What problem does it solve? Developing variational quantum algorithms and quantum machine learning models requires a framework that unifies circuit construction, automatic differentiation, and classical ML integration, which is difficult to assemble from low-level tools. ## Core Features & Use Cases - Differentiable Quantum Circuits: Define QNodes on simulators like default.qubit and compute gradients via parameter-shift, backpropagation, or finite-difference methods. - Hybrid ML Integration: Embed quantum layers inside PyTorch, TensorFlow, or JAX models for end-to-end training of quantum neural networks. - Variational Algorithm Support: Implement VQE, QAOA, and QNN workflows with built-in circuit templates and flexible parameter management. - Use Case: A researcher prototyping a variational quantum eigensolver can define a parameterized ansatz, compute expectation values of a Hamiltonian, and optimize parameters with gradient descent, all within one PennyLane workflow. ## Quick Start Ask the AI to write a PennyLane circuit that creates a two-qubit QNode on default.qubit, applies an RY rotation and CNOT, and returns the expectation value and its gradient.