Digital quantum simulation for spin and fermionic systems

This is the reference documentation for the qat.fermion module. Its aim is to provide 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.

This includes, among others:

• objects to help you define fermionic and spin Hamiltonians,

• spin-to-fermion transformations, such as Jordan-Wigner, Bravyi-Kitaev or parity basis transformations,

• variational quantum eigensolver (VQE) tools, including a module to construct a UCC ansatz,

• tools aimed at atomic and molecule studies (active space selection, basis transformations,…etc),

• a trotterization module,

• a quantum phase estimation module,

• an adaptative ansatz VQE plugin (ADAPT-VQE),

• a natural gradient-based optimizer,

• a sequential hybrid classical-quantum optimizer,

• a zero noise extrapolator plugin for multiqubit noise mitigation,

• …

qat.fermion features have been broken down into three parts.

We also provide the following Jupyter notebooks:

• Spin-fermions transforms

• Variational Quantum Eigensolver for fermions

• VQE for a H2 molecule using the UCC ansatz

• VQE for a LiH molecule using the UCC ansatz

• Quantum Phase Estimation on the Hubbard molecule

• Advanced VQE: Quantum Subspace Expansion

• Natural gradient-based optimizer

• Optimizing circuits with the sequential optimization plugin

• Running several optimizations and keeping the best one with MultipleLaunchesPlugin

• Mitigating multiqubit noise (QLM users only)

• The source code documentation is available here.

• The changelog is available here.