Operator
class qiskit.quantum_info.Operator(data, input_dims=None, output_dims=None)
Bases: LinearOp
Matrix operator class
This represents a matrix operator that will evolve()
a Statevector
by matrix-vector multiplication
and will evolve()
a DensityMatrix
by left and right multiplication
Initialize an operator object.
Parameters
- data (QuantumCircuit orOperation or BaseOperator or matrix) – data to initialize operator.
- input_dims (tuple) – the input subsystem dimensions. [Default: None]
- output_dims (tuple) – the output subsystem dimensions. [Default: None]
Raises
QiskitError – if input data cannot be initialized as an operator.
Additional Information:
If the input or output dimensions are None, they will be automatically determined from the input data. If the input data is a Numpy array of shape (2**N, 2**N) qubit systems will be used. If the input operator is not an N-qubit operator, it will assign a single subsystem with dimension specified by the shape of the input.
Attributes
atol
Default value: 1e-08
data
The underlying Numpy array.
dim
Return tuple (input_shape, output_shape).
num_qubits
Return the number of qubits if a N-qubit operator or None otherwise.
qargs
Return the qargs for the operator.
rtol
Default value: 1e-05
settings
Return operator settings.
Methods
adjoint
adjoint()
Return the adjoint of the Operator.
Return type
Self
apply_permutation
apply_permutation(perm, front=False)
Modifies operator’s data by composing it with a permutation.
Parameters
- perm (list) – permutation pattern, describing which qubits occupy the positions 0, 1, 2, etc. after applying the permutation.
- front (bool) – When set to
True
the permutation is applied before the operator, when set toFalse
the permutation is applied after the operator.
Returns
The modified operator.
Return type
Raises
QiskitError – if the size of the permutation pattern does not match the dimensions of the operator.
compose
compose(other, qargs=None, front=False)
Return the operator composition with another Operator.
Parameters
- other (Operator) – a Operator object.
- qargs (list or None) – Optional, a list of subsystem positions to apply other on. If None apply on all subsystems (default: None).
- front (bool) – If True compose using right operator multiplication, instead of left multiplication [default: False].
Returns
The composed Operator.
Return type
Raises
QiskitError – if other cannot be converted to an operator, or has incompatible dimensions for specified subsystems.
Composition (&
) by default is defined as left matrix multiplication for matrix operators, while @
(equivalent to dot()
) is defined as right matrix multiplication. That is that A & B == A.compose(B)
is equivalent to B @ A == B.dot(A)
when A
and B
are of the same type.
Setting the front=True
kwarg changes this to right matrix multiplication and is equivalent to the dot()
method A.dot(B) == A.compose(B, front=True)
.
conjugate
conjugate()
Return the conjugate of the Operator.
copy
copy()
Make a deep copy of current operator.
dot
dot(other, qargs=None)
Return the right multiplied operator self * other.
Parameters
- other (Operator) – an operator object.
- qargs (list or None) – Optional, a list of subsystem positions to apply other on. If None apply on all subsystems (default: None).
Returns
The right matrix multiplied Operator.
Return type
The dot product can be obtained using the @
binary operator. Hence a.dot(b)
is equivalent to a @ b
.
draw
draw(output=None, **drawer_args)
Return a visualization of the Operator.
repr: String of the state’s __repr__
.
text: ASCII TextMatrix that can be printed in the console.
latex: An IPython Latex object for displaying in Jupyter Notebooks.
latex_source: Raw, uncompiled ASCII source to generate array using LaTeX.
Parameters
- output (str) – Select the output method to use for drawing the state. Valid choices are repr, text, latex, latex_source, Default is repr.
- drawer_args – Arguments to be passed directly to the relevant drawing function or constructor (TextMatrix(), array_to_latex()). See the relevant function under qiskit.visualization for that function’s documentation.
Returns
Drawing of the Operator.
Return type
str
or TextMatrix
or IPython.display.Latex
Raises
ValueError – when an invalid output method is selected.
equiv
equiv(other, rtol=None, atol=None)
Return True if operators are equivalent up to global phase.
Parameters
- other (Operator) – an operator object.
- rtol (float) – relative tolerance value for comparison.
- atol (float) – absolute tolerance value for comparison.
Returns
True if operators are equivalent up to global phase.
Return type
expand
expand(other)
Return the reverse-order tensor product with another Operator.
