---
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: 2026-07-29T12:55:59Z
day: '13'
ddc:
- '530'
- '539'
degree_awarded: PhD
department:
- _id: GradSch
- _id: GeKa
doi: 10.15479/AT-ISTA-19836
doi_confirm: '1'
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date_created: 2025-06-18T08:50:16Z
date_updated: 2026-04-01T22:30:07Z
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file_id: '19851'
file_name: SaezMollejo_PhDFinal_pdfa-1b.pdf
file_size: 22382376
relation: main_file
file_date_updated: 2026-04-01T22:30:07Z
has_accepted_license: '1'
language:
- iso: eng
license: https://creativecommons.org/licenses/by/4.0/
month: '06'
oa: 1
oa_version: Published Version
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'
...
---
OA_place: publisher
_id: '18076'
abstract:
- lang: eng
text: "The new era of Ge has opened up new possibilities in quantum computing. The
maturity of Ge\r\nspin qubits is unquestioned, while hybrid semiconductor-superconductor
Ge circuits are on track\r\nto enter the game. Gate-tunable transmons (gatemons)
employing semiconductor Josephson\r\njunctions have recently emerged as building
blocks for such hybrid quantum circuits. In this\r\nthesis, we present a gatemon
fabricated in planar Germanium. We induce superconductivity\r\nin a two-dimensional
hole gas by evaporating aluminum atop a thin spacer, which separates\r\nthe superconductor
from the Ge quantum well. The Josephson junction is then integrated\r\ninto an
Xmon circuit and capacitively coupled to a transmission line resonator. We showcase\r\nthe
qubit tunability in a broad frequency range with resonator and two-tone spectroscopy.\r\nTime-domain
characterizations reveal energy relaxation and coherence times up to 75 ns. Our\r\nresults,
combined with the recent advances in the spin qubit field, pave the way towards
novel\r\nhybrid and protected qubits in a group IV, CMOS-compatible material."
acknowledged_ssus:
- _id: NanoFab
- _id: M-Shop
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Oliver
full_name: Sagi, Oliver
id: 71616374-A8E9-11E9-A7CA-09ECE5697425
last_name: Sagi
citation:
ama: Sagi O. Hybrid circuits on planar Germanium. 2024. doi:10.15479/at:ista:18076
apa: Sagi, O. (2024). Hybrid circuits on planar Germanium. Institute of Science
and Technology Austria. https://doi.org/10.15479/at:ista:18076
chicago: Sagi, Oliver. “Hybrid Circuits on Planar Germanium.” Institute of Science
and Technology Austria, 2024. https://doi.org/10.15479/at:ista:18076.
ieee: O. Sagi, “Hybrid circuits on planar Germanium,” Institute of Science and Technology
Austria, 2024.
ista: Sagi O. 2024. Hybrid circuits on planar Germanium. Institute of Science and
Technology Austria.
mla: Sagi, Oliver. Hybrid Circuits on Planar Germanium. Institute of Science
and Technology Austria, 2024, doi:10.15479/at:ista:18076.
short: O. Sagi, Hybrid Circuits on Planar Germanium, Institute of Science and Technology
Austria, 2024.
corr_author: '1'
date_created: 2024-09-16T12:58:36Z
date_published: 2024-09-18T00:00:00Z
date_updated: 2026-04-16T12:20:39Z
day: '18'
ddc:
- '539'
degree_awarded: PhD
department:
- _id: GradSch
- _id: GeKa
doi: 10.15479/at:ista:18076
ec_funded: 1
file:
- access_level: open_access
checksum: d01d0e2846c2f3ac5bb14d321554a4cd
content_type: application/pdf
creator: osagi
date_created: 2024-09-18T14:13:01Z
date_updated: 2024-09-18T14:13:01Z
file_id: '18093'
file_name: OliverSagi_Thesis_pdfa.pdf
file_size: 86679095
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success: 1
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checksum: 0543f473d509ee545f4ed3a56f742f4b
content_type: application/x-zip-compressed
creator: osagi
date_created: 2024-09-18T14:14:02Z
date_updated: 2024-09-19T09:20:33Z
file_id: '18094'
file_name: Thesis_OliverSagi.zip
file_size: 172098524
relation: source_file
file_date_updated: 2024-09-19T09:20:33Z
has_accepted_license: '1'
language:
- iso: eng
license: https://creativecommons.org/licenses/by-nc-sa/4.0/
month: '09'
oa: 1
oa_version: Published Version
page: '111'
project:
- _id: bd8bd29e-d553-11ed-ba76-f0070d4b237a
grant_number: P36507
name: Merging spin and superconducting qubits in planar Ge
- _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
- _id: 237E5020-32DE-11EA-91FC-C7463DDC885E
call_identifier: H2020
grant_number: '862046'
name: TOPOLOGICALLY PROTECTED AND SCALABLE QUANTUM BITS
publication_identifier:
issn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
related_material:
record:
- id: '17202'
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: Hybrid circuits on planar Germanium
tmp:
image: /images/cc_by_nc_sa.png
legal_code_url: https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode
name: Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC
BY-NC-SA 4.0)
short: CC BY-NC-SA (4.0)
type: dissertation
user_id: ba8df636-2132-11f1-aed0-ed93e2281fdd
year: '2024'
...
