NLocal
class qiskit.circuit.library.NLocal(num_qubits=None, rotation_blocks=None, entanglement_blocks=None, entanglement=None, reps=1, insert_barriers=False, parameter_prefix='θ', overwrite_block_parameters=True, skip_final_rotation_layer=False, skip_unentangled_qubits=False, initial_state=None, name='nlocal', flatten=None)
Bases: BlueprintCircuit
The n-local circuit class.
The structure of the n-local circuit are alternating rotation and entanglement layers. In both layers, parameterized circuit-blocks act on the circuit in a defined way. In the rotation layer, the blocks are applied stacked on top of each other, while in the entanglement layer according to the entanglement strategy. The circuit blocks can have arbitrary sizes (smaller equal to the number of qubits in the circuit). Each layer is repeated reps times, and by default a final rotation layer is appended.
For instance, a rotation block on 2 qubits and an entanglement block on 4 qubits using 'linear' entanglement yields the following circuit.
┌──────┐ ░ ┌──────┐ ░ ┌──────┐
┤0 ├─░─┤0 ├──────────────── ... ─░─┤0 ├
│ Rot │ ░ │ │┌──────┐ ░ │ Rot │
┤1 ├─░─┤1 ├┤0 ├──────── ... ─░─┤1 ├
├──────┤ ░ │ Ent ││ │┌──────┐ ░ ├──────┤
┤0 ├─░─┤2 ├┤1 ├┤0 ├ ... ─░─┤0 ├
│ Rot │ ░ │ ││ Ent ││ │ ░ │ Rot │
┤1 ├─░─┤3 ├┤2 ├┤1 ├ ... ─░─┤1 ├
├──────┤ ░ └──────┘│ ││ Ent │ ░ ├──────┤
┤0 ├─░─────────┤3 ├┤2 ├ ... ─░─┤0 ├
│ Rot │ ░ └──────┘│ │ ░ │ Rot │
┤1 ├─░─────────────────┤3 ├ ... ─░─┤1 ├
└──────┘ ░ └──────┘ ░ └──────┘
| |
+---------------------------------+
repeated reps timesIf specified, barriers can be inserted in between every block. If an initial state object is provided, it is added in front of the NLocal.
The n_local() function constructs a functionally equivalent circuit, but faster.
The class qiskit.circuit.library.n_local.n_local.NLocal is deprecated as of Qiskit 2.1. It will be removed in Qiskit 3.0. This applies to NLocal subclasses too. Use the corresponding function from the module qiskit.circuit.library.n_local instead.
Parameters
- num_qubits (int | None) – The number of qubits of the circuit.
- rotation_blocks (QuantumCircuit |list[QuantumCircuit] | qiskit.circuit.Instruction |list[qiskit.circuit.Instruction] | None) – The blocks used in the rotation layers. If multiple are passed, these will be applied one after another (like new sub-layers).
- entanglement_blocks (QuantumCircuit |list[QuantumCircuit] | qiskit.circuit.Instruction |list[qiskit.circuit.Instruction] | None) – The blocks used in the entanglement layers. If multiple are passed, these will be applied one after another. To use different entanglements for the sub-layers, see
get_entangler_map(). - entanglement (list[int] | list[list[int]] | None) – The indices specifying on which qubits the input blocks act. If
None, the entanglement blocks are applied at the top of the circuit. - reps (int) – Specifies how often the rotation blocks and entanglement blocks are repeated.
- insert_barriers (bool) – If
True, barriers are inserted in between each layer. IfFalse, no barriers are inserted. - parameter_prefix (str) – The prefix used if default parameters are generated.
- overwrite_block_parameters (bool |list[list[Parameter]]) – If the parameters in the added blocks should be overwritten. If
False, the parameters in the blocks are not changed. - skip_final_rotation_layer (bool) – Whether a final rotation layer is added to the circuit.
- skip_unentangled_qubits (bool) – If
True, the rotation gates act only on qubits that are entangled. IfFalse, the rotation gates act on all qubits. - initial_state (QuantumCircuit | None) – A
QuantumCircuitobject which can be used to describe an initial state prepended to the NLocal circuit. - name (str | None) – The name of the circuit.
- flatten (bool | None) – Set this to
Trueto output a flat circuit instead of nesting it inside multiple layers of gate objects. By default currently the contents of the output circuit will be wrapped in nested objects for cleaner visualization. However, if you’re using this circuit for anything besides visualization its strongly recommended to set this flag toTrueto avoid a large performance overhead for parameter binding.
Raises
- ValueError – If
repsparameter is less than or equal to 0. - TypeError – If
repsparameter is not an int value.
Attributes
entanglement
Get the entanglement strategy.
Returns
The entanglement strategy, see get_entangler_map() for more detail on how the format is interpreted.
entanglement_blocks
The blocks in the entanglement layers.
Returns
The blocks in the entanglement layers.
flatten
Returns whether the circuit is wrapped in nested gates/instructions or flattened.
initial_state
Return the initial state that is added in front of the n-local circuit.
