TaperedQubitMapper#

class TaperedQubitMapper(mapper, z2symmetries=<qiskit.quantum_info.analysis.z2_symmetries.Z2Symmetries object>)[source]#

Bases: QubitMapper

The wrapper around qubit mappers implementing the logic to reduce the size of a problem (operator) based on mathematical Z2Symmetries that can be automatically detected in the operator.

The following attributes can be read and updated once the TaperedQubitMapper object has been constructed.

mapper#

Object defining the mapping of second quantized operators to Pauli operators.

z2symmetries#

Symmetries to use to reduce the Pauli operators.

Parameters:

  • mapper (QubitMapper) – QubitMapper object implementing the mapping of second quantized operators to Pauli operators.

  • z2symmetries (Z2Symmetries) – Z2Symmetries object defining the symmetries to use to reduce the Pauli operators.

Raises:

ValueError – If the input mapper is already a TaperedQubitMapper.

Methods

map(second_q_ops, *, register_length=None)[source]#

Maps a second quantized operator or a list, dict of second quantized operators based on the current mapper.

Parameters:

  • second_q_ops (SparseLabelOp | ListOrDictType[SparseLabelOp]) – A second quantized operator, or list thereof.

  • register_length (int | None) – when provided, this will be used to overwrite the register_length attribute of the SparseLabelOp being mapped. This is possible because the register_length is considered a lower bound in a SparseLabelOp.

Returns:

A qubit operator in the form of a SparsePauliOp, or list (resp. dict) thereof if a list (resp. dict) of second quantized operators was supplied.

Return type:

SparsePauliOp | None | ListOrDictType[SparsePauliOp | None]

map_clifford(second_q_ops, *, register_length=None)[source]#

Maps a second quantized operator or a list, dict of second quantized operators based on the internal mapper. Then, composes all mapped pauli operators with the clifford operations defined by the internal Z2Symmetries to prepare for the symmetry reduction. This composition gives isospectral operators and exposes redundant qubits for later tapering.

Parameters:

  • second_q_ops (SparseLabelOp | ListOrDictType[SparseLabelOp]) – A second quantized operator, or list (resp. dict) thereof.

  • register_length (int | None) – when provided, this will be used to overwrite the register_length attribute of the operator being mapped. This is possible because the

  • SparseLabelOp. (register_length is considered a lower bound in a) –

Returns:

A qubit operator in the form of a SparsePauliOp, or list (resp. dict) thereof if a list (resp. dict) of second quantized operators was supplied.

Return type:

SparsePauliOp | ListOrDictType[SparsePauliOp]

classmethod mode_based_mapping(second_q_op, register_length=None)#

Utility method to map a SparseLabelOp to a qubit operator using a pauli table.

Parameters:

  • second_q_op (SparseLabelOp) – the SparseLabelOp to be mapped.

  • register_length (int | None) – when provided, this will be used to overwrite the register_length attribute of the operator being mapped. This is possible because the register_length is considered a lower bound.

Returns:

The qubit operator corresponding to the problem-Hamiltonian in the qubit space.

Raises:

QiskitNatureError – If number length of pauli table does not match the number of operator modes, or if the operator has unexpected label content

Return type:

SparsePauliOp

classmethod pauli_table(register_length)#

Generates a Pauli-lookup table mapping from modes to pauli pairs.

The generated table is processed by QubitMapper.sparse_pauli_operators().

Parameters:

register_length (int) – the register length for which to generate the table.

Returns:

A list of tuples in which the first and second Pauli operator the real and imaginary Pauli strings, respectively.

Return type:

list[tuple[Pauli, Pauli]]

classmethod sparse_pauli_operators(register_length)#

Generates the cached SparsePauliOp terms.

This uses QubitMapper.pauli_table() to construct a list of operators used to translate the second-quantization symbols into qubit operators.

Parameters:

register_length (int) – the register length for which to generate the operators.

Returns:

Two lists stored in a tuple, consisting of the creation and annihilation operators, applied on the individual modes.

Return type:

tuple[list[SparsePauliOp], list[SparsePauliOp]]

taper_clifford(pauli_ops, *, check_commutes=True, suppress_none=True)[source]#

Applies the symmetry reduction on a SparsePauliOp or a list (resp. dict). This method implies that the second quantized operators were already mapped to Pauli operators and composed with the clifford operations defined in the symmetry, for example using the map_clifford method.

Parameters:

  • pauli_ops (SparsePauliOp | ListOrDictType[SparsePauliOp]) – A pauli operator already evolved with the symmetry clifford operations.

  • check_commutes (bool) – If the commutativity of operators with symmetries must be checked before any calculation.

  • suppress_none (bool) – If None should be placed in the output list where an operator did not commute with symmetry, to maintain order, or whether that should be suppressed where the output list length may then be smaller than the input.

Returns:

A qubit operator in the form of a SparsePauliOp, or list (resp. dict) thereof if a list (resp. dict) of second quantized operators was supplied.

Return type:

SparsePauliOp | None | ListOrDictType[SparsePauliOp | None]