Large scattering lengths and long-range interactions in ultracold atomic gases

Risto Sarjonen

Large scattering lengths and long-range interactions in ultracold atomic gases

Julkaisun otsikon käännös: Large scattering lengths and long-range interactions in ultracold atomic gases

Risto Sarjonen

Teknillisen fysiikan laitos

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Tässä väitöskirjassa käsitellään bosonisia ja fermionisia kvanttikaasuja. Työn ensimmäisessä osassa mallinnetaan eräässä Bose-kaasussa tehdyn Braggin sirontakokeen tulokset variaatiolaskentaan perustuvan monen kappaleen teorian avulla. Kokeessa sirontapituus pystyttiin säätämään suureksi Feshbach-resonanssin avulla ja tämän takia olemassa olevia malleja ei voitu käyttää tulosten selittämiseen. Tämä teki kokeesta erityisen kiinnostavan tutkimuskohteen. Ensin kehitimme joukon ad hoc -potentiaaleja, joilla sovitimme havaitun eksitaatiospektrin. Myöhemmin hyödynsimme T-matriisiformalismia Feshbach-resonanssin kuvaamisessa ja tällöin pystyimme mallintamaan myös sidottujen tilojen energioita. Yhteenvetona mallista voidaan todeta, että se mallintaa havaitun eksitaatiospektrin ja antaa oikean sidotun tilan energian joissain tapauksissa. Tämän työn toisessa osassa tutkitaan fermionisia kvanttikaasuja. Erityisesti tutkimme spin-riippuvaan optiseen hilaan vangittuja spin-1/2 hiukkasia. Hilageometriassa ylös-spin komponentti liikkuu hunajakennohilassa, mutta alas-spin komponentti on rajoitettu hunajakennohilan alihilaan, nimittäin kolmiohilaan. Sisällytimme malliimme attraktiivisen kontaktivuorovaikutuksen ja lähinaapurivuorovaikutuksen ja muotoilimme lähinaapurivuorovaikutusta kuvaavan termin siten, että se ottaa huomioon spontaanin ajankääntösymmetrian rikkoutumisen mahdollisuuden. Lisäksi otimme huomioon Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) faasin mahdollisuuden. Keskiarvotetun kentän approksimaation puitteissa osoitimme, että FFLO tila on systeemin perustila useissa tapauksissa. Lisäksi osoitimme, että ajankääntösymmetria rikkoutuu spontaanisti, jos lähinaapurivuorovaikutus on riittävän voimakas. Lopuksi näytimme myös, että ajankääntösymmetria rikkoutuu joissain tapauksissa myös FFLO faasissa. Toisin sanoen löysimme faasin, jossa ajankääntösymmetria ja spatiaalinen symmetria rikkoutuvat yhtä aikaa.

Julkaisun otsikon käännös	Large scattering lengths and long-range interactions in ultracold atomic gases
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Törmä, Päivi, Vastuuprofessori Törmä, Päivi, Ohjaaja
Kustantaja	Aalto University
Painoksen ISBN	978-952-60-6121-4
Sähköinen ISBN	978-952-60-6122-1
Tila	Julkaistu - 2015
OKM-julkaisutyyppi	G5 Tohtorinväitöskirja (artikkeli)

Tutkimusalat

kvanttikaasut
Bosen-Einsteinin kondensaatti
Feshbach-resonanssi
optinen hila
suprajuoksevuus
topologiset faasit

Pääsy asiakirjaan

http://urn.fi/URN:ISBN:978-952-60-6122-1Lisenssi: Määrittelemätön

SFX-saatavuus

Koko teksti

Siteeraa tätä

@phdthesis{c4673e21b3ba4e78b05fe7e3d0e3ba46,

title = "Large scattering lengths and long-range interactions in ultracold atomic gases",

abstract = "This thesis studies bosonic and fermionic quantum gases. In the first part, a variational many-body theory is used to explain a Bragg scattering experiment carried out on a bosonic quantum gas [S.B. Papp et al. Bragg Spectroscopy of a Strongly Interacting 85Rb Bose-Einstein Condensate. Phys. Rev. Lett. 101, 135301 (2008)]. A key feature in the experiment was the use of a Feshbach resonance, which made large values of the scattering length accessible. Due to the large values of the scattering length, existing models such as the Beliaev model could not be used to explain the observations, and therefore the experiment was a particularly interesting one to analyze. In our first approach, we constructed ad hoc potentials that fitted the observed excitation spectrum, and later we improved our approach by using T-matrix formalism to describe the Feshbach resonant system. All in all, the phenomenological model we developed fits the observed excitation spectrum and yields correct molecular Feshbach resonance state energies in certain cases. The second part of this thesis studies fermionic quantum gases. We focus on studying a gas of spin-1/2 particles confined to a spin-dependent optical lattice. The lattice geometry is such that the up-spin component is loaded in a honeycomb lattice, and the down-spin component is confined to the underlying triangular lattice. We considered attractive on-site and nearest-neighbor interactions, and formulated the nearest-neighbor interaction term in such a way that it takes into account the possibility of spontaneous time-reversal symmetry breaking. Furthermore, we took into account the possibility of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, which breaks spatial symmetry. Within a mean-field approximation, we showed that the FFLO state is the ground state of the system in many instances. In addition, we found out that the system spontaneously breaks time-reversal symmetry if the nearest-neighbor interaction strength is large. Due to the time-reversal symmetry breaking, the system has topologically non-trivial phases characterized by nonzero Chern numbers. Finally, there were also cases where the time-reversal symmetry was broken in the FFLO phase, and thus we found a phase where spatial and time-reversal symmetries are simultaneously broken.",

keywords = "quantum gases, Bose-Einstein condensate, Feshbach resonance, optical lattice, superfluidity, FFLO, topological phases, kvanttikaasut, Bosen-Einsteinin kondensaatti, Feshbach-resonanssi, optinen hila, suprajuoksevuus, topologiset faasit, quantum gases, Bose-Einstein condensate, Feshbach resonance, optical lattice, superfluidity, FFLO, topological phases",

author = "Risto Sarjonen",

year = "2015",

language = "English",

isbn = "978-952-60-6121-4",

series = "Aalto University publication series DOCTORAL DISSERTATIONS",

publisher = "Aalto University",

number = "34",

school = "Aalto University",

}

TY - THES

T1 - Large scattering lengths and long-range interactions in ultracold atomic gases

