{"id":"https://openalex.org/W7214156960","doi":"https://doi.org/10.26434/chemrxiv.15009412/v1","title":"Quantum Subspace Expansion for Molecular Excited States: Representability, Stability, and Practical Considerations","display_name":"Quantum Subspace Expansion for Molecular Excited States: Representability, Stability, and Practical Considerations","publication_year":2026,"publication_date":"2026-09-24","ids":{"openalex":"https://openalex.org/W7214156960","doi":"https://doi.org/10.26434/chemrxiv.15009412/v1"},"language":"en","primary_location":{"id":"doi:10.26434/chemrxiv.15009412/v1","doi":"https://doi.org/10.26434/chemrxiv.15009412/v1","is_oa":true,"landing_page_url":"https://doi.org/10.26434/chemrxiv.15009412/v1","pdf_url":"https://chemrxiv.org/doi/pdf/10.26434/chemrxiv.15009412/v1","source":{"id":"https://openalex.org/S4393918830","display_name":"ChemRxiv","issn_l":"2573-2293","issn":["2573-2293"],"is_oa":false,"is_in_doaj":false,"is_core":false,"listed_in":[],"host_organization":null,"host_organization_name":null,"host_organization_lineage":[],"host_organization_lineage_names":[],"type":"repository"},"license":"cc-by","license_id":"https://openalex.org/licenses/cc-by","version":"acceptedVersion","is_accepted":true,"is_published":false,"raw_source_name":null,"raw_type":"posted-content"},"volume":null,"type":"preprint","is_traditional":true,"indexed_in":["crossref"],"open_access":{"is_oa":true,"oa_status":"green","oa_url":"https://chemrxiv.org/doi/pdf/10.26434/chemrxiv.15009412/v1","any_repository_has_fulltext":true},"authorships":[{"author_position":"first","author":{"id":"https://openalex.org/A5040264177","display_name":"Naythan Z. X. Yeo","orcid":null,"observed_orcids":[]},"institutions":[{"id":"https://openalex.org/I115228651","display_name":"Agency for Science, Technology and Research","ror":"https://ror.org/036wvzt09","country_code":"SG","type":"government","lineage":["https://openalex.org/I115228651"]},{"id":"https://openalex.org/I4405277092","display_name":"Institute of Advanced Intelligence and Computing","ror":"https://ror.org/01eczt548","country_code":"SG","type":"facility","lineage":["https://openalex.org/I4405277092"]}],"countries":["SG"],"is_corresponding":false,"raw_author_name":"Naythan Z. X. Yeo","raw_affiliation_strings":["Institute of Advanced Intelligence and Computing (IAIC, Agency for Science, Technology and Research (A*STAR, 1 Fusionopolis Way, Connexis, Republic of Singapore, 138632"],"raw_orcid":null,"affiliations":[{"raw_affiliation_string":"Institute of Advanced Intelligence and Computing (IAIC, Agency for Science, Technology and Research (A*STAR, 1 Fusionopolis Way, Connexis, Republic of Singapore, 138632","institution_ids":["https://openalex.org/I115228651","https://openalex.org/I4405277092"]}]},{"author_position":"last","author":{"id":"https://openalex.org/A5048111200","display_name":"Shi Jun Ang","orcid":"https://orcid.org/0000-0002-3569-639X","observed_orcids":["https://orcid.org/0000-0002-3569-639X"]},"institutions":[{"id":"https://openalex.org/I115228651","display_name":"Agency for Science, Technology and Research","ror":"https://ror.org/036wvzt09","country_code":"SG","type":"government","lineage":["https://openalex.org/I115228651"]},{"id":"https://openalex.org/I4405277092","display_name":"Institute of Advanced Intelligence and Computing","ror":"https://ror.org/01eczt548","country_code":"SG","type":"facility","lineage":["https://openalex.org/I4405277092"]}],"countries":["SG"],"is_corresponding":false,"raw_author_name":"Shi Jun Ang","raw_affiliation_strings":["Institute of Advanced Intelligence and Computing (IAIC, Agency for Science, Technology and Research (A*STAR, 1 Fusionopolis Way, Connexis, Republic of Singapore, 138632"],"raw_orcid":"https://orcid.org/0000-0002-3569-639X","affiliations":[{"raw_affiliation_string":"Institute of Advanced Intelligence and Computing (IAIC, Agency for Science, Technology and Research (A*STAR, 1 Fusionopolis Way, Connexis, Republic of Singapore, 