Incoherent error mitigation
Zero-noise extrapolation for analog blocks
Zero-noise extrapolation (ZNE) is an error mitigation technique in which the expectation value computed at different noise levels is extrapolated to the zero noise limit (ideal expectation) using a class of functions. In digital computing, this is typically implemented by "folding" the circuit at a local (involves inverting gates locally) or global level (involves inverting blocks of gates). This allows to artificially increase the noise levels by integer folds1. In the analog ZNE variation, analog blocks are time stretched to again artificially increase in noise1. Using ZNE on neutral atoms would require stretching the register to scale the interaction hamiltonian appropriately.
from qadence import QuantumModel, QuantumCircuit, kron, chain, AnalogRX, AnalogRZ, PI, BackendName, DiffMode, Z
import numpy as np
analog_block = chain(AnalogRX(PI / 2.0), AnalogRZ(PI))
observable = [Z(0) + Z(1)]
circuit = QuantumCircuit(2, analog_block)
model_noiseless = QuantumModel(
circuit=circuit, observable=observable, backend=BackendName.PULSER, diff_mode=DiffMode.GPSR
)
from qadence.noise import Noise
from qadence_protocols import Mitigations
import torch
noise = Noise(protocol=Noise.DEPOLARIZING, options={"noise_probs": [0.2]})
model = QuantumModel(
circuit=circuit, observable=observable, backend=BackendName.PULSER, diff_mode=DiffMode.GPSR
)
for data_points in [2,5]:
options = {"stretches": torch.linspace(1, 3, data_points)}
mitigate = Mitigations(protocol=Mitigations.ANALOG_ZNE, options=options)
mitigated_expectation = mitigate(model=model, noise=noise)