ffsim.random.random_fermion_operator

ffsim.random.random_fermion_operator(norb, *, n_terms=None, max_term_length=None, num_and_spin_conserving=False, seed=None)[source]

Sample a random fermion operator.

The terms are sampled independently and uniformly: the length of a term is uniform in [1, max_term_length], and each of its actions is a creation or annihilation operator, a spin, and an orbital, each chosen uniformly. If num_and_spin_conserving is set to True, then a term is instead built from a uniform number of excitations, each of which pairs a creation with an annihilation operator acting on the same spin. Coefficients are standard complex Gaussians. Because repeated terms are combined, the sampled operator may have fewer than n_terms terms.

Parameters:

  • norb (int) – The number of spatial orbitals.

  • n_terms (int | None) – The number of terms to include in the operator. If not specified, norb is used.

  • max_term_length (int | None) – The maximum length of a term. If not specified, 2 * norb is used.

  • num_and_spin_conserving (bool) – Whether to sample an operator that conserves particle number and the z component of spin.

  • seed – A seed to initialize the pseudorandom number generator. Should be a valid input to np.random.default_rng.

Return type:

FermionOperator

Returns:

The sampled fermion operator.