qml.transforms

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

Transforms

Transforms that act on QNodes

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

classical_jacobian(qnode[, argnum, expand_fn])

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

batch_params(tape[, all_operations])

Transform a QNode to support an initial batch dimension for operation parameters.

draw(qnode[, charset, wire_order, …])

Create a function that draws the given qnode.

get_unitary_matrix(circuit[, wire_order])

Construct the matrix representation of a quantum circuit.

metric_tensor(tape[, approx, diag_approx, …])

Returns a function that computes the block-diagonal approximation of the metric tensor of a given QNode or quantum tape.

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.

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 and select instances of two-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.

two_qubit_decomposition(U, wires)

Decompose a two-qubit unitary \(U\) 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.

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(*args, **kwargs)

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.

create_expand_fn(depth, stop_at[, docstring])

Create a function for expanding a tape to a given depth, and with a specific stopping criterion.

expand_invalid_trainable(tape[, _depth])

Expand out a tape so that it supports differentiation of requested operations.

expand_multipar(tape[, _depth])

Expand out a tape so that all its parametrized operations have a single parameter.

expand_nonunitary_gen(tape[, _depth])

Expand out a tape so that all its parametrized operations have a unitary generator.