quantrs2_device/vqa_support/
circuits.rs

1//! Parametric circuit definitions and execution for VQA
2//!
3//! This module provides parametric quantum circuits commonly used
4//! in variational quantum algorithms.
5
6use crate::DeviceResult;
7use quantrs2_core::qubit::QubitId;
8use scirs2_core::random::prelude::*;
9use std::collections::HashMap;
10
11/// Parametric circuit configuration
12#[derive(Debug, Clone)]
13pub struct ParametricCircuitConfig {
14    /// Number of qubits
15    pub num_qubits: usize,
16    /// Circuit depth
17    pub depth: usize,
18    /// Ansatz type
19    pub ansatz: AnsatzType,
20    /// Parameter mapping
21    pub parameter_map: HashMap<String, usize>,
22}
23
24/// Available ansatz types
25#[derive(Debug, Clone)]
26pub enum AnsatzType {
27    /// Hardware efficient ansatz
28    HardwareEfficient,
29    /// QAOA ansatz
30    QAOA,
31    /// Real amplitudes ansatz
32    RealAmplitudes,
33    /// Custom ansatz
34    Custom(String),
35}
36
37impl Default for ParametricCircuitConfig {
38    fn default() -> Self {
39        Self {
40            num_qubits: 4,
41            depth: 3,
42            ansatz: AnsatzType::HardwareEfficient,
43            parameter_map: HashMap::new(),
44        }
45    }
46}
47
48/// Parametric circuit representation
49#[derive(Debug, Clone)]
50pub struct ParametricCircuit {
51    /// Configuration
52    pub config: ParametricCircuitConfig,
53    /// Current parameters
54    pub parameters: Vec<f64>,
55    /// Parameter bounds
56    pub bounds: Vec<(f64, f64)>,
57    /// Circuit structure metadata
58    pub structure: CircuitStructure,
59}
60
61/// Circuit structure metadata
62#[derive(Debug, Clone)]
63pub struct CircuitStructure {
64    /// Gate sequence description
65    pub gates: Vec<ParametricGate>,
66    /// Qubit connectivity required
67    pub connectivity: Vec<(usize, usize)>,
68    /// Circuit depth estimate
69    pub estimated_depth: usize,
70}
71
72/// Parametric gate representation
73#[derive(Debug, Clone)]
74pub struct ParametricGate {
75    /// Gate type
76    pub gate_type: GateType,
77    /// Qubits involved
78    pub qubits: Vec<usize>,
79    /// Parameter indices
80    pub parameter_indices: Vec<usize>,
81    /// Gate metadata
82    pub metadata: std::collections::HashMap<String, String>,
83}
84
85/// Gate types for VQA circuits
86#[derive(Debug, Clone, PartialEq, Eq)]
87pub enum GateType {
88    /// Rotation X gate
89    RX,
90    /// Rotation Y gate
91    RY,
92    /// Rotation Z gate
93    RZ,
94    /// CNOT gate
95    CNOT,
96    /// CZ gate
97    CZ,
98    /// Hadamard gate
99    H,
100    /// Pauli X gate
101    X,
102    /// Pauli Y gate
103    Y,
104    /// Pauli Z gate
105    Z,
106    /// Custom parameterized gate
107    Custom(String),
108}
109
110impl ParametricCircuit {
111    /// Create new parametric circuit
112    pub fn new(config: ParametricCircuitConfig) -> Self {
113        let (num_params, structure) = Self::generate_circuit_structure(&config);
114
115        Self {
116            config,
117            parameters: vec![0.0; num_params],
118            bounds: vec![(-std::f64::consts::PI, std::f64::consts::PI); num_params],
119            structure,
120        }
121    }
122
123    /// Generate circuit structure based on ansatz type
124    fn generate_circuit_structure(config: &ParametricCircuitConfig) -> (usize, CircuitStructure) {
125        match &config.ansatz {
126            AnsatzType::HardwareEfficient => Self::generate_hardware_efficient(config),
127            AnsatzType::QAOA => Self::generate_qaoa(config),
128            AnsatzType::RealAmplitudes => Self::generate_real_amplitudes(config),
129            AnsatzType::Custom(name) => Self::generate_custom(config, name),
130        }
131    }
132
133    /// Generate hardware-efficient ansatz
134    fn generate_hardware_efficient(config: &ParametricCircuitConfig) -> (usize, CircuitStructure) {
135        let mut gates = Vec::new();
136        let mut connectivity = Vec::new();
137        let mut param_count = 0;
138
139        for layer in 0..config.depth {
140            // Single-qubit rotations
141            for qubit in 0..config.num_qubits {
142                // RY rotation for each qubit
143                gates.push(ParametricGate {
144                    gate_type: GateType::RY,
145                    qubits: vec![qubit],
146                    parameter_indices: vec![param_count],
147                    metadata: std::iter::once(("layer".to_string(), layer.to_string())).collect(),
148                });
149                param_count += 1;
150
151                // RZ rotation for each qubit
152                gates.push(ParametricGate {
153                    gate_type: GateType::RZ,
154                    qubits: vec![qubit],