---
OA_place: publisher
_id: '18129'
abstract:
- lang: eng
text: "State-of-the-art quantum computers, with roughly a thousand qubits, face
a crucial technological challenge of scaling up. Spins confined in quantum dots
(QDs) are a promising candidate\r\nfor qubits due to their long coherence, tunability,
control, and readout. However, their natural\r\ncoupling is the short-ranged (∼
100 nm) exchange interaction, limited to nearest neighbours.\r\nLong-ranged (∼
1 mm) qubit interactions mediated by a photon could be engineered through a\r\ncoherent
spin-photon coupling. Achieving a strong coupling to a photon is inherently challenging
in QDs due to the small dipole moment of the confined charge. However, the potential
of\r\nhigh-impedance resonators to compensate for this has gained significant
attention in the past\r\ndecade. Nevertheless, previous QD circuit quantum electrodynamics
implementations have not\r\nexceeded the impedance of ∼ 3.8 kΩ, leaving opportunities
for significant improvement. The\r\nlarge kinetic inductance of granular aluminium
(grAl) could provide an order-of-magnitude\r\nenhancement. However, fully exploiting
the potential of disordered or granular superconductors\r\nis challenging as their
impedances close to the superconductor-to-insulator transition are\r\ndifficult
to control reproducibly. We report on the realization of a wireless ohmmeter which\r\nallows
in situ resistance measurements during film deposition and, therefore, indirect
control\r\nof the kinetic inductance of grAl films. This allows us to reproducibly
fabricate resonators\r\nwith characteristic impedance exceeding the resistance
quantum, even reaching 22.3 kW, due\r\nto the large sheet kinetic inductance of
up to 3 nH □−1\r\n. By integrating an 8 kW resonator\r\nwith a germanium double
QD, we demonstrate a strong charge-photon coupling with the\r\nhighest rate reported,
566 MHz. The demonstrated method and grAl properties make these\r\nresonators
suitable for boosting the spin-photon coupling strength, a crucial requirement
for\r\nfast, high-fidelity, long-distance two-qubit gates.\r\n"
acknowledged_ssus:
- _id: M-Shop
- _id: NanoFab
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Marian
full_name: Janik, Marian
id: 396A1950-F248-11E8-B48F-1D18A9856A87
last_name: Janik
orcid: 0009-0003-9037-8831
citation:
ama: Janik M. Strong charge-photon coupling in Germanium enabled by granular aluminium
superinductors. 2024. doi:10.15479/at:ista:18129
apa: Janik, M. (2024). Strong charge-photon coupling in Germanium enabled by
granular aluminium superinductors. Institute of Science and Technology Austria.
https://doi.org/10.15479/at:ista:18129
chicago: Janik, Marian. “Strong Charge-Photon Coupling in Germanium Enabled by Granular
Aluminium Superinductors.” Institute of Science and Technology Austria, 2024.
https://doi.org/10.15479/at:ista:18129.
ieee: M. Janik, “Strong charge-photon coupling in Germanium enabled by granular
aluminium superinductors,” Institute of Science and Technology Austria, 2024.
ista: Janik M. 2024. Strong charge-photon coupling in Germanium enabled by granular
aluminium superinductors. Institute of Science and Technology Austria.
