simulation

# Cirq 中的模拟 本指南涵盖量子电路模拟，包括精确模拟和噪声模拟、参数扫描以及量子虚拟机 (QVM)。 ## 精确模拟 ### 基础模拟 python import cirq import numpy as np # 创建电路 q0, q1 = cirq.LineQubit.range(2) circuit = cirq.Circuit( cirq.H(q0), cirq.CNOT(q0, q1), cirq.measure(q0, q1, key='result') ) # 模拟 simulator = cirq.Simulator() result = simulator.run(circuit, repetitions=1000) # 获取测量结果 print(result.histogram(key='result')) ### 态矢量模拟 python # 不进行测量以获取最终状态 simulator = cirq.Simulator() result = simulator.simulate(circuit_without_measurement) # 访问态矢量 state_vector = result.final_state_vector print(f"态矢量: {state_vector}") # 获取振幅 print(f"|00⟩ 的振幅: {state_vector[0]}") print(f"|11⟩ 的振幅: {state_vector[3]}") ### 密度矩阵模拟 python # 使用密度矩阵模拟器处理混合态 simulator = cirq.DensityMatrixSimulator() result = simulator.simulate(circuit) # 访问密度矩阵 density_matrix = result.final_density_matrix print(f"密度矩阵形状: {density_matrix.shape}") ### 逐步模拟 python # 逐时刻模拟 simulator = cirq.Simulator() for step in simulator.simulate_moment_steps(circuit): print(f"时刻 {step.moment} 后的状态: {step.state_vector()}") ## 采样与测量 ### 多次运行 (Shots) python # 多次运行电路 result = simulator.run(circuit, repetitions=10000) # 访问测量计数 counts = result.histogram(key='result') print(f"测量计数: {counts}") # 获取原始测量数据 measurements = result.measurements['result'] print(f"形状: {measurements.shape}") # (重复次数, 量子比特数) ### 期望值 python # 测量可观测量期望值 from cirq import PauliString observable = PauliString({q0: cirq.Z, q1: cirq.Z}) result = simulator.simulate_expectation_values( circuit, observables=[observable] ) print(f"⟨ZZ⟩ = {result[0]}") ## 参数扫描 ### 参数扫描 python import sympy # 创建参数化电路 theta = sympy.Symbol('theta') q = cirq.LineQubit(0) circuit = cirq.Circuit( cirq.ry(theta)(q), cirq.measure(q, key='m') ) # 定义参数扫描 sweep = cirq.Linspace(key='theta', start=0, stop=2*np.pi, length=50) # 运行扫描 sim