138632","institution_ids":["https://openalex.org/I115228651","https://openalex.org/I4405277092"]}]}],"institutions":[],"countries_distinct_count":1,"institutions_distinct_count":2,"corresponding_author_ids":[],"corresponding_institution_ids":[],"apc_list":null,"apc_paid":null,"fwci":null,"has_fulltext":true,"cited_by_count":0,"citation_normalized_percentile":null,"cited_by_percentile_year":null,"biblio":{"volume":null,"issue":null,"first_page":null,"last_page":null},"is_retracted":false,"is_paratext":false,"is_xpac":false,"primary_topic":{"id":"https://openalex.org/T10682","display_name":"Quantum Computing Algorithms and Architecture","score":0.9320999979972839,"subfield":{"id":"https://openalex.org/subfields/1702","display_name":"Artificial Intelligence"},"field":{"id":"https://openalex.org/fields/17","display_name":"Computer Science"},"domain":{"id":"https://openalex.org/domains/3","display_name":"Physical Sciences"}},"topics":[{"id":"https://openalex.org/T10682","display_name":"Quantum Computing Algorithms and Architecture","score":0.9320999979972839,"subfield":{"id":"https://openalex.org/subfields/1702","display_name":"Artificial Intelligence"},"field":{"id":"https://openalex.org/fields/17","display_name":"Computer Science"},"domain":{"id":"https://openalex.org/domains/3","display_name":"Physical Sciences"}},{"id":"https://openalex.org/T10002","display_name":"Advanced Chemical Physics Studies","score":0.05559999868273735,"subfield":{"id":"https://openalex.org/subfields/3107","display_name":"Atomic and Molecular Physics, and Optics"},"field":{"id":"https://openalex.org/fields/31","display_name":"Physics and Astronomy"},"domain":{"id":"https://openalex.org/domains/3","display_name":"Physical Sciences"}},{"id":"https://openalex.org/T11804","display_name":"Quantum many-body systems","score":0.002099999925121665,"subfield":{"id":"https://openalex.org/subfields/3107","display_name":"Atomic and Molecular Physics, and Optics"},"field":{"id":"https://openalex.org/fields/31","display_name":"Physics and Astronomy"},"domain":{"id":"https://openalex.org/domains/3","display_name":"Physical Sciences"}}],"keywords":[{"id":"https://openalex.org/keywords/excited-states","display_name":"excited states","score":0.8299999833106995},{"id":"https://openalex.org/keywords/quantum-chemistry","display_name":"quantum chemistry","score":0.42500001192092896},{"id":"https://openalex.org/keywords/representability","display_name":"representability","score":0.7179999947547913},{"id":"https://openalex.org/keywords/numerical-stability","display_name":"numerical stability","score":0.949999988079071},{"id":"https://openalex.org/keywords/overlap-matrix","display_name":"overlap matrix","score":0.6190000176429749},{"id":"https://openalex.org/keywords/active-space","display_name":"active space","score":0.6800000071525574},{"id":"https://openalex.org/keywords/measurement-cost","display_name":"measurement cost","score":0.7139999866485596},{"id":"https://openalex.org/keywords/organic-compounds","display_name":"organic compounds","score":0.9150000214576721},{"id":"https://openalex.org/keywords/variational-quantum-algorithms","display_name":"variational quantum algorithms","score":0.6330000162124634}],"concepts":[{"id":"https://openalex.org/C32834561","wikidata":"https://www.wikidata.org/wiki/Q660730","display_name":"Subspace topology","level":2,"score":0.7317000031471252},{"id":"https://openalex.org/C130787639","wikidata":"https://www.wikidata.org/wiki/Q5645293","display_name":"Hamiltonian (control theory)","level":2,"score":0.6179999709129333},{"id":"https://openalex.org/C158693339","wikidata":"https://www.wikidata.org/wiki/Q190524","display_name":"Eigenvalues and eigenvectors","level":2,"score":0.6039000153541565},{"id":"https://openalex.org/C181500209","wikidata":"https://www.wikidata.org/wiki/Q215328","display_name":"Excited