[{"oa_version":"Preprint","publication_status":"published","_id":"22619","title":"Low-noise quantum dots in ultra-shallow Ge/SiGe heterostructures for prototyping hybrid semiconducting–superconducting devices","intvolume":"       129","oa":1,"arxiv":1,"OA_type":"green","main_file_link":[{"url":"https://doi.org/10.48550/arXiv.2602.21363","open_access":"1"}],"year":"2026","das_tickbox":"1","abstract":[{"text":"Planar germanium is currently the only semiconducting platform where high-coherence spin qubits and proximity-induced superconductivity have each been demonstrated. Recent research into spin qubits in Ge/SiGe heterostructures has focused on increasing the thickness of the SiGe capping layer, reporting improvements in the electrostatic noise levels. Meanwhile, heterostructures with thinner capping layers remain rather unexplored, despite the potential advantages for proximity-induced superconductivity. Here, we study a Ge/SiGe heterostructure with a thin SiGe cap d - 4nm and investigate its viability to host low-noise quantum dots. To keep the thermal budget compatible with superconducting layers, low-temperature oxide deposition processes were developed and implemented for the gate dielectrics. The charge noise level of the fabricated devices is estimated to be 1.8  +- 1.0 μeV/ square HZ⁠, comparable to devices fabricated on shallow heterostructures (⁠ d - 20nm⁠) with high-temperature deposited oxides. Low charge noise levels, together with the straightforward integration of superconductors, make this heterostructure an attractive platform for prototyping hybrid semiconducting–superconducting devices.","lang":"eng"}],"project":[{"grant_number":"101115315","name":"Quantum bits with Kitaev Transmons","_id":"bdc2ca30-d553-11ed-ba76-cf164a5bb811"},{"grant_number":"F8606","name":"Center for Correlated Quantum Materials and Solid State Quantum Systems: Conventional  and unconventional topological superconductors","_id":"34a66131-11ca-11ed-8bc3-a31681c6b03e"},{"grant_number":"PAT 7682124","name":"Superconducting spin qubits in planar Ge","_id":"5b9e579c-ab3d-11f0-914f-88754c5b5a3f"},{"_id":"bd8bd29e-d553-11ed-ba76-f0070d4b237a","name":"Merging spin and superconducting qubits in planar Ge","grant_number":"P36507"},{"grant_number":"101150858","name":"Realization and Manipulation of a Planar hybrid superconducting Andreev spin qubit in Germanium","_id":"8ea8abf7-16d5-11f0-9cad-c41e56ec8bb3"}],"external_id":{"arxiv":["2602.21363"]},"publication_identifier":{"issn":["0003-6951"],"eissn":["1077-3118"]},"supplementarymaterial":"yes","article_number":"033505","publisher":"AIP Publishing","issue":"3","type":"journal_article","department":[{"_id":"GeKa"},{"_id":"GradSch"},{"_id":"NanoFab"}],"date_updated":"2026-08-03T11:08:39Z","month":"07","date_published":"2026-07-20T00:00:00Z","acknowledged_ssus":[{"_id":"M-Shop"},{"_id":"NanoFab"}],"publication":"Applied Physics Letters","status":"public","author":[{"id":"1fd0975f-8b61-11ed-b69e-d149334f28c5","last_name":"Borovkov","first_name":"Maksim","full_name":"Borovkov, Maksim"},{"first_name":"Yona A","last_name":"Schell","id":"fe39122d-06bb-11ec-a33b-9e22b40e40a5","full_name":"Schell, Yona A"},{"full_name":"Sokolova, Dina","first_name":"Dina","last_name":"Sokolova","id":"2d2d62f8-72f0-11ef-b75a-8ec3e8a60032"},{"last_name":"Roux","id":"53f93ea2-803f-11ed-ab7e-b283135794ef","first_name":"Kevin