NBodyTerm Class

N-body interaction terms defined by an ordered list of operators and relative displacements on a hypercubic lattice.

class edlgt.modeling.nbody_term.NBodyTerm(op_list, op_names_list, distances, **kwargs)[source]

Bases: QMBTerm

Ordered N-body term generated from a site and fixed displacements.

Initialize an N-body lattice term.

Parameters:

  • op_list (list) – Operators participating in the N-body term.

  • op_names_list (list[str]) – Labels corresponding to op_list.

  • distances (list[tuple]) – Relative lattice displacements from the starting site to each additional operator. Its length must be len(op_list) - 1.

  • **kwargs – Additional arguments forwarded to QMBTerm.

Raises:

ValueError – If len(distances) != len(op_list) - 1.

get_hamiltonian(strength, add_dagger=False, mask=None)[source]

Assemble the lattice-summed N-body Hamiltonian term.

Parameters:

  • strength (scalar) – Coupling constant multiplying the term.

  • add_dagger (bool, optional) – If True, add the Hermitian conjugate of the assembled term.

  • mask (numpy.ndarray, optional) – Boolean mask selecting the starting sites where the term is applied.

Returns:

Return type depends on the current workflow:

  • if self.sector_configs is None: sparse matrix Hamiltonian term;

  • otherwise: (row_list, col_list, value_list) as three NumPy arrays in the symmetry-reduced basis.

Return type:

scipy.sparse.spmatrix or tuple

Raises:
get_Hamiltonian(strength, add_dagger=False, mask=None)

Assemble the lattice-summed N-body Hamiltonian term.

Parameters:

  • strength (scalar) – Coupling constant multiplying the term.

  • add_dagger (bool, optional) – If True, add the Hermitian conjugate of the assembled term.

  • mask (numpy.ndarray, optional) – Boolean mask selecting the starting sites where the term is applied.

Returns:

Return type depends on the current workflow:

  • if self.sector_configs is None: sparse matrix Hamiltonian term;

  • otherwise: (row_list, col_list, value_list) as three NumPy arrays in the symmetry-reduced basis.

Return type:

scipy.sparse.spmatrix or tuple

Raises:
get_expval(psi, component='real', print_values=True)[source]

Compute site-resolved expectation values of the N-body term.

Parameters:

  • psi (edlgt.modeling.qmb_state.QMB_state) – Quantum state used to evaluate the term.

  • component (str, optional) – Output component selector: "real" or "imag".

  • print_values (bool, optional) – If True, log the measured values site by site.

Returns:

Results are stored in self.obs as a 1D NumPy array.

Return type:

None

Raises:

TypeError – If psi is not a QMB_state.

get_nbody_neighbors(coords)[source]

Compute the ordered lattice sites touched by the N-body pattern.

Parameters:

coords (tuple) – Coordinates of the starting site.

Returns:

(neighbor_coords, neighbor_sites). If the pattern exits the lattice under open boundaries, returns (None, None).

Return type:

tuple

Notes

Distances are interpreted as displacements from the starting site coords (not cumulative displacements between successive operators).