---
DOAJ_listed: '1'
OA_place: publisher
OA_type: gold
_id: '19424'
abstract:
- lang: eng
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."
acknowledged_ssus:
- _id: M-Shop
- _id: NanoFab
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."
article_number: '3862'
article_processing_charge: Yes
article_type: original
arxiv: 1
author:
- first_name: Jaime
full_name: Saez Mollejo, Jaime
id: e0390f72-f6e0-11ea-865d-862393336714
last_name: Saez Mollejo
- first_name: Daniel
full_name: Jirovec, Daniel
id: 4C473F58-F248-11E8-B48F-1D18A9856A87
last_name: Jirovec
orcid: 0000-0002-7197-4801
- first_name: Yona A
full_name: Schell, Yona A
id: fe39122d-06bb-11ec-a33b-9e22b40e40a5
last_name: Schell
- first_name: Josip
full_name: Kukucka, Josip
id: 3F5D8856-F248-11E8-B48F-1D18A9856A87
last_name: Kukucka
- first_name: Stefano
full_name: Calcaterra, Stefano
last_name: Calcaterra
- first_name: Daniel
full_name: Chrastina, Daniel
last_name: Chrastina
- first_name: Giovanni
full_name: Isella, Giovanni
last_name: Isella
- first_name: Maximilian
full_name: Rimbach-Russ, Maximilian
last_name: Rimbach-Russ
- first_name: Stefano
full_name: Bosco, Stefano
last_name: Bosco
- first_name: Georgios
full_name: Katsaros, Georgios
id: 38DB5788-F248-11E8-B48F-1D18A9856A87
last_name: Katsaros
orcid: 0000-0001-8342-202X
citation:
ama: Saez Mollejo J, Jirovec D, Schell YA, et al. Exchange anisotropies in microwave-driven
singlet-triplet qubits. Nature Communications. 2025;16. doi:10.1038/s41467-025-58969-y
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. Nature Communications. Springer Nature. https://doi.org/10.1038/s41467-025-58969-y
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.” Nature Communications. Springer Nature, 2025. https://doi.org/10.1038/s41467-025-58969-y.
ieee: J. Saez Mollejo et al., “Exchange anisotropies in microwave-driven
singlet-triplet qubits,” Nature Communications, vol. 16. Springer Nature,
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.
mla: Saez Mollejo, Jaime, et al. “Exchange Anisotropies in Microwave-Driven Singlet-Triplet
Qubits.” Nature Communications, vol. 16, 3862, Springer Nature, 2025, doi:10.1038/s41467-025-58969-y.
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).
corr_author: '1'
date_created: 2025-03-19T13:28:12Z
date_published: 2025-04-24T00:00:00Z
date_updated: 2026-05-02T22:31:13Z
day: '24'
ddc:
- '530'
department:
- _id: GeKa
doi: 10.1038/s41467-025-58969-y
external_id:
arxiv:
- '2408.03224'
isi:
- '001475587400022'
pmid:
- '40274808'
file:
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has_accepted_license: '1'
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month: '04'
oa: 1
oa_version: Published Version
pmid: 1
project:
- _id: 34c0acea-11ca-11ed-8bc3-8775e10fd452
grant_number: '101069515'
name: Integrated Germanium Quantum Technology
- _id: 34a66131-11ca-11ed-8bc3-a31681c6b03e
grant_number: F8606
name: 'Center for Correlated Quantum Materials and Solid State Quantum Systems:
Conventional and unconventional topological superconductors'
- _id: c0977eea-5a5b-11eb-8a69-a862db0cf4d1
grant_number: I05060
name: High impedance circuit quantum electrodynamics with hole spins
- _id: 262116AA-B435-11E9-9278-68D0E5697425
name: Hybrid Semiconductor - Superconductor Quantum Devices
publication: Nature Communications
publication_identifier:
eissn:
- 2041-1723
publication_status: published
publisher: Springer Nature
quality_controlled: '1'
related_material:
link:
- description: News on ISTA website
relation: research_data
url: https://ista.ac.at/en/news/the-shadow-of-an-electron/
record:
- id: '19409'
relation: research_data
status: public
- id: '19836'
relation: dissertation_contains
status: public
scopus_import: '1'
status: public
title: Exchange anisotropies in microwave-driven singlet-triplet qubits
tmp:
image: /images/cc_by.png
legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode
name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)
short: CC BY (4.0)
type: journal_article
user_id: ba8df636-2132-11f1-aed0-ed93e2281fdd
volume: 16
year: '2025'
...
---
OA_place: publisher
_id: '19836'
abstract:
- lang: eng
text: "Over the past century, researchers have been fascinated by the quantum nature
of the\r\nphysical world, initially striving to understand its fundamental principles
and consequences, and\r\neventually progressing toward engineering systems that
can control and manipulate quantum\r\nproperties. Today, we stand at the dawn
of the quantum technology era. While some quantum\r\ntechnologies follow well-defined
roadmaps, others are still in the exciting and uncertain early\r\nstages of development.
