qat.fermion.hamiltonians.SpinHamiltonian

class qat.fermion.hamiltonians.SpinHamiltonian(nqbits: int, terms: List[Term], constant_coeff: float = 0.0)

Implementation of a spin Hamiltonian.

Parameters

• nqbits (int) – the total number of qubits

• terms (List[Term]) – the list of terms

• constant_coeff (float) – constant term

nbqbits

the total number of qubits

Type

int

terms

the list of terms

Type

List[Term]

constant_coeff

constant term

Type

float

matrix

the corresponding matrix (None by default, can be set by calling get_matrix method)

Type

np.ndarray

Example

from qat.core import Term
from qat.fermion import SpinHamiltonian

hamiltonian = SpinHamiltonian(2, [Term(0.3, "X", [0]), Term(-0.4, "ZY", [0, 1])])

print(f"H = {hamiltonian}")
print(f"H matrix: {hamiltonian.get_matrix()}")

H = 0.3 * (X|[0]) +
-0.4 * (ZY|[0, 1])
H matrix: [[0. +0.j  0. +0.4j 0.3+0.j  0. +0.j ]
 [0. -0.4j 0. +0.j  0. +0.j  0.3+0.j ]
 [0.3+0.j  0. +0.j  0. +0.j  0. -0.4j]
 [0. +0.j  0.3+0.j  0. +0.4j 0. +0.j ]]

copy()

Deepcopy the current class.

Returns

Copy of the SpinHamiltonian.

Return type

SpinHamiltonian

dag() → SpinHamiltonian

Compute the conjugate transpose of the Hamiltonian.

Returns

Conjugate transpose of the SpinHamiltonian operator

Return type

SpinHamiltonian

get_matrix(sparse: bool = False) → ndarray

This function returns the matrix corresponding to \(H\) in the computational basis.

Parameters

• sparse (Optional[bool]) – Whether to return in sparse representation.

• False. (Defaults to) –

Returns

The matrix of the SpinHamiltonian.

Return type

np.ndarray

Warning

This method should not be used if the SpinHamiltonian is too large.