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Kvantna kinetička teorija za ultrahladne dipolne Fermi gasove

dc.contributor.advisorBalaž, Antun
dc.contributor.otherVasić, Ivana
dc.contributor.otherDamnjanović, Milan
dc.contributor.otherKnežević, Milan O.
dc.creatorVeljić, Vladimir
dc.date.accessioned2020-06-23T12:16:10Z
dc.date.available2020-06-23T12:16:10Z
dc.date.available2020-07-03T09:51:33Z
dc.date.issued2019-10-04
dc.identifier.urihttp://eteze.bg.ac.rs/application/showtheses?thesesId=7415
dc.identifier.urihttp://nardus.mpn.gov.rs/handle/123456789/12302
dc.identifier.urihttps://fedorabg.bg.ac.rs/fedora/get/o:21890/bdef:Content/download
dc.identifier.urihttp://vbs.rs/scripts/cobiss?command=DISPLAY&base=70036&RID=51956239
dc.description.abstractInteractions between particles play an important role in quantum degenerate gases. In fact, the system’s behavior is usually largely determined by the strength, range, and symmetry of the interactions, even if very weak. For more than two decades after the first experimental realization of a Bose-Einstein condensate (BEC) in 1995, investigations of ultracold atomic gases have mainly considered contact-type interactions, which model the short-range van der Waals interactions between the atoms in terms of a single parameter, the s-wave scattering length. However, some atomic or molecules species possess a magnetic or electric dipole moment and additionally interact among each other via the dipole-dipole interaction (DDI), which is long-ranged and anisotropic. Signatures of the DDI have been first observed in a BEC of chromium atoms in 2005. In the last several years, a new class of atoms from the lanthanide series, e.g., dysprosium and erbium, with stronger dipolar properties, have come into play. This permits a more full-fledged study of dipolar effects in BECs. Furthermore, ultracold molecules and highly excited Rydberg atoms are other promising examples for futures studies of systems where dipolar interaction will be even more dominant, but they still need experimental efforts to achieve the desired quantum regime. Whereas the weak DDI in a chromium BEC is well described with the Gross-Pitaevskii equation, stronger dipolar interactions certainly necessitate a beyond-mean-field description within a Bogoliubov theory. In parallel to research on bosons, cold fermions also trigger great interest because they are actually often found in nature, e.g., within the electron gas of metals, as neutrons of heavy stars, or as quarks in plasmas as constituent elements of composite particles. Contrary to Bose systems, quantum degeneracy in experiments is much more difficult to achieve in Fermi systems, since s-wave scattering is absent between identical fermions, due to the Pauli exclusion principle. It was first achieved in 1999 for alkali atoms using a technique based on the sympathetic cooling with a second spin state, another species, or a different isotope. For highly magnetic atoms, quantum degeneracy was achieved for dysprosium in 2012 using the standard sympathetic cooling technique, while in 2014 erbium was cooled deep into the degenerate regime using a direct evaporative cooling mediated by dipolar collisions. This direct cooling scheme ivallows producing very dense Fermi gas down to 10% of the Fermi temperature. Furthermore, a novel kind of strongly dipolar quantum gases became available in the last several years. These are weakly bound polar molecules produced from atoms with large magnetic dipole moments, such as erbium. Only very recently a quantum degenerate dipolar Fermi gas of potassium-rubidium molecules has been experimentally realized. Unlike previously considered magnetic systems, heteronuclear molecules such as potassium-rubidium possess large electric dipole moments. The next natural step is to polarize this system in a preferential direction by an external electric field, such that the DDI dominates the behavior of the system, which would open up the realm for experimental investigation of strong dipolar Fermi gases...sr