state","level":2,"score":0.5625},{"id":"https://openalex.org/C121332964","wikidata":"https://www.wikidata.org/wiki/Q413","display_name":"Physics","level":0,"score":0.5552999973297119},{"id":"https://openalex.org/C99844830","wikidata":"https://www.wikidata.org/wiki/Q102441924","display_name":"Scaling","level":2,"score":0.5067999958992004},{"id":"https://openalex.org/C121864883","wikidata":"https://www.wikidata.org/wiki/Q677916","display_name":"Statistical physics","level":1,"score":0.5008000135421753},{"id":"https://openalex.org/C84114770","wikidata":"https://www.wikidata.org/wiki/Q46344","display_name":"Quantum","level":2,"score":0.4832000136375427},{"id":"https://openalex.org/C185798385","wikidata":"https://www.wikidata.org/wiki/Q1161707","display_name":"Benchmark (surveying)","level":2,"score":0.46619999408721924},{"id":"https://openalex.org/C17020691","wikidata":"https://www.wikidata.org/wiki/Q139677","display_name":"Operator (biology)","level":5,"score":0.39890000224113464},{"id":"https://openalex.org/C62520636","wikidata":"https://www.wikidata.org/wiki/Q944","display_name":"Quantum mechanics","level":1,"score":0.3828999996185303},{"id":"https://openalex.org/C41008148","wikidata":"https://www.wikidata.org/wiki/Q21198","display_name":"Computer science","level":0,"score":0.36959999799728394},{"id":"https://openalex.org/C135715101","wikidata":"https://www.wikidata.org/wiki/Q3299275","display_name":"Hamiltonian matrix","level":4,"score":0.36570000648498535},{"id":"https://openalex.org/C106487976","wikidata":"https://www.wikidata.org/wiki/Q685816","display_name":"Matrix (chemical analysis)","level":2,"score":0.3628999888896942},{"id":"https://openalex.org/C33332235","wikidata":"https://www.wikidata.org/wiki/Q18362","display_name":"Theoretical physics","level":1,"score":0.32359999418258667},{"id":"https://openalex.org/C84551667","wikidata":"https://www.wikidata.org/wiki/Q155640","display_name":"Potential energy","level":2,"score":0.31929999589920044},{"id":"https://openalex.org/C91682802","wikidata":"https://www.wikidata.org/wiki/Q620538","display_name":"Multidimensional scaling","level":2,"score":0.30889999866485596},{"id":"https://openalex.org/C11413529","wikidata":"https://www.wikidata.org/wiki/Q8366","display_name":"Algorithm","level":1,"score":0.2912999987602234},{"id":"https://openalex.org/C186370098","wikidata":"https://www.wikidata.org/wiki/Q442787","display_name":"Energy (signal processing)","level":2,"score":0.2782000005245209},{"id":"https://openalex.org/C2777027219","wikidata":"https://www.wikidata.org/wiki/Q1284190","display_name":"Constant (computer programming)","level":2,"score":0.25529998540878296}],"mesh":[],"locations_count":1,"locations":[{"id":"doi:10.26434/chemrxiv.15009412/v1","doi":"https://doi.org/10.26434/chemrxiv.15009412/v1","is_oa":true,"landing_page_url":"https://doi.org/10.26434/chemrxiv.15009412/v1","pdf_url":"https://chemrxiv.org/doi/pdf/10.26434/chemrxiv.15009412/v1","source":{"id":"https://openalex.org/S4393918830","display_name":"ChemRxiv","issn_l":"2573-2293","issn":["2573-2293"],"is_oa":false,"is_in_doaj":false,"is_core":false,"listed_in":[],"host_organization":null,"host_organization_name":null,"host_organization_lineage":[],"host_organization_lineage_names":[],"type":"repository"},"license":"cc-by","license_id":"https://openalex.org/licenses/cc-by","version":"acceptedVersion","is_accepted":true,"is_published":false,"raw_source_name":null,"raw_type":"posted-content"}],"best_oa_location":{"id":"doi:10.26434/chemrxiv.15009412/v1","doi":"https://doi.org/10.26434/chemrxiv.15009412/v1","is_oa":true,"landing_page_url":"https://doi.org/10.26434/chemrxiv.15009412/v1","pdf_url":"https://chemrxiv.org/doi/pdf/10.26434/chemrxiv.15009412/v1","source":{"id":"https://openalex.org/S4393918830","display_name":"ChemRxiv","issn_l":"2573-2293","issn":["2573-2293"],"is_oa":false,"is_in_doaj":false,"is_core":false,"listed_in":[],"host_organization":null,"host_organization_name":null,"host_organization_lineage":[],"host_organization_lineage_names":[],"type":"repository"},"license":"cc-by","license_id":"https://openalex.org/licenses/cc-by","version":"acceptedVersion","is_accepted":true,"is_published":false,"raw_source_name":null,"raw_type":"posted-content"},"sustainable_development_goals":[],"study_designs":[],"awards":[],"funders":[{"id":"https://openalex.org/F4320320709","display_name":"National