---
_id: '10759'
abstract:
- lang: eng
text: In this Thesis, I study composite quantum impurities with variational techniques,
both inspired by machine learning as well as fully analytic. I supplement this
with exploration of other applications of machine learning, in particular artificial
neural networks, in many-body physics. In Chapters 3 and 4, I study quasiparticle
systems with variational approach. I derive a Hamiltonian describing the angulon
quasiparticle in the presence of a magnetic field. I apply analytic variational
treatment to this Hamiltonian. Then, I introduce a variational approach for non-additive
systems, based on artificial neural networks. I exemplify this approach on the
example of the polaron quasiparticle (Fröhlich Hamiltonian). In Chapter 5, I continue
using artificial neural networks, albeit in a different setting. I apply artificial
neural networks to detect phases from snapshots of two types physical systems.
Namely, I study Monte Carlo snapshots of multilayer classical spin models as well
as molecular dynamics maps of colloidal systems. The main type of networks that
I use here are convolutional neural networks, known for their applicability to
image data.
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Wojciech
full_name: Rzadkowski, Wojciech
id: 48C55298-F248-11E8-B48F-1D18A9856A87
last_name: Rzadkowski
orcid: 0000-0002-1106-4419
citation:
ama: Rzadkowski W. Analytic and machine learning approaches to composite quantum
impurities. 2022. doi:10.15479/at:ista:10759
apa: Rzadkowski, W. (2022). Analytic and machine learning approaches to composite
quantum impurities. Institute of Science and Technology Austria. https://doi.org/10.15479/at:ista:10759
chicago: Rzadkowski, Wojciech. “Analytic and Machine Learning Approaches to Composite
Quantum Impurities.” Institute of Science and Technology Austria, 2022. https://doi.org/10.15479/at:ista:10759.
ieee: W. Rzadkowski, “Analytic and machine learning approaches to composite quantum
impurities,” Institute of Science and Technology Austria, 2022.
ista: Rzadkowski W. 2022. Analytic and machine learning approaches to composite
quantum impurities. Institute of Science and Technology Austria.
mla: Rzadkowski, Wojciech. Analytic and Machine Learning Approaches to Composite
Quantum Impurities. Institute of Science and Technology Austria, 2022, doi:10.15479/at:ista:10759.
short: W. Rzadkowski, Analytic and Machine Learning Approaches to Composite Quantum
Impurities, Institute of Science and Technology Austria, 2022.
date_created: 2022-02-16T13:27:37Z
date_published: 2022-02-21T00:00:00Z
date_updated: 2024-08-07T07:16:53Z
day: '21'
ddc:
- '530'
degree_awarded: PhD
department:
- _id: GradSch
- _id: MiLe
doi: 10.15479/at:ista:10759
ec_funded: 1
file:
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checksum: 0fc54ad1eaede879c665ac9b53c93e22
content_type: application/zip
creator: wrzadkow
date_created: 2022-02-21T13:58:16Z
date_updated: 2022-02-22T07:20:12Z
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content_type: application/pdf
creator: wrzadkow
date_created: 2022-02-21T14:02:54Z
date_updated: 2022-02-21T14:02:54Z
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file_name: Rzadkowski_thesis_final.pdf
file_size: 13307331
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has_accepted_license: '1'
language:
- iso: eng
month: '02'
oa: 1
oa_version: Published Version
page: '120'
project:
- _id: 2564DBCA-B435-11E9-9278-68D0E5697425
call_identifier: H2020
grant_number: '665385'
name: International IST Doctoral Program
publication_identifier:
issn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
related_material:
record:
- id: '10762'
relation: part_of_dissertation
status: public
- id: '7956'
relation: part_of_dissertation
status: public
- id: '415'
relation: part_of_dissertation
status: public
- id: '8644'
relation: part_of_dissertation
status: public
status: public
supervisor:
- first_name: Mikhail
full_name: Lemeshko, Mikhail
id: 37CB05FA-F248-11E8-B48F-1D18A9856A87
last_name: Lemeshko
orcid: 0000-0002-6990-7802
title: Analytic and machine learning approaches to composite quantum impurities
type: dissertation
user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1
year: '2022'
...
