qiskit.transpiler.CouplingMap

class CouplingMap(couplinglist=None, description=None)

Directed graph specifying fixed coupling.

Nodes correspond to physical qubits (integers) and directed edges correspond to permitted CNOT gates

Create coupling graph. By default, the generated coupling has no nodes.

Parameters

• couplinglist (list or None) – An initial coupling graph, specified as an adjacency list containing couplings, e.g. [[0,1], [0,2], [1,2]].

• description (str) – A string to describe the coupling map.

__init__(couplinglist=None, description=None)

Create coupling graph. By default, the generated coupling has no nodes.

Parameters

• couplinglist (list or None) – An initial coupling graph, specified as an adjacency list containing couplings, e.g. [[0,1], [0,2], [1,2]].

• description (str) – A string to describe the coupling map.

Methods

__init__([couplinglist, description])	Create coupling graph.
add_edge(src, dst)	Add directed edge to coupling graph.
add_physical_qubit(physical_qubit)	Add a physical qubit to the coupling graph as a node.
distance(physical_qubit1, physical_qubit2)	Returns the undirected distance between physical_qubit1 and physical_qubit2.
draw()	Draws the coupling map.
from_full(num_qubits[, bidirectional])	Return a fully connected coupling map on n qubits.
from_grid(num_rows, num_columns[, bidirectional])	Return qubits connected on a grid of num_rows x num_columns.
from_line(num_qubits[, bidirectional])	Return a fully connected coupling map on n qubits.
from_ring(num_qubits[, bidirectional])	Return a fully connected coupling map on n qubits.
get_edges()	Gets the list of edges in the coupling graph.
is_connected()	Test if the graph is connected.
largest_connected_component()	Return a set of qubits in the largest connected component.
make_symmetric()	Convert uni-directional edges into bi-directional.
neighbors(physical_qubit)	Return the nearest neighbors of a physical qubit.
reduce(mapping)	Returns a reduced coupling map that corresponds to the subgraph of qubits selected in the mapping.
shortest_undirected_path(physical_qubit1, …)	Returns the shortest undirected path between physical_qubit1 and physical_qubit2.
size()	Return the number of physical qubits in this graph.
subgraph(nodelist)	Return a CouplingMap object for a subgraph of self.

Attributes

distance_matrix	Return the distance matrix for the coupling map.
is_symmetric	Test if the graph is symmetric.
physical_qubits	Returns a sorted list of physical_qubits

add_edge(src, dst)

Add directed edge to coupling graph.

src (int): source physical qubit dst (int): destination physical qubit

add_physical_qubit(physical_qubit)

Add a physical qubit to the coupling graph as a node.

physical_qubit (int): An integer representing a physical qubit.

Raises

CouplingError – if trying to add duplicate qubit

distance(physical_qubit1, physical_qubit2)

Returns the undirected distance between physical_qubit1 and physical_qubit2.

Parameters

• physical_qubit1 (int) – A physical qubit

• physical_qubit2 (int) – Another physical qubit

Returns

The undirected distance

Return type

int

Raises

CouplingError – if the qubits do not exist in the CouplingMap

property distance_matrix

Return the distance matrix for the coupling map.

draw()

Draws the coupling map.

This function needs pydot, which in turn needs Graphviz to be installed. Additionally, pillow will need to be installed.

Returns

Drawn coupling map.

Return type

PIL.Image

Raises

ImportError – when pydot or pillow are not installed.

classmethod from_full(num_qubits, bidirectional=True)

Return a fully connected coupling map on n qubits.

classmethod from_grid(num_rows, num_columns, bidirectional=True)

Return qubits connected on a grid of num_rows x num_columns.

classmethod from_line(num_qubits, bidirectional=True)

Return a fully connected coupling map on n qubits.

classmethod from_ring(num_qubits, bidirectional=True)

Return a fully connected coupling map on n qubits.

get_edges()

Gets the list of edges in the coupling graph.

Returns

Each edge is a pair of physical qubits.

Return type

Tuple(int,int)

is_connected()

Test if the graph is connected.

Return True if connected, False otherwise

property is_symmetric

Test if the graph is symmetric.

Return True if symmetric, False otherwise

largest_connected_component()

Return a set of qubits in the largest connected component.

make_symmetric()

Convert uni-directional edges into bi-directional.

neighbors(physical_qubit)

Return the nearest neighbors of a physical qubit.

Directionality matters, i.e. a neighbor must be reachable by going one hop in the direction of an edge.

property physical_qubits

Returns a sorted list of physical_qubits

reduce(mapping)

Returns a reduced coupling map that corresponds to the subgraph of qubits selected in the mapping.

Parameters

mapping (list) – A mapping of reduced qubits to device qubits.

Returns

A reduced coupling_map for the selected qubits.

Return type

CouplingMap

Raises

CouplingError – Reduced coupling map must be connected.

shortest_undirected_path(physical_qubit1, physical_qubit2)

Returns the shortest undirected path between physical_qubit1 and physical_qubit2.

Parameters

• physical_qubit1 (int) – A physical qubit

• physical_qubit2 (int) – Another physical qubit

Returns

The shortest undirected path

Return type

List

Raises

CouplingError – When there is no path between physical_qubit1, physical_qubit2.

size()

Return the number of physical qubits in this graph.

subgraph(nodelist)

Return a CouplingMap object for a subgraph of self.

nodelist (list): list of integer node labels