Progress in Quantum-Computer Calculations

A special issue of Nanomaterials (ISSN 2079-4991). This special issue belongs to the section "Theory and Simulation of Nanostructures".

Deadline for manuscript submissions: closed (30 June 2022) | Viewed by 3917

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Institute of Physics of Materials of the Czech Academy of Sciences, Brno, Czech Republic
Interests: computational materials science; multi-scale modelling; solid-state physics and chemistry; magnetism; phase stability and transformations; nanosystems; quantum technologies; quantum computers
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Special Issue Information

Dear colleagues,

Electronic structure calculations have become an indispensable theoretical tool in physics, chemistry, and materials science. After four decades of rapid development, these calculations now allow us to study systems consisting of up to a few thousands of atoms. Further upscaling to yet bigger systems, such as those encountered in nanoparticles and other nanosystems, is all too often hindered by limited computer power of classical (super-)computers. Fortunately, there is a newly emerging class of quantum computers that should soon provide an exponentially higher computer power. Albeit promising, quantum computers are still in their infancy, and basic algorithms need to be developed.

This Special Issue welcomes submissions focused primarily (but not solely) on recent developments in the broad field of quantum computers and their applications, especially software tools allowing for electronic structure calculations on quantum computers in physics, chemistry or materials science, as well as calculations on (i) either classical computer simulators of quantum processors or (ii) actual quantum computers.

Dr. Martin Friák
Guest Editor

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Keywords

  • quantum computers
  • quantum algorithms
  • variational quantum eigensolvers
  • nanosystems
  • electronic structure
  • quantum technologies

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Published Papers (2 papers)

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Research

9 pages, 2365 KiB  
Article
Electronic Structure of Monolayer FeSe on Si(001) from First Principles
by Karel Carva, Petru Vlaic and Jan Honolka
Nanomaterials 2022, 12(2), 270; https://doi.org/10.3390/nano12020270 - 14 Jan 2022
Viewed by 2451
Abstract
The huge increase in the superconducting transition temperature of FeSe induced by an interface to SrTiO3 remains unexplained to date. However, there are numerous indications of the critical importance of specific features of the FeSe band topology in the vicinity of the [...] Read more.
The huge increase in the superconducting transition temperature of FeSe induced by an interface to SrTiO3 remains unexplained to date. However, there are numerous indications of the critical importance of specific features of the FeSe band topology in the vicinity of the Fermi surface. Here, we explore how the electronic structure of FeSe changes when located on another lattice matched substrate, namely a Si(001) surface, by first-principles calculations based on the density functional theory. We study non-magnetic (NM) and checkerboard anti-ferromagnetic (AFM) magnetic orders in FeSe and determine which interface arrangement is preferred. Our calculations reveal interesting effects of Si proximity on the FeSe band structure. Bands corresponding to hole pockets at the Γ point in NM FeSe are generally pushed down below the Fermi level, except for one band responsible for a small remaining hole pocket. Bands forming electron pockets centered at the M point of the Brillouin zone become less dispersive, and one of them is strongly hybridized with Si. We explain these changes by a redistribution of electrons between different Fe 3d orbitals rather than charge transfer to/from Si, and we also notice an associated loss of degeneracy between dxz and dyz orbitals. Full article
(This article belongs to the Special Issue Progress in Quantum-Computer Calculations)
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22 pages, 1299 KiB  
Article
The Cost of Improving the Precision of the Variational Quantum Eigensolver for Quantum Chemistry
by Ivana Miháliková, Matej Pivoluska, Martin Plesch, Martin Friák, Daniel Nagaj and Mojmír Šob
Nanomaterials 2022, 12(2), 243; https://doi.org/10.3390/nano12020243 - 14 Jan 2022
Cited by 11 | Viewed by 3011
Abstract
New approaches into computational quantum chemistry can be developed through the use of quantum computing. While universal, fault-tolerant quantum computers are still not available, and we want to utilize today’s noisy quantum processors. One of their flagship applications is the variational quantum eigensolver [...] Read more.
New approaches into computational quantum chemistry can be developed through the use of quantum computing. While universal, fault-tolerant quantum computers are still not available, and we want to utilize today’s noisy quantum processors. One of their flagship applications is the variational quantum eigensolver (VQE)—an algorithm for calculating the minimum energy of a physical Hamiltonian. In this study, we investigate how various types of errors affect the VQE and how to efficiently use the available resources to produce precise computational results. We utilize a simulator of a noisy quantum device, an exact statevector simulator, and physical quantum hardware to study the VQE algorithm for molecular hydrogen. We find that the optimal method of running the hybrid classical-quantum optimization is to: (i) allow some noise in intermediate energy evaluations, using fewer shots per step and fewer optimization iterations, but ensure a high final readout precision; (ii) emphasize efficient problem encoding and ansatz parametrization; and (iii) run all experiments within a short time-frame, avoiding parameter drift with time. Nevertheless, current publicly available quantum resources are still very noisy and scarce/expensive, and even when using them efficiently, it is quite difficult to perform trustworthy calculations of molecular energies. Full article
(This article belongs to the Special Issue Progress in Quantum-Computer Calculations)
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