mla: Janik, Marian. Strong Charge-Photon Coupling in Germanium Enabled by Granular
Aluminium Superinductors. Institute of Science and Technology Austria, 2024,
doi:10.15479/at:ista:18129.
short: M. Janik, Strong Charge-Photon Coupling in Germanium Enabled by Granular
Aluminium Superinductors, Institute of Science and Technology Austria, 2024.
corr_author: '1'
date_created: 2024-09-23T17:25:43Z
date_published: 2024-09-24T00:00:00Z
date_updated: 2026-06-03T07:16:03Z
day: '24'
ddc:
- '539'
degree_awarded: PhD
department:
- _id: GradSch
- _id: GeKa
doi: 10.15479/at:ista:18129
file:
- access_level: closed
checksum: dc15958f6400b5bdaa28bf58fc7a4056
content_type: application/x-zip-compressed
creator: mjanik
date_created: 2024-09-23T17:15:09Z
date_updated: 2025-05-23T22:30:09Z
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file_id: '18130'
file_name: janik_thesis.zip
file_size: 156207943
relation: source_file
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content_type: application/pdf
creator: mjanik
date_created: 2024-09-23T17:15:30Z
date_updated: 2025-05-23T22:30:09Z
embargo: 2025-05-23
file_id: '18131'
file_name: janik_thesis_pdfa.pdf
file_size: 96195684
relation: main_file
file_date_updated: 2025-05-23T22:30:09Z
has_accepted_license: '1'
language:
- iso: eng
month: '09'
oa: 1
oa_version: Published Version
page: '164'
project:
- _id: c0977eea-5a5b-11eb-8a69-a862db0cf4d1
grant_number: I05060
name: High impedance circuit quantum electrodynamics with hole spins
- _id: bd8bd29e-d553-11ed-ba76-f0070d4b237a
grant_number: P36507
name: Merging spin and superconducting qubits in planar Ge
- _id: 237B3DA4-32DE-11EA-91FC-C7463DDC885E
call_identifier: FWF
grant_number: P32235
name: Towards scalable hut wire quantum devices
- _id: 34c0acea-11ca-11ed-8bc3-8775e10fd452
grant_number: '101069515'
name: Integrated Germanium Quantum Technology
- _id: eb9b30ac-77a9-11ec-83b8-871f581d53d2
name: Protected states of quantum matter
publication_identifier:
issn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
related_material:
record:
- id: '18144'
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: Strong charge-photon coupling in Germanium enabled by granular aluminium superinductors
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: ba8df636-2132-11f1-aed0-ed93e2281fdd
year: '2024'
...
---
OA_place: publisher
_id: '13286'
abstract:
- lang: eng
text: Semiconductor-superconductor hybrid systems are the harbour of many intriguing
mesoscopic phenomena. This material combination leads to spatial variations of
the superconducting properties, which gives rise to Andreev bound states (ABSs).
Some of these states might exhibit remarkable properties that render them highly
desirable for topological quantum computing. The most prominent and hunted of
such states are Majorana zero modes (MZMs), quasiparticles equals to their own
quasiparticles that they follow non-abelian statistics. In this thesis, we first
introduce the general framework of such hybrid systems and, then, we unveil a
series of mesoscopic phenomena that we discovered. Firstly, we show tunneling
spectroscopy experiments on full-shell nanowires (NWs) showing that unwanted quantum-dot
states coupled to superconductors (Yu-Shiba-Rusinov states) can mimic MZMs signatures.
Then, we introduce a novel protocol which allowed the integration of tunneling
spectroscopy with Coulomb spectroscopy within the same device. Employing this
approach on both full-shell NWs and partial-shell NWs, we demonstrated that longitudinally
confined states reveal charge transport phenomenology similar to the one expected
for MZMs. These findings shed light on the intricate interplay between superconductivity
and quantum confinement, which brought us to explore another material platform,
i.e. a two-dimensional Germanium hole gas. After developing a robust way to induce
superconductivity in such system, we showed how to engineer the proximity effect
and we revealed a superconducting hard gap. Finally, we created a superconducting
radio frequency driven ideal diode and a generator of non-sinusoidal current-phase
relations. Our results open the path for the exploration of protected superconducting
qubits and more complex hybrid devices in planar Germanium, like Kitaev chains
and hybrid qubit devices.
acknowledged_ssus:
- _id: NanoFab
- _id: M-Shop
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Marco
full_name: Valentini, Marco
id: C0BB2FAC-D767-11E9-B658-BC13E6697425
last_name: Valentini
citation:
ama: 'Valentini M. Mesoscopic phenomena in hybrid semiconductor-superconductor nanodevices :
From full-shell nanowires to two-dimensional hole gas in germanium. 2023. doi:10.15479/at:ista:13286'
apa: 'Valentini, M. (2023). Mesoscopic phenomena in hybrid semiconductor-superconductor
nanodevices : From full-shell nanowires to two-dimensional hole gas in germanium.
