QNodes

A qnetvo.NetworkAnsatz() is executed on a PennyLane QNode object. The output of the QNode execution can either be the probility of obtaining each output or the expectation of an observable. The considered cost function dictates which type of QNode measurement is applied.

Probability QNodes

qnetvo.joint_probs_qnode(network_ansatz, **qnode_kwargs)

Constructs a qnode that computes the joint probabilities in the computational basis across all measurement wires.

Parameters:

network_ansatz (NetworkAnsatz) – A NetworkAnsatz class specifying the quantum network simulation.

Returns:

A qnode called as qnode(settings) for evaluating the joint probabilities of the network ansatz.

Return type:

pennylane.QNode

Density Matrix QNodes

qnetvo.density_matrix_qnode(network_ansatz, wires=None, **qnode_kwargs)

Constructs a qnode that computes the density matrix in the computational basis across specified wires, or across all wires if no specific wires are provided.

Parameters:

• network_ansatz (NetworkAnsatz) – A NetworkAnsatz class specifying the quantum network simulation.

• wires (list[int] or None) – The wires on which the node operates. If None, the density matrix will be computed across all wires in the network ansatz.

Returns:

A qnode called as qnode(settings) for evaluating the (reduced) density matrix of the network ansatz.

Return type:

pennylane.QNode

Raises:

ValueError – If the specified wires are not a subset of the wires in the network ansatz.

Parity Observable QNodes

qnetvo.local_parity_expval_qnode(network_ansatz, **qnode_kwargs)

Constructs a qnode that computes expectation values for the local parity observable at each measurement node.

Parameters:

network_ansatz (NetworkAnsatz) – A NetworkAnsatz class specifying the quantum network simulation.

Returns:

A qnode that performs a local parity measurement at measurement nodes. The qnode is called as qnode(settings).

Return type:

qml.QNode

qnetvo.global_parity_expval_qnode(network_ansatz, **qnode_kwargs)

Constructs a qnode that computes expectation values for the local parity observable at each measurement node.

Parameters:

network_ansatz (NetworkAnsatz) – A NetworkAnsatz class specifying the quantum network simulation.

Returns:

A qnode the performs a global parity measurement and is called as qnode(settings).

Return type:

qml.QNode

Helper Functions for Parity Observables

qnetvo.parity_observable(wires)

Constructs the parity observable for the provided wires in the computational basis.

Parameters:

wires (qml.wires.Wires) – A list of MeasureNode classes for which to construct the observables.

Returns:

A parity qml.Observable across all wires.

qnetvo.local_parity_observables(measure_nodes)

Constructs a list of dichotomic observables for each measurement node. The observables are constructed as products of qml.PauliZ qubit operators and therefore, a \(+1\) outcome corresponds to an Even parity bit string whereas a \(-1\) outcome corresponds to an Odd parity bit string.

Parameters:

measure_nodes (list[ MeasureNode ]) – A list of MeasureNode classes for which to construct the observables.

qnetvo.parity_vector(n_qubits)

Constructs a vector with elements \(\pm 1\) describing the parity of an \(n\)-bit string measured from \(n\)-qubits. The (+) and (-) elements indicate even and odd parity respectively and are placed in the index corresponding to the bit string’s value.

Parameters:

n_qubits (int) – The number of qubits for which to consider the parity vector.

Raises:

ValueError – If n_qubits < 1.

qnetvo.even_parity_ids(n_qubits)

Constructs the list ids corresponding to even parity bit strings with respect to the vector returned by parity_vector.

Parameters:

n_qubits (int) – The number of qubits for which to consider the parity vector.