CouplingMap

CouplingMap.add_edge(src, dst)

Add directed edge to coupling graph.

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

CouplingMap.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

CouplingMap.compute_distance_matrix()

Compute the full distance matrix on pairs of nodes.

The distance map self._dist_matrix is computed from the graph using all_pairs_shortest_path_length. This is normally handled internally by the distance_matrix attribute or the distance() method but can be called if you’re accessing the distance matrix outside of those or want to pre-generate it.

CouplingMap.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

CouplingMap.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

MissingOptionalLibraryError – when pydot or pillow are not installed.

classmethod CouplingMap.from_full(num_qubits, bidirectional=True)

Return a fully connected coupling map on n qubits.

Return type

CouplingMap

classmethod CouplingMap.from_grid(num_rows, num_columns, bidirectional=True)

Return a coupling map of qubits connected on a grid of num_rows x num_columns.

Return type

CouplingMap

classmethod CouplingMap.from_heavy_hex(distance, bidirectional=True)

Return a heavy hexagon graph coupling map.

A heavy hexagon graph is described in:

https://journals.aps.org/prx/abstract/10.1103/PhysRevX.10.011022

Parameters

• distance (int) – The code distance for the generated heavy hex graph. The value for distance can be any odd positive integer. The distance relates to the number of qubits by: $n = \frac{5d^2 - 2d - 1}{2}$ where $n$ is the number of qubits and $d$ is the distance parameter.
• bidirectional (bool) – Whether the edges in the output coupling graph are bidirectional or not. By default this is set to True

Returns

A heavy hex coupling graph

Return type

CouplingMap

classmethod CouplingMap.from_heavy_square(distance, bidirectional=True)

Return a heavy square graph coupling map.

A heavy square graph is described in:

https://journals.aps.org/prx/abstract/10.1103/PhysRevX.10.011022

Parameters

• distance (int) – The code distance for the generated heavy square graph. The value for distance can be any odd positive integer. The distance relates to the number of qubits by: $n = 3d^2 - 2d$ where $n$ is the number of qubits and $d$ is the distance parameter.
• bidirectional (bool) – Whether the edges in the output coupling graph are bidirectional or not. By default this is set to True

Returns

A heavy square coupling graph

Return type

CouplingMap

classmethod CouplingMap.from_hexagonal_lattice(rows, cols, bidirectional=True)

Return a hexagonal lattice graph coupling map.

Parameters

• rows (int) – The number of rows to generate the graph with.
• cols (int) – The number of columns to generate the graph with.
• bidirectional (bool) – Whether the edges in the output coupling graph are bidirectional or not. By default this is set to True

Returns

A hexagonal lattice coupling graph

Return type

CouplingMap

classmethod CouplingMap.from_line(num_qubits, bidirectional=True)

Return a coupling map of n qubits connected in a line.

Return type

CouplingMap

classmethod CouplingMap.from_ring(num_qubits, bidirectional=True)

Return a coupling map of n qubits connected to each of their neighbors in a ring.

Return type

CouplingMap

CouplingMap.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)

CouplingMap.is_connected()

Test if the graph is connected.

Return True if connected, False otherwise

CouplingMap.largest_connected_component()

Return a set of qubits in the largest connected component.

CouplingMap.make_symmetric()

Convert uni-directional edges into bi-directional.

CouplingMap.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.

CouplingMap.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.

CouplingMap.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.

CouplingMap.size()

Return the number of physical qubits in this graph.

CouplingMap.subgraph(nodelist)

Return a CouplingMap object for a subgraph of self.

nodelist (list): list of integer node labels

Return the distance matrix for the coupling map.

Test if the graph is symmetric.

Return True if symmetric, False otherwise

Returns a sorted list of physical_qubits