Molecular excited state calculations with adaptive wavefunctions on a quantum eigensolver emulation: reducing circuit depth and separating spin states

Chan, Hans Hon Sang; Fitzpatrick, Nathan; Segarra‐Martí, Javier; Bearpark, Michael J.; Tew, David P.

doi:10.1039/d1cp02227j

Cited by 17 publications

(24 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Equally we are interested in other types of UCC ansatze which involve higher-order correlation effects, such as MP3 or MP4, or triple excitation UCCSD(T) which could be important for strongly correlated systems and could improve further the accuracy as mentioned earlier 49 . We are also motivated to implement additional algorithms going beyond VQE, such as VQD (ADAPT-VQD) and QITE(ADAPT-QITE) that allow to determine excited state energies 105,72,73,106,107 .…”

Section: Discussionmentioning

confidence: 99%

“…Indeed, such approaches were also engineered not only for ground states but also to tackle excited states without undesired spin symmetry crossing over to lower states during VQE optimizations. They have been also used in connection with the variational Quantum Deflation algorithm (VQD), that is used to determine the energies of the ground and excited states 73 .…”

Section: Uccgsd and K-upccgsd Ansatze Uccgsdmentioning

confidence: 99%

See 1 more Smart Citation

Open Source Variational Quantum Eigensolver Extension of the Quantum Learning Machine (QLM) for Quantum Chemistry

Haidar¹,

Rančić²,

Ayral³

et al. 2022

Preprint

View full text Add to dashboard Cite

Quantum Chemistry (QC) is one of the most promising applications of Quantum Computing. However, present quantum processing units (QPUs) are still subject to large errors. Therefore, noisy intermediate-scale quantum (NISQ) hardware is limited in terms of qubits counts and circuit depths. Specific algorithms such as Variational Quantum Eigensolvers (VQEs) can potentially overcome such issues.Here, we introduce a novel open-source QC package, denoted OpenVQE, providing tools for using and developing chemically-inspired adaptive methods derived from Unitary Coupled Cluster (UCC). It facilitates the development and testing of VQE algorithms. It is able to use the Atos Quantum Learning Machine (QLM), a general quantum programming framework enabling to write, optimize and simulate quantum computing programs. The QLM comes with a specific, freely available and open-source module, myQLM-fermion, that provides key tools to perform QC computations on a quantum computer (fermionic second quantization tools, UCC ansatz, etc). We give an extensive introduction to myQLM-fermion. Our package, Open-VQE, largely extends the QC capabilities of the QLM by providing: (i) the functions to generate the different types of excitations beyond the commonly used UCCSD ansatz; (ii) a new implementation of the "adaptive derivative assembled pseudo-Trotter method" (ADAPT-VQE), written in simple class structure python codes.Interoperability with other major quantum programming frameworks is ensured thanks to myQLM, which allows users to easily build their own code and execute it on existing QPUs such as IBM, Google, Rigetti or Microsoft, etc. The combined OpenVQE/myQLM-fermion libraries facilitate the implementation, testing and development of variational quantum algorithms, thus helping choose the best compromise to run QC computations on present quantum computers while offering the possibility to test large molecules. We provide extensive benchmarks for several molecules associated to qubit counts ranging from 4 up to 24 where we focus our work on reaching chemical accuracy, reducing the number of circuit gates and optimizing parameters and operators between "fixed-length" UCC and ADAPT-VQE ansatze.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Uccgsd and K-upccgsd Ansatze Uccgsdmentioning

confidence: 99%

Open Source Variational Quantum Eigensolver Extension of the Quantum Learning Machine (QLM) for Quantum Chemistry

Haidar¹,

Rančić²,

Ayral³

et al. 2022

Preprint

View full text Add to dashboard Cite

show abstract

“…10,11 Moreover, spin symmetry corresponding to the Ŝ2 operator is not conserved because the non-commuting spin components of unpaired two-body operators appear independently in the unitary product. 12 The ADAPT-VQE 13 algorithm, and its extensions, [14][15][16][17] iteratively build a UPS from a pool of one-and two-body fermionic operators, selecting the operator with the largest energy improvement at each step. Although promising, these approaches are not guaranteed to converge to the exact state 18,19 or identify the most accurate representation with the fewest number of operators, and can spontaneously break spin symmetry.…”

Section: Unitary Product Statesmentioning

confidence: 99%

Exact electronic states with shallow quantum circuits through global optimisation

Burton¹,

Marti-Dafcik²,

Tew³

et al. 2022

Preprint

Self Cite

View full text Add to dashboard Cite

Quantum computers promise to revolutionise electronic simulations by overcoming the exponential scaling of many-electron problems. While electronic wave functions can be represented using a product of fermionic unitary operators, shallow quantum circuits for exact states have not yet been achieved. We construct universal wave functions from gate-efficient, symmetry-preserving fermionic operators by introducing an algorithm that globally optimises the wave function in the discrete ansatz design and the continuous parameter spaces. Our approach maximises the accuracy that can be obtained with near-term quantum circuits. Highly accurate numerical simulations on strongly correlated molecules, including water and molecular nitrogen, and the condensed-matter Hubbard model, demonstrate that our algorithm reliably advances the state-of-the-art, defining a new paradigm for quantum simulations featuring strong electron correlation.

show abstract

“…In ref , we proposed a quantum algorithm for the calculation of the molecular excited states, which relies solely on the optimization of the ground state wave function, followed by the measurement of “excited” matrix elements. Alternative algorithms are reported in the literature, see, for instance, refs − . Within this approach, excited states | n ⟩ are generated by applying an excitation operator of the general form to the ground state |0⟩ of the system, where | n ⟩ is the shorthand notation for the n th excited state of the electronic structure Hamiltonian.…”

Section: Calculation Of the Potential Energy Surfacesmentioning

confidence: 99%

Molecular Quantum Dynamics: A Quantum Computing Perspective

2021

View full text Add to dashboard Cite

show abstract

Molecular excited state calculations with adaptive wavefunctions on a quantum eigensolver emulation: reducing circuit depth and separating spin states

Abstract: Using adaptive wavefunctions and spin restrictions to compute excited state energies of LiH in a VQE emulation greatly reduces ansatz depth, showing promise as a routine for molecular excited state calculations on near-term quantum computers.

Cited by 17 publications

References 33 publications

Open Source Variational Quantum Eigensolver Extension of the Quantum Learning Machine (QLM) for Quantum Chemistry

Open Source Variational Quantum Eigensolver Extension of the Quantum Learning Machine (QLM) for Quantum Chemistry

Exact electronic states with shallow quantum circuits through global optimisation

Molecular Quantum Dynamics: A Quantum Computing Perspective

Contact Info

Product

Resources

About