quantrs2_core/error_correction/
ldpc.rs

1//! Quantum Low-Density Parity-Check (LDPC) codes
2
3use super::pauli::{Pauli, PauliString};
4use super::stabilizer::StabilizerCode;
5use crate::error::QuantRS2Result;
6
7/// Quantum Low-Density Parity-Check (LDPC) codes
8#[derive(Debug, Clone)]
9pub struct QuantumLDPCCode {
10    /// Number of physical qubits
11    pub n: usize,
12    /// Number of logical qubits
13    pub k: usize,
14    /// Maximum stabilizer weight
15    pub max_weight: usize,
16    /// X-type stabilizers
17    pub x_stabilizers: Vec<PauliString>,
18    /// Z-type stabilizers
19    pub z_stabilizers: Vec<PauliString>,
20}
21
22impl QuantumLDPCCode {
23    /// Create a bicycle code (CSS LDPC)
24    pub fn bicycle_code(a: usize, b: usize) -> Self {
25        let n = 2 * a * b;
26        let k = 2;
27        let max_weight = 6; // Typical for bicycle codes
28
29        let mut x_stabilizers = Vec::new();
30        let mut z_stabilizers = Vec::new();
31
32        // Generate bicycle code stabilizers
33        for i in 0..a {
34            for j in 0..b {
35                // X-type stabilizer
36                let mut x_paulis = vec![Pauli::I; n];
37                let base_idx = i * b + j;
38
39                // Create a 6-cycle in the Cayley graph
40                x_paulis[base_idx] = Pauli::X;
41                x_paulis[(base_idx + 1) % (a * b)] = Pauli::X;
42                x_paulis[(base_idx + b) % (a * b)] = Pauli::X;
43                x_paulis[a * b + base_idx] = Pauli::X;
44                x_paulis[a * b + (base_idx + 1) % (a * b)] = Pauli::X;
45                x_paulis[a * b + (base_idx + b) % (a * b)] = Pauli::X;
46
47                x_stabilizers.push(PauliString::new(x_paulis));
48
49                // Z-type stabilizer (similar structure)
50                let mut z_paulis = vec![Pauli::I; n];
51                z_paulis[base_idx] = Pauli::Z;
52                z_paulis[(base_idx + a) % (a * b)] = Pauli::Z;
53                z_paulis[(base_idx + 1) % (a * b)] = Pauli::Z;
54                z_paulis[a * b + base_idx] = Pauli::Z;
55                z_paulis[a * b + (base_idx + a) % (a * b)] = Pauli::Z;
56                z_paulis[a * b + (base_idx + 1) % (a * b)] = Pauli::Z;
57
58                z_stabilizers.push(PauliString::new(z_paulis));
59            }
60        }
61
62        Self {
63            n,
64            k,
65            max_weight,
66            x_stabilizers,
67            z_stabilizers,
68        }
69    }
70
71    /// Convert to stabilizer code representation
72    pub fn to_stabilizer_code(&self) -> QuantRS2Result<StabilizerCode> {
73        let mut stabilizers = self.x_stabilizers.clone();
74        stabilizers.extend(self.z_stabilizers.clone());
75
76        // Create logical operators (simplified)
77        let logical_x = vec![
78            PauliString::new(vec![Pauli::X; self.n]),
79            PauliString::new(vec![Pauli::Y; self.n]),
80        ];
81        let logical_z = vec![
82            PauliString::new(vec![Pauli::Z; self.n]),
83            PauliString::new(vec![Pauli::Y; self.n]),
84        ];
85
86        StabilizerCode::new(
87            self.n,
88            self.k,
89            4, // Typical distance for bicycle codes
90            stabilizers,
91            logical_x,
92            logical_z,
93        )
94    }
95}
quantrs2_core/error_correction/ldpc.rs

quantrs2_core/error_correction/
ldpc.rs
