| 1. |
- Barucha-Dobrautz, Werner, 1987, et al.
(författare)
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Toward Real Chemical Accuracy on Current Quantum Hardware Through the Transcorrelated Method
- 2024
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Ingår i: Journal of Chemical Theory and Computation. - 1549-9626 .- 1549-9618. ; 20:10, s. 4146-4160
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Tidskriftsartikel (refereegranskat)abstract
- Quantum computing is emerging as a new computational paradigm with the potential to transform several research fields including quantum chemistry. However, current hardware limitations (including limited coherence times, gate infidelities, and connectivity) hamper the implementation of most quantum algorithms and call for more noise-resilient solutions. We propose an explicitly correlated Ansatz based on the transcorrelated (TC) approach to target these major roadblocks directly. This method transfers, without any approximation, correlations from the wave function directly into the Hamiltonian, thus reducing the resources needed to achieve accurate results with noisy quantum devices. We show that the TC approach allows for shallower circuits and improves the convergence toward the complete basis set limit, providing energies within chemical accuracy to experiment with smaller basis sets and, thus, fewer qubits. We demonstrate our method by computing bond lengths, dissociation energies, and vibrational frequencies close to experimental results for the hydrogen dimer and lithium hydride using two and four qubits, respectively. To demonstrate our approach’s current and near-term potential, we perform hardware experiments, where our results confirm that the TC method paves the way toward accurate quantum chemistry calculations already on today’s quantum hardware.
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| 2. |
- Kovyrshin, Arseny, et al.
(författare)
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A quantum computing implementation of nuclearelectronic orbital (NEO) theory: Toward an exact pre-Born-Oppenheimer formulation of molecular quantum systems
- 2023
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Ingår i: Journal of Chemical Physics. - 1089-7690 .- 0021-9606. ; 158:21
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Tidskriftsartikel (refereegranskat)abstract
- Nuclear quantum phenomena beyond the Born-Oppenheimer approximation are known to play an important role in a growing number of chemical and biological processes. While there exists no unique consensus on a rigorous and efficient implementation of coupled electron-nuclear quantum dynamics, it is recognized that these problems scale exponentially with system size on classical processors and, therefore, may benefit from quantum computing implementations. Here, we introduce a methodology for the efficient quantum treatment of the electron-nuclear problem on near-term quantum computers, based upon the Nuclear-Electronic Orbital (NEO) approach. We generalize the electronic two-qubit tapering scheme to include nuclei by exploiting symmetries inherent in the NEO framework, thereby reducing the Hamiltonian dimension, number of qubits, gates, and measurements needed for calculations. We also develop parameter transfer and initialization techniques, which improve convergence behavior relative to conventional initialization. These techniques are applied to H2 and malonaldehyde for which results agree with NEO full configuration interaction and NEO complete active space configuration interaction benchmarks for ground state energy to within 10-6 hartree and entanglement entropy to within 10-4. These implementations therefore significantly reduce resource requirements for full quantum simulations of molecules on near-term quantum devices while maintaining high accuracy.
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| 3. |
- Kovyrshin, Arseny, et al.
(författare)
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Nonadiabatic Nuclear-Electron Dynamics: A Quantum Computing Approach
- 2023
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Ingår i: Journal of Physical Chemistry Letters. - 1948-7185. ; 14:31, s. 7065-7072
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Tidskriftsartikel (refereegranskat)abstract
- Coupled quantum electron-nuclear dynamics is oftenassociatedwith the Born-Huang expansion of the molecular wave functionand the appearance of nonadiabatic effects as a perturbation. On theother hand, native multicomponent representations of electrons andnuclei also exist, which do not rely on any a priori approximation.However, their implementation is hampered by prohibitive scaling.Consequently, quantum computers offer a unique opportunity for extendingtheir use to larger systems. Here, we propose a quantum algorithmfor simulating the time-evolution of molecular systems and apply itto proton transfer dynamics in malonaldehyde, described as a rigidscaffold. The proposed quantum algorithm can be easily generalizedto include the explicit dynamics of the classically described molecularscaffold. We show how entanglement between electronic and nucleardegrees of freedom can persist over long times if electrons do notfollow the nuclear displacement adiabatically. The proposed quantumalgorithm may become a valid candidate for the study of such phenomenawhen sufficiently powerful quantum computers become available.