Institute of Science and Technology Austria. https://doi.org/10.15479/at:ista:13286'
chicago: 'Valentini, Marco. “Mesoscopic Phenomena in Hybrid Semiconductor-Superconductor
Nanodevices : From Full-Shell Nanowires to Two-Dimensional Hole Gas in Germanium.”
Institute of Science and Technology Austria, 2023. https://doi.org/10.15479/at:ista:13286.'
ieee: 'M. Valentini, “Mesoscopic phenomena in hybrid semiconductor-superconductor
nanodevices : From full-shell nanowires to two-dimensional hole gas in germanium,”
Institute of Science and Technology Austria, 2023.'
ista: 'Valentini M. 2023. Mesoscopic phenomena in hybrid semiconductor-superconductor
nanodevices : From full-shell nanowires to two-dimensional hole gas in germanium.
Institute of Science and Technology Austria.'
mla: 'Valentini, Marco. Mesoscopic Phenomena in Hybrid Semiconductor-Superconductor
Nanodevices : From Full-Shell Nanowires to Two-Dimensional Hole Gas in Germanium.
Institute of Science and Technology Austria, 2023, doi:10.15479/at:ista:13286.'
short: 'M. Valentini, Mesoscopic Phenomena in Hybrid Semiconductor-Superconductor
Nanodevices : From Full-Shell Nanowires to Two-Dimensional Hole Gas in Germanium,
Institute of Science and Technology Austria, 2023.'
corr_author: '1'
date_created: 2023-07-24T14:10:45Z
date_published: 2023-07-21T00:00:00Z
date_updated: 2026-06-03T07:16:01Z
day: '21'
ddc:
- '530'
degree_awarded: PhD
department:
- _id: GradSch
- _id: GeKa
doi: 10.15479/at:ista:13286
ec_funded: 1
file:
- access_level: closed
checksum: 666ee31c7eade89679806287c062fa14
content_type: application/x-zip-compressed
creator: mvalenti
date_created: 2023-08-11T09:27:39Z
date_updated: 2023-08-11T10:01:34Z
file_id: '14033'
file_name: PhD_thesis_Valentini_final.zip
file_size: 56121429
relation: source_file
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content_type: application/pdf
creator: mvalenti
date_created: 2023-08-11T14:39:17Z
date_updated: 2023-08-11T14:39:17Z
file_id: '14035'
file_name: PhD_thesis_Valentini_final_validated.pdf
file_size: 38199711
relation: main_file
file_date_updated: 2023-08-11T14:39:17Z
has_accepted_license: '1'
language:
- iso: eng
month: '07'
oa: 1
oa_version: Published Version
page: '184'
project:
- _id: 262116AA-B435-11E9-9278-68D0E5697425
name: Hybrid Semiconductor - Superconductor Quantum Devices
- _id: 237E5020-32DE-11EA-91FC-C7463DDC885E
call_identifier: H2020
grant_number: '862046'
name: TOPOLOGICALLY PROTECTED AND SCALABLE QUANTUM BITS
- _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'
publication_identifier:
issn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
related_material:
record:
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relation: research_data
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relation: part_of_dissertation
status: public
- id: '8910'
relation: part_of_dissertation
status: public
- id: '13312'
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: 'Mesoscopic phenomena in hybrid semiconductor-superconductor nanodevices :
From full-shell nanowires to two-dimensional hole gas in germanium'
tmp:
image: /images/cc_by_nc_sa.png
legal_code_url: https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode
name: Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC
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short: CC BY-NC-SA (4.0)
type: dissertation
user_id: ba8df636-2132-11f1-aed0-ed93e2281fdd
year: '2023'
...
