qml.estimator.templates.QFT

class QFT(num_wires=None, wires=None)

Bases: ResourceOperator

Resource class for QFT.

Parameters:

• num_wires (int | None) – the number of qubits the operation acts upon

• wires (Sequence[int], None) – the wires the operation acts on

Resources:

The resources are obtained from the standard decomposition of QFT as presented in (chapter 5) Nielsen, M.A. and Chuang, I.L. (2011) Quantum Computation and Quantum Information.

See also

The corresponding PennyLane operation QFT.

Example

The resources for this operation are computed using:

>>> import pennylane.estimator as qre
>>> qft = qre.QFT(3)
>>> gate_set = {"SWAP", "Hadamard", "ControlledPhaseShift"}
>>> print(qre.estimate(qft, gate_set))
--- Resources: ---
Total wires: 3
    algorithmic wires: 3
    allocated wires: 0
    zero state: 0
    any state: 0
Total gates : 7
'SWAP': 1,
'ControlledPhaseShift': 3,
'Hadamard': 3

Usage Details

This operation provides an alternative decomposition method when an appropriately sized phase gradient state is available. This decomposition can be used as a custom decomposition using the operation’s phase_grad_resource_decomp method and the ResourceConfig class. See the following example for more details.

>>> import pennylane.estimator as qre
>>> config = qre.ResourceConfig()
>>> config.set_decomp(qre.QFT, qre.QFT.phase_grad_resource_decomp)
>>> print(qre.estimate(qre.QFT(3), config=config))
--- Resources: ---
Total wires: 4
    algorithmic wires: 3
    allocated wires: 1
    zero state: 1
    any state: 0
Total gates : 17
'Toffoli': 5,
'CNOT': 6,
'Hadamard': 6

Attributes

resource_keys
resource_params	Returns a dictionary containing the minimal information needed to compute the resources.

resource_keys = {'num_wires'}

resource_params

Returns a dictionary containing the minimal information needed to compute the resources.

Returns:

A dictionary containing the resource parameters:

• num_wires (int): the number of qubits the operation acts upon

Return type:

dict

Methods

phase_grad_resource_decomp(num_wires)	Returns a list representing the resources of the operator.
resource_decomp(num_wires)	Returns a list representing the resources of the operator.
resource_rep(num_wires)	Returns a compressed representation containing only the parameters of the Operator that are needed to compute the resources.
tracking_name(num_wires)	Returns the tracking name built with the operator's parameters.

classmethod phase_grad_resource_decomp(num_wires)

Returns a list representing the resources of the operator. Each object in the list represents a gate and the number of times it occurs in the circuit.

Note

This decomposition assumes an appropriately sized phase gradient state is available. Users should ensure the cost of constructing such a state has been accounted for. See also PhaseGradient.

Parameters:

num_wires (int) – the number of qubits the operation acts upon

Resources:

The resources are obtained as presented in the article Turning Gradients into Additions into QFTs. Specifically, following the figure titled “8 qubit Quantum Fourier Transform with gradient shifts”

Returns:

A list of GateCount objects, where each object represents a specific quantum gate and the number of times it appears in the decomposition.

Return type:

list[GateCount]

classmethod resource_decomp(num_wires)

Returns a list representing the resources of the operator. Each object in the list represents a gate and the number of times it occurs in the circuit.

Parameters:

num_wires (int) – the number of qubits the operation acts upon

Resources:

The resources are obtained from the standard decomposition of QFT as presented in (Chapter 5) Nielsen, M.A. and Chuang, I.L. (2011) Quantum Computation and Quantum Information.

Returns:

A list of GateCount objects, where each object represents a specific quantum gate and the number of times it appears in the decomposition.

Return type:

list[GateCount]

classmethod resource_rep(num_wires)

Returns a compressed representation containing only the parameters of the Operator that are needed to compute the resources.

Parameters:

num_wires (int) – the number of qubits the operation acts upon

Returns:

the operator in a compressed representation

Return type:

CompressedResourceOp

static tracking_name(num_wires)

Returns the tracking name built with the operator’s parameters.

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