WeightedPauliOperator

class WeightedPauliOperator(paulis, basis=None, z2_symmetries=None, atol=1e-12, name=None)

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Weighted Pauli Operator

Parameters

paulis (list[[complex, Pauli]]) – the list of weighted Paulis, where a weighted pauli is composed of a length-2 list and the first item is the weight and the second item is the Pauli object.
basis (list[tuple(object, [int])], optional) – the grouping basis, each element is a tuple composed of the basis and the indices to paulis which are belonged to that group. e.g., if tpb basis is used, the object will be a pauli. By default, the group is equal to non-grouping, each pauli is its own basis.
z2_symmetries (Z2Symmetries) – recording the z2 symmetries info
atol (float, optional) – the threshold used in truncating paulis
name (str, optional) – the name of operator.

Attributes

atol

get atol

basis

returns basis

name

returns name

num_qubits

Number of qubits required for the operator.

Returns

number of qubits

Return type

int

paulis

get paulis

z2_symmetries

returns z2 symmetries

Methods

mul

WeightedPauliOperator.__mul__(other)

Overload self * other

add

WeightedPauliOperator.add(other, copy=False)

Perform self + other.

Parameters

other (WeightedPauliOperator) – to-be-combined operator
copy (bool) – working on a copy or self, if False, the results are written back to self.

Returns

operator

Return type

WeightedPauliOperator

anticommute_with

WeightedPauliOperator.anticommute_with(other)

Anti commutes with

chop

WeightedPauliOperator.chop(threshold=None, copy=False)

Eliminate the real and imagine part of weight in each pauli by threshold. If pauli’s weight is less then threshold in both real and imaginary parts, the pauli is removed.

Note

If weight is real-only, the imaginary part is skipped.

Parameters

threshold (float) – the threshold is used to remove the paulis
copy (bool) – chop on a copy or self

Returns

if copy is True, the original operator is unchanged; otherwise,

the operator is mutated.

Return type

WeightedPauliOperator

commute_with

WeightedPauliOperator.commute_with(other)

Commutes with

construct_evaluation_circuit

WeightedPauliOperator.construct_evaluation_circuit(wave_function, statevector_mode, qr=None, cr=None, use_simulator_snapshot_mode=False, circuit_name_prefix='')

Construct the circuits for evaluation, which calculating the expectation <psi|H|psi>.

At statevector mode: to simplify the computation, we do not build the whole circuit for <psi|H|psi>, instead of that we construct an individual circuit <psi|, and a bundle circuit for H|psi>

Parameters

wave_function (QuantumCircuit) – the quantum circuit.
statevector_mode (bool) – indicate which type of simulator are going to use.
qr (QuantumRegister, optional) – the quantum register associated with the input_circuit
cr (ClassicalRegister, optional) – the classical register associated with the input_circuit
use_simulator_snapshot_mode (bool, optional) – if aer_provider is used, we can do faster evaluation for pauli mode on statevector simulation
circuit_name_prefix (str, optional) – a prefix of circuit name

Returns

a list of quantum circuits and each circuit with a unique name:

circuit_name_prefix + Pauli string

Return type

list[QuantumCircuit]

Raises

AquaError – if Operator is empty
AquaError – if quantum register is not provided explicitly and cannot find quantum register with q as the name
AquaError – The provided qr is not in the wave_function

copy

WeightedPauliOperator.copy()

Get a copy of self

evaluate_with_result

WeightedPauliOperator.evaluate_with_result(result, statevector_mode, use_simulator_snapshot_mode=False, circuit_name_prefix='')

This method can be only used with the circuits generated by the construct_evaluation_circuit() method with the same circuit_name_prefix name since the circuit names are tied to some meanings.

Calculate the evaluated value with the measurement results.

Parameters

result (qiskit.Result) – the result from the backend.
statevector_mode (bool) – indicate which type of simulator are used.
use_simulator_snapshot_mode (bool) – if aer_provider is used, we can do faster evaluation for pauli mode on statevector simulation
circuit_name_prefix (str) – a prefix of circuit name

Returns

the mean value float: the standard deviation

Return type

float

Raises

AquaError - if Operator is empty

evaluate_with_statevector

WeightedPauliOperator.evaluate_with_statevector(quantum_state)

Parameters

quantum_state (numpy.ndarray) - a quantum state.

Returns

the mean value float: the standard deviation

Return type

float

Raises

AquaError - if Operator is empty

evaluation_instruction

WeightedPauliOperator.evaluation_instruction(statevector_mode, use_simulator_snapshot_mode=False)

Parameters

statevector_mode (bool) – will it be run on statevector simulator or not
use_simulator_snapshot_mode (bool) – will it use qiskit aer simulator operator mode

Returns

Pauli-instruction pair.

Return type

dict

Raises

AquaError - if Operator is empty

evolve

WeightedPauliOperator.evolve(state_in=None, evo_time=0, num_time_slices=1, quantum_registers=None, expansion_mode='trotter', expansion_order=1)

Carry out the eoh evolution for the operator under supplied specifications.

