Published April 11, 2024 | Version v1
Preprint Open

Extension of the Trotterized Unitary Coupled Cluster to Triple Excitations

  • 1. ROR icon Sorbonne Université
  • 2. TotalEnergies
  • 3. Sorbonne University

Description

The Trotterized Unitary Coupled Cluster Single and Double (UCCSD) ansatz has recently attracted interest due to its use in Variation Quantum Eigensolver (VQE) molecular simulations on quantum computers. However, when the size of molecules increases, UCCSD becomes less interesting as it cannot achieve sufficient accuracy. Including higher-order excitations is therefore mandatory to recover the UCC’s missing correlation effects. Here, we extend the Trotterized UCC approach via the addition of (true) Triple T excitations introducing UCCSDT. We also include both spin and orbital symmetries. Indeed, in practice, the latter help to reduce unnecessary circuit excitations and thus accelerate the optimization process enabling researchers to tackle larger molecules. Our initial numerical tests (12–14 qubits) show that UCCSDT improves the overall accuracy by at least two orders of magnitude with respect to standard UCCSD. Overall, the UCCSDT ansatz is shown to reach chemical accuracy and to be competitive with the CCSD(T) gold-standard classical method of quantum chemistry.

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Additional details

Related works

Is previous version of
Journal article: 10.1021/acs.jpca.3c01753 (DOI)

Funding

European Commission
NExt ApplicationS of Quantum Computing 951821