Qiskit わざとNoisyな回路

参考Qiskitチュートリアル:Qiskit Aer: Simulators

一般に量子回路では，CNOT数が増えるとノイズ増加するので，Qiskitで確認してみる．

IBMQ ExperienceのNotebook上で実行した．

##準備
必要なライブラリをimport

%matplotlib inline
# Importing standard Qiskit libraries and configuring account
from qiskit import QuantumCircuit, execute, Aer, IBMQ
from qiskit.compiler import transpile, assemble
from qiskit.tools.jupyter import *
from qiskit.visualization import *
# Loading your IBM Q account(s)
provider = IBMQ.load_account()

from qiskit.providers.aer import noise
from qiskit import QuantumCircuit, QuantumRegister, ClassicalRegister
from qiskit.tools.visualization import plot_histogram
from qiskit.tools.monitor import job_monitor

provider.backends()

device = provider.get_backend('ibmq_essex')
properties = device.properties()
coupling_map = device.configuration().coupling_map

##関数の定義

注意: CNOTが連続するとQiskitが勝手に消してくれるので，消されないようにqc.barrier()を追加.

def qc_noise(nn):
    q = QuantumRegister(2)
    c = ClassicalRegister(2)
    qc = QuantumCircuit(q,c) 
    qc.h( q[0] )
    qc.cx( q[0], q[1] )
    for ii in range(nn):
        #CNOTが連続するとQiskitが勝手に消してくれるので，消されないようにする
        qc.barrier() 
        qc.cx( q[1], q[0] )
    
    qc.measure(q,c)
    
    return qc

回路の例

nn = 5とすると，

上記のような回路が作られる．

noise_model, basis_gates, simulatorの設定

noise_model = noise.device.basic_device_noise_model(properties)
print(noise_model)

>>NoiseModel:
  Basis gates: ['cx', 'id', 'u2', 'u3']
  Instructions with noise: ['measure', 'id', 'u3', 'cx', 'u2']
  Qubits with noise: [0, 1, 2, 3, 4]
  Specific qubit errors: [('id', [0]), ('id', [1]), ('id', [2]), ('id', [3]), ('id', [4]), ('u2', [0]), ('u2', [1]), ('u2', [2]), ('u2', [3]), ('u2', [4]), ('u3', [0]), ('u3', [1]), ('u3', [2]), ('u3', [3]), ('u3', [4]), ('cx', [0, 1]), ('cx', [1, 0]), ('cx', [1, 2]), ('cx', [1, 3]), ('cx', [2, 1]), ('cx', [3, 1]), ('cx', [3, 4]), ('cx', [4, 3]), ('measure', [0]), ('measure', [1]), ('measure', [2]), ('measure', [3]), ('measure', [4])]

# Get the basis gates for the noise model
basis_gates = noise_model.basis_gates

# Select the QasmSimulator from the Aer provider
simulator = Aer.get_backend('qasm_simulator')

測定結果

result_noise = execute(qc_noise(0), simulator, 
                       noise_model=noise_model,
                       coupling_map=coupling_map,
                       basis_gates=basis_gates).result()
counts_noise = result_noise.get_counts()
plot_histogram(counts_noise, title="Counts for qc_noise(0)")

qc_noise(10), qc_noise(100), qc_noise(500)で測定してみる．

nn=500になると，大きく結果が異なってしまう．