2::from_shape_vec(
(2, 2),
vec![
Complex::new(0.0, 0.0),
Complex::new(0.0, -p_y.sqrt()),
Complex::new(0.0, p_y.sqrt()),
Complex::new(0.0, 0.0),
],
)
.expect("2x2 matrix creation"),
Array2::from_shape_vec(
(2, 2),
vec![
Complex::new(p_z.sqrt(), 0.0),
Complex::new(0.0, 0.0),
Complex::new(0.0, 0.0),
Complex::new(-p_z.sqrt(), 0.0),
],
)
.expect("2x2 matrix creation"),
]
}
Self::ThermalRelaxation { t1, t2, time } => {
let p1 = 1.0 - (-time / t1).exp();
let p2 = 1.0 - (-time / t2).exp();
let gamma = p1;
let lambda = (p2 - p1 / 2.0).max(0.0);
vec![
Array2::from_shape_vec(
(2, 2),
vec![
Complex::new(1.0, 0.0),
Complex::new(0.0, 0.0),
Complex::new(0.0, 0.0),
Complex::new((1.0 - gamma) * (1.0 - lambda).sqrt(), 0.0),
],
)
.expect("2x2 matrix creation"),
Array2::from_shape_vec(
(2, 2),
vec![
Complex::new(0.0, 0.0),
Complex::new(gamma.sqrt(), 0.0),
Complex::new(0.0, 0.0),
Complex::new(0.0, 0.0),
],
)
.expect("2x2 matrix creation"),
]
}
}
}
/// Apply noise model to a density matrix
pub fn apply_to_density_matrix(
&self,
rho: &Array2<Complex>,
) -> QuantRS2Result<Array2<Complex>> {
let kraus_ops = self.kraus_operators();
let dim = rho.nrows();
let mut result = Array2::<Complex>::zeros((dim, dim));
for k in &kraus_ops {
let k_rho = k.dot(rho);
let k_dag = k.t().mapv(|x| x.conj());
let k_rho_k_dag = k_rho.dot(&k_dag);
result = result + k_rho_k_dag;
}
Ok(result)
}
}