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:
- 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>
- nbqbits
the number of qbits on which the observable acts
- Type
int
- constant_coeff
a constant additive term
- Type
float
- dump(fname)
Dumps the observable in a binary file (.circ)
- Parameters
fname (str) – the file name
- classmethod load(fname)
Loads an observable from a binary file.
- Parameters
fname (str) – the file name
- Returns
an observable
- Return type
- 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.