Returns
The initial state.
insert_barriers
If barriers are inserted in between the layers or not.
Returns
True, if barriers are inserted in between the layers, False if not.
num_layers
Return the number of layers in the n-local circuit.
Returns
The number of layers in the circuit.
num_parameters_settable
The number of total parameters that can be set to distinct values.
This does not change when the parameters are bound or exchanged for same parameters, and therefore is different from num_parameters which counts the number of unique Parameter objects currently in the circuit.
Returns
The number of parameters originally available in the circuit.
This quantity does not require the circuit to be built yet.
num_qubits
Returns the number of qubits in this circuit.
Returns
The number of qubits.
ordered_parameters
The parameters used in the underlying circuit.
This includes float values and duplicates.
Examples
>>> # prepare circuit ...
>>> print(nlocal)
┌───────┐┌──────────┐┌──────────┐┌──────────┐
q_0: ┤ Ry(1) ├┤ Ry(θ[1]) ├┤ Ry(θ[1]) ├┤ Ry(θ[3]) ├
└───────┘└──────────┘└──────────┘└──────────┘
>>> nlocal.parameters
{Parameter(θ[1]), Parameter(θ[3])}
>>> nlocal.ordered_parameters
[1, Parameter(θ[1]), Parameter(θ[1]), Parameter(θ[3])]Returns
The parameters objects used in the circuit.
parameter_bounds
The parameter bounds for the unbound parameters in the circuit.
Returns
A list of pairs indicating the bounds, as (lower, upper). None indicates an unbounded parameter in the corresponding direction. If None is returned, problem is fully unbounded.
preferred_init_points
The initial points for the parameters. Can be stored as initial guess in optimization.
Returns
The initial values for the parameters, or None, if none have been set.
reps
The number of times rotation and entanglement block are repeated.
Returns
The number of repetitions.
rotation_blocks
The blocks in the rotation layers.
Returns
The blocks in the rotation layers.
name
Type: str
A human-readable name for the circuit.
Example
from qiskit import QuantumCircuit
qc = QuantumCircuit(2, 2, name="my_circuit")
print(qc.name)my_circuitMethods
add_layer
add_layer(other, entanglement=None, front=False)
Append another layer to the NLocal.
Parameters
- other (QuantumCircuit |qiskit.circuit.Instruction) – The layer to compose, can be another NLocal, an Instruction or Gate, or a QuantumCircuit.
- entanglement (list[int] | str |list[list[int]] | None) – The entanglement or qubit indices.
- front (bool) – If True,
otheris appended to the front, else to the back.
Returns
self, such that chained composes are possible.
Raises
TypeError – If other is not compatible, i.e. is no Instruction and does not have a to_instruction method.
Return type
assign_parameters
assign_parameters(parameters, inplace=False, **kwargs)
Assign parameters to the n-local circuit.
This method also supports passing a list instead of a dictionary. If a list is passed, the list must have the same length as the number of unbound parameters in the circuit. The parameters are assigned in the order of the parameters in ordered_parameters().
Returns
A copy of the NLocal circuit with the specified parameters.
Raises
AttributeError – If the parameters are given as list and do not match the number of parameters.
Parameters
- parameters (Mapping[Parameter, ParameterExpression |float] | Sequence[ParameterExpression |float]) –
- inplace (bool) –
Return type
QuantumCircuit | None
get_entangler_map
get_entangler_map(rep_num, block_num, num_block_qubits)
Get the entangler map for in the repetition rep_num and the block block_num.
The entangler map for the current block is derived from the value of self.entanglement. Below the different cases are listed, where i and j denote the repetition number and the block number, respectively, and n the number of qubits in the block.
| entanglement type | entangler map |
|---|
| None | [[0, ..., n - 1]] |
| str (e.g 'full') | the specified connectivity on n qubits |
| List[int] | [entanglement] |
| List[List[int]] | entanglement |
| List[List[List[int]]] | entanglement[i] |
| List[List[List[List[int]]]] | entanglement[i][j] |
| List[str] | the connectivity specified in entanglement[i] |
| List[List[str]] | the connectivity specified in entanglement[i][j] |
| Callable[int, str] | same as List[str] |
| Callable[int, List[List[int]]] | same as List[List[List[int]]] |
Note that all indices are to be taken modulo the length of the array they act on, i.e. no out-of-bounds index error will be raised but we re-iterate from the beginning of the list.
Parameters
- rep_num (int) – The current repetition we are in.
- block_num (int) – The block number within the entanglement layers.
- num_block_qubits (int) – The number of qubits in the block.
Returns
The entangler map for the current block in the current repetition.
Raises
ValueError – If the value of entanglement could not be cast to a corresponding entangler map.
Return type
get_unentangled_qubits
get_unentangled_qubits()
Get the indices of unentangled qubits in a set.
Returns
The unentangled qubits.
Return type
print_settings
print_settings()
Returns information about the setting.
Returns
The class name and the attributes/parameters of the instance as str.
Return type