jordan_wigner

jordan_wigner(operator, num_qubits)

Map an operator to a SparseObservable under the Jordan-Wigner transformation.

This is the type-agnostic entry point to the Jordan-Wigner transformation. It dispatches on the concrete type of operator to the appropriate direct implementation. Today only FermionOperator is supported, delegating to fermion_jordan_wigner(); any other operator type raises a TypeError until a direct implementation exists for it.

Parameters:

  • operator (OperatorTrait) – the operator to map.

  • num_qubits (int) – the number of qubits for the resulting qubit operator. This must be strictly greater than the largest mode index in operator (any additional qubits are padded with the identity).

Returns:

The mapped qubit operator.

Raises:

  • TypeError – if operator is of a type for which no Jordan-Wigner implementation exists.

  • ValueError – if num_qubits is too small to hold the operator’s support.

Return type:

SparseObservable

>>> from qiskit_fermions.mappers.library import jordan_wigner
>>> from qiskit_fermions.operators import FermionOperator
>>> fop = FermionOperator.from_dict({((True, 0), (False, 0)): 0.1})
>>> jordan_wigner(fop, 2).simplify()
<SparseObservable with 2 terms on 2 qubits: (0.05+0j)() + (-0.05+0j)(Z_0)>

An operator type without a direct implementation raises a TypeError:

>>> from qiskit_fermions.operators import MajoranaOperator
>>> mop = MajoranaOperator.from_dict({(0, 1): 1.0})
>>> jordan_wigner(mop, 2)
Traceback (most recent call last):
...
TypeError: jordan_wigner does not support operator type 'MajoranaOperator'; only FermionOperator is supported today.