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Quantum Machine Learning

What is Quantum ML? Using quantum computers for machine learning tasks, potentially offering speedups for certain algorithms.

Quantum Computing Basics

ConceptDescription
QubitQuantum bit (superposition of 0 and 1)
SuperpositionState can be both 0 and 1
EntanglementQubits correlated across distance
InterferenceAmplify correct answers
DecoherenceQuantum state collapse (noise)

Quantum Hardware

CompanyQubitsType
IBM1000+Superconducting
Google100Superconducting
IonQ32Trapped ion
Rigetti84Superconducting
D-Wave5000+Quantum annealing

QML Approaches

Variational Quantum Circuits

import pennylane as qml

dev = qml.device("default.qubit", wires=4)

@qml.qnode(dev)
def quantum_classifier(inputs, weights):
    # Encode classical data
    qml.AngleEmbedding(inputs, wires=range(4))

    # Parameterized quantum layers
    qml.StronglyEntanglingLayers(weights, wires=range(4))

    # Measurement
    return qml.expval(qml.PauliZ(0))

# Train like classical NN
optimizer = qml.GradientDescentOptimizer()
for epoch in range(100):
    weights = optimizer.step(cost_fn, weights)

Quantum Kernels Use quantum computer to compute kernel for SVM:

from qiskit_machine_learning.kernels import FidelityQuantumKernel

kernel = FidelityQuantumKernel(feature_map=ZZFeatureMap(4))
svc = SVC(kernel=kernel.evaluate)
svc.fit(X_train, y_train)

Current Limitations

LimitationImpact
Noise (NISQ era)Limits circuit depth
Qubit countSmall problems only
Error correctionNot yet scalable
Classical simulationCan simulate small circuits

Realistic Timeline

MilestoneEstimated
Quantum advantage (contrived)Now
Useful advantage2028-2035
Large-scale QML2035+

Where to Experiment

PlatformAccess
IBM QuantumFree tier
Amazon BraketAWS
Google CirqSimulator + hardware
Xanadu CloudPhotonic

Best Practices

quantumqmlquantum ml

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