Etienne Robert","full_name":"Roux, Kevin Etienne Robert"},{"first_name":"Paul","id":"85b43b21-15b2-11ec-abd3-e2c252cc2285","last_name":"Falthansl-Scheinecker","full_name":"Falthansl-Scheinecker, Paul"},{"last_name":"Fabris","id":"298cf6f3-1ff6-11ee-9fa6-d94cfa0b3352","first_name":"Giorgio","full_name":"Fabris, Giorgio"},{"last_name":"Shah","id":"de191434-4e7e-11ef-bf4b-9a056fc19fc3","first_name":"Devashish C","full_name":"Shah, Devashish C","orcid":"0009-0007-5829-7707"},{"first_name":"Jaime","id":"e0390f72-f6e0-11ea-865d-862393336714","last_name":"Saez Mollejo","full_name":"Saez Mollejo, Jaime"},{"first_name":"Rodolfo","id":"bc4ea1dc-00ce-11ec-8a4e-b325ca8b9876","last_name":"Previdi","full_name":"Previdi, Rodolfo"},{"full_name":"Taha, Inas","last_name":"Taha","first_name":"Inas"},{"last_name":"Genç","first_name":"Aziz","full_name":"Genç, Aziz"},{"full_name":"Arbiol, Jordi","last_name":"Arbiol","first_name":"Jordi"},{"full_name":"Calcaterra, Stefano","last_name":"Calcaterra","first_name":"Stefano"},{"full_name":"Oliveira, Afonso De Cerdeira","first_name":"Afonso De Cerdeira","last_name":"Oliveira"},{"first_name":"Daniel","last_name":"Chrastina","full_name":"Chrastina, Daniel"},{"last_name":"Isella","first_name":"Giovanni","full_name":"Isella, Giovanni"},{"full_name":"Bubis, Anton","first_name":"Anton","last_name":"Bubis","id":"1f6212b5-f795-11ec-9c0c-de4780302890"},{"first_name":"Georgios","last_name":"Katsaros","id":"38DB5788-F248-11E8-B48F-1D18A9856A87","orcid":"0000-0001-8342-202X","full_name":"Katsaros, Georgios"}],"date_created":"2026-08-02T22:01:53Z","day":"20","language":[{"iso":"eng"}],"researchdata_availability":"yes","OA_place":"repository","related_material":{"record":[{"status":"public","id":"22242","relation":"research_data"}]},"article_type":"original","corr_author":"1","acknowledgement":"We sincerely thank Nick van Loo, Greg Mazur, Dhananjay Joshi, and Srijit Goswami for their inputs on low-temperature HfOx deposition; Matias Urdampilleta and Daniel Jirovec for discussions; and Kristen Léonard for the careful reading of the manuscript. This research was supported by the Scientific Service Units of ISTA through resources provided by the Miba Machine Shop and the Nanofabrication facility. The authors acknowledge support from the NOMIS Foundation; the European Innovation Council Pathfinder Grant No. 101115315 (QuKiT); the FWF Projects with DOI:10.55776/F86, DOI:10.55776/PAT7682124, and DOI:10.55776/P36507; and the HE-MSCA-PF project with DOI:10.3030/101150858. ICN2 is supported by the Severo Ochoa Program from Spanish MCIN/AEI (Grant No.: CEX2021-001214-S) and is funded by the CERCA Program/Generalitat de Catalunya. ICN2 acknowledges funding from Generalitat de Catalunya (No. 2021SGR00457). We acknowledge support from the CSIC Interdisciplinary Thematic Platform (PTI+) on Quantum Technologies (PTI-QTEP+).","scopus_import":"1","article_processing_charge":"No","citation":{"mla":"Borovkov, Maksim, et al. “Low-Noise Quantum Dots in Ultra-Shallow Ge/SiGe Heterostructures for Prototyping Hybrid Semiconducting–Superconducting Devices.” <i>Applied Physics Letters</i>, vol. 129, no. 3, 033505, AIP Publishing, 2026, doi:<a href=\"https://doi.org/10.1063/5.0333142\">10.1063/5.0333142</a>.","ama":"Borovkov M, Schell YA, Sokolova D, et al. Low-noise quantum dots in ultra-shallow Ge/SiGe heterostructures for prototyping hybrid semiconducting–superconducting devices. <i>Applied Physics Letters</i>. 