AU - Sarjonen, Risto

PY - 2015

Y1 - 2015

N2 - This thesis studies bosonic and fermionic quantum gases. In the first part, a variational many-body theory is used to explain a Bragg scattering experiment carried out on a bosonic quantum gas [S.B. Papp et al. Bragg Spectroscopy of a Strongly Interacting 85Rb Bose-Einstein Condensate. Phys. Rev. Lett. 101, 135301 (2008)]. A key feature in the experiment was the use of a Feshbach resonance, which made large values of the scattering length accessible. Due to the large values of the scattering length, existing models such as the Beliaev model could not be used to explain the observations, and therefore the experiment was a particularly interesting one to analyze. In our first approach, we constructed ad hoc potentials that fitted the observed excitation spectrum, and later we improved our approach by using T-matrix formalism to describe the Feshbach resonant system. All in all, the phenomenological model we developed fits the observed excitation spectrum and yields correct molecular Feshbach resonance state energies in certain cases. The second part of this thesis studies fermionic quantum gases. We focus on studying a gas of spin-1/2 particles confined to a spin-dependent optical lattice. The lattice geometry is such that the up-spin component is loaded in a honeycomb lattice, and the down-spin component is confined to the underlying triangular lattice. We considered attractive on-site and nearest-neighbor interactions, and formulated the nearest-neighbor interaction term in such a way that it takes into account the possibility of spontaneous time-reversal symmetry breaking. Furthermore, we took into account the possibility of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, which breaks spatial symmetry. Within a mean-field approximation, we showed that the FFLO state is the ground state of the system in many instances. In addition, we found out that the system spontaneously breaks time-reversal symmetry if the nearest-neighbor interaction strength is large. Due to the time-reversal symmetry breaking, the system has topologically non-trivial phases characterized by nonzero Chern numbers. Finally, there were also cases where the time-reversal symmetry was broken in the FFLO phase, and thus we found a phase where spatial and time-reversal symmetries are simultaneously broken.

AB - This thesis studies bosonic and fermionic quantum gases. In the first part, a variational many-body theory is used to explain a Bragg scattering experiment carried out on a bosonic quantum gas [S.B. Papp et al. Bragg Spectroscopy of a Strongly Interacting 85Rb Bose-Einstein Condensate. Phys. Rev. Lett. 101, 135301 (2008)]. A key feature in the experiment was the use of a Feshbach resonance, which made large values of the scattering length accessible. Due to the large values of the scattering length, existing models such as the Beliaev model could not be used to explain the observations, and therefore the experiment was a particularly interesting one to analyze. In our first approach, we constructed ad hoc potentials that fitted the observed excitation spectrum, and later we improved our approach by using T-matrix formalism to describe the Feshbach resonant system. All in all, the phenomenological model we developed fits the observed excitation spectrum and yields correct molecular Feshbach resonance state energies in certain cases. The second part of this thesis studies fermionic quantum gases. We focus on studying a gas of spin-1/2 particles confined to a spin-dependent optical lattice. The lattice geometry is such that the up-spin component is loaded in a honeycomb lattice, and the down-spin component is confined to the underlying triangular lattice. We considered attractive on-site and nearest-neighbor interactions, and formulated the nearest-neighbor interaction term in such a way that it takes into account the possibility of spontaneous time-reversal symmetry breaking. Furthermore, we took into account the possibility of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, which breaks spatial symmetry. Within a mean-field approximation, we showed that the FFLO state is the ground state of the system in many instances. In addition, we found out that the system spontaneously breaks time-reversal symmetry if the nearest-neighbor interaction strength is large. Due to the time-reversal symmetry breaking, the system has topologically non-trivial phases characterized by nonzero Chern numbers. Finally, there were also cases where the time-reversal symmetry was broken in the FFLO phase, and thus we found a phase where spatial and time-reversal symmetries are simultaneously broken.

KW - quantum gases

KW - Bose-Einstein condensate

KW - Feshbach resonance

KW - optical lattice

KW - superfluidity

KW - FFLO

KW - topological phases

KW - kvanttikaasut

KW - Bosen-Einsteinin kondensaatti

KW - Feshbach-resonanssi

KW - optinen hila

KW - suprajuoksevuus

KW - topologiset faasit

KW - quantum gases

KW - Bose-Einstein condensate

KW - Feshbach resonance

KW - optical lattice

KW - superfluidity

KW - FFLO

KW - topological phases

M3 - Doctoral Thesis

SN - 978-952-60-6121-4

T3 - Aalto University publication series DOCTORAL DISSERTATIONS

PB - Aalto University

ER -

Large scattering lengths and long-range interactions in ultracold atomic gases

Abstrakti

Tutkimusalat

Pääsy asiakirjaan

SFX-saatavuus

Sormenjälki

Siteeraa tätä