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We achieve it by filtering a product state at the given energy with a Lorentzian filter of width <mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\"><mml:mi>&amp;#x03B4;<\/mml:mi><\/mml:math>. Given a local Hamiltonian on <mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\"><mml:mi>N<\/mml:mi><\/mml:math> qubits, we construct a parent Hamiltonian whose ground state corresponds to the filtered product state with variable energy variance proportional to <mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\"><mml:mi>&amp;#x03B4;<\/mml:mi><mml:msqrt><mml:mi>N<\/mml:mi><\/mml:msqrt><\/mml:math>. We prove that the parent Hamiltonian is gapped and its ground state can be efficiently implemented in <mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\"><mml:mrow class=\"MJX-TeXAtom-ORD\"><mml:mi mathvariant=\"normal\">p<\/mml:mi><mml:mi mathvariant=\"normal\">o<\/mml:mi><mml:mi mathvariant=\"normal\">l<\/mml:mi><mml:mi mathvariant=\"normal\">y<\/mml:mi><\/mml:mrow><mml:mo stretchy=\"false\">(<\/mml:mo><mml:mi>N<\/mml:mi><mml:mo>,<\/mml:mo><mml:mn>1<\/mml:mn><mml:mrow class=\"MJX-TeXAtom-ORD\"><mml:mo>\/<\/mml:mo><\/mml:mrow><mml:mi>&amp;#x03B4;<\/mml:mi><mml:mo stretchy=\"false\">)<\/mml:mo><\/mml:math> time via adiabatic evolution. We numerically benchmark the algorithm for a particular non-integrable model and find that the adiabatic evolution time to prepare the filtered state with a width <mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\"><mml:mi>&amp;#x03B4;<\/mml:mi><\/mml:math> is independent of the system size <mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\"><mml:mi>N<\/mml:mi><\/mml:math>. Furthermore, the adiabatic evolution can be implemented with circuit depth <mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\"><mml:mrow class=\"MJX-TeXAtom-ORD\"><mml:mi class=\"MJX-tex-caligraphic\" mathvariant=\"script\">O<\/mml:mi><\/mml:mrow><mml:mo stretchy=\"false\">(<\/mml:mo><mml:msup><mml:mi>N<\/mml:mi><mml:mn>2<\/mml:mn><\/mml:msup><mml:msup><mml:mi>&amp;#x03B4;<\/mml:mi><mml:mrow class=\"MJX-TeXAtom-ORD\"><mml:mo>&amp;#x2212;<\/mml:mo><mml:mn>4<\/mml:mn><\/mml:mrow><\/mml:msup><mml:mo stretchy=\"false\">)<\/mml:mo><\/mml:math>. Our algorithm provides a way to study the finite energy regime of many body systems in quantum simulators by directly preparing a finite energy state, providing access to an approximation of the microcanonical properties at an arbitrary energy.<\/jats:p>","DOI":"10.22331\/q-2024-06-27-1389","type":"journal-article","created":{"date-parts":[[2024,6,27]],"date-time":"2024-06-27T12:20:58Z","timestamp":1719490858000},"page":"1389","update-policy":"https:\/\/doi.org\/10.22331\/q-crossmark-policy-page","source":"Crossref","is-referenced-by-count":8,"title":["Efficient Quantum Algorithm for Filtering Product States"],"prefix":"10.22331","volume":"8","author":[{"given":"Reinis","family":"Irmejs","sequence":"first","affiliation":[{"name":"Max-Planck-Institut f\u00fcr Quantenoptik, Hans-Kopfermann-Stra\u00dfe 1, D-85748 Garching, Germany"},{"name":"Munich Center for Quantum Science and Technology (MCQST), Schellingstra\u00dfe 4, D-80799 Munich, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Mari Carmen","family":"Ba\u00f1uls","sequence":"additional","affiliation":[{"name":"Max-Planck-Institut f\u00fcr Quantenoptik, Hans-Kopfermann-Stra\u00dfe 1, D-85748 Garching, Germany"},{"name":"Munich Center for Quantum Science and Technology (MCQST), Schellingstra\u00dfe 4, D-80799 Munich, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"J. Ignacio","family":"Cirac","sequence":"additional","affiliation":[{"name":"Max-Planck-Institut f\u00fcr Quantenoptik, Hans-Kopfermann-Stra\u00dfe 1, D-85748 Garching, Germany"},{"name":"Munich Center for Quantum Science and Technology (MCQST), Schellingstra\u00dfe 4, D-80799 Munich, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"9598","published-online":{"date-parts":[[2024,6,27]]},"reference":[{"key":"0","doi-asserted-by":"publisher","unstructured":"David Deutsch. ``Quantum theory, the church\u2013turing principle and the universal quantum computer&apos;&apos;. Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences 400, 97\u2013117 (1985).","DOI":"10.1098\/rspa.1985.0070"},{"key":"1","doi-asserted-by":"publisher","unstructured":"Seth Lloyd. ``Universal quantum simulators&apos;&apos;. 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