2026;129(3). doi:<a href=\"https://doi.org/10.1063/5.0333142\">10.1063/5.0333142</a>","apa":"Borovkov, M., Schell, Y. A., Sokolova, D., Roux, K. E. R., Falthansl-Scheinecker, P., Fabris, G., … Katsaros, G. (2026). Low-noise quantum dots in ultra-shallow Ge/SiGe heterostructures for prototyping hybrid semiconducting–superconducting devices. <i>Applied Physics Letters</i>. AIP Publishing. <a href=\"https://doi.org/10.1063/5.0333142\">https://doi.org/10.1063/5.0333142</a>","chicago":"Borovkov, Maksim, Yona A Schell, Dina Sokolova, Kevin Etienne Robert Roux, Paul Falthansl-Scheinecker, Giorgio Fabris, Devashish C Shah, et al. “Low-Noise Quantum Dots in Ultra-Shallow Ge/SiGe Heterostructures for Prototyping Hybrid Semiconducting–Superconducting Devices.” <i>Applied Physics Letters</i>. AIP Publishing, 2026. <a href=\"https://doi.org/10.1063/5.0333142\">https://doi.org/10.1063/5.0333142</a>.","ista":"Borovkov M, Schell YA, Sokolova D, Roux KER, Falthansl-Scheinecker P, Fabris G, Shah DC, Saez Mollejo J, Previdi R, Taha I, Genç A, Arbiol J, Calcaterra S, Oliveira ADC, Chrastina D, Isella G, Bubis A, Katsaros G. 2026. Low-noise quantum dots in ultra-shallow Ge/SiGe heterostructures for prototyping hybrid semiconducting–superconducting devices. Applied Physics Letters. 129(3), 033505.","short":"M. Borovkov, Y.A. Schell, D. Sokolova, K.E.R. Roux, P. Falthansl-Scheinecker, G. Fabris, D.C. Shah, J. Saez Mollejo, R. Previdi, I. Taha, A. Genç, J. Arbiol, S. Calcaterra, A.D.C. Oliveira, D. Chrastina, G. Isella, A. Bubis, G. Katsaros, Applied Physics Letters 129 (2026).","ieee":"M. Borovkov <i>et al.</i>, “Low-noise quantum dots in ultra-shallow Ge/SiGe heterostructures for prototyping hybrid semiconducting–superconducting devices,” <i>Applied Physics Letters</i>, vol. 129, no. 3. AIP Publishing, 2026."},"quality_controlled":"1","volume":129,"dataavailabilitystatement":"The data that support the findings of this study are openly available in Institute of Science and Technology repository at http://doi.org/10.15479/AT-ISTA-22242, Ref. 50.","doi":"10.1063/5.0333142","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87"},{"year":"2025","abstract":[{"text":"Hole spin qubits are rapidly emerging as the workhorse of semiconducting quantum processors because of their large spin-orbit interaction, enabling fast all-electric operations at low power. However, spin-orbit interaction also causes non-uniformities in devices, resulting in locally varying qubit energies and site-dependent anisotropies. While these anisotropies can be used to drive single-spins, if not properly harnessed, they can hinder the path toward large-scale quantum processors. Here, we report on microwave-driven singlet-triplet qubits in planar germanium and use them to investigate the anisotropy of two spins in a double quantum dot. We show two distinct operating regimes depending on the magnetic field direction. For in-plane fields, the two spins are largely anisotropic, and electrically tunable, which enables to measure all the available transitions; coherence times exceeding 3 $\\mu$s are extracted. For out-of-plane fields, they have an isotropic response but preserve the substantial