qat.core.Observable

Check this notebook for an example of use and manipulation of observables.

class qat.core.Observable(nqbits, matrix=None, pauli_terms=None, ising=None, constant_coeff=0.0)

Class describing an observable (i.e some Hermitian operator) over the Hilbert space spanned by a list of qbits.

The observable is stored as a sum of Terms, each composed of a Pauli operator and a real coefficient. It is also possible to store it with an Ising object which represents an Ising Hamiltonian.

The purpose of this class is mainly to efficiently automatize the sampling of this observable on the final state obtained after a computation.

Construction:

An Observable object can be constructed in various ways:

using a matrix representation:

using a list of Term:

or using an Ising object from the Ising:

Parameters:

  • nqbits (int) – number of qubits

  • matrix (np.array, optional) – the matrix representing the observable. Defaults to None.

  • pauli_terms (list<Term>, optional) – the list of products of Pauli operators representing the observable. Defaults to None.

  • ising (Ising, optional) – an object representing an Ising encoded problem. Defaults to None.

  • constant_coeff (float) – a constant additive term

terms

the list of products of Pauli operators representing the observable.

Type:

list<Term>

ising

represents an Ising encoded problem (present if terms is None)

Type:

Ising, optional

nbqbits

the number of qbits on which the observable acts

Type:

int

constant_coeff

a constant additive term

Type:

float

dump(fname)

Dumps the Qaptiva object in a binary file

Warning

The filename name can be extended to have extension ".obs"

Parameters:

fname (str) – the file name

classmethod load(fname)

Loads a Qaptiva object from a binary file

Warning

The filename name can be extended to have an extension

Parameters:

fname (str) – the file name

Returns:

An instance of the loaded object

to_matrix(sparse: bool = True)

Returns the matrix representation of the Observable.

Parameters:

sparse (bool, optional) – If a sparse matrix should be returned. Default to True.

Returns:

numpy.ndarray or scipy.sparse.spmatrix

Note

Not implemented for other representation than using Pauli chains.