What is quantum machine learning?

QML applies quantum computing to machine learning, or uses ML to optimize quantum systems. The field has attracted significant hype, but also serious research. Here's what's actually being studied:

Variational quantum circuits

Parameterized quantum circuits trained by gradient descent, analogous to neural networks. The parameters are updated classically while the circuit runs on quantum hardware. These are the most practical QML models on current NISQ devices.

Quantum kernels

Quantum computers can efficiently compute certain kernel functions that are exponentially expensive classically. Quantum kernel methods use this to power support vector machines and other kernel-based classifiers. The catch: quantum-accessible data is needed for practical speedup.

Quantum neural networks

Layered variational circuits designed to mimic the structure of classical neural networks. They suffer from barren plateaus (vanishing gradients at scale) - an active research problem. Promising in theory, limited in practice so far.

QML is still a research-stage field. No QML model currently outperforms classical ML on a real-world task of practical scale. That may change as hardware improves - and the theoretical foundations are solid - but courses that promise job-ready QML skills should be read skeptically.

Quantum machine learning courses

Sorted by rating. Covers variational circuits, PennyLane, quantum kernels, and hybrid quantum-classical models.

Best frameworks for quantum ML

The three tools that dominate QML development today.

Qiskit Machine Learning

IBM's QML extension for Qiskit. Integrates with scikit-learn and provides implementations of quantum neural networks, quantum kernels, and variational classifiers. Good choice if you're already in the Qiskit ecosystem.

See Qiskit courses →

TensorFlow Quantum

Google's hybrid quantum-classical ML framework built on Cirq. Designed for those already using TensorFlow. Less actively developed than PennyLane but useful if TF is your primary ML framework.

Frequently asked questions

What is quantum machine learning?
Quantum machine learning (QML) is the application of quantum computing to machine learning tasks, or the use of classical ML techniques to improve quantum algorithms. The most active research direction is variational quantum circuits (VQCs) used as trainable models, analogous to classical neural networks. Other approaches include quantum kernel methods (using quantum computers to compute kernel functions) and quantum-enhanced sampling. Most QML is still in the research stage.
Is quantum machine learning better than classical ML?
Honestly, not yet - and possibly not in general. Current quantum hardware is too noisy and small to outperform classical ML on real tasks. Some theoretical quantum speedups exist (e.g., for certain kernel computations on quantum-accessible data), but practical advantage on industry-scale problems has not been demonstrated. QML is worth studying because the field is moving fast and some applications may emerge as hardware improves, but healthy skepticism is warranted.
What is PennyLane used for?
PennyLane, developed by Xanadu, is the leading open-source framework for quantum machine learning. It integrates with PyTorch, TensorFlow, and JAX, allowing you to build hybrid classical-quantum models using familiar ML workflows. PennyLane supports automatic differentiation of quantum circuits, making it possible to train variational circuits with gradient descent just like a neural network. It runs on simulators and on real quantum hardware via plugins for IBM, AWS Braket, and others.
Do I need to know machine learning before learning QML?
Yes, a working knowledge of classical ML is strongly recommended before diving into QML. You should understand gradient descent, neural network training, and the basics of supervised and unsupervised learning. QML courses assume this background and focus on adapting those ideas to quantum circuits. If you're new to ML, spend time with classical ML first - frameworks like scikit-learn and PyTorch - before picking up QML resources.