"""
Janus 噪声模拟器
基于密度矩阵的带噪声量子电路模拟器
"""
from __future__ import annotations
from typing import List, Optional, Union, Dict
import numpy as np
from .density_matrix import DensityMatrix
from .statevector import Statevector
from .result import SimulatorResult, Counts
from .noise import NoiseModel, NoiseChannel
from .exceptions import SimulatorError, ParameterBindingError
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class NoisySimulator:
"""
噪声模拟器
使用密度矩阵进行带噪声的量子电路模拟
Example:
from janus.simulator import NoisySimulator
from janus.simulator.noise import NoiseModel, depolarizing_channel
# 创建噪声模型
noise_model = NoiseModel()
noise_model.add_all_qubit_quantum_error(
depolarizing_channel(0.01), ['cx']
)
# 模拟
sim = NoisySimulator(noise_model)
result = sim.run(circuit, shots=1000)
"""
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def __init__(
self,
noise_model: Optional[NoiseModel] = None,
seed: Optional[Union[int, np.random.Generator]] = None
):
"""
初始化噪声模拟器
Args:
noise_model: 噪声模型
seed: 随机数种子
"""
self._noise_model = noise_model
self._seed = seed
if seed is not None:
if isinstance(seed, np.random.Generator):
self._rng = seed
else:
self._rng = np.random.default_rng(seed)
else:
self._rng = np.random.default_rng()
@property
def noise_model(self) -> Optional[NoiseModel]:
"""获取噪声模型"""
return self._noise_model
@noise_model.setter
def noise_model(self, value: NoiseModel):
"""设置噪声模型"""
self._noise_model = value
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def run(
self,
circuit,
shots: int = 1024,
initial_state: Optional[Union[DensityMatrix, Statevector, np.ndarray]] = None,
parameter_binds: Optional[Dict] = None,
measure_qubits: Optional[List[int]] = None
) -> SimulatorResult:
"""
运行噪声模拟
Args:
circuit: 要模拟的电路
shots: 测量次数
initial_state: 初始状态
parameter_binds: 参数绑定
measure_qubits: 要测量的量子比特
Returns:
SimulatorResult: 模拟结果
"""
# 绑定参数
if parameter_binds:
circuit = self._bind_parameters(circuit, parameter_binds)
# 准备初始状态
dm = self._prepare_initial_state(circuit.n_qubits, initial_state)
dm.seed(self._rng)
# 演化电路（带噪声）
dm = self._evolve_with_noise(dm, circuit)
# 确定测量的量子比特
if measure_qubits is None:
if circuit.measured_qubits is not None:
measure_qubits = circuit.measured_qubits
else:
measure_qubits = list(range(circuit.n_qubits))
# 采样测量（可能带读出错误）
counts = self._sample_with_readout_error(dm, shots, measure_qubits)
# 构建结果
result = SimulatorResult(
counts=dict(counts),
statevector=None, # 噪声模拟不返回状态向量
shots=shots,
metadata={
'num_qubits': circuit.n_qubits,
'circuit_depth': circuit.depth,
'measured_qubits': measure_qubits,
'simulator': 'noisy',
'purity': dm.purity()
}
)
return result
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def density_matrix(
self,
circuit,
initial_state: Optional[Union[DensityMatrix, Statevector, np.ndarray]] = None,
parameter_binds: Optional[Dict] = None
) -> DensityMatrix:
"""
获取电路的最终密度矩阵
Args:
circuit: 要模拟的电路
initial_state: 初始状态
parameter_binds: 参数绑定
Returns:
DensityMatrix: 最终密度矩阵
"""
if parameter_binds:
circuit = self._bind_parameters(circuit, parameter_binds)
dm = self._prepare_initial_state(circuit.n_qubits, initial_state)
return self._evolve_with_noise(dm, circuit)
def _prepare_initial_state(
self,
num_qubits: int,
initial_state: Optional[Union[DensityMatrix, Statevector, np.ndarray]]
) -> DensityMatrix:
"""准备初始状态"""
if initial_state is None:
sv = Statevector.from_int(0, num_qubits)
return DensityMatrix.from_statevector(sv)
elif isinstance(initial_state, DensityMatrix):
if initial_state.num_qubits != num_qubits:
raise SimulatorError(
f"Initial state has {initial_state.num_qubits} qubits, "
f"but circuit has {num_qubits} qubits"
)
return initial_state.copy()
elif isinstance(initial_state, Statevector):
if initial_state.num_qubits != num_qubits:
raise SimulatorError(
f"Initial state has {initial_state.num_qubits} qubits, "
f"but circuit has {num_qubits} qubits"
)
return DensityMatrix.from_statevector(initial_state)
elif isinstance(initial_state, np.ndarray):
if initial_state.ndim == 1:
return DensityMatrix.from_statevector(Statevector(initial_state))
else:
return DensityMatrix(initial_state)
else:
raise SimulatorError(f"Invalid initial state type: {type(initial_state)}")
def _evolve_with_noise(self, dm: DensityMatrix, circuit) -> DensityMatrix:
"""带噪声演化"""
from janus.circuit.parameter import is_parameterized
for inst in circuit.instructions:
if is_parameterized(inst.operation):
raise ParameterBindingError(
f"Circuit contains unbound parameter in gate {inst.name}"
)
# 应用门
matrix = inst.operation.to_matrix()
dm.evolve(matrix, inst.qubits)
# 应用噪声
if self._noise_model is not None:
error = self._noise_model.get_gate_error(inst.name, inst.qubits)
if error is not None:
# 对每个量子比特应用单比特噪声
if error.num_qubits == 1:
for q in inst.qubits:
dm.apply_channel(error.kraus_ops, [q])
else:
# 多比特噪声直接应用到所有相关量子比特
dm.apply_channel(error.kraus_ops, inst.qubits)
return dm
def _sample_with_readout_error(
self,
dm: DensityMatrix,
shots: int,
measure_qubits: List[int]
) -> Counts:
"""带读出错误的采样"""
# 先进行理想采样
counts = dm.sample_counts(shots, measure_qubits)
# 如果没有噪声模型或没有读出错误，直接返回
if self._noise_model is None:
return counts
# 应用读出错误
new_counts = {}
for bitstring, count in counts.items():
# 对每个采样结果应用读出错误
for _ in range(count):
noisy_bits = list(bitstring)
for i, q in enumerate(measure_qubits):
error = self._noise_model.get_readout_error(q)
if error is not None:
p0_given_1, p1_given_0 = error
bit_idx = len(bitstring) - 1 - i
if noisy_bits[bit_idx] == '0':
if self._rng.random() < p1_given_0:
noisy_bits[bit_idx] = '1'
else:
if self._rng.random() < p0_given_1:
noisy_bits[bit_idx] = '0'
noisy_bitstring = ''.join(noisy_bits)
new_counts[noisy_bitstring] = new_counts.get(noisy_bitstring, 0) + 1
return Counts(new_counts)
def _bind_parameters(self, circuit, parameter_binds: Dict):
"""绑定参数"""
from janus.circuit.parameter import Parameter
if hasattr(circuit, 'bind_parameters'):
return circuit.bind_parameters(parameter_binds)
import copy
bound_circuit = copy.deepcopy(circuit)
for inst in bound_circuit.instructions:
new_params = []
for param in inst.operation.params:
if isinstance(param, Parameter):
if param in parameter_binds:
new_params.append(parameter_binds[param])
elif param.name in parameter_binds:
new_params.append(parameter_binds[param.name])
else:
raise ParameterBindingError(
f"No binding provided for parameter {param.name}"
)
else:
new_params.append(param)
inst.operation.params = new_params
return bound_circuit