In the fields of quantum computing and quantum simulation, research\r\nis being
conducted across a wide variety of platforms. Each of these demonstrates control
over\r\nquantum properties but also faces challenges in scaling up to the level
of a mature technology.\r\nThis thesis explores some of the fundamental properties
of hole spin qubits in planar germanium.\r\nSemiconductor spin qubits are considered
strong candidates for the realization of quantum\r\nprocessors, owing to their
long relaxation and coherence times, as well as their compatibility\r\nwith existing
semiconductor industry infrastructure. Among these, hole spin qubits in planar\r\ngermanium
are particularly promising. Their advantages include a large effective mass, which\r\neases
fabrication constraints; inherent protection from hyperfine noise; and strong
spin-orbit\r\ninteraction, which enables fast and purely electrical control. However,
spin-orbit coupling also\r\nintroduces site-dependent variability across qubits,
particularly in the g-tensors and spin-flip\r\ntunneling, which might cause that
the quantization axes are not aligned. In this thesis, we\r\ninvestigate the tilt
between the quantization axes of two hole spins hosted in a double quantum\r\ndot
as a function of both the magnetic field direction and various electrostatic configurations,\r\ndemonstrating
that both parameters influence this tilt. We conclude by introducing a machine-learning-assisted
routine to automatically tune baseband spin qubits. This approach may prove\r\nto
be a powerful tool for characterizing spin-orbit effects and gaining deeper insight
into the\r\nphysics governing spin qubit behavior.\r\n"
acknowledged_ssus:
- _id: NanoFab
- _id: M-Shop
acknowledgement: "This research was supported by the Scientific Service Units of ISTA
through resources provided\r\nby the MIBA Machine Shop and the Nanofabrication facility.
We acknowledge the support from\r\nthe European Commission with the project Integrated
Germanium Quantum Technology (with\r\nDOI:10.3030/101069515), the NOMIS Foundation,
the HORIZON-RIA 101069515 project and\r\nthe FWF Projects Center for Correlated
Quantum Materials and Solid State Quantum Systems:\r\nConventional and unconventional
topological superconductors (with DOI:10.55776/F86) and\r\nHigh impedance circuit
quantum electrodynamics with hole spins (with DOI:10.55776/I5060).\r\n"
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Jaime
full_name: Saez Mollejo, Jaime
id: e0390f72-f6e0-11ea-865d-862393336714
last_name: Saez Mollejo
citation:
ama: 'Saez Mollejo J. Singlet-triplet qubits in planar Germanium : From exchange
anisotropies to autonomous tuning . 2025. doi:10.15479/AT-ISTA-19836'
apa: 'Saez Mollejo, J. (2025). Singlet-triplet qubits in planar Germanium : From
exchange anisotropies to autonomous tuning . Institute of Science and Technology
Austria. https://doi.org/10.15479/AT-ISTA-19836'
chicago: 'Saez Mollejo, Jaime. “Singlet-Triplet Qubits in Planar Germanium : From
Exchange Anisotropies to Autonomous Tuning .” Institute of Science and Technology
Austria, 2025. https://doi.org/10.15479/AT-ISTA-19836.'
ieee: 'J. Saez Mollejo, “Singlet-triplet qubits in planar Germanium : From exchange
anisotropies to autonomous tuning ,” Institute of Science and Technology Austria,
2025.'
ista: 'Saez Mollejo J. 2025. Singlet-triplet qubits in planar Germanium : From exchange
anisotropies to autonomous tuning . Institute of Science and Technology Austria.'
mla: 'Saez Mollejo, Jaime. Singlet-Triplet Qubits in Planar Germanium : From
Exchange Anisotropies to Autonomous Tuning . Institute of Science and Technology
Austria, 2025, doi:10.15479/AT-ISTA-19836.'
short: 'J. Saez Mollejo, Singlet-Triplet Qubits in Planar Germanium : From Exchange
Anisotropies to Autonomous Tuning , Institute of Science and Technology Austria,
2025.'
corr_author: '1'
date_created: 2025-06-13T09:01:50Z
date_published: 2025-06-13T00:00:00Z
date_updated: 2026-04-28T13:29:28Z
day: '13'
ddc:
- '530'
- '539'
degree_awarded: PhD
department:
- _id: GradSch
- _id: GeKa
doi: 10.15479/AT-ISTA-19836
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language:
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month: '06'
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page: '175'
project:
- _id: 34c0acea-11ca-11ed-8bc3-8775e10fd452
grant_number: '101069515'
name: Integrated Germanium Quantum Technology
- _id: 34a66131-11ca-11ed-8bc3-a31681c6b03e
grant_number: F8606
name: 'Center for Correlated Quantum Materials and Solid State Quantum Systems:
Conventional and unconventional topological superconductors'
- _id: c0977eea-5a5b-11eb-8a69-a862db0cf4d1
grant_number: I05060
name: High impedance circuit quantum electrodynamics with hole spins
publication_identifier:
issn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
related_material:
record:
- id: '19424'
relation: part_of_dissertation
status: public
status: public
supervisor:
- first_name: Georgios
full_name: Katsaros, Georgios
id: 38DB5788-F248-11E8-B48F-1D18A9856A87
last_name: Katsaros
orcid: 0000-0001-8342-202X
title: 'Singlet-triplet qubits in planar Germanium : From exchange anisotropies to
autonomous tuning '
tmp:
image: /images/cc_by.png
legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode
name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)
short: CC BY (4.0)
type: dissertation
user_id: 8b945eb4-e2f2-11eb-945a-df72226e66a9
year: '2025'
...