Research Foundation Singapore","ror":"https://ror.org/03cpyc314"}],"has_content":{"grobid_xml":true,"pdf":true},"content_urls":{"pdf":"https://content.openalex.org/works/W7214156960.pdf","grobid_xml":"https://content.openalex.org/works/W7214156960.grobid-xml"},"referenced_works_count":1,"referenced_works":["https://openalex.org/W4415311959"],"related_works":["https://openalex.org/W7172391752","https://openalex.org/W4416032113","https://openalex.org/W7134831891","https://openalex.org/W7148935794","https://openalex.org/W4377967042","https://openalex.org/W7203455391","https://openalex.org/W4415463442","https://openalex.org/W7102748421","https://openalex.org/W7151789359","https://openalex.org/W7221398957"],"abstract_inverted_index":{"Accurate":[0],"treatment":[1],"of":[2,27,93,99,132,151,215],"excited":[3],"states":[4,35],"remains":[5],"challenging":[6],"for":[7,32,155,201],"classical":[8],"electronic-structure":[9],"methods,":[10],"motivating":[11],"quantum":[12],"algorithms":[13],"that":[14,48,105,178],"may":[15],"provide":[16,212],"more":[17,202,229],"favorable":[18],"resource":[19],"scaling.":[20],"We":[21],"systematically":[22],"assess":[23],"the":[24,41,54,74,81,91,100,141,179,187,191],"practical":[25,230],"performance":[26],"Quantum":[28],"Subspace":[29],"Expansion":[30],"(QSE)":[31],"low-lying":[33],"electronic":[34,61],"across":[36,217],"28":[37],"organic":[38,219],"molecules":[39],"from":[40],"Thiel":[42],"benchmark":[43],"set.":[44],"Statevector":[45],"simulations":[46],"reveal":[47],"QSE":[49,76,101,216],"representability":[50,89],"depends":[51],"strongly":[52],"on":[53],"target":[55,82],"state,":[56],"active":[57],"space,":[58],"and":[59,172,193,206],"molecular":[60],"structure,":[62],"with":[63,108,140],"multiconfigurational":[64],"character":[65],"emerging":[66],"as":[67],"an":[68,129,213],"important":[69],"factor.":[70],"In":[71],"several":[72],"cases,":[73],"one-body":[75],"subspace":[77],"cannot":[78,115],"adequately":[79],"represent":[80],"states,":[83],"while":[84,186,224],"explicit":[85],"double-excitation":[86],"operators":[87],"improve":[88],"at":[90],"cost":[92,150],"a":[94,147,165],"larger":[95],"operator":[96],"space.":[97],"Analysis":[98],"overlap":[102,194],"matrix":[103],"shows":[104],"although":[106],"eigenmodes":[107],"small":[109],"eigenvalues":[110],"drive":[111],"numerical":[112,170],"instability,":[113],"they":[114],"be":[116],"discarded":[117],"indiscriminately":[118],"without":[119],"compromising":[120],"spectral":[121],"accuracy.":[122],"Under":[123],"finite-shot":[124,188],"sampling,":[125],"energy":[126],"errors":[127],"exhibit":[128,182],"empirical":[130],"scaling":[131],"approximately":[133,152],"n2":[134],"orb/":[135],"\u221a":[136],"Nshots,":[137],"which,":[138],"combined":[139],"growth":[142],"in":[143,190],"measurement":[144,149,173,205],"groups,":[145],"yields":[146],"total":[148],"O(n11":[153],"orb)":[154],"constant":[156],"accuracy":[157],"under":[158],"our":[159,210],"direct-estimation":[160],"protocol.":[161],"These":[162],"results":[163,211],"expose":[164],"central":[166],"tension":[167],"between":[168],"representability,":[169],"stability,":[171],"cost.":[174],"Encouragingly,":[175],"we":[176],"find":[177],"projected":[180],"matrices":[181,195],"recurring":[183],"structural":[184],"patterns,":[185],"perturbations":[189],"Hamiltonian":[192],"show":[196],"nontrivial":[197],"covariance,":[198],"suggesting":[199],"opportunities":[200],"efficient":[203],"structure-aware":[204],"reconstruction":[207],"strategies.":[208],"Overall,":[209],"assessment":[214],"chemically-relevant":[218],"molecules,":[220],"identifying":[221],"present":[222],"limitations":[223],"highlighting":[225],"potential":[226],"routes":[227],"toward":[228],"future":[231],"implementations.":[232]},"counts_by_year":[],"updated_date":"2026-11-04T10:54:05.112534","created_date":"2026-09-25T00:00:00"}