energy difference required to address the singlet-triplet qubit. Even in this field direction, where the qubit lifetime\r\nis strongly affected by nuclear spins, we find 400 ns coherence times. Our work adds a valuable tool to investigate and harness the anisotropy of spin qubits and can be implemented in any large-scale NxN device, facilitating the path towards scalable quantum processors.","lang":"eng"}],"OA_type":"gold","APC_amount":"7068 EUR","DOAJ_listed":"1","arxiv":1,"pmid":1,"intvolume":"        16","oa":1,"publication_status":"published","_id":"19424","title":"Exchange anisotropies in microwave-driven singlet-triplet qubits","oa_version":"Published Version","publisher":"Springer Nature","article_number":"3862","publication_identifier":{"eissn":["2041-1723"]},"external_id":{"pmid":["40274808"],"isi":["001475587400022"],"arxiv":["2408.03224"]},"tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"project":[{"grant_number":"101069515","name":"Integrated Germanium Quantum Technology","_id":"34c0acea-11ca-11ed-8bc3-8775e10fd452"},{"grant_number":"F8606","_id":"34a66131-11ca-11ed-8bc3-a31681c6b03e","name":"Center for Correlated Quantum Materials and Solid State Quantum Systems: Conventional  and unconventional topological superconductors"},{"_id":"c0977eea-5a5b-11eb-8a69-a862db0cf4d1","name":"High impedance circuit quantum electrodynamics with hole spins","grant_number":"I05060"},{"_id":"262116AA-B435-11E9-9278-68D0E5697425","name":"Hybrid Semiconductor - Superconductor Quantum Devices"},{"call_identifier":"FWF","_id":"3AC91DDA-15DF-11EA-824D-93A3E7B544D1","name":"FWF Open Access Fund"}],"corr_author":"1","article_type":"original","acknowledgement":"We thank A. Crippa for helpful discussions. This research was supported by the Scientific Service Units of ISTA through resources provided by the MIBA Machine Shop and the Nanofabrication facility. This research and related results were made possible with the support of the NOMIS Foundation, the HORIZON-RIA 101069515 project and the FWF Projects with DOI:10.55776/F86 and DOI:10.55776/I5060. M.R.-R. acknowledges support from the Netherlands Organization of Scientific Research (NWO) under Veni grant VI.Veni.212.223. The\r\nResearch of S.B. and M.R.-R. was sponsored in part by the Army Research Office and was accomplished under Award Number: W911NF-23-1-0110. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Office or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation herein.","OA_place":"publisher","related_material":{"record":[{"status":"public","id":"19409","relation":"research_data"},{"relation":"dissertation_contains","id":"19836","status":"public"}],"link":[{"description":"News on ISTA website","relation":"research_data","url":"https://ista.ac.at/en/news/the-shadow-of-an-electron/"}]},"language":[{"iso":"eng"}],"day":"24","date_created":"2025-03-19T13:28:12Z","file_date_updated":"2025-05-05T07:08:23Z","author":[{"id":"e0390f72-f6e0-11ea-865d-862393336714","last_name":"Saez Mollejo","first_name":"Jaime","full_name":"Saez Mollejo, Jaime"},{"id":"4C473F58-F248-11E8-B48F-1D18A9856A87","last_name":"Jirovec","first_name":"Daniel","full_name":"Jirovec, Daniel","orcid":"0000-0002-7197-4801"},{"id":"fe39122d-06bb-11ec-a33b-9e22b40e40a5","last_name":"Schell","first_name":"Yona A","full_name":"Schell, Yona