PennyLane Metal

PennyLane Metal is a PennyLane quantum simulator for Apple silicon, built exclusively on Metal 4. It provides the metal.qubit device, where state evolution, noise channels, measurements, sampling, and adjoint gradients all run on the GPU.

• Pure circuits use a state vector; noisy circuits use a density-matrix execution model, selected automatically.
• Native Metal adjoint Jacobians and VJPs for the parameterized gate set.
• Broad native gate, measurement, and noise-channel coverage — see supported operations.
• Device-aware memory admission with a queryable resource planner — see memory and resources.

Requirements

• macOS 26.0 or newer on Apple silicon
• A Metal 4-capable Apple GPU (M1 or newer)
• Python 3.10–3.14

Installation

pip install pennylane-metal

Binary wheels are published for macOS 26+ (arm64) and CPython 3.10–3.14.

Building from the sdist or a git checkout additionally requires Xcode 26 with the Metal Toolchain component (xcodebuild -downloadComponent MetalToolchain) and CMake 3.24+; then pip install .. See docs/DEVELOPMENT.md for the full workflow.

Quickstart

import pennylane as qml

dev = qml.device("metal.qubit", wires=2)

@qml.qnode(dev)
def bell_state():
    qml.H(0)
    qml.CNOT([0, 1])
    return qml.probs(wires=[0, 1])

print(bell_state())  # [0.5, 0.0, 0.0, 0.5]

Gradients use the native Metal adjoint method:

@qml.qnode(dev, diff_method="adjoint")
def expectation(angle):
    qml.RX(angle, 0)
    qml.CNOT([0, 1])
    return qml.expval(qml.Z(0))

angle = qml.numpy.array(0.37, requires_grad=True)
print(qml.grad(expectation)(angle))  # -sin(0.37)

Performance

A 22-qubit, depth-10 RY/CNOT circuit with an analytic expectation value (Apple M1 Max, macOS 26, pennylane-metal 0.2.0):

Device	Time per execution
default.qubit	5808 ms
lightning.qubit	973 ms
metal.qubit	98 ms

Each execution carries a fixed ~1 ms GPU dispatch cost, so CPU simulators remain faster for very small circuits; the GPU advantage grows with qubit count and depth. Reproduce with benchmarks/benchmark_metal.py — see docs/DEVELOPMENT.md.

Capabilities and limits

Area	Summary
Gates	Native one/two/multi-qubit set incl. excitation families, arbitrary unitaries
Measurements	State, probs, expval, var, purity, entropies (analytic); shots via Metal sampling
Noise	Standard channels plus arbitrary multi-wire Kraus maps, all on GPU
Gradients	Native adjoint/VJP (pure states); parameter-shift for noisy circuits
Precision	complex64; capacity is device-memory-bound (2**n state vector, 4**n density matrix)
Not supported	Mid-circuit measurements, reset, postselection, classical conditionals

Full details: docs/SUPPORTED_OPERATIONS.md and docs/RESOURCES.md.

Documentation

• Supported operations — gates, measurements, channels, differentiation, batching
• Memory and resources — memory budgets, capacity queries, resource estimation
• Architecture — layer ownership and data-flow rules
• Development — building, testing, benchmarks, releasing

Development

python -m venv .venv
.venv/bin/pip install -e '.[dev]'
.venv/bin/pytest

See docs/DEVELOPMENT.md for CMake iteration builds, Metal API validation runs, and the release process.

License

Apache 2.0