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| 4. |
- Nykänen, Anton, et al.
(författare)
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Toward Accurate Post-Born-Oppenheimer Molecular Simulations on Quantum Computers: An Adaptive Variational Eigensolver with Nuclear-Electronic Frozen Natural Orbitals
- 2023
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Ingår i: Journal of Chemical Theory and Computation. - 1549-9626 .- 1549-9618. ; 19:24, s. 9269-9277
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Tidskriftsartikel (refereegranskat)abstract
- Nuclear quantum effects such as zero-point energy and hydrogen tunneling play a central role in many biological and chemical processes. The nuclear-electronic orbital (NEO) approach captures these effects by treating selected nuclei quantum mechanically on the same footing as electrons. On classical computers, the resources required for an exact solution of NEO-based models grow exponentially with system size. By contrast, quantum computers offer a means of solving this problem with polynomial scaling. However, due to the limitations of current quantum devices, NEO simulations are confined to the smallest systems described by minimal basis sets, whereas realistic simulations beyond the Born-Oppenheimer approximation require more sophisticated basis sets. For this purpose, we herein extend a hardware-efficient ADAPT-VQE method to the NEO framework in the frozen natural orbital (FNO) basis. We demonstrate on H2 and D2 molecules that the NEO-FNO-ADAPT-VQE method reduces the CNOT count by several orders of magnitude relative to the NEO unitary coupled cluster method with singles and doubles while maintaining the desired accuracy. This extreme reduction in the CNOT gate count is sufficient to permit practical computations employing the NEO method─an important step toward accurate simulations involving nonclassical nuclei and non-Born-Oppenheimer effects on near-term quantum devices. We further show that the method can capture isotope effects, and we demonstrate that inclusion of correlation energy systematically improves the prediction of difference in the zero-point energy (ΔZPE) between isotopes.
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| 5. |
- Sokolov, Igor O., et al.
(författare)
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Orders of magnitude increased accuracy for quantum many-body problems on quantum computers via an exact transcorrelated method
- 2023
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Ingår i: Physical Review Research. - 2643-1564. ; 5:2
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Tidskriftsartikel (refereegranskat)abstract
- Transcorrelated methods provide an efficient way of partially transferring the description of electronic correlations from the ground-state wave function directly into the underlying Hamiltonian. In particular, Dobrautz et al. [Phys. Rev. B 99, 075119 (2019)2469-995010.1103/PhysRevB.99.075119] have demonstrated that the use of momentum-space representation, combined with a nonunitary similarity transformation, results in a Hubbard Hamiltonian that possesses a significantly more "compact"ground-state wave function, dominated by a single Slater determinant. This compactness/single-reference character greatly facilitates electronic structure calculations. As a consequence, however, the Hamiltonian becomes non-Hermitian, posing problems for quantum algorithms based on the variational principle. We overcome these limitations with the Ansatz-based quantum imaginary-time evolution algorithm and apply the transcorrelated method in the context of digital quantum computing. We demonstrate that this approach enables up to four orders of magnitude more accurate and compact solutions in various instances of the Hubbard model at intermediate interaction strength (U/t=4), enabling the use of shallower quantum circuits for wave-function Ansätzes. In addition, we propose a more efficient implementation of the quantum imaginary-time evolution algorithm in quantum circuits that is tailored to non-Hermitian problems. To validate our approach, we perform hardware experiments on the ibmq_lima quantum computer. Our work paves the way for the use of exact transcorrelated methods for the simulations of ab initio systems on quantum computers.
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