Glossary

mode

: One ordered single-particle label combination in FermionModes or BosonModes.

Fock state

: One occupation-number basis state. Fermionic occupations are 0 or 1; bosonic occupations are non-negative integers.

Fock basis

: Ordered occupation-number basis spanning a finite many-body sector.

Fock vector

: A ket represented by coefficients in the ordered basis of a built sector.

Fock bra

: Hermitian adjoint of a Fock-space ket, used in expressions such as psi.dag * O * psi.

fixed-particle-number sector

: Subspace with a fixed eigenvalue \(N\) of the total number operator.

symmetry-constrained sector

: A fixed-particle-number sector with additional fixed eigenvalues of commuting number operators, such as \(N_\uparrow\) and \(N_\downarrow\). Such constraints are specified with NParticleSector.project_particles(...) before build().

operator expression

: A second-quantized sum or ordered product constructed from creation, annihilation, number, and scalar operators.

CSC

: Compressed sparse column format used by the explicit sparse Hamiltonian matrix.

matrix-free eigensolve

: Partial eigensolution in which ARPACK receives the action of \(H\) on vectors through a LinearOperator instead of an explicitly stored Hamiltonian matrix.

natural occupations

: Eigenvalues of the one-body density matrix \(\rho^{(1)}_{ij}=\langle a_i^\dagger a_j\rangle\).