Parameters
other (Operator) – a Operator object.
Returns
the tensor product , where
is the current Operator, and is the other Operator.
Return type
from_circuit
classmethod from_circuit(circuit, ignore_set_layout=False, layout=None, final_layout=None)
Create a new Operator object from a QuantumCircuit
While a QuantumCircuit
object can passed directly as data
to the class constructor this provides no options on how the circuit is used to create an Operator
. This constructor method lets you control how the Operator
is created so it can be adjusted for a particular use case.
By default this constructor method will permute the qubits based on a configured initial layout (i.e. after it was transpiled). It also provides an option to manually provide a Layout
object directly.
Parameters
- circuit (QuantumCircuit) – The
QuantumCircuit
to create an Operator object from. - ignore_set_layout (bool) – When set to
True
if the inputcircuit
has a layout set it will be ignored - layout (Layout) – If specified this kwarg can be used to specify a particular layout to use to permute the qubits in the created
Operator
. If this is specified it will be used instead of a layout contained in thecircuit
input. If specified the virtual bits in theLayout
must be present in thecircuit
input. - final_layout (Layout) – If specified this kwarg can be used to represent the output permutation caused by swap insertions during the routing stage of the transpiler.
Returns
An operator representing the input circuit
Return type
from_label
classmethod from_label(label)
Return a tensor product of single-qubit operators.
Parameters
label (string) – single-qubit operator string.
Returns
The N-qubit operator.
Return type
Raises
QiskitError – if the label contains invalid characters, or the length of the label is larger than an explicitly specified num_qubits.
Additional Information:
The labels correspond to the single-qubit matrices: ‘I’: [[1, 0], [0, 1]] ‘X’: [[0, 1], [1, 0]] ‘Y’: [[0, -1j], [1j, 0]] ‘Z’: [[1, 0], [0, -1]] ‘H’: [[1, 1], [1, -1]] / sqrt(2) ‘S’: [[1, 0], [0 , 1j]] ‘T’: [[1, 0], [0, (1+1j) / sqrt(2)]] ‘0’: [[1, 0], [0, 0]] ‘1’: [[0, 0], [0, 1]] ‘+’: [[0.5, 0.5], [0.5 , 0.5]] ‘-’: [[0.5, -0.5], [-0.5 , 0.5]] ‘r’: [[0.5, -0.5j], [0.5j , 0.5]] ‘l’: [[0.5, 0.5j], [-0.5j , 0.5]]
input_dims
input_dims(qargs=None)
Return tuple of input dimension for specified subsystems.
is_unitary
is_unitary(atol=None, rtol=None)
Return True if operator is a unitary matrix.
output_dims
output_dims(qargs=None)
Return tuple of output dimension for specified subsystems.
power
power(n)
Return the matrix power of the operator.
Parameters
n (float) – the power to raise the matrix to.
Returns
the resulting operator O ** n
.
Return type
Raises
QiskitError – if the input and output dimensions of the operator are not equal.
reshape
reshape(input_dims=None, output_dims=None, num_qubits=None)
Return a shallow copy with reshaped input and output subsystem dimensions.
Parameters
- input_dims (None or tuple) – new subsystem input dimensions. If None the original input dims will be preserved [Default: None].
- output_dims (None or tuple) – new subsystem output dimensions. If None the original output dims will be preserved [Default: None].
- num_qubits (None or int) – reshape to an N-qubit operator [Default: None].
Returns
returns self with reshaped input and output dimensions.
Return type
BaseOperator
Raises
QiskitError – if combined size of all subsystem input dimension or subsystem output dimensions is not constant.
reverse_qargs
reverse_qargs()
Return an Operator with reversed subsystem ordering.
For a tensor product operator this is equivalent to reversing the order of tensor product subsystems. For an operator the returned operator will be .
Returns
the operator with reversed subsystem order.
Return type
tensor
tensor(other)
Return the tensor product with another Operator.
Parameters
other (Operator) – a Operator object.
Returns
the tensor product , where
is the current Operator, and is the other Operator.
Return type
The tensor product can be obtained using the ^
binary operator. Hence a.tensor(b)
is equivalent to a ^ b
.
to_instruction
to_instruction()
Convert to a UnitaryGate instruction.
to_matrix
to_matrix()
Convert operator to NumPy matrix.
to_operator
transpose
transpose()
Return the transpose of the Operator.