---
OA_place: publisher
_id: '10058'
abstract:
- lang: eng
text: 'Quantum information and computation has become a vast field paved with opportunities
for researchers and investors. As large multinational companies and international
funds are heavily investing in quantum technologies it is still a question which
platform is best suited for the task of realizing a scalable quantum processor.
In this work we investigate hole spins in Ge quantum wells. These hold great promise
as they possess several favorable properties: a small effective mass, a strong
spin-orbit coupling, long relaxation time and an inherent immunity to hyperfine
noise. All these characteristics helped Ge hole spin qubits to evolve from a single
qubit to a fully entangled four qubit processor in only 3 years. Here, we investigated
a qubit approach leveraging the large out-of-plane g-factors of heavy hole states
in Ge quantum dots. We found this qubit to be reproducibly operable at extremely
low magnetic field and at large speeds while maintaining coherence. This was possible
because large differences of g-factors in adjacent dots can be achieved in the
out-of-plane direction. In the in-plane direction the small g-factors, on the
other hand, can be altered very effectively by the confinement potentials. Here,
we found that this can even lead to a sign change of the g-factors. The resulting
g-factor difference alters the dynamics of the system drastically and produces
effects typically attributed to a spin-orbit induced spin-flip term. The investigations
carried out in this thesis give further insights into the possibilities of holes
in Ge and reveal new physical properties that need to be considered when designing
future spin qubit experiments.'
acknowledged_ssus:
- _id: M-Shop
- _id: NanoFab
acknowledgement: The author gratefully acknowledges support by the Austrian Science
Fund (FWF), grants No P30207, and the Nomis foundation.
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Daniel
full_name: Jirovec, Daniel
id: 4C473F58-F248-11E8-B48F-1D18A9856A87
last_name: Jirovec
orcid: 0000-0002-7197-4801
citation:
ama: Jirovec D. Singlet-Triplet qubits and spin-orbit interaction in 2-dimensional
Ge hole gases. 2021. doi:10.15479/at:ista:10058
apa: Jirovec, D. (2021). Singlet-Triplet qubits and spin-orbit interaction in
2-dimensional Ge hole gases. Institute of Science and Technology Austria.
https://doi.org/10.15479/at:ista:10058
chicago: Jirovec, Daniel. “Singlet-Triplet Qubits and Spin-Orbit Interaction in
2-Dimensional Ge Hole Gases.” Institute of Science and Technology Austria, 2021.
https://doi.org/10.15479/at:ista:10058.
ieee: D. Jirovec, “Singlet-Triplet qubits and spin-orbit interaction in 2-dimensional
Ge hole gases,” Institute of Science and Technology Austria, 2021.
ista: Jirovec D. 2021. Singlet-Triplet qubits and spin-orbit interaction in 2-dimensional
Ge hole gases. Institute of Science and Technology Austria.
mla: Jirovec, Daniel. Singlet-Triplet Qubits and Spin-Orbit Interaction in 2-Dimensional
Ge Hole Gases. Institute of Science and Technology Austria, 2021, doi:10.15479/at:ista:10058.
short: D. Jirovec, Singlet-Triplet Qubits and Spin-Orbit Interaction in 2-Dimensional
Ge Hole Gases, Institute of Science and Technology Austria, 2021.
corr_author: '1'
date_created: 2021-09-30T07:53:49Z
date_published: 2021-10-05T00:00:00Z
date_updated: 2026-04-08T07:12:19Z
day: '05'
ddc:
- '621'
- '539'
degree_awarded: PhD
department:
- _id: GradSch
- _id: GeKa
doi: 10.15479/at:ista:10058
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embargo: 2022-10-06
file_id: '10087'
file_name: PHD_Thesis_pdfa2b_1.pdf
file_size: 26910829
relation: main_file
file_date_updated: 2022-12-20T23:30:07Z
has_accepted_license: '1'
keyword:
- qubits
- quantum computing
- holes
language:
- iso: eng
month: '10'
oa: 1
oa_version: Published Version
page: '151'
project:
- _id: 2641CE5E-B435-11E9-9278-68D0E5697425
call_identifier: FWF
grant_number: P30207
name: Hole spin orbit qubits in Ge quantum wells
publication_identifier:
issn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
related_material:
record:
- id: '10066'
relation: part_of_dissertation
status: public
- id: '10065'
relation: part_of_dissertation
status: public
- id: '8831'
relation: part_of_dissertation
status: public
- id: '8909'
relation: part_of_dissertation
status: public
- id: '5816'
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 and spin-orbit interaction in 2-dimensional Ge hole
gases
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: ba8df636-2132-11f1-aed0-ed93e2281fdd
year: '2021'
...
