qml.transforms

This subpackage contains QNode, quantum function, device, and tape transforms.

Transforms

Transforms that act on QNodes

Thes transforms accept QNodes, and return new transformed functions that compute the desired quantity.

classical_jacobian(qnode)

Returns a function to extract the Jacobian matrix of the classical part of a QNode.

draw(qnode[, charset, wire_order, …])

Create a function that draws the given qnode.

metric_tensor(qnode[, diag_approx, …])

Returns a function that returns the value of the metric tensor of a given QNode.

specs(qnode[, max_expansion])

Resource information about a quantum circuit.

Transforms that act on quantum functions

These transforms accept quantum functions (Python functions containing quantum operations) that are used to construct QNodes.

adjoint(fn)

Create a function that applies the adjoint (inverse) of the provided operation or template.

ctrl(fn, control)

Create a method that applies a controlled version of the provided method.

invisible(fn)

A transform to make a quantum function non-recordable or invisible within a QNode or quantum tape context.

apply_controlled_Q(fn, wires, target_wire, …)

Provides the circuit to apply a controlled version of the \(\mathcal{Q}\) unitary defined in this paper.

quantum_monte_carlo(fn, wires, target_wire, …)

Provides the circuit to perform the quantum Monte Carlo estimation algorithm.

Transforms for circuit compilation

This set of transforms accept quantum functions, and perform basic circuit compilation tasks.

compile

Compile a circuit by applying a series of transforms to a quantum function.

cancel_inverses

Quantum function transform to remove any operations that are applied next to their (self-)inverse.

commute_controlled

Quantum function transform to move commuting gates past control and target qubits of controlled operations.

merge_rotations

Quantum function transform to combine rotation gates of the same type that act sequentially.

single_qubit_fusion

Quantum function transform to fuse together groups of single-qubit operations into a general single-qubit unitary operation (Rot).

unitary_to_rot

Quantum function transform to decomposes all instances of single-qubit QubitUnitary operations to parametrized single-qubit operations.

There are also utility functions and decompositions available that assist with both transforms, and decompositions within the larger PennyLane codebase.

zyz_decomposition(U, wire)

Recover the decomposition of a single-qubit matrix \(U\) in terms of elementary operations.

Transforms that act on tapes

These transforms accept quantum tapes, and return one or more tapes as well as a classical processing function.

measurement_grouping(tape, obs_list, coeffs_list)

Returns a list of measurement optimized tapes, and a classical processing function, for evaluating the expectation value of a provided Hamiltonian.

metric_tensor_tape(tape[, diag_approx, wrt])

Returns a list of tapes, and a classical processing function, for computing the block diagonal metric tensor approximation of an input tape on hardware.

hamiltonian_expand(tape[, group])

Splits a tape measuring a Hamiltonian expectation into mutliple tapes of Pauli expectations, and provides a function to recombine the results.

Decorators and utility functions

The following decorators and convenience functions are provided to help build custom QNode, quantum function, and tape transforms:

single_tape_transform(transform_fn)

For registering a tape transform that takes a tape and outputs a single new tape.

batch_transform(transform_fn[, expand_fn, …])

Class for registering a tape transform that takes a tape, and outputs a batch of tapes to be independently executed on a quantum device.

qfunc_transform(tape_transform)

Given a function which defines a tape transform, convert the function into one that applies the tape transform to quantum functions (qfuncs).

make_tape(fn)

Returns a function that generates the tape from a quantum function without any operation queuing taking place.