---
_id: '8958'
abstract:
- lang: eng
text: "The oft-quoted dictum by Arthur Schawlow: ``A diatomic molecule has one atom
too many'' has been disavowed. Inspired by the possibility to experimentally manipulate
and enhance chemical reactivity in helium nanodroplets, we investigate the rotation
of coupled cold molecules in the presence of a many-body environment.\r\nIn this
thesis, we introduce new variational approaches to quantum impurities and apply
them to the Fröhlich polaron - a quasiparticle formed out of an electron (or other
point-like impurity) in a polar medium, and to the angulon - a quasiparticle formed
out of a rotating molecule in a bosonic bath.\r\nWith this theoretical toolbox,
we reveal the self-localization transition for the angulon quasiparticle. We show
that, unlike for polarons, self-localization of angulons occurs at finite impurity-bath
coupling already at the mean-field level. The transition is accompanied by the
spherical-symmetry breaking of the angulon ground state and a discontinuity in
the first derivative of the ground-state energy. Moreover, the type of symmetry
breaking is dictated by the symmetry of the microscopic impurity-bath interaction,
which leads to a number of distinct self-localized states. \r\nFor the system
containing multiple impurities, by analogy with the bipolaron, we introduce the
biangulon quasiparticle describing two rotating molecules that align with respect
to each other due to the effective attractive interaction mediated by the excitations
of the bath. We study this system from the strong-coupling regime to the weak
molecule-bath interaction regime. We show that the molecules tend to have a strong
alignment in the ground state, the biangulon shows shifted angulon instabilities
and an additional spectral instability, where resonant angular momentum transfer
between the molecules and the bath takes place. Finally, we introduce a diagonalization
scheme that allows us to describe the transition from two separated angulons to
a biangulon as a function of the distance between the two molecules."
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Xiang
full_name: Li, Xiang
id: 4B7E523C-F248-11E8-B48F-1D18A9856A87
last_name: Li
citation:
ama: Li X. Rotation of coupled cold molecules in the presence of a many-body environment.
2020. doi:10.15479/AT:ISTA:8958
apa: Li, X. (2020). Rotation of coupled cold molecules in the presence of a many-body
environment. Institute of Science and Technology Austria. https://doi.org/10.15479/AT:ISTA:8958
chicago: Li, Xiang. “Rotation of Coupled Cold Molecules in the Presence of a Many-Body
Environment.” Institute of Science and Technology Austria, 2020. https://doi.org/10.15479/AT:ISTA:8958.
ieee: X. Li, “Rotation of coupled cold molecules in the presence of a many-body
environment,” Institute of Science and Technology Austria, 2020.
ista: Li X. 2020. Rotation of coupled cold molecules in the presence of a many-body
environment. Institute of Science and Technology Austria.
mla: Li, Xiang. Rotation of Coupled Cold Molecules in the Presence of a Many-Body
Environment. Institute of Science and Technology Austria, 2020, doi:10.15479/AT:ISTA:8958.
short: X. Li, Rotation of Coupled Cold Molecules in the Presence of a Many-Body
Environment, Institute of Science and Technology Austria, 2020.
