quantrs2_core/error_correction/
concatenated.rs

1//! Concatenated quantum error correction codes
2
3use super::pauli::{Pauli, PauliString};
4use super::stabilizer::StabilizerCode;
5use crate::error::{QuantRS2Error, QuantRS2Result};
6use scirs2_core::Complex64;
7
8/// Concatenated quantum error correction codes
9#[derive(Debug, Clone)]
10pub struct ConcatenatedCode {
11    /// Inner code (applied first)
12    pub inner_code: StabilizerCode,
13    /// Outer code (applied to logical qubits of inner code)
14    pub outer_code: StabilizerCode,
15}
16
17impl ConcatenatedCode {
18    /// Create a new concatenated code
19    pub const fn new(inner_code: StabilizerCode, outer_code: StabilizerCode) -> Self {
20        Self {
21            inner_code,
22            outer_code,
23        }
24    }
25
26    /// Get total number of physical qubits
27    pub const fn total_qubits(&self) -> usize {
28        self.inner_code.n * self.outer_code.n
29    }
30
31    /// Get number of logical qubits
32    pub const fn logical_qubits(&self) -> usize {
33        self.inner_code.k * self.outer_code.k
34    }
35
36    /// Get effective distance
37    pub const fn distance(&self) -> usize {
38        self.inner_code.d * self.outer_code.d
39    }
40
41    /// Encode a logical state
42    pub fn encode(&self, logical_state: &[Complex64]) -> QuantRS2Result<Vec<Complex64>> {
43        if logical_state.len() != 1 << self.logical_qubits() {
44            return Err(QuantRS2Error::InvalidInput(
45                "Logical state dimension mismatch".to_string(),
46            ));
47        }
48
49        // First encode with outer code
50        let outer_encoded = self.encode_with_code(logical_state, &self.outer_code)?;
51
52        // Then encode each logical qubit of outer code with inner code
53        let mut final_encoded = vec![Complex64::new(0.0, 0.0); 1 << self.total_qubits()];
54
55        // This is a simplified encoding - proper implementation would require
56        // tensor product operations and proper state manipulation
57        for (i, &amplitude) in outer_encoded.iter().enumerate() {
58            if amplitude.norm() > 1e-10 {
59                final_encoded[i * (1 << self.inner_code.n)] = amplitude;
60            }
61        }
62
63        Ok(final_encoded)
64    }
65
66    /// Correct errors using concatenated decoding
67    pub fn correct_error(
68        &self,
69        encoded_state: &[Complex64],
70        error: &PauliString,
71    ) -> QuantRS2Result<Vec<Complex64>> {
72        if error.paulis.len() != self.total_qubits() {
73            return Err(QuantRS2Error::InvalidInput(
74                "Error must act on all physical qubits".to_string(),
75            ));
76        }
77
78        // Simplified error correction - apply error and return corrected state
79        // In practice, would implement syndrome extraction and decoding
80        let mut corrected = encoded_state.to_vec();
81
82        // Apply error (simplified)
83        for (i, &pauli) in error.paulis.iter().enumerate() {
84            if pauli != Pauli::I && i < corrected.len() {
85                // Simplified error application
86                corrected[i] *= -1.0;
87            }
88        }
89
90        Ok(corrected)
91    }
92
93    /// Encode with a specific code
94    fn encode_with_code(
95        &self,
96        state: &[Complex64],
97        code: &StabilizerCode,
98    ) -> QuantRS2Result<Vec<Complex64>> {
99        // Simplified encoding - proper implementation would use stabilizer formalism
100        let mut encoded = vec![Complex64::new(0.0, 0.0); 1 << code.n];
101
102        for (i, &amplitude) in state.iter().enumerate() {
103            if i < encoded.len() {
104                encoded[i * (1 << (code.n - code.k))] = amplitude;
105            }
106        }
107
108        Ok(encoded)
109    }
110}
quantrs2_core/error_correction/concatenated.rs

quantrs2_core/error_correction/
concatenated.rs
