Cesium Bose-Einstein condensates in confined geometries

Mežnaršič, Tadej (author), Jeglič, Peter (mentor), Žitko, Rok (comentor)

I present the first cold atom setup in Slovenia capable of producing a Bose-Einstein condenstate (BEC) of cesium. This thesis describes the experimental apparatus, the path to the BEC and two experiments in a quasi-one-dimensional trapping geometry. In the first experiment we investigated the formation of solitary matter-waves (solitons), which maintain their shape indefinitely inside the confining channel potential. This is the first experimental realization of solitons with cesium atoms. In addition to single solitons, soliton trains are formed inside the potential and train like structures outside the confining channel. Along with experiments the theory of solitons in the framework of Gross-Pitaevskii equation (GPE) is presented. In the second experiment we used the solitons as a source of matter-wave jets, which form when the condensate is subjected to periodic modulation of interatomic interaction. The jets are characterized with respect to the modulation amplitude and frequency as well as its duration. Conditions for the formation of jets in different velocity modes are explored with numerical simulations of GPE, resulting in a phase diagram for jet formation. The relatively rare incommensurate jets are confirmed experimentally. Finally, we show that jet number correlations are sub-Poissonian, indicating the possibility of quantum entanglement between the jets.

• Language: English
• Keywords: Bose-Einstein condensate, soliton, soliton train, Gross-Pitaevskii equation, matter-wave jets, Bose fireworks, sub-Poissonian correlations
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FMF - Faculty of Mathematics and Physics
• Year: 2022
• PID: 20.500.12556/RUL-135693
• COBISS.SI-ID: 102329091
• Publication date in RUL: 26.03.2022

MEŽNARŠIČ, Tadej, 2022, Cesium Bose-Einstein condensates in confined geometries [online]. Doctoral dissertation. [Accessed 14 April 2025]. Retrieved from: https://repozitorij.uni-lj.si/IzpisGradiva.php?lang=eng&id=135693

Secondary language

• Language: Slovenian
• Title: Prostorsko omejeni Bose-Einsteinovi kondenzati cezija

Abstract

Predstavljam prvi eksperiment s hladnimi atomi v Sloveniji. Opisujem eksperimentalno napravo, našo pot do Bose-Einsteinovega kondenzata cezija ter dva eksperimenta v kvazienodimenzionalni pasti. V prvem eksperimentu smo raziskali proces nastanka snovnega solitona, valovnega paketa, ki v potencialnem kanalu svojo obliko ohranja v nedogled. S tem smo kot prvi dokazali obstoj solitona s cezijevimi atomi. Poleg posameznih solitonov v kanalu lahko pride tudi do nastanka solitonskih vlakov, kjer so solitoni nanizani v vrsto. Temu podoben niz valovnih paketov pa nam je iz podolgovatega oblaka nepričakovano uspelo ustvariti tudi v odsotnosti potenciala. Predstavim tudi teorijo solitonov v okviru enačbe Grossa in Pitaevskega (GPE). V drugem eksperimentu solitone uporabimo kot začetno stanje za nastanek Bosejevih ognjemetov, izstrelitve paketov snovnih valov, ki so posledica periodične modulacije interakcije med atomi znotraj kondenzata. Ognjemete karakteriziramo v odvisnosti od frekvence, amplitude in dolžine modulacijskega pulza. Uspelo nam je opaziti tudi redke "zlate" ognjemete, katerih hitrost ni preprosto povezana z vzbujevalno frekvenco. Bolj podrobno pogoje za nastanek različnih hitrostnih komponent ognjemetov preučimo z uporabo numeričnih simulacij GPE, s pomočjo katerih sestavimo fazni diagram. Na koncu pokažemo še, da je število v paru nasprotnih ognjemetov subpoissonsko korelirano, kar nakazuje možnost kvante prepletenosti med izstreljenimi paketi atomov.

• Keywords: Bose-Einsteinov kondenzat, soliton, solitonski vlak, enačba Grossa in Pitaevskega, Bosejevi ognjemeti, subpoissonske korelacije