qat.fermion

qat.fermion module aims at providing tools for describing and solving spin and fermionic problems. The code of qat.fermion is open-source and part of the myQLM suite. The source code can be found here.

Hamiltonians constructors

To help you write your own Hamiltonian for various spin and fermionic systems, we provide various Hamiltonian classes.

`qat.fermion.hamiltonians.ElectronicStructureHamiltonian`	Electronic structure hamiltonian constructor
`qat.fermion.hamiltonians.SpinHamiltonian`	Spin hamiltonian constructor

Common many-body Hamiltonians

Some of the most common models have their own Hamiltonian generators.

`qat.fermion.hamiltonians.make_anderson_model()`	The single-impurity Anderson Model
`qat.fermion.hamiltonians.make_embedded_model()`	The generalized impurity Hamiltonian
`qat.fermion.hamiltonians.make_hubbard_model()`	Hubbard model hamiltonian

The spin-fermion transforms

Various fermionic-to-spin transforms are provided.

`qat.fermion.transforms.transform_to_bk_basis()`	Fermionic to spin using Bravyi-Kitaev encoding
`qat.fermion.transforms.transform_to_jw_basis()`	Fermionic to spin using Jordan-Wigner encoding
`qat.fermion.transforms.transform_to_parity_basis()`	Fermionic to spin using parity encoding

Fermionic ansatz circuits

We provide various common ansatz generators.

`qat.fermion.circuits.make_compressed_ldca_circ()`	Constructs a compressed version of the LDCA ansatz circuit (only for Qaptiva™ users)
`qat.fermion.circuits.make_general_hwe_circ()`	Constructs a hardware efficient ansatz
`qat.fermion.circuits.make_ldca_circ()`	Constructs a LDCA circuit
`qat.fermion.circuits.make_mr_circ()`	Constructs a small one-parameter Multi-Reference (MR) circuit on 4 qubits
`qat.fermion.circuits.make_mrep_circ()`	Constructs the 8-qubit Multi-Reference Excitation Preserving (MREP) ansatz
`qat.fermion.circuits.make_shallow_circ()`	Constructs the 8-parameter circuit proposed in Keen et al. article (2019)

Atomic and molecular studies

We provide helper classes aimed at automating various aspects of atomic and molecular studies.

`qat.fermion.chemistry.wrapper.MolecularHamiltonian`	Molecular hamiltonian helper class
`qat.fermion.chemistry.wrapper.MoleculeInfo`	Helper class for handling molecular systems computations

Unitary Coupled-Cluster (UCC)

We provide various tools specific to UCC.

`qat.fermion.chemistry.ucc.compute_active_space_integrals()`	Restrict one- and two-body integrals for given list of active indices
`qat.fermion.chemistry.ucc.construct_ucc_ansatz()`	Builds the parametric state preparation circuit implementing the provided cluster operator
`qat.fermion.chemistry.ucc.convert_to_h_integrals()`	Converts one and two-body integrals to electronic structure hamiltonian terms
`qat.fermion.chemistry.ucc.get_cluster_ops()`	Compute the cluster operators
`qat.fermion.chemistry.ucc.get_hf_ket()`	Get Hartree-Fock state stored as a vector with right-to-left orbitals indexing
`qat.fermion.chemistry.ucc.guess_init_params()`	Find initial parameters using Møller-Plesset perturbation theory
`qat.fermion.chemistry.ucc.select_active_orbitals()`	Selects the right active space and freezes core electrons according to their natural orbitals occupation numbers
`qat.fermion.chemistry.ucc.transform_integrals_to_new_basis()`	Change one and two-body integrals to new basis

Quantum subspace expansion

An implementation of the quantum subspace expansion is available.

qat.fermion.chemistry.qse.apply_quantum_subspace_expansion()

Apply quantum subspace expansion to a given Hamiltonian

Quantum phase estimation

An implementation of the quantum phase estimation algorithm is available.

qat.fermion.phase_estimation.perform_phase_estimation()

Perform quantum phase estimation on an ElectronicStructureHamiltonian

Utility functions

Two utility functions may be used to speed up your own implementations.

`qat.fermion.trotterisation.make_trotterisation_routine()`	Trotterizes (first order) the evolution operator of a Hamiltonian
`qat.fermion.chemistry.pyscf_tools.perform_pyscf_computation()`	Helper function to perform various calculations using PySCF