qml.pauli.is_pauli_word

is_pauli_word(observable)

Checks if an observable instance consists only of Pauli and Identity Operators.

A Pauli word can be either:

• A single pauli operator (see PauliX for an example).

• A Tensor instance containing Pauli operators.

• A Prod instance containing Pauli operators.

• A SProd instance containing a valid Pauli word.

• A Hamiltonian instance with only one term.

Warning

This function will only confirm that all operators are Pauli or Identity operators, and not whether the Observable is mathematically a Pauli word. If an Observable consists of multiple Pauli operators targeting the same wire, the function will return True regardless of any complex coefficients.

Parameters

observable (Operator) – the operator to be examined

Returns

true if the input observable is a Pauli word, false otherwise.

Return type

bool

Example

>>> is_pauli_word(qml.Identity(0))
True
>>> is_pauli_word(qml.PauliX(0) @ qml.PauliZ(2))
True
>>> is_pauli_word(qml.PauliZ(0) @ qml.Hadamard(1))
False
>>> is_pauli_word(4 * qml.PauliX(0) @ qml.PauliZ(0))
True

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