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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.