date_created: 2020-12-21T09:44:30Z
date_published: 2020-12-21T00:00:00Z
date_updated: 2024-08-07T07:16:53Z
day: '21'
ddc:
- '539'
degree_awarded: PhD
department:
- _id: MiLe
doi: 10.15479/AT:ISTA:8958
ec_funded: 1
file:
- access_level: open_access
checksum: 3994c54a1241451d561db1d4f43bad30
content_type: application/pdf
creator: xli
date_created: 2020-12-22T10:55:56Z
date_updated: 2020-12-22T10:55:56Z
file_id: '8967'
file_name: THESIS_Xiang_Li.pdf
file_size: 3622305
relation: main_file
success: 1
- access_level: closed
checksum: 0954ecfc5554c05615c14de803341f00
content_type: application/x-zip-compressed
creator: xli
date_created: 2020-12-22T10:56:03Z
date_updated: 2020-12-30T07:18:03Z
file_id: '8968'
file_name: THESIS_Xiang_Li.zip
file_size: 4018859
relation: source_file
file_date_updated: 2020-12-30T07:18:03Z
has_accepted_license: '1'
language:
- iso: eng
month: '12'
oa: 1
oa_version: Published Version
page: '125'
project:
- _id: 26031614-B435-11E9-9278-68D0E5697425
call_identifier: FWF
grant_number: P29902
name: Quantum rotations in the presence of a many-body environment
- _id: 2688CF98-B435-11E9-9278-68D0E5697425
call_identifier: H2020
grant_number: '801770'
name: 'Angulon: physics and applications of a new quasiparticle'
publication_identifier:
issn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
related_material:
record:
- id: '5886'
relation: part_of_dissertation
status: public
- id: '1120'
relation: part_of_dissertation
status: public
- id: '8587'
relation: part_of_dissertation
status: public
status: public
supervisor:
- first_name: Mikhail
full_name: Lemeshko, Mikhail
id: 37CB05FA-F248-11E8-B48F-1D18A9856A87
last_name: Lemeshko
orcid: 0000-0002-6990-7802
title: Rotation of coupled cold molecules in the presence of a many-body environment
type: dissertation
user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1
year: '2020'
...
---
_id: '1189'
abstract:
- lang: eng
text: "Within the scope of this thesis, we show that a driven-dissipative system
with\r\nfew ultracold atoms can exhibit dissipatively bound states, even if the
atom-atom\r\ninteraction is purely repulsive. This bond arises due to the dipole-dipole
inter-\r\naction, which is restricted to one of the lower electronic energy states,
resulting\r\nin the distance-dependent coherent population trapping. The quality
of this al-\r\nready established method of dissipative binding is improved and
the application\r\nis extended to higher dimensions and a larger number of atoms.
\ Here, we simu-\r\nlate two- and three-atom systems using an adapted approach
to the Monte Carlo\r\nwave-function method and analyse the results. Finally,
\ we examine the possi-\r\nbility of finding a setting allowing trimer
\ states but prohibiting dimer states.\r\nIn the context of open quantum systems,
such a three-body bound states corre-\r\nsponds to the driven-dissipative analogue
of a Borromean state. These states can\r\nbe detected in modern experiments with
dipolar and Rydberg-dressed ultracold\r\natomic gases.\r\n"
article_processing_charge: No
author:
- first_name: Clemens
full_name: Jochum, Clemens
last_name: Jochum
citation:
ama: Jochum C. Dissipative Few-Body Quantum Systems. 2016.
apa: Jochum, C. (2016). Dissipative Few-Body Quantum Systems. Technical University
Vienna.
chicago: Jochum, Clemens. “Dissipative Few-Body Quantum Systems.” Technical University
Vienna, 2016.
ieee: C. Jochum, “Dissipative Few-Body Quantum Systems,” Technical University Vienna,
2016.
ista: Jochum C. 2016. Dissipative Few-Body Quantum Systems. Technical University
Vienna.
mla: Jochum, Clemens. Dissipative Few-Body Quantum Systems. Technical University
Vienna, 2016.
short: C. Jochum, Dissipative Few-Body Quantum Systems, Technical University Vienna,
2016.
date_created: 2018-12-11T11:50:37Z
date_published: 2016-11-28T00:00:00Z
date_updated: 2021-01-12T06:48:57Z
day: '28'
extern: '1'
language:
- iso: eng
main_file_link:
- open_access: '1'
url: http://repositum.tuwien.ac.at/obvutwhs/content/titleinfo/1517088
month: '11'
oa: 1
oa_version: Published Version
page: '94'
publication_status: published
publisher: Technical University Vienna
publist_id: '6164'
status: public
supervisor:
- first_name: Mikhail
full_name: Lemeshko, Mikhail
id: 37CB05FA-F248-11E8-B48F-1D18A9856A87
last_name: Lemeshko
orcid: 0000-0002-6990-7802
- first_name: Peter
full_name: Rabl, Peter
last_name: Rabl
title: Dissipative Few-Body Quantum Systems
type: dissertation
user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87
year: '2016'
...