155                    parameter_indices: vec![param_count],
156                    metadata: std::iter::once(("layer".to_string(), layer.to_string())).collect(),
157                });
158                param_count += 1;
159            }
160
161            // Entangling layer with CNOT gates
162            for qubit in 0..config.num_qubits {
163                let target = (qubit + 1) % config.num_qubits;
164
165                gates.push(ParametricGate {
166                    gate_type: GateType::CNOT,
167                    qubits: vec![qubit, target],
168                    parameter_indices: vec![], // Non-parametric
169                    metadata: std::iter::once(("layer".to_string(), layer.to_string())).collect(),
170                });
171
172                connectivity.push((qubit, target));
173            }
174        }
175
176        let structure = CircuitStructure {
177            gates,
178            connectivity,
179            estimated_depth: config.depth * 3, // RY + RZ + CNOT per layer
180        };
181
182        (param_count, structure)
183    }
184
185    /// Generate QAOA ansatz
186    fn generate_qaoa(config: &ParametricCircuitConfig) -> (usize, CircuitStructure) {
187        let mut gates = Vec::new();
188        let mut connectivity = Vec::new();
189        let param_count = 2 * config.depth; // 2 parameters per layer (γ, β)
190
191        // Initial superposition layer
192        for qubit in 0..config.num_qubits {
193            gates.push(ParametricGate {
194                gate_type: GateType::H,
195                qubits: vec![qubit],
196                parameter_indices: vec![],
197                metadata: std::iter::once(("layer".to_string(), "initial".to_string())).collect(),
198            });
199        }
200
201        // QAOA layers
202        for layer in 0..config.depth {
203            let gamma_idx = layer * 2;
204            let beta_idx = layer * 2 + 1;
205
206            // Problem Hamiltonian layer (ZZ interactions)
207            for qubit in 0..config.num_qubits {
208                let neighbor = (qubit + 1) % config.num_qubits;
209
210                // ZZ interaction implemented as CNOT-RZ-CNOT
211                gates.push(ParametricGate {
212                    gate_type: GateType::CNOT,
213                    qubits: vec![qubit, neighbor],
214                    parameter_indices: vec![],
215                    metadata: [
216                        ("layer".to_string(), layer.to_string()),
217                        ("type".to_string(), "problem".to_string()),
218                    ]
219                    .into_iter()
220                    .collect(),
221                });
222
223                gates.push(ParametricGate {
224                    gate_type: GateType::RZ,
225                    qubits: vec![neighbor],
226                    parameter_indices: vec![gamma_idx],
227                    metadata: [
228                        ("layer".to_string(), layer.to_string()),
229                        ("type".to_string(), "problem".to_string()),
230                    ]
231                    .into_iter()
232                    .collect(),
233                });
234
235                gates.push(ParametricGate {
236                    gate_type: GateType::CNOT,
237                    qubits: vec![qubit, neighbor],
238                    parameter_indices: vec![],
239                    metadata: [
240                        ("layer".to_string(), layer.to_string()),
241                        ("type".to_string(), "problem".to_string()),
242                    ]
243                    .into_iter()
244                    .collect(),
245                });
246
247                connectivity.push((qubit, neighbor));
248            }
249
250            // Mixer Hamiltonian layer (X rotations)
251            for qubit in 0..config.num_qubits {
252                gates.push(ParametricGate {
253                    gate_type: GateType::RX,
254                    qubits: vec![qubit],
255                    parameter_indices: vec![beta_idx],
256                    metadata: [
257                        ("layer".to_string(), layer.to_string()),
258                        ("type".to_string(), "mixer".to_string()),
259                    ]
260                    .into_iter()
261                    .collect(),
262                });
263            }
264        }
265
266        let structure = CircuitStructure {
267            gates,
268            connectivity,
269            estimated_depth: config.num_qubits
270                + config.depth * (3 * config.num_qubits + config.num_qubits), // H + (CNOT-RZ-CNOT + RX) per layer
271        };
272
273        (param_count, structure)
274    }
275
276    /// Generate real amplitudes ansatz
