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- """
- Provides an extremely basic graph structure, based on neighbour lists
- """
-
- import itertools as it
- import clifford
- import json
- import qi
- import networkx as nx
-
- class GraphState(object):
-
- def __init__(self, nodes=[]):
- self.adj, self.node = {}, {}
- self.add_nodes(nodes)
-
- def add_node(self, v, position = None, meta = {}):
- """ Add a node """
- assert not v in self.node
- self.adj[v] = {}
- self.node[v] = {"vop": clifford.by_name["hadamard"],
- "position": position}
- self.node[v].update(meta)
-
- def add_nodes(self, nodes):
- """ Add a buncha nodes """
- for n in nodes:
- self.add_node(n)
-
- def add_edge(self, v1, v2, data = {}):
- """ Add an edge between two vertices in the self """
- assert v1 != v2
- self.adj[v1][v2] = data
- self.adj[v2][v1] = data
-
- def add_edges(self, edges):
- """ Add a buncha edges """
- for (v1, v2) in edges:
- self.add_edge(v1, v2)
-
- def del_edge(self, v1, v2):
- """ Delete an edge between two vertices in the self """
- del self.adj[v1][v2]
- del self.adj[v2][v1]
-
- def has_edge(self, v1, v2):
- """ Test existence of an edge between two vertices in the self """
- return v2 in self.adj[v1]
-
- def toggle_edge(self, v1, v2):
- """ Toggle an edge between two vertices in the self """
- if self.has_edge(v1, v2):
- self.del_edge(v1, v2)
- else:
- self.add_edge(v1, v2)
-
- def edgelist(self):
- """ Describe a graph as an edgelist """
- # TODO: inefficient
- edges = set(tuple(sorted((i, n)))
- for i, v in self.adj.items()
- for n in v)
- return tuple(edges)
-
- def remove_vop(self, a, avoid):
- """ Reduces VOP[a] to the identity """
- #TODO: inefficient
- others = set(self.adj[a]) - {avoid}
- swap_qubit = others.pop() if others else avoid
- for v in reversed(clifford.decompositions[self.node[a]["vop"]]):
- self.local_complementation(a if v == "x" else swap_qubit)
-
- def local_complementation(self, v):
- """ As defined in LISTING 1 of Anders & Briegel """
- for i, j in it.combinations(self.adj[v], 2):
- self.toggle_edge(i, j)
-
- msqx_h = clifford.conjugation_table[clifford.by_name["msqx"]]
- sqz_h = clifford.conjugation_table[clifford.by_name["sqz"]]
- self.node[v]["vop"] = clifford.times_table[self.node[v]["vop"], msqx_h]
- for i in self.adj[v]:
- self.node[i]["vop"] = clifford.times_table[self.node[i]["vop"], sqz_h]
-
- def act_local_rotation(self, v, op):
- """ Act a local rotation """
- rotation = clifford.by_name[str(op)]
- self.node[v]["vop"] = clifford.times_table[rotation, self.node[v]["vop"]]
-
- def act_hadamard(self, qubit):
- """ Shorthand """
- self.act_local_rotation(qubit, 10)
-
- def act_cz(self, a, b):
- """ Act a controlled-phase gate on two qubits """
- #TODO: inefficient
- if set(self.adj[a]) - {b}:
- self.remove_vop(a, b)
- if set(self.adj[b]) - {a}:
- self.remove_vop(b, a)
- if set(self.adj[a]) - {b}:
- self.remove_vop(a, b)
- edge = int(self.has_edge(a, b))
- new_edge, self.node[a]["vop"], self.node[
- b]["vop"] = clifford.cz_table[edge, self.node[a]["vop"], self.node[b]["vop"]]
- if new_edge != edge:
- self.toggle_edge(a, b)
-
- def measure_z(self, node, force=None):
- """ Measure the graph in the Z-basis """
- res = force if force else np.random.choice([0, 1])
-
- # Disconnect
- for neighbour in self.adj[node]:
- self.del_edge(node, neighbour)
- if res:
- self.act_local_rotation(neighbour, "pz")
-
- # Rotate
- if res:
- self.act_local_rotation(node, "px")
- self.act_local_rotation(node, "hadamard")
- else:
- self.act_local_rotation(node, "hadamard")
-
- return res
-
- def measure_x(self, i):
- """ Measure the graph in the X-basis """
- # TODO
- pass
-
- def measure_y(self, i):
- """ Measure the graph in the Y-basis """
- # TODO
- pass
-
- def order(self):
- """ Get the number of qubits """
- return len(self.node)
-
- def __str__(self):
- """ Represent as a string for quick debugging """
- node = {key: clifford.get_name(value["vop"])
- for key, value in self.node.items()}
- nbstr = str(self.adj)
- return "graph:\n node: {}\n adj: {}\n".format(node, nbstr)
-
- def to_json(self):
- """ Convert the graph to JSON form """
- return {"node": self.node, "adj": self.adj}
-
- def from_json(self, data):
- """ Reconstruct from JSON """
- self.__init__([])
- #TODO
-
- def to_state_vector(self):
- """ Get the full state vector """
- if len(self.node) > 15:
- raise ValueError("Cannot build state vector: too many qubits")
- state = qi.CircuitModel(len(self.node))
- for i in range(len(self.node)):
- state.act_hadamard(i)
- for i, j in self.edgelist():
- state.act_cz(i, j)
- for i, n in self.node.items():
- state.act_local_rotation(i, clifford.unitaries[n["vop"]])
- return state
-
- def to_stabilizer(self):
- """ Get the stabilizer of this graph """
- # TODO: VOPs are not implemented yet
- output = ""
- for a in self.adj:
- for b in self.adj:
- if a == b:
- output += " X "
- elif a in self.adj[b]:
- output += " Z "
- else:
- output += " I "
- output += "\n"
- return output
-
- def adj_list(self):
- """ For comparison with Anders and Briegel's C++ implementation """
- rows = []
- for key, node in self.node.items():
- adj = " ".join(map(str, sorted(self.adj[key])))
- vop = clifford.get_name(node["vop"])
- s = "Vertex {}: VOp {}, neighbors {}".format(key, vop, adj)
- rows.append(s)
- return " \n".join(rows) + " \n"
-
- def __eq__(self, other):
- """ Check equality between graphs """
- return self.adj == other.adj and self.node == other.node
-
-
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