Editing Quantum algorithm (section)

=== Variational quantum eigensolver ===
The [[variational quantum eigensolver]] (VQE) algorithm applies classical optimization to minimize the energy expectation value of an [[Ansatz|ansatz state]] to find the ground state of a Hermitian operator, such as a molecule's Hamiltonian.<ref>{{Cite journal |last1=Peruzzo |first1=Alberto |last2=McClean |first2=Jarrod |last3=Shadbolt |first3=Peter |last4=Yung |first4=Man-Hong |last5=Zhou |first5=Xiao-Qi |last6=Love |first6=Peter J. |last7=Aspuru-Guzik |first7=Alán |last8=O’Brien |first8=Jeremy L. |date=2014-07-23 |title=A variational eigenvalue solver on a photonic quantum processor |journal=Nature Communications |language=En |volume=5 |issue=1 |pages=4213 |arxiv=1304.3061 |bibcode=2014NatCo...5.4213P |doi=10.1038/ncomms5213 |issn=2041-1723 |pmc=4124861 |pmid=25055053}}</ref> It can also be extended to find excited energies of molecular Hamiltonians.<ref>{{cite journal|last1=Higgott|first1=Oscar|last2=Wang|first2=Daochen|last3=Brierley|first3=Stephen|title=Variational Quantum Computation of Excited States|journal=Quantum|year=2019|volume=3|pages=156|doi=10.22331/q-2019-07-01-156|arxiv=1805.08138|bibcode=2019Quant...3..156H |s2cid=119185497}}</ref>