Simulating Models of Challenging Correlated Molecules and Materials on the Sycamore Quantum Processor

Tazhigulov, Ruslan N.; Sun, Shi-Ning; Haghshenas, Reza; Zhai, Huanchen; Tan, Adrian T. K.; Rubin, Nicholas C.; Babbush, Ryan; Minnich, Austin J.; Chan, Garnet Kin‐Lic

doi:10.1103/prxquantum.3.040318

Cited by 33 publications

(20 citation statements)

References 30 publications

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“…As far as the potential gains in scaling are concerned, a recent study suggests that the exponential nature of quantum advantage in quantum chemistry cannot be taken for granted in most cases, although the authors are careful to point out that quantum computers may still be very useful in quantum chemistry. Thus, the search is on for specific chemical systems where quantum computers could be most beneficially applied. − …”

Section: Quantum Information Theorymentioning

confidence: 99%

Measuring Electron Correlation: The Impact of Symmetry and Orbital Transformations

Ivanov

Blunt

Holzmann

et al. 2023

J. Chem. Theory Comput.

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In this perspective, the various measures of electron correlation used in wave function theory, density functional theory and quantum information theory are briefly reviewed. We then focus on a more traditional metric based on dominant weights in the full configuration solution and discuss its behavior with respect to the choice of the N-electron and the one-electron basis. The impact of symmetry is discussed, and we emphasize that the distinction among determinants, configuration state functions and configurations as reference functions is useful because the latter incorporate spin-coupling into the reference and should thus reduce the complexity of the wave function expansion. The corresponding notions of single determinant, single spin-coupling and single configuration wave functions are discussed and the effect of orbital rotations on the multireference character is reviewed by analyzing a simple model system. In molecular systems, the extent of correlation effects should be limited by finite system size and in most cases the appropriate choices of one-electron and N-electron bases should be able to incorporate these into a low-complexity reference function, often a single configurational one.

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Section: Quantum Information Theorymentioning

confidence: 99%

Measuring Electron Correlation: The Impact of Symmetry and Orbital Transformations

Ivanov

Blunt

Holzmann

et al. 2023

J. Chem. Theory Comput.

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“…Early experimental demonstrations of quantum simulation algorithms have focused on computing ground-and excited-state energies of small molecules [4][5][6][7] or few-site spin [6] and fermionic models [8]. More recently, the scale of quantum simulation experiments has increased in terms of numbers of qubits, diversity of gate sets, and complexity of algorithms, as manifested in simulation of models based on real molecules and materials [9][10][11], various phases of matter such as thermal [12,13], topological [14,15] and many-body localized states [16,17], as well as holographic quantum simulation using quantum tensor networks [18][19][20]. As quantum advantages in random sampling have been established on quantum hardware [21,22], focus has turned to the experimental demonstration of quantum advantages in problems of physical significance [23].…”

Section: Introductionmentioning

confidence: 99%

Quantum Computation of Frequency-Domain Molecular Response Properties Using a Three-Qubit iToffoli Gate

Brian¹,

Koh²,

Kim³

et al. 2023

Preprint

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The quantum computation of molecular response properties on near-term quantum hardware is a topic of significant interest. While computing time-domain response properties is in principle straightforward due to the natural ability of quantum computers to simulate unitary time evolution, circuit depth limitations restrict the maximum time that can be simulated and hence the extraction of frequency-domain properties. Computing properties directly in the frequency domain is therefore desirable, but the circuits require large depth when the typical hardware gate set consisting of single-and two-qubit gates is used. Here, we report the experimental quantum computation of the response properties of diatomic molecules directly in the frequency domain using a three-qubit iToffoli gate, enabling a reduction in circuit depth by a factor of two. We show that the molecular properties obtained with the iToffoli gate exhibit comparable or better agreement with theory than those obtained with the native CZ gates. Our work is among the first demonstrations of the practical usage of a native multi-qubit gate in quantum simulation, with diverse potential applications to the simulation of quantum many-body systems on near-term digital quantum computers.

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“…This potential quantum advantage has recently excited both hardware and software communities generating rapid progress in the field. Several quantum algorithms have been developed, and among them, the Variational Quantum Eigensolver (VQE) − appears well suited for its practical implementation on present Noisy Intermediate Scaled Quantum (NISQ) devices. , VQE simulations have been performed numerically for molecules using various virtual noiseless simulators − and have been tested experimentally on actual NISQ devices. ,− An important component in VQE is the parametrized ansatz, which represents the trial wave function and is implemented as a quantum circuit, composed of unitary quantum gates, that measures the energy expectation value of the trial wave function and then its parameters are updated in a classical optimization loop. The Unitary Coupled-Cluster (UCC) ansatz was used when VQE was initially proposed and has gained lots of attention since then.…”

Section: Introductionmentioning

confidence: 99%

Extension of the Trotterized Unitary Coupled Cluster to Triple Excitations

et al. 2023

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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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Simulating Models of Challenging Correlated Molecules and Materials on the Sycamore Quantum Processor

Cited by 33 publications

References 30 publications

Measuring Electron Correlation: The Impact of Symmetry and Orbital Transformations

Measuring Electron Correlation: The Impact of Symmetry and Orbital Transformations

Quantum Computation of Frequency-Domain Molecular Response Properties Using a Three-Qubit iToffoli Gate

Extension of the Trotterized Unitary Coupled Cluster to Triple Excitations

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