Subspace methods for electronic structure simulations on quantum computers

Electronic Structure, Journal Year: 2024, Volume and Issue: 6(1), P. 013001 - 013001

Published: March 1, 2024

Abstract Quantum subspace methods (QSMs) are a class of quantum computing algorithms where the time-independent Schrödinger equation for system is projected onto underlying Hilbert space. This projection transforms into an eigenvalue problem determined by measurements carried out on device. The then solved classical computer, yielding approximations to ground- and excited-state energies wavefunctions. QSMs examples hybrid quantum–classical methods, device supported computational resources employed tackle problem. rapidly gaining traction as strategy simulate electronic wavefunctions computers, thus their design, development, application key research field at interface between computation structure (ES). In this review, we provide self-contained introduction QSMs, with emphasis ES molecules. We present theoretical foundations applications discuss implementation hardware, illustrating impact noise performance.

Language: Английский

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Quantum Equation of Motion with Orbital Optimization for Computing Molecular Properties in Near-Term Quantum Computing

Journal of Chemical Theory and Computation, Journal Year: 2024, Volume and Issue: 20(9), P. 3613 - 3625

Published: May 3, 2024

Determining the properties of molecules and materials is one premier applications quantum computing. A major question in field how to use imperfect near-term computers solve problems practical value. Inspired by recently developed variants counterpart equation-of-motion (qEOM) approach orbital-optimized variational eigensolver (oo-VQE), we present a algorithm (oo-VQE-qEOM) for calculation molecular computing expectation values on computer. We perform noise-free simulations BeH2 series STO-3G/6-31G/6-31G* basis sets H4 H2O 6-31G using an active space four electrons spatial orbitals (8 qubits) evaluate excitation energies, electronic absorption, and, twisted H4, circular dichroism spectra. demonstrate that proposed can reproduce results conventional classical CASSCF calculations these systems.

Language: Английский

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Accurate and gate-efficient quantum Ansätze for electronic states without adaptive optimization

Physical Review Research, Journal Year: 2024, Volume and Issue: 6(2)

Published: June 20, 2024

The ability of quantum computers to overcome the exponential memory scaling many-body problems is expected transform chemistry. Quantum algorithms require accurate representations electronic states on a device, but current approximations struggle combine chemical accuracy and gate efficiency while preserving physical symmetries, rely measurement-intensive adaptive methods that tailor wave function each molecule. In this contribution, we present symmetry-preserving gate-efficient provides chemically molecular energies with well-defined circuit structure. Our approach exploits local qubit connectivity, orbital optimization, connections generalized valence bond theory maximize obtained shallow circuits. Numerical simulations for molecules weak strong electron correlation, including benzene, water, singlet-triplet gap in tetramethyleneethane, demonstrate are achieved as much 84% fewer two-qubit gates compared state-of-the-art techniques. Published by American Physical Society 2024

Language: Английский

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Which Options Exist for NISQ-Friendly Linear Response Formulations?

Journal of Chemical Theory and Computation, Journal Year: 2024, Volume and Issue: 20(9), P. 3551 - 3565

Published: April 25, 2024

Linear response (LR) theory is a powerful tool in classic quantum chemistry crucial to understanding photoinduced processes and biology. However, performing simulations for large systems the case of strong electron correlation remains challenging. Quantum computers are poised facilitate simulation such systems, recently, linear formulation (qLR) was introduced [Kumar et al., J. Chem. Theory Comput. 2023, 19, 9136–9150]. To apply qLR near-term beyond minimal basis set, we here introduce resource-efficient theory, using truncated active-space version multiconfigurational self-consistent field LR ansatz. Therein, investigate eight different formalisms that utilize novel operator transformations allow equations be performed on hardware. Simulating excited state potential energy curves absorption spectra various test cases, identify two promising candidates, dubbed "proj LRSD" "all-proj LRSD".

Language: Английский

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Understanding and mitigating noise in molecular quantum linear response for spectroscopic properties on quantum computers

Chemical Science, Journal Year: 2025, Volume and Issue: 16(10), P. 4456 - 4468

Published: Jan. 1, 2025

The promise of quantum computing to circumvent the exponential scaling chemistry has sparked a race develop algorithms for architecture. However, most works neglect quantum-inherent shot noise, let alone effect current noisy devices. Here, we present comprehensive study linear response (qLR) theory obtaining spectroscopic properties on simulated fault-tolerant computers and present-day near-term hardware. This work introduces novel metrics analyze predict origins noise in algorithm, proposes an Ansatz-based error mitigation technique, reveals significant impact Pauli saving reducing measurement costs subspace methods. Our hardware results using up cc-pVTZ basis set serve as proof principle absorption spectra general approach with accuracy classical multi-configurational Importantly, our exemplify that substantial improvements rates speed are necessary lift computational from concept actual field.

