qml.pauli.pauli_word_to_string

pauli_word_to_string(pauli_word, wire_map=None)

Convert a Pauli word to a string.

A Pauli word can be either:

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

• A Prod instance containing Pauli operators.

• A SProd instance containing a Pauli operator.

• A Sum instance with only one term.

Given a Pauli in observable form, convert it into string of characters from ['I', 'X', 'Y', 'Z']. This representation is required for functions such as PauliRot.

Warning

This method ignores any potential coefficient multiplying the Pauli word:

>>> qml.pauli.pauli_word_to_string(3 * qml.X(0) @ qml.Y(1))
'XY'

Warning

This method assumes all Pauli operators are acting on different wires, ignoring any extra operators:

>>> qml.pauli.pauli_word_to_string(qml.X(0) @ qml.Y(0) @ qml.Y(0))
'X'

Parameters

• pauli_word (Union[Observable, Prod, SProd, Sum]) – an observable, either a single-qubit observable representing a Pauli group element, or a tensor product of single-qubit observables.

• wire_map (dict[Union[str, int], int]) – dictionary containing all wire labels used in the Pauli word as keys, and unique integer labels as their values

Returns

The string representation of the observable in terms of 'I', 'X', 'Y', and/or 'Z'.

Return type

str

Raises

TypeError – if the input observable is not a proper Pauli word.

Example

>>> wire_map = {'a' : 0, 'b' : 1, 'c' : 2}
>>> pauli_word = qml.X('a') @ qml.Y('c')
>>> pauli_word_to_string(pauli_word, wire_map=wire_map)
'XIY'

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