A"},{"full_name":"Kukucka, Josip","first_name":"Josip","last_name":"Kukucka","id":"3F5D8856-F248-11E8-B48F-1D18A9856A87"},{"first_name":"Stefano","last_name":"Calcaterra","full_name":"Calcaterra, Stefano"},{"full_name":"Chrastina, Daniel","first_name":"Daniel","last_name":"Chrastina"},{"full_name":"Isella, Giovanni","last_name":"Isella","first_name":"Giovanni"},{"full_name":"Rimbach-Russ, Maximilian","last_name":"Rimbach-Russ","first_name":"Maximilian"},{"full_name":"Bosco, Stefano","last_name":"Bosco","first_name":"Stefano"},{"full_name":"Katsaros, Georgios","orcid":"0000-0001-8342-202X","id":"38DB5788-F248-11E8-B48F-1D18A9856A87","last_name":"Katsaros","first_name":"Georgios"}],"status":"public","date_published":"2025-04-24T00:00:00Z","month":"04","acknowledged_ssus":[{"_id":"M-Shop"},{"_id":"NanoFab"}],"ddc":["530"],"publication":"Nature Communications","date_updated":"2026-08-24T22:31:08Z","type":"journal_article","has_accepted_license":"1","department":[{"_id":"GeKa"}],"doi":"10.1038/s41467-025-58969-y","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","quality_controlled":"1","citation":{"short":"J. Saez Mollejo, D. Jirovec, Y.A. Schell, J. Kukucka, S. Calcaterra, D. Chrastina, G. Isella, M. Rimbach-Russ, S. Bosco, G. Katsaros, Nature Communications 16 (2025).","ista":"Saez Mollejo J, Jirovec D, Schell YA, Kukucka J, Calcaterra S, Chrastina D, Isella G, Rimbach-Russ M, Bosco S, Katsaros G. 2025. Exchange anisotropies in microwave-driven singlet-triplet qubits. Nature Communications. 16, 3862.","ieee":"J. Saez Mollejo <i>et al.</i>, “Exchange anisotropies in microwave-driven singlet-triplet qubits,” <i>Nature Communications</i>, vol. 16. Springer Nature, 2025.","apa":"Saez Mollejo, J., Jirovec, D., Schell, Y. A., Kukucka, J., Calcaterra, S., Chrastina, D., … Katsaros, G. (2025). Exchange anisotropies in microwave-driven singlet-triplet qubits. <i>Nature Communications</i>. Springer Nature. <a href=\"https://doi.org/10.1038/s41467-025-58969-y\">https://doi.org/10.1038/s41467-025-58969-y</a>","ama":"Saez Mollejo J, Jirovec D, Schell YA, et al. Exchange anisotropies in microwave-driven singlet-triplet qubits. <i>Nature Communications</i>. 2025;16. doi:<a href=\"https://doi.org/10.1038/s41467-025-58969-y\">10.1038/s41467-025-58969-y</a>","mla":"Saez Mollejo, Jaime, et al. “Exchange Anisotropies in Microwave-Driven Singlet-Triplet Qubits.” <i>Nature Communications</i>, vol. 16, 3862, Springer Nature, 2025, doi:<a href=\"https://doi.org/10.1038/s41467-025-58969-y\">10.1038/s41467-025-58969-y</a>.","chicago":"Saez Mollejo, Jaime, Daniel Jirovec, Yona A Schell, Josip Kukucka, Stefano Calcaterra, Daniel Chrastina, Giovanni Isella, Maximilian Rimbach-Russ, Stefano Bosco, and Georgios Katsaros. “Exchange Anisotropies in Microwave-Driven Singlet-Triplet Qubits.” <i>Nature Communications</i>. Springer Nature, 2025. <a href=\"https://doi.org/10.1038/s41467-025-58969-y\">https://doi.org/10.1038/s41467-025-58969-y</a>."},"volume":16,"isi":1,"file":[{"access_level":"open_access","date_created":"2025-05-05T07:08:23Z","relation":"main_file","success":1,"file_name":"2025_NatureComm_SaezMollejo.pdf","creator":"dernst","checksum":"13fe84cddc9d4e47213bf17acdac70d7","date_updated":"2025-05-05T07:08:23Z","file_id":"19645","file_size":1548756,"content_type":"application/pdf"}],"article_processing_charge":"Yes","scopus_import":"1"}]