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Learn.: Sci. Technol."],"published-print":{"date-parts":[[2020,3,1]]},"abstract":"<jats:title>Abstract<\/jats:title>\n               <jats:p>The characterization of an operator by its eigenvectors and eigenvalues allows us to know its action over any quantum state. Here, we propose a protocol to obtain an approximation of the eigenvectors of an arbitrary Hermitian quantum operator. This protocol is based on measurement and feedback processes, which characterize a reinforcement learning protocol. Our proposal is composed of two systems, a black box named environment and a quantum state named agent. The role of the environment is to change any quantum state by a unitary matrix <jats:inline-formula>\n                     <jats:tex-math>\n\n<\/jats:tex-math>\n                     <mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" overflow=\"scroll\">\n                        <mml:msub>\n                           <mml:mrow>\n                              <mml:mover accent=\"true\">\n                                 <mml:mrow>\n                                    <mml:mi>U<\/mml:mi>\n                                 <\/mml:mrow>\n                                 <mml:mrow>\n                                    <mml:mo>\u02c6<\/mml:mo>\n                                 <\/mml:mrow>\n                              <\/mml:mover>\n                           <\/mml:mrow>\n                           <mml:mrow>\n                              <mml:mi>E<\/mml:mi>\n                           <\/mml:mrow>\n                        <\/mml:msub>\n                        <mml:mo>=<\/mml:mo>\n                        <mml:msup>\n                           <mml:mrow>\n                              <mml:mi mathvariant=\"normal\">e<\/mml:mi>\n                           <\/mml:mrow>\n                           <mml:mrow>\n                              <mml:mo>\u2212<\/mml:mo>\n                              <mml:mi mathvariant=\"normal\">i<\/mml:mi>\n                              <mml:mi>\u03c4<\/mml:mi>\n                              <mml:msub>\n                                 <mml:mrow>\n                                    <mml:mover accent=\"true\">\n                                       <mml:mrow>\n                                          <mml:mi mathvariant=\"italic\">\ue23b<\/mml:mi>\n                                       <\/mml:mrow>\n                                       <mml:mrow>\n                                          <mml:mo>\u02c6<\/mml:mo>\n                                       <\/mml:mrow>\n                                    <\/mml:mover>\n                                 <\/mml:mrow>\n                                 <mml:mrow>\n                                    <mml:mi>E<\/mml:mi>\n                                 <\/mml:mrow>\n                              <\/mml:msub>\n                           <\/mml:mrow>\n                        <\/mml:msup>\n                     <\/mml:math>\n                     <jats:inline-graphic xmlns:xlink=\"http:\/\/www.w3.org\/1999\/xlink\" xlink:href=\"mlstab43b4ieqn1.gif\" xlink:type=\"simple\"\/>\n                  <\/jats:inline-formula> where <jats:inline-formula>\n                     <jats:tex-math>\n\n<\/jats:tex-math>\n                     <mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" overflow=\"scroll\">\n                        <mml:msub>\n                           <mml:mrow>\n                              <mml:mover accent=\"true\">\n                                 <mml:mrow>\n                                    <mml:mi mathvariant=\"italic\">\ue23b<\/mml:mi>\n                                 <\/mml:mrow>\n                                 <mml:mrow>\n                                    <mml:mo>\u02c6<\/mml:mo>\n                                 <\/mml:mrow>\n                              <\/mml:mover>\n                           <\/mml:mrow>\n                           <mml:mrow>\n                              <mml:mi>E<\/mml:mi>\n                           <\/mml:mrow>\n                        <\/mml:msub>\n                     <\/mml:math>\n                     <jats:inline-graphic xmlns:xlink=\"http:\/\/www.w3.org\/1999\/xlink\" xlink:href=\"mlstab43b4ieqn2.gif\" xlink:type=\"simple\"\/>\n                  <\/jats:inline-formula> is a Hermitian operator, and <jats:italic>\u03c4<\/jats:italic> is a real parameter. The agent is a quantum state which adapts to some eigenvector of <jats:inline-formula>\n                     <jats:tex-math>\n\n<\/jats:tex-math>\n                     <mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" overflow=\"scroll\">\n                        <mml:msub>\n                           <mml:mrow>\n                              <mml:mover accent=\"true\">\n                                 <mml:mrow>\n                                    <mml:mi mathvariant=\"italic\">\ue23b<\/mml:mi>\n                                 <\/mml:mrow>\n                                 <mml:mrow>\n                                    <mml:mo>\u02c6<\/mml:mo>\n                                 <\/mml:mrow>\n                              <\/mml:mover>\n                           <\/mml:mrow>\n                           <mml:mrow>\n                              <mml:mi>E<\/mml:mi>\n                           <\/mml:mrow>\n                        <\/mml:msub>\n                     <\/mml:math>\n                     <jats:inline-graphic xmlns:xlink=\"http:\/\/www.w3.org\/1999\/xlink\" xlink:href=\"mlstab43b4ieqn3.gif\" xlink:type=\"simple\"\/>\n                  <\/jats:inline-formula> by repeated interactions with the environment, feedback process, and semi-random rotations. With this proposal, we can obtain an approximation of the eigenvectors of a random qubit operator with average fidelity over 90% in less than 10 iterations, and surpass 98% in less than 300 iterations. Moreover, for the two-qubit cases, the four eigenvectors are obtained with fidelities above 89% in 8000 iterations for a random operator, and fidelities of 99% for an operator with the Bell states as eigenvectors. This protocol can be useful to implement semi-autonomous quantum devices which should be capable of extracting information and deciding with minimal resources and without human intervention.<\/jats:p>","DOI":"10.1088\/2632-2153\/ab43b4","type":"journal-article","created":{"date-parts":[[2020,2,4]],"date-time":"2020-02-04T17:52:17Z","timestamp":1580838737000},"page":"015002","update-policy":"https:\/\/doi.org\/10.1088\/crossmark-policy","source":"Crossref","is-referenced-by-count":18,"title":["Reinforcement learning for semi-autonomous approximate quantum eigensolver"],"prefix":"10.1088","volume":"1","author":[{"given":"F","family":"Albarr\u00e1n-Arriagada","sequence":"first","affiliation":[]},{"given":"J C","family":"Retamal","sequence":"additional","affiliation":[]},{"given":"E","family":"Solano","sequence":"additional","affiliation":[]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9504-8685","authenticated-orcid":false,"given":"L","family":"Lamata","sequence":"additional","affiliation":[]}],"member":"266","published-online":{"date-parts":[[2020,2,4]]},"reference":[{"key":"mlstab43b4bib1","author":"Adcock","year":"2015"},{"key":"mlstab43b4bib2","doi-asserted-by":"publisher","DOI":"10.1038\/nature23474","article-title":"Quantum machine learning","volume":"549","author":"Biamonte","year":"2017","journal-title":"Nature"},{"key":"mlstab43b4bib3","doi-asserted-by":"publisher","DOI":"10.1103\/PhysRevLett.117.130501","article-title":"Quantum-enhanced machine learning","volume":"117","author":"Dunjko","year":"2016","journal-title":"Phys. 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