Z2Symmetries

class qiskit.opflow.primitive_ops.Z2Symmetries(symmetries, sq_paulis, sq_list, tapering_values=None, tol=1e-14)

Bases: object

Deprecated: Z2 Symmetries

Deprecated since version 0.24.0: The class qiskit.opflow.primitive_ops.tapered_pauli_sum_op.Z2Symmetries is deprecated as of qiskit-terra 0.24.0. It will be removed no earlier than 3 months after the release date. For code migration guidelines, visit https://qisk.it/opflow_migration.

Parameters:

• symmetries (List[Pauli]) – the list of Pauli objects representing the Z_2 symmetries

• sq_paulis (List[Pauli]) – the list of single - qubit Pauli objects to construct the Clifford operators

• sq_list (List[int]) – the list of support of the single-qubit Pauli objects used to build the Clifford operators

• tapering_values (List[int] | None) – values determines the sector.

• tol (float) – Tolerance threshold for ignoring real and complex parts of a coefficient.

Raises:

OpflowError – Invalid paulis

Attributes

cliffords

Get clifford operators, build based on symmetries and single-qubit X. :returns: a list of unitaries used to diagonalize the Hamiltonian.

settings

Return operator settings.

sq_list

returns sq list

sq_paulis

returns sq paulis

symmetries

return symmetries

tapering_values

returns tapering values

tol

Tolerance threshold for ignoring real and complex parts of a coefficient.

Methods

consistent_tapering(operator)

Tapering the operator with the same manner of how this tapered operator is created. i.e., using the same Cliffords and tapering values.

Parameters:

operator (PauliSumOp) – the to-be-tapered operator

Returns:

The tapered operator

Raises:

OpflowError – The given operator does not commute with the symmetry

Return type:

OperatorBase

convert_clifford(operator)

This method operates the first part of the tapering. It converts the operator by composing it with the clifford unitaries defined in the current symmetry.

Parameters:

operator (PauliSumOp) – to-be-tapered operator

Returns:

PauliSumOp corresponding to the converted operator.

Raises:

OpflowError – Z2 symmetries, single qubit pauli and single qubit list cannot be empty

Return type:

OperatorBase

copy()

Get a copy of self. :returns: copy

Return type:

Z2Symmetries

classmethod find_Z2_symmetries(operator)

Finds Z2 Pauli-type symmetries of an Operator.

Returns:

a z2_symmetries object contains symmetries, single-qubit X, single-qubit list.

Return type:

Z2Symmetries

is_empty()

Check the z2_symmetries is empty or not. :returns: Empty or not

Return type:

bool

taper(operator)

Taper an operator based on the z2_symmetries info and sector defined by tapering_values. The tapering_values will be stored into the resulted operator for a record.

The tapering is a two-step algorithm which first converts the operator into a PauliSumOp with same eigenvalues but where some qubits are only acted upon with the Pauli operators I or X. The number M of these redundant qubits is equal to the number M of identified symmetries.

The second step of the reduction consists in replacing these qubits with the possible eigenvalues of the corresponding Pauli X, giving 2^M new operators with M less qubits. If an eigenvalue sector was previously identified for the solution, then this reduces to 1 new operator with M less qubits.

Parameters:

operator (PauliSumOp) – the to-be-tapered operator

Returns:

[PauliSumOp]; otherwise, PauliSumOp

Return type:

If tapering_values is None

Raises:

OpflowError – Z2 symmetries, single qubit pauli and single qubit list cannot be empty

taper_clifford(operator)

This method operates the second part of the tapering. This function assumes that the input operators have already been transformed using convert_clifford(). The redundant qubits due to the symmetries are dropped and replaced by their two possible eigenvalues. The tapering_values will be stored into the resulted operator for a record.

Parameters:

operator (PauliSumOp) – Partially tapered operator resulting from a call to convert_clifford()

Returns:

[PauliSumOp]; otherwise, PauliSumOp

Return type:

If tapering_values is None

Raises:

OpflowError – Z2 symmetries, single qubit pauli and single qubit list cannot be empty