---
OA_place: publisher
_id: '7996'
abstract:
- lang: eng
text: "Quantum computation enables the execution of algorithms that have exponential
complexity. This might open the path towards the synthesis of new materials or
medical drugs, optimization of transport or financial strategies etc., intractable
on even the fastest classical computers. A quantum computer consists of interconnected
two level quantum systems, called qubits, that satisfy DiVincezo’s criteria. Worldwide,
there are ongoing efforts to find the qubit architecture which will unite quantum
error correction compatible single and two qubit fidelities, long distance qubit
to qubit coupling and \r\n calability. Superconducting qubits have gone the furthest
in this race, demonstrating an algorithm running on 53 coupled qubits, but still
the fidelities are not even close to those required for realizing a single logical
qubit. emiconductor qubits offer extremely good characteristics, but they are
currently investigated across different platforms. Uniting those good characteristics
into a single platform might be a big step towards the quantum computer realization.\r\nHere
we describe the implementation of a hole spin qubit hosted in a Ge hut wire double
quantum dot. The high and tunable spin-orbit coupling together with a heavy hole
state character is expected to allow fast spin manipulation and long coherence
times. Furthermore large lever arms, for hut wire devices, should allow good coupling
to superconducting resonators enabling efficient long distance spin to spin coupling
and a sensitive gate reflectometry spin readout. The developed cryogenic setup
(printed circuit board sample holders, filtering, high-frequency wiring) enabled
us to perform low temperature spin dynamics experiments. Indeed, we measured the
fastest single spin qubit Rabi frequencies reported so far, reaching 140 MHz,
while the dephasing times of 130 ns oppose the long decoherence predictions. In
order to further investigate this, a double quantum dot gate was connected directly
to a lumped element\r\nresonator which enabled gate reflectometry readout. The
vanishing inter-dot transition signal, for increasing external magnetic field,
revealed the spin nature of the measured quantity."
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Josip
full_name: Kukucka, Josip
id: 3F5D8856-F248-11E8-B48F-1D18A9856A87
last_name: Kukucka
citation:
ama: Kukucka J. Implementation of a hole spin qubit in Ge hut wires and dispersive
spin sensing. 2020. doi:10.15479/AT:ISTA:7996
apa: Kukucka, J. (2020). Implementation of a hole spin qubit in Ge hut wires
and dispersive spin sensing. Institute of Science and Technology Austria.
https://doi.org/10.15479/AT:ISTA:7996
chicago: Kukucka, Josip. “Implementation of a Hole Spin Qubit in Ge Hut Wires and
Dispersive Spin Sensing.” Institute of Science and Technology Austria, 2020. https://doi.org/10.15479/AT:ISTA:7996.
ieee: J. Kukucka, “Implementation of a hole spin qubit in Ge hut wires and dispersive
spin sensing,” Institute of Science and Technology Austria, 2020.
ista: Kukucka J. 2020. Implementation of a hole spin qubit in Ge hut wires and dispersive
spin sensing. Institute of Science and Technology Austria.
mla: Kukucka, Josip. Implementation of a Hole Spin Qubit in Ge Hut Wires and
Dispersive Spin Sensing. Institute of Science and Technology Austria, 2020,
doi:10.15479/AT:ISTA:7996.
short: J. Kukucka, Implementation of a Hole Spin Qubit in Ge Hut Wires and Dispersive
Spin Sensing, Institute of Science and Technology Austria, 2020.
