000996714 001__ 996714
000996714 005__ 20230207201737.0
000996714 0247_ $$2Handle$$a2128/33864
000996714 037__ $$aFZJ-2023-01139
000996714 041__ $$aEnglish
000996714 1001_ $$0P:(DE-Juel1)174485$$aJattana, Manpreet Singh$$b0$$eCorresponding author$$ufzj
000996714 245__ $$aApplications of variational methods for quantum computers$$f - 2022-11-28
000996714 260__ $$aAachen$$c2023
000996714 300__ $$avii, 160
000996714 3367_ $$2DataCite$$aOutput Types/Dissertation
000996714 3367_ $$2ORCID$$aDISSERTATION
000996714 3367_ $$2BibTeX$$aPHDTHESIS
000996714 3367_ $$02$$2EndNote$$aThesis
000996714 3367_ $$0PUB:(DE-HGF)11$$2PUB:(DE-HGF)$$aDissertation / PhD Thesis$$bphd$$mphd$$s1675750555_24839
000996714 3367_ $$2DRIVER$$adoctoralThesis
000996714 502__ $$aDissertation, RWTH Aachen University, 2022$$bDissertation$$cRWTH Aachen University$$d2022$$o2022-11-28
000996714 520__ $$aThe primary subject of this dissertation is the analysis and improvement of variational methods that combine the use of classical and gate based quantum computers. The secondary subject is the development of matrix based error mitigation and benchmarking protocols for noisy quantum computers. Variational methods run on quantum computer emulators are used to find the ground state energies of the Heisenberg and Hubbard models and selected molecules in chemistry. An algorithm is developed and deployed to automate the creation of variational circuits. The theory and overview of variational methods and gradient based optimisation algorithms are presented. We learn that while variational methods make it possible to use current generation quantum computers, guarantees of always finding the ground state energy are elusive. We introduce noise in our emulations and adapt the optimisation algorithms to withstand it. We observe the emergence of local minima and barren plateaus which hinder variational methods from finding the ground state energies. It is discerned that clever choices of initial states and parameters are necessary ingredients for success. We develop the technique of quasi-dynamical evolution inspired by quantum annealing. It overcomes the limitations of standard variational algorithms by systematically improving the ground state energy estimate. Our tests show that the heuristic improves the energy estimate even in facile settings. We introduce seven criteria for ideal error mitigation protocols. A new protocol is developed on its basis. Our tests on IBM Q quantum computers show noticeable error mitigation. The matrix generated during the execution of the protocol helps detect and visualise errors and biases. We invent and use small depth quantum circuits for benchmarking quantum computers.
000996714 536__ $$0G:(DE-HGF)POF4-5111$$a5111 - Domain-Specific Simulation & Data Life Cycle Labs (SDLs) and Research Groups (POF4-511)$$cPOF4-511$$fPOF IV$$x0
000996714 536__ $$0G:(EU-Grant)820363$$aOpenSuperQ - An Open Superconducting Quantum Computer (820363)$$c820363$$fH2020-FETFLAG-2018-03$$x1
000996714 8564_ $$uhttps://juser.fz-juelich.de/record/996714/files/PhDThesis_ManpreetJattana.pdf$$yOpenAccess
000996714 909CO $$ooai:juser.fz-juelich.de:996714$$popenaire$$popen_access$$pdriver$$pVDB$$pec_fundedresources$$pdnbdelivery
000996714 9101_ $$0I:(DE-588b)5008462-8$$6P:(DE-Juel1)174485$$aForschungszentrum Jülich$$b0$$kFZJ
000996714 9131_ $$0G:(DE-HGF)POF4-511$$1G:(DE-HGF)POF4-510$$2G:(DE-HGF)POF4-500$$3G:(DE-HGF)POF4$$4G:(DE-HGF)POF$$9G:(DE-HGF)POF4-5111$$aDE-HGF$$bKey Technologies$$lEngineering Digital Futures – Supercomputing, Data Management and Information Security for Knowledge and Action$$vEnabling Computational- & Data-Intensive Science and Engineering$$x0
000996714 9141_ $$y2023
000996714 915__ $$0StatID:(DE-HGF)0510$$2StatID$$aOpenAccess
000996714 920__ $$lyes
000996714 9201_ $$0I:(DE-Juel1)JSC-20090406$$kJSC$$lJülich Supercomputing Center$$x0
000996714 980__ $$aphd
000996714 980__ $$aVDB
000996714 980__ $$aUNRESTRICTED
000996714 980__ $$aI:(DE-Juel1)JSC-20090406
000996714 9801_ $$aFullTexts