EDUG · Effects of disorder in ultra-cold gases
6РП — Действия „Мария Кюри“
- Период
- 2006-11-01 → 2008-10-31
- Финансиране от ЕС
- 158 218 €
- Участници
- 1
- Схема
- EIF
Линиите свързват координатора с партньорите. За проекти отпреди 2014 г. CORDIS не винаги дава точни координати. Тези точки са на ниво град или държава.
Накратко на български
Ултрастудените атомни газове се изследват в условия на случайни смущения, например при превръщането на двойки фермиони в молекули. Това помага да се разбере как примесите влияят върху стабилността на свръхтечностите и локализацията на частиците.
Кратко обяснение, генерирано от езиков модел по текста на CORDIS. Оригиналът е по-долу.
Резултати накратко
Final Activity Report Summary - EDUG (Effects of disorder in ultra-cold gases)
This project was devoted to the study of ultra-cold atomic gases subject to random potentials. We have considered both the case of bosonic and fermionic atoms. In the presence of attractive interactions fermionic atoms can bind in Cooper pairs and become superfluids. When the interaction strength is enhanced (by tuning the scattering length near a Feshbach resonance), these pairs progressively transform into artificial molecules following Bose statistics and can therefore undergo Bose-Einstein condensation. An important goal of my project was then to investigate how disorder affects superfluidity and condensation of pairs as the interaction strength is enhanced and molecules are formed. The main results of this study have been published in a first class international journal. There I showed that Fermi superfluids with resonant interactions are the most stable against disorder. Moreover, I explicitely showed that the superfluid order parameter is affected by impurities as the interaction strength increases, pointing out that Anderson's celebrated theorem is only valid for sufficiently weak interactions. The problem of disorder in interacting Bose gases is also extremely rich and interesting. A considerable effort has been devoted to build a theory describing the localisation of Bogoliubov excitations induced by the disorder. This allows me to systematically compute measurable correlations functions, which is my final goal. In the framework of an international collaboration, I have also obtained new exact results for the energy absorption spectrum of disordered one dimensional bosons in a periodically modulated optical lattice.
Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз
Цел на проекта
The project is devoted to the theoretical study of disordered ultra-cold gases. We focus on two problems:1. BOSE-EINSTEIN CONDENSATION NEAR RESONANT IMPURITIES: by tuning the atom-impurity scattering length near a Feshbach resonance, atoms can be trapped into a bound state localized around the impurity. We first solve (exactly) the problem of two interacting bosons in the presence of the impurity using Green functions. We then write an ansatz for the many-bosons condensate wavefunction and calculate the energy spectrum of elementary excitations. We determine the limiting number of bosons above which the condensate is unstable due to the repulsive boson-boson interaction and estimate the lifetime of the condensate against decay due to inelastic processes. Finally, we consider many impurities randomly distributed on an optical lattice. We derive an effective low-energy lattice Hamiltonian and we investigate the resulting quantum phase diagram numerically.2. DISORDER EFFECTS IN FERMI SUPERFLUIDS: starting from the Bogoliubov-De Gennes equations of BCS theory, we investigate the local properties of the gas near a single impurity. We calculate the energy spectrum of quasiparticles and the spatial profiles of the atoms density and the gap parameter. We then discuss the effects of a quenched disorder on the condensate fraction and super-fluid density of the gas across the BEC-BCS crossover. We discuss explicitly the most interesting case of tuning the fermion-impurity scattering length near a resonance. The formation of bound states fermion-impurity is detrimental to super-fluidity, as it breaks Cooper pairs. We generalise the Abrikosov and Gorkov theory for superconductors with paramagnetic impurities to this novel system. We calculate energy gap and super-fluid density as a function of impurity concentrations and scattering lengths. Finally we discuss methods to detect the predicted gapless super-fluid phase in trapped Fermi gases.
Оригинален текст от CORDIS (на английски).
Участници
- LABORATOIRE DE PHYSIQUE THEORIQUE ET MODELES STATISTIQUES · ORSAYКоординаторНиво градФранция
Връзки
Данни: CORDIS, © Европейски съюз