Quantum optimization algorithms: Difference between revisions

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Within the QAOA section: possible degeneracy of classical objective function and hence objective hamiltonian is consistently accounted for by e.g. replacing "the optimal solution" with "an optimal solution"/"optimal solutions". New reference (DOI: 10.1088/1367-2630/ad59bb) is added for convergence of QAOA for degenerate problems.
m For reference (DOI: 10.1088/1367-2630/ad59bb): Replaced specific publishing date with publishing year
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=== Generalization of QAOA to constrained combinatorial optimisation ===
In principle the optimal value of <math> C(z) </math> can be reached up to arbitrary precision, this is guaranteed by the adiabatic theorem<ref>{{cite arXiv|last1=Farhi|first1=Edward|last2=Goldstone|first2=Jeffrey|last3=Gutmann|first3=Sam|title=A Quantum Approximate Optimization Algorithm|eprint=1411.4028|class=quant-ph|year=2014}}</ref><ref>{{Cite journal|last1=Binkowski|first1=Lennart |last2=Koßmann|first2=Gereon |last3=Ziegler|first3=Timo |last4=Schwonnek|first4=René |dateyear=2024-07-01|title=Elementary proof of QAOA convergence|journal=New Journal of Physics|volume=26|issue=7|pages=073001|doi=10.1088/1367-2630/ad59bb|arxiv=2302.04968 }}</ref> or alternatively by the universality of the QAOA unitaries.<ref>{{Cite journal|last1=Morales|first1=M. E. |last2=Biamonte|first2=J. D.|last3=Zimborás|first3=Z. |date=2019-09-20|title=On the universality of the quantum approximate optimization algorithm|journal=Quantum Information Processing|volume=19|issue=9 |pages=291|doi=10.1007/s11128-020-02748-9|arxiv=1909.03123 }}</ref> However, it is an open question whether this can be done in a feasible way.
For example, it was shown that QAOA exhibits a strong dependence on the ratio of a problem's [[Constraint (mathematics)|constraint]] to [[Variable (mathematics)|variables]] (problem density) placing a limiting restriction on the algorithm's capacity to minimize a corresponding [[Loss function|objective function]].<ref name=":0">{{Cite journal|last1=Akshay|first1=V.|last2=Philathong|first2=H.|last3=Morales|first3=M. E. S.|last4=Biamonte|first4=J. D.|date=2020-03-05|title=Reachability Deficits in Quantum Approximate Optimization|journal=Physical Review Letters|volume=124|issue=9|pages=090504|doi=10.1103/PhysRevLett.124.090504|pmid=32202873|arxiv=1906.11259|bibcode=2020PhRvL.124i0504A|s2cid=195699685}}</ref>