Browsing by Author "Khamoshi, Armin"

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    AGP-based unitary coupled cluster theory for quantum computers
    (IOP Publishing, 2022) Khamoshi, Armin; Chen, Guo P.; Evangelista, Francesco A.; Scuseria, Gustavo E.
    Electronic structure methods typically benefit from symmetry breaking and restoration, specially in the strong correlation regime. The same goes for ansätze on a quantum computer. We develop a unitary coupled cluster method based on the antisymmetrized geminal power (AGP)—a state formally equivalent to the number-projected Bardeen–Cooper–Schrieffer wavefunction. We demonstrate our method for the single-band Fermi–Hubbard Hamiltonian in one and two dimensions. We also explore post-selection as a state preparation step to obtain correlated AGP and prove that it scales no worse than O(√M) in the number of measurements, thereby making it a less expensive alternative to gauge integration to restore particle number symmetry.
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    Correlating AGP on quantum and classical computers: A theoretical and computational study
    (2022-08-05) Khamoshi, Armin; Scuseria, Gustavo E
    Conventional methods to solve quantum many-body problems in physics and chemistry often struggle in the strongly correlated regime. Recent advances in quantum computing hardware have opened up new ways to tackle the strong correlation problem; however, existing hybrid quantum-classical algorithms typically start from conventional classical methods or take inspiration from them. In this thesis, we develop novel correlation methods on classical and quantum computers that are based the anti-symmetrized geminal power (AGP) wavefunction---a state equivalent to the number projected Bardeen--Cooper--Schrieffer (BCS) wavefunction. Our methods fall under the larger category of merging coupled cluster theory with symmetry--breaking and restoration. We showcase benchmark calculations for model Hamiltonians that exhibit strong correlation that are prototypical of those in molecules and condensed matter systems and demonstrate that our methods have the potential to address strong correlation in attractive and repulsive systems on an equal footing.
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    State Preparation of Antisymmetrized Geminal Power on a Quantum Computer without Number Projection
    (American Chemical Society, 2023) Khamoshi, Armin; Dutta, Rishab; Scuseria, Gustavo E.
    The antisymmetrized geminal power (AGP) is equivalent to the number projected Bardeen–Cooper–Schrieffer (PBCS) wave function. It is also an elementary symmetric polynomial (ESP) state. We generalize previous research on deterministically implementing the Dicke state to a state preparation algorithm for an ESP state, or equivalently AGP, on a quantum computer. Our method is deterministic and has polynomial cost, and it does not rely on number symmetry breaking and restoration. We also show that our circuit is equivalent to a disentangled unitary paired coupled cluster operator and a layer of unitary Jastrow operator acting on a single Slater determinant. The method presented herein highlights the ability of disentangled unitary coupled cluster to capture nontrivial entanglement properties that are hardly accessible with traditional Hartree–Fock based electronic structure methods.