Source code for qutip_qip.operations.measurement

from collections.abc import Iterable
import numbers
import os

import numpy as np

from qutip import basis, Qobj
from qutip.measurement import measurement_statistics
from .gates import expand_operator


__all__ = ["Measurement"]


[docs]class Measurement: """ Representation of a quantum measurement, with its required parameters, and target qubits. Parameters ---------- name : string Measurement name. targets : list or int Gate targets. classical_store : int Result of the measurment is stored in this classical register of the circuit. """ def __init__(self, name, targets=None, index=None, classical_store=None): """ Create a measurement with specified parameters. """ self.name = name self.targets = None self.classical_store = classical_store self.index = index if not isinstance(targets, Iterable) and targets is not None: self.targets = [targets] else: self.targets = targets for ind_list in [self.targets]: if isinstance(ind_list, Iterable): all_integer = all( [isinstance(ind, numbers.Integral) for ind in ind_list] ) if not all_integer: raise ValueError("Index of a qubit must be an integer")
[docs] def measurement_comp_basis(self, state): """ Measures a particular qubit (determined by the target) whose ket vector/ density matrix is specified in the computational basis and returns collapsed_states and probabilities (retains full dimension). Parameters ---------- state : ket or oper state to be measured on specified by ket vector or density matrix Returns ------- collapsed_states : List of Qobjs the collapsed state obtained after measuring the qubits and obtaining the qubit specified by the target in the state specified by the index. probabilities : List of floats the probability of measuring a state in a the state specified by the index. """ n = int(np.log2(state.shape[0])) target = self.targets[0] if target < n: op0 = basis(2, 0) * basis(2, 0).dag() op1 = basis(2, 1) * basis(2, 1).dag() measurement_ops = [op0, op1] else: raise ValueError("target is not valid") measurement_ops = [ expand_operator(op, N=n, targets=self.targets) for op in measurement_ops ] return measurement_statistics(state, measurement_ops)
def __str__(self): str_name = ("Measurement(%s, target=%s, classical_store=%s)") % ( self.name, self.targets, self.classical_store, ) return str_name def __repr__(self): return str(self) def _repr_latex_(self): return str(self) def _to_qasm(self, qasm_out): """ Pipe output of measurement to QasmOutput object. Parameters ---------- qasm_out: QasmOutput object to store QASM output. """ qasm_out.output( "measure q[{}] -> c[{}]".format( self.targets[0], self.classical_store ) )