Language: Английский

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Characterizing Conical Intersections of Nucleobases on Quantum Computers

Journal of Chemical Theory and Computation, Journal Year: 2025, Volume and Issue: unknown

Published: Jan. 28, 2025

Hybrid quantum-classical computing algorithms offer significant potential for accelerating the calculation of electronic structure strongly correlated molecules. In this work, we present first quantum simulation conical intersections (CIs) in a biomolecule, cytosine, using superconducting computer. We apply contracted eigensolver (CQE)─with comparisons to conventional variational deflation (VQD)─to compute near-degenerate ground and excited states associated with intersection, key feature governing photostability DNA RNA. The CQE is based on an exact ansatz many-electron molecules absence noise─a critically important property resolving at CIs. Both methods demonstrate promising accuracy when compared diagonalization, even noisy intermediate-scale computers, highlighting their advancing understanding photochemical photobiological processes. ability simulate these critical our knowledge biological processes like repair mutation, implications molecular biology medical research.

Language: Английский

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Quantum Simulation of Molecular Response Properties in the NISQ Era

Journal of Chemical Theory and Computation, Journal Year: 2023, Volume and Issue: 19(24), P. 9136 - 9150

Published: Dec. 6, 2023

Accurate modeling of the response molecular systems to an external electromagnetic field is challenging on classical computers, especially in regime strong electronic correlation. In this article, we develop a quantum linear (qLR) theory calculate properties near-term computers. Inspired by recently developed variants counterpart equation motion (qEOM) theory, qLR formalism employs "killer condition" satisfying excitation operator manifolds that offer number theoretical advantages along with reduced resource requirements. We also used qEOM framework work state-specific properties. Further, through noiseless simulations, show calculated using approach are more accurate than ones obtained from coupled-cluster-based models due improved quality ground-state wave function ADAPT-VQE algorithm.

Language: Английский

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Folded Spectrum VQE: A Quantum Computing Method for the Calculation of Molecular Excited States

Journal of Chemical Theory and Computation, Journal Year: 2024, Volume and Issue: 20(6), P. 2491 - 2504

Published: March 16, 2024

The recent developments of quantum computing present novel potential pathways for chemistry as the scaling computational power computers could be harnessed to naturally encode and solve electronic structure problems. Theoretically exact algorithms have been proposed (e.g., phase estimation), but limited capabilities current noisy intermediate-scale devices motivated development less demanding hybrid algorithms. In this context, variational eigensolver (VQE) algorithm was successfully introduced an effective method compute ground-state energies small molecules. This study investigates folded spectrum (FS) extension VQE computation molecular excited states. It provides possibility directly states around a selected target energy using same or circuit calculation. Inspired by variance-based methods from Monte Carlo literature, FS minimizes variance, thus, in principle, requiring computationally expensive squared Hamiltonian applied. We alleviate potentially poor employing Pauli grouping procedure identify sets commuting strings that can evaluated simultaneously. allows significant reduction cost. applied FS-VQE molecules (H2, LiH), obtaining all with chemical accuracy on ideal simulators. Furthermore, we explore application error mitigation techniques, demonstrating improved simulators compared simulations without mitigation.

Language: Английский

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Two Algorithms for Excited-State Quantum Solvers: Theory and Application to EOM-UCCSD

The Journal of Physical Chemistry A, Journal Year: 2023, Volume and Issue: 127(31), P. 6552 - 6566

Published: July 28, 2023

Near-term quantum devices promise to revolutionize chemistry, but simulations using the current noisy intermediate-scale (NISQ) are not practical due their high susceptibility errors. This motivated design of NISQ algorithms leveraging classical and resources. While several developments have shown promising results for ground-state simulations, extending excited states remains challenging. paper presents two cost-efficient excited-state inspired by Davidson algorithm. We implemented method into self-consistent equation-of-motion unitary coupled-cluster (q-sc-EOM-UCC) adapted hardware. The circuit strategies generating desired discussed, implemented, tested. demonstrate performance accuracy proposed (q-sc-EOM-UCC/Davidson its variational variant) H2, H4, LiH, H2O molecules. Similar scheme, q-sc-EOM-UCC/Davidson capable targeting a small number character.

Language: Английский

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Spin-Flip Unitary Coupled Cluster Method: Toward Accurate Description of Strong Electron Correlation on Quantum Computers

The Journal of Physical Chemistry Letters, Journal Year: 2023, Volume and Issue: 14(35), P. 7876 - 7882

Published: Aug. 28, 2023

Quantum computers have emerged as a promising platform to simulate strong electron correlation that is crucial catalysis and photochemistry. However, owing the choice of trial wave function employed in variational quantum eigensolver (VQE) algorithm, accurate simulation restricted certain classes correlated phenomena. Herein, we combine spin-flip (SF) formalism with unitary coupled cluster singles doubles (UCCSD) method via equation-of-motion (qEOM) approach allow for an efficient large family strongly problems. We show developed qEOM-SF-UCCSD/VQE outperforms its UCCSD/VQE counterpart cis-trans isomerization ethylene, automerization cyclobutadiene predicted barrier heights are good agreement experimentally determined values. The developments presented herein will further stimulate investigation this simulations other types correlated/entangled phenomena on computers.

Language: Английский

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