dc.description.abstractInterakcije izmedu ˇcestica igraju vaˇznu ulogu u razumevanju ponaˇsanja degeneri- - sanih kvantnih gasova, koje je u velikoj meri odredeno jaˇcinom, dometom i simetri- - jama interakcija, ˇcak i ako su veoma slabe. Tokom viˇse od dve decenije nakon prve eksperimentalne realizacije Boze-Ajnˇstajn kondenzatacije 1995. godine, istraˇzivanje ultrahladnih atomskih gasova je uglavnom bilo fokusirano na prouˇcavanje kontaktnih interakcija izmedu atoma, ˇsto je jednoparametarski model za kratkodometne van - der Valsove interakcije, koji kao parametar uzima u obzir samo duˇzinu rasejanja u simetriˇcnom (s) kanalu. Medutim, neke vrste atoma ili molekula poseduju magnetni - ili elektiˇcni dipolni moment, pa moramo da uzmemo u obzir i dipol-dipol interakcije (DDI) izmedu ˇcestica. DDI su dugodometne i anizotropne, i njihov uticaj je prvi put - eksperimentalno izmeren u kondenzovanom gasu atoma hroma 2005. godine. Nova klasa atoma iz grupe lantanoida, kao ˇsto su disprozijum i erbijum, sa jaˇcim dipolnim osobinama, postala je dostupna u poslednjih nekoliko godina. Ovo omogu´cava potpunije istraˇzivanje dipolnih efekata u Boze-Ajnˇstajn-kondenzovanim sistemima. Dalje, ultrahladni molekuli i visoko pobudeni Ridbergovi atomi predstavljaju druge mogu´ce - pravce za prouˇcavanje sistema u kojima ´ce dipolna interakcija biti joˇs znaˇcajnija, ali ovo zahteva dodatne eksperimentalne napore kako bi se dostigao ˇzeljeni kvantni reˇzim. Dok se slaba DDI izmedu atoma hroma u kondenzovanim sistemima moˇze dobro opisati - Gros-Pitaevski jednaˇcinom, prisustvo jake DDI zahteva uraˇcunavanje efekata koji nisu prisutni u teoriji srednjeg polja u Bogoljubovljevoj teoriji. Paralelno sa istraˇzivanjima bozona, hladni fermioni su takode izazvali veliko in- - teresovanje jer se ˇcesto sre´cu u prirodi, na primer u sistemima kao ˇsto je elektronski gas u metalu, u sistemima neutrona u masivnim zvezdama, ili kao kvarkovi koji ˇcine kvark-gluonsku plazmu u kompozitnim ˇcesticama. Za razliku od bozonskih sistema, postizanje kvantne degeneracije u eksperimentima je mnogo teˇze za fermionske sisteme, jer zbog Paulijevog principa iskluˇcenja nema rasejanja u s-kanalu za identiˇcne fermione. Kvantna degeneracija hladnih fermiona je ostvarena prvi put 1999. godine za alkalne atome koriˇs´cenjem tehnike zasnovane na simpatetiˇcnom hladenju pomo´cu - atoma u drugom spinskom stanju, druge vrste atoma, ili razliˇcitog izotopa. Kod atoma sa jakim magnetnim momentom, kvantna degeneracija je ostvarena tek 2012. godine viiza disprozijum, koriˇs´cenjem standardne tehnike simpatetiˇcnog hladenja, a 2014. go- - dine za erbijum, koji je ohladen duboko u degenerisani reˇzim koriˇs´cenjem direktnog - evaporativnog hladenja pomo´cu dipolnog rasejanja. Ova direktna tehnika hla - denja je - omogu´cila stvaranje veoma gustog Fermi gasa na oko 10% Fermi temperature. Pored toga, nova vrsta jako dipolnog kvantnog gasa je postala eksperimentalno dostupna u poslednjih nekoliko godina. U pitanju su slabo vezani polarni molekuli proizvedeni od atoma sa velikim magnetnim dipolnim momentima, kao ˇsto je erbijum. Tek proˇsle godine je eksperimentalno realizovan i kvantno-degenerisani dipolni Fermi gas molekula kalijum-rubidijuma. Za razliku od prethodno razmatranih magnetnih sistema, heteronuklearni molekuli kao ˇsto je kalijum-rubidijum poseduju jak elektriˇcni dipolni moment. Sledec´ci prirodni korak je polarizacija takvog sistema u ˇzeljenom pravcu pomo´cu spoljaˇsnjeg elektriˇcnog polja, tako da DDI dominira u ponaˇsanju sistema. Ovo bi otvorilo novo polje za eksperimentalno istraˇzivanje Fermi gasova sa jakom DDI...en
dc.formatapplication/pdf
dc.languageen
dc.publisherУниверзитет у Београду, Физички факултетsr
dc.relationinfo:eu-repo/grantAgreement/MESTD/Basic Research (BR or ON)/171017/RS//
dc.rightsopenAccessen
dc.sourceУниверзитет у Београдуsr
dc.subjectFermi gas, dipole-dipole interaction, Fermi surface, Hartree-Fock theorysr
dc.subjectFermi gas, dipol-dipol interakcija, Fermi povrˇsina, Hartri-Fok teorijaen
dc.titleQuantum kinetic theory for ultracold dipolar Fermi gasessr
dc.title.alternativeKvantna kinetička teorija za ultrahladne dipolne Fermi gasoveen
dc.typedoctoralThesis
dc.rights.licenseBY-NC-SA
dc.identifier.fulltexthttp://nardus.mpn.gov.rs/bitstream/id/25335/Disertacija.pdf
dc.identifier.fulltexthttp://nardus.mpn.gov.rs/bitstream/id/25336/IzvestajKomisije22515.pdf


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