Parameters

state_in (QuantumCircuit) – a circuit describes the input state
evo_time (Union(complex, float, Parameter, ParameterExpression)) – The evolution time
num_time_slices (int) – The number of time slices for the expansion
quantum_registers (QuantumRegister) – The QuantumRegister to build the QuantumCircuit off of
expansion_mode (str) – The mode under which the expansion is to be done. Currently support ‘trotter’, which follows the expansion as discussed in https://www.science.org/doi/10.1126/science.273.5278.1073, and ‘suzuki’, which corresponds to the discussion in https://arxiv.org/pdf/quant-ph/0508139.pdf
expansion_order (int) – The order for suzuki expansion

Returns

The constructed circuit.

Return type

QuantumCircuit

Raises

AquaError – quantum_registers must be in the provided state_in circuit
AquaError – if operator is empty

evolve_instruction

WeightedPauliOperator.evolve_instruction(evo_time=0, num_time_slices=1, expansion_mode='trotter', expansion_order=1)

Carry out the eoh evolution for the operator under supplied specifications.

Parameters

evo_time (Union(complex, float, Parameter, ParameterExpression)) – The evolution time
num_time_slices (int) – The number of time slices for the expansion
expansion_mode (str) – The mode under which the expansion is to be done. Currently support ‘trotter’, which follows the expansion as discussed in https://www.science.org/doi/10.1126/science.273.5278.1073, and ‘suzuki’, which corresponds to the discussion in https://arxiv.org/pdf/quant-ph/0508139.pdf
expansion_order (int) – The order for suzuki expansion

Returns

The constructed QuantumCircuit.

Return type

QuantumCircuit

Raises

ValueError – Number of time slices should be a non-negative integer
NotImplementedError – expansion mode not supported
AquaError – if operator is empty

from_dict

classmethod WeightedPauliOperator.from_dict(dictionary, before_04=False)

Load paulis from a dictionary to construct an Operator. The dictionary must comprise the key ‘paulis’ having a value which is an array of pauli dicts. Each dict in this array must be represented by label and coeff (real and imag) such as in the following example:

{'paulis':
    [
        {'label': 'IIII',
         'coeff': {'real': -0.33562957575267038, 'imag': 0.0}},
        {'label': 'ZIII',
         'coeff': {'real': 0.28220597164664896, 'imag': 0.0}},
         ...
    ]
 }

Parameters

dictionary (dict) – dictionary, which contains a list of Paulis and coefficients.
before_04 (bool) – support the format before Aqua 0.4.

Returns

the operator created from the input dictionary.

Return type

WeightedPauliOperator

Raises

AquaError - Invalid dictionary

from_file

classmethod WeightedPauliOperator.from_file(file_name, before_04=False)

Load paulis in a file to construct an Operator.

Parameters

file_name (str) – path to the file, which contains a list of Paulis and coefficients.
before_04 (bool) – support the format before Aqua 0.4.

Returns

the loaded operator.

Return type

WeightedPauliOperator

from_list

classmethod WeightedPauliOperator.from_list(paulis, weights=None, name=None)

Create a WeightedPauliOperator via a pair of list.

Parameters

paulis (list[Pauli]) – the list of Paulis
weights (list[complex], optional) – the list of weights, if it is None, all weights are 1.
name (str, optional) – name of the operator.

Returns

operator

Return type

WeightedPauliOperator

Raises

ValueError - The length of weights and paulis must be the same

is_empty

WeightedPauliOperator.is_empty()

Check Operator is empty or not.

Returns

True if empty, False otherwise

Return type

bool

multiply

WeightedPauliOperator.multiply(other)

Perform self * other, and the phases are tracked.

Parameters

other (WeightedPauliOperator) - an operator

Returns

the multiplied operator

Return type

WeightedPauliOperator

print_details

WeightedPauliOperator.print_details()

Print out the operator in details.

Returns

a formatted string describes the operator.

Return type

str

reorder_paulis

WeightedPauliOperator.reorder_paulis()

Reorder the paulis based on the basis and return the reordered paulis.

Returns

the ordered paulis based on the basis.

Return type

list[list[complex, paulis]]

rounding

WeightedPauliOperator.rounding(decimals, copy=False)

Rounding the weight.

Parameters

decimals (int) – rounding the weight to the decimals.
copy (bool) – chop on a copy or self

Returns

operator

Return type

WeightedPauliOperator

simplify

WeightedPauliOperator.simplify(copy=False)

Merge the paulis whose bases are identical and the pauli with zero coefficient would be removed.

Note

This behavior of this method is slightly changed, it will remove the paulis whose weights are zero.

Parameters

copy (bool) - simplify on a copy or self

Returns

the simplified operator

Return type

WeightedPauliOperator

sub

WeightedPauliOperator.sub(other, copy=False)

Perform self - other.

Parameters

other (WeightedPauliOperator) – to-be-combined operator
copy (bool) – working on a copy or self, if False, the results are written back to self.

Returns

operator

Return type

WeightedPauliOperator

to_dict

WeightedPauliOperator.to_dict()

Save operator to a dict in pauli representation.

Returns

a dictionary contains an operator with pauli representation.

Return type

dict

to_file

WeightedPauliOperator.to_file(file_name)

Save operator to a file in pauli representation.

Parameters

file_name (str) - path to the file

to_opflow

WeightedPauliOperator.to_opflow(reverse_endianness=False)

to op flow

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