corr_author: '1'
date_created: 2020-06-22T09:22:23Z
date_published: 2020-06-22T00:00:00Z
date_updated: 2026-04-08T07:27:13Z
day: '22'
ddc:
- '530'
degree_awarded: PhD
department:
- _id: GeKa
doi: 10.15479/AT:ISTA:7996
file:
- access_level: closed
checksum: 467e52feb3e361ce8cf5fe8d5c254ece
content_type: application/x-zip-compressed
creator: dernst
date_created: 2020-06-22T09:22:04Z
date_updated: 2020-07-14T12:48:07Z
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file_size: 392794743
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file_size: 28453247
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has_accepted_license: '1'
language:
- iso: eng
month: '06'
oa: 1
oa_version: Published Version
page: '178'
publication_identifier:
issn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
related_material:
record:
- id: '77'
relation: part_of_dissertation
status: public
- id: '7541'
relation: part_of_dissertation
status: public
- id: '23'
relation: part_of_dissertation
status: public
- id: '840'
relation: part_of_dissertation
status: public
- id: '1328'
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: Implementation of a hole spin qubit in Ge hut wires and dispersive spin sensing
type: dissertation
user_id: ba8df636-2132-11f1-aed0-ed93e2281fdd
year: '2020'
...
---
OA_place: publisher
_id: '69'
abstract:
- lang: eng
text: 'A qubit, a unit of quantum information, is essentially any quantum mechanical
two-level system which can be coherently controlled. Still, to be used for computation,
it has to fulfill criteria. Qubits, regardless of the system in which they are
realized, suffer from decoherence. This leads to loss of the information stored
in the qubit. The upper bound of the time scale on which decoherence happens is
set by the spin relaxation time. In this thesis I studied a two-level system consisting
of a Zeeman-split hole spin confined in a quantum dot formed in a Ge hut wire.
Such Ge hut wires have emerged as a promising material system for the realization
of spin qubits, due to the combination of two significant properties: long spin
coherence time as expected for group IV semiconductors due to the low hyperfine
interaction and a strong valence band spin-orbit coupling. Here, I present how
to fabricate quantum dot devices suitable for electrical transport measurements.
Coupled quantum dot devices allowed the realization of a charge sensor, which
is electrostatically and tunnel coupled to a quantum dot. By integrating the charge
sensor into a radio-frequency reflectometry setup, I performed for the first time
single-shot readout measurements of hole spins and extracted the hole spin relaxation
times in Ge hut wires.'
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Lada
full_name: Vukušić, Lada
id: 31E9F056-F248-11E8-B48F-1D18A9856A87
last_name: Vukušić
orcid: 0000-0003-2424-8636
citation:
ama: Vukušić L. Charge sensing and spin relaxation times of holes in Ge hut wires.
2018. doi:10.15479/AT:ISTA:TH_1047
apa: Vukušić, L. (2018). Charge sensing and spin relaxation times of holes in
Ge hut wires. Institute of Science and Technology Austria. https://doi.org/10.15479/AT:ISTA:TH_1047
chicago: Vukušić, Lada. “Charge Sensing and Spin Relaxation Times of Holes in Ge
Hut Wires.” Institute of Science and Technology Austria, 2018. https://doi.org/10.15479/AT:ISTA:TH_1047.
ieee: L. Vukušić, “Charge sensing and spin relaxation times of holes in Ge hut wires,”
Institute of Science and Technology Austria, 2018.
ista: Vukušić L. 2018. Charge sensing and spin relaxation times of holes in Ge hut
wires. Institute of Science and Technology Austria.
mla: Vukušić, Lada. Charge Sensing and Spin Relaxation Times of Holes in Ge Hut
Wires. Institute of Science and Technology Austria, 2018, doi:10.15479/AT:ISTA:TH_1047.
short: L. Vukušić, Charge Sensing and Spin Relaxation Times of Holes in Ge Hut Wires,
Institute of Science and Technology Austria, 2018.
corr_author: '1'
date_created: 2018-12-11T11:44:28Z
date_published: 2018-09-01T00:00:00Z
date_updated: 2026-04-08T14:09:47Z
day: '01'
ddc:
- '530'
- '600'
degree_awarded: PhD
department:
- _id: GeKa
- _id: GradSch
doi: 10.15479/AT:ISTA:TH_1047
file:
- access_level: open_access
checksum: c570b656e30749cd65b1c7e13a9ce0a8
content_type: application/pdf
creator: dernst
date_created: 2019-04-09T07:00:40Z
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file_name: 2018_Thesis_Vukusic.pdf
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file_date_updated: 2020-07-14T12:47:44Z
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language:
- iso: eng
month: '09'
oa: 1
oa_version: Published Version
page: '103'
publication_identifier:
issn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
publist_id: '7985'
pubrep_id: '1047'
related_material:
record:
- id: '23'
relation: part_of_dissertation
status: public
- id: '840'
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: Charge sensing and spin relaxation times of holes in Ge hut wires
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: ba8df636-2132-11f1-aed0-ed93e2281fdd
year: '2018'
...
