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DEVELOPMENT OF THEORETICAL AND COMPUTATIONAL METHODS FOR FEWBODY PROCESSES IN ULTRACOLD QUANTUM GASES
 Date Issued:
 2006
 Abstract/Description:
 We are developing theoretical and computational methods to study two related threebody processes in ultracold quantum gases: threebody resonances and threebody recombination. Threebody recombination causes the ultracold gas to heat up and atoms to leave the trap where they are confined. Therefore, it is an undesirable effect in the process of forming ultracold quantum gases. Metastable threebody states (resonances) are formed in the ultracold gas. When decaying they also give additional kinetic energy to the gas, that leads to the heating too. In addition, a reliable method to obtain threebody resonances would be useful in a number of problems in other fields of physics, for example, in models of metastable nuclei or to study dissociative recombination of H3 +. Our project consists of employing computer modeling to develop a method to obtain threebody resonances. The method uses a novel twostep diagonalization approach to solve the threebody Schrödinger equation. The approach employs the SVD method of Tolstikhin et al. coupled with a complex absorbing potential. We tested this method on a model system of three identical bosons with nucleon mass and compared it to the results of a previous study. This model can be employed to understand the 3He nucleus . We found one threebody bound state and four resonances. We are also studying Efimov resonances using a 4Hebased model. In a system of identical spinless bosons, Efimov states are a series of loosely bound threebody states which begin to appear as the energy of the twobody bound state approaches zero . Although they were predicted 35 years ago, recent evidence of Efimov states found by Kraemer et al. in a gas of ultracold Cs atoms has sparked great interest by theorists and experimentalists. Efimov resonances are a kind of predissociated Efimov trimer. To search for Efimov resonances we tune the diatom interaction potential, V(r): V(r) → λV(r) as Esry et al. did . We calculated the first two values of λ for which there is a "condensation" (infinite number) of Efimov states. They are λEfimov1 = 0.9765 and λEfimov2 = 6.834. We performed calculations for λ = 2.4, but found no evidence of Efimov resonances. For future work we plan to work with λ ≈ 4 and λ ≈ λEfimov2 where we might see dwave and higher lwave Efimov resonances. There is also a manybody project that forms part of this thesis and consists of a direct diagonalization of the Bogolyubov Hamiltonian, which describes elementary excitations of a gas of bosons interacting through a pairwise interaction. We would like to reproduce the corresponding energy spectrum. So far we have performed several convergence tests, but have not observed the desired energy spectrum. We show preliminary results.
Title:  DEVELOPMENT OF THEORETICAL AND COMPUTATIONAL METHODS FOR FEWBODY PROCESSES IN ULTRACOLD QUANTUM GASES. 
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Name(s): 
Blandon, Juan, Author Kokoouline, Viatcheslav , Committee Chair University of Central Florida, Degree Grantor 

Type of Resource:  text  
Date Issued:  2006  
Publisher:  University of Central Florida  
Language(s):  English  
Abstract/Description:  We are developing theoretical and computational methods to study two related threebody processes in ultracold quantum gases: threebody resonances and threebody recombination. Threebody recombination causes the ultracold gas to heat up and atoms to leave the trap where they are confined. Therefore, it is an undesirable effect in the process of forming ultracold quantum gases. Metastable threebody states (resonances) are formed in the ultracold gas. When decaying they also give additional kinetic energy to the gas, that leads to the heating too. In addition, a reliable method to obtain threebody resonances would be useful in a number of problems in other fields of physics, for example, in models of metastable nuclei or to study dissociative recombination of H3 +. Our project consists of employing computer modeling to develop a method to obtain threebody resonances. The method uses a novel twostep diagonalization approach to solve the threebody Schrödinger equation. The approach employs the SVD method of Tolstikhin et al. coupled with a complex absorbing potential. We tested this method on a model system of three identical bosons with nucleon mass and compared it to the results of a previous study. This model can be employed to understand the 3He nucleus . We found one threebody bound state and four resonances. We are also studying Efimov resonances using a 4Hebased model. In a system of identical spinless bosons, Efimov states are a series of loosely bound threebody states which begin to appear as the energy of the twobody bound state approaches zero . Although they were predicted 35 years ago, recent evidence of Efimov states found by Kraemer et al. in a gas of ultracold Cs atoms has sparked great interest by theorists and experimentalists. Efimov resonances are a kind of predissociated Efimov trimer. To search for Efimov resonances we tune the diatom interaction potential, V(r): V(r) → λV(r) as Esry et al. did . We calculated the first two values of λ for which there is a "condensation" (infinite number) of Efimov states. They are λEfimov1 = 0.9765 and λEfimov2 = 6.834. We performed calculations for λ = 2.4, but found no evidence of Efimov resonances. For future work we plan to work with λ ≈ 4 and λ ≈ λEfimov2 where we might see dwave and higher lwave Efimov resonances. There is also a manybody project that forms part of this thesis and consists of a direct diagonalization of the Bogolyubov Hamiltonian, which describes elementary excitations of a gas of bosons interacting through a pairwise interaction. We would like to reproduce the corresponding energy spectrum. So far we have performed several convergence tests, but have not observed the desired energy spectrum. We show preliminary results.  
Identifier:  CFE0001320 (IID), ucf:47026 (fedora)  
Note(s): 
20060801 M.S. Sciences, Department of Physics Masters This record was generated from author submitted information. 

Subject(s): 
threebody resonances ultracold quantum gas fewbody processes manybody processes 

Persistent Link to This Record:  http://purl.flvc.org/ucf/fd/CFE0001320  
Restrictions on Access:  public  
Host Institution:  UCF 