277    fn generate_real_amplitudes(config: &ParametricCircuitConfig) -> (usize, CircuitStructure) {
278        let mut gates = Vec::new();
279        let mut connectivity = Vec::new();
280        let mut param_count = 0;
281
282        for layer in 0..config.depth {
283            // RY rotations only (for real amplitudes)
284            for qubit in 0..config.num_qubits {
285                gates.push(ParametricGate {
286                    gate_type: GateType::RY,
287                    qubits: vec![qubit],
288                    parameter_indices: vec![param_count],
289                    metadata: std::iter::once(("layer".to_string(), layer.to_string())).collect(),
290                });
291                param_count += 1;
292            }
293
294            // Linear entangling layer
295            for qubit in 0..(config.num_qubits - 1) {
296                gates.push(ParametricGate {
297                    gate_type: GateType::CNOT,
298                    qubits: vec![qubit, qubit + 1],
299                    parameter_indices: vec![],
300                    metadata: std::iter::once(("layer".to_string(), layer.to_string())).collect(),
301                });
302                connectivity.push((qubit, qubit + 1));
303            }
304        }
305
306        // Final RY layer
307        for qubit in 0..config.num_qubits {
308            gates.push(ParametricGate {
309                gate_type: GateType::RY,
310                qubits: vec![qubit],
311                parameter_indices: vec![param_count],
312                metadata: std::iter::once(("layer".to_string(), "final".to_string())).collect(),
313            });
314            param_count += 1;
315        }
316
317        let structure = CircuitStructure {
318            gates,
319            connectivity,
320            estimated_depth: config.depth * 2 + 1, // RY + CNOT per layer + final RY
321        };
322
323        (param_count, structure)
324    }
325
326    /// Generate custom ansatz
327    const fn generate_custom(
328        _config: &ParametricCircuitConfig,
329        _name: &str,
330    ) -> (usize, CircuitStructure) {
331        // Placeholder for custom ansatz - would be implemented based on specific requirements
332        let structure = CircuitStructure {
333            gates: Vec::new(),
334            connectivity: Vec::new(),
335            estimated_depth: 1,
336        };
337        (0, structure)
338    }
339
340    /// Update circuit parameters
341    pub fn set_parameters(&mut self, params: Vec<f64>) -> DeviceResult<()> {
342        if params.len() != self.parameters.len() {
343            return Err(crate::DeviceError::InvalidInput(format!(
344                "Parameter count mismatch: expected {}, got {}",
345                self.parameters.len(),
346                params.len()
347            )));
348        }
349        self.parameters = params;
350        Ok(())
351    }
352
353    /// Get parameter count
354    pub fn parameter_count(&self) -> usize {
355        self.parameters.len()
356    }
357
358    /// Get circuit depth estimate
359    pub const fn circuit_depth(&self) -> usize {
360        self.structure.estimated_depth
361    }
362
363    /// Get required connectivity
364    pub fn required_connectivity(&self) -> &[(usize, usize)] {
365        &self.structure.connectivity
366    }
367
368    /// Get gate sequence
369    pub fn gates(&self) -> &[ParametricGate] {
370        &self.structure.gates
371    }
372
373    /// Generate random initial parameters
374    pub fn random_parameters(&self) -> Vec<f64> {
375        use scirs2_core::random::prelude::*;
376        let mut rng = thread_rng();
377
378        self.bounds
379            .iter()
380            .map(|(min, max)| rng.gen_range(*min..*max))
381            .collect()
382    }
383
384    /// Set parameter bounds
385    pub fn set_bounds(&mut self, bounds: Vec<(f64, f64)>) -> DeviceResult<()> {
386        if bounds.len() != self.parameters.len() {
387            return Err(crate::DeviceError::InvalidInput(
388                "Bounds count mismatch".to_string(),
389            ));
390        }
391        self.bounds = bounds;
392        Ok(())
393    }
394
395    /// Validate parameters are within bounds
396    pub fn validate_parameters(&self) -> DeviceResult<()> {
397        for (i, (&param, &(min, max))) in self.parameters.iter().zip(self.bounds.iter()).enumerate()
398        {
399            if param < min || param > max {
400                return Err(crate::DeviceError::InvalidInput(format!(
401                    "Parameter {i} ({param}) out of bounds [{min}, {max}]"
402                )));
403            }
404        }
405        Ok(())
406    }
407}
quantrs2_device/vqa_support/circuits.rs

quantrs2_device/vqa_support/
circuits.rs