---
OA_place: publisher
_id: '49'
abstract:
- lang: eng
text: Nowadays, quantum computation is receiving more and more attention as an alternative
to the classical way of computing. For realizing a quantum computer, different
devices are investigated as potential quantum bits. In this thesis, the focus
is on Ge hut wires, which turned out to be promising candidates for implementing
hole spin quantum bits. The advantages of Ge as a material system are the low
hyperfine interaction for holes and the strong spin orbit coupling, as well as
the compatibility with the highly developed CMOS processes in industry. In addition,
Ge can also be isotopically purified which is expected to boost the spin coherence
times. The strong spin orbit interaction for holes in Ge on the one hand enables
the full electrical control of the quantum bit and on the other hand should allow
short spin manipulation times. Starting with a bare Si wafer, this work covers
the entire process reaching from growth over the fabrication and characterization
of hut wire devices up to the demonstration of hole spin resonance. From experiments
with single quantum dots, a large g-factor anisotropy between the in-plane and
the out-of-plane direction was found. A comparison to a theoretical model unveiled
the heavy-hole character of the lowest energy states. The second part of the thesis
addresses double quantum dot devices, which were realized by adding two gate electrodes
to a hut wire. In such devices, Pauli spin blockade was observed, which can serve
as a read-out mechanism for spin quantum bits. Applying oscillating electric fields
in spin blockade allowed the demonstration of continuous spin rotations and the
extraction of a lower bound for the spin dephasing time. Despite the strong spin
orbit coupling in Ge, the obtained value for the dephasing time is comparable
to what has been recently reported for holes in Si. All in all, the presented
results point out the high potential of Ge hut wires as a platform for long-lived,
fast and fully electrically tunable hole spin quantum bits.
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Hannes
full_name: Watzinger, Hannes
id: 35DF8E50-F248-11E8-B48F-1D18A9856A87
last_name: Watzinger
citation:
ama: Watzinger H. Ge hut wires - from growth to hole spin resonance. 2018. doi:10.15479/AT:ISTA:th_1033
apa: Watzinger, H. (2018). Ge hut wires - from growth to hole spin resonance.
Institute of Science and Technology Austria. https://doi.org/10.15479/AT:ISTA:th_1033
chicago: Watzinger, Hannes. “Ge Hut Wires - from Growth to Hole Spin Resonance.”
Institute of Science and Technology Austria, 2018. https://doi.org/10.15479/AT:ISTA:th_1033.
ieee: H. Watzinger, “Ge hut wires - from growth to hole spin resonance,” Institute
of Science and Technology Austria, 2018.
ista: Watzinger H. 2018. Ge hut wires - from growth to hole spin resonance. Institute
of Science and Technology Austria.
mla: Watzinger, Hannes. Ge Hut Wires - from Growth to Hole Spin Resonance.
Institute of Science and Technology Austria, 2018, doi:10.15479/AT:ISTA:th_1033.
short: H. Watzinger, Ge Hut Wires - from Growth to Hole Spin Resonance, Institute
of Science and Technology Austria, 2018.
corr_author: '1'
date_created: 2018-12-11T11:44:21Z
date_published: 2018-07-30T00:00:00Z
date_updated: 2026-07-31T09:15:25Z
day: '30'
ddc:
- '530'
degree_awarded: PhD
department:
- _id: GeKa
- _id: GradSch
doi: 10.15479/AT:ISTA:th_1033
doi_confirm: '1'
file:
- access_level: open_access
checksum: b653b5216251f938ddbeafd1de88667c
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date_created: 2019-04-09T07:13:27Z
date_updated: 2020-07-14T12:46:35Z
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file_name: 2018_Thesis_Watzinger_source.zip
file_size: 21830697
relation: source_file
file_date_updated: 2020-07-14T12:46:35Z
has_accepted_license: '1'
language:
- iso: eng
month: '07'
oa: 1
oa_version: Published Version
page: '77'
publication_identifier:
issn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
publist_id: '8005'
pubrep_id: '1033'
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: Ge hut wires - from growth to hole spin resonance
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: '2018'
...