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Tesi etd-05102016-165834


Thesis type
Tesi di laurea magistrale
Author
CAPECCHI, DEBORAH
URN
etd-05102016-165834
Title
Experimental investigations of many-body and multi-level effects in cold Rydberg gases
Struttura
FISICA
Corso di studi
FISICA
Commissione
relatore Morsch, Oliver
Parole chiave
  • Rydberg atoms
  • many-body systems
  • Cold atoms
Data inizio appello
26/05/2016;
Consultabilità
completa
Riassunto analitico
Atoms in highly excited states, known as Rydberg atoms, have been proposed as a possi-<br>ble candidate to simulate many-body problems with cold atoms. While ground state atoms<br>interact weakly, in Rydberg atoms the high dipole moments enable strong interactions. To<br>take advantage of this peculiarity, we need a simple representation of Rydberg atoms, that<br>helps to separate single-particle dynamics from many-body behavior. Ideally, we would like to<br>associate Rydberg atoms with a two-level system considering only ground and excited state.<br>However not only many-body effects, which we are mainly interested in, modify the two level<br>picture by shifting the energy of the excited state, but also multi-level atomic structure mod-<br>ifies the model with the introduction of additional levels. In this thesis we investigate the<br>deviations from the simple two-level model arising in a sample of cold Rb atoms excited to<br>Rydberg state, due to many-body and multi-level effects.<br>Manybody effects discussed in this thesis focus mainly on van der Waals interaction that<br>may shift, broaden or split the Rydberg state. Such variations contain information on the<br>sample geometry and the atom motion. To probe them we use a de-excitation technique that<br>transfers atoms with a specific energy to a fast decaying level. The same technique also allows<br>us to observe the emergence of multi-level effects in Rydberg decay. Multilevel effects arise<br>from the interaction of a Rydberg state with the black body radiation of a room temperature<br>environment. That radiation couples the orginal Rydberg state to other Rydberg states that<br>are closely spaced in energy and spreads the initial population over a number of different<br>Rydberg states, each with its own properties.<br>By using de-excitation to selectively remove atoms from a given state we are able to separate<br>its population from that of other Rydberg levels and to observe its evolution over time. De-<br>excitation technique used to probe both effects is characterized within the thesis. Multilevel<br>effects arise also during excitation, the use of two-photon excitation introduces a virtual level<br>close to a real atomic level. The proximity of the virtual and the real level makes it probable<br>to populate the latter. We discuss the possibility to neglect population of the real level to<br>recover the two-level model. Our measurements show the limits of the two-level model in<br>excitation, decay and de-excitation of Rydberg atoms, and demonstrate the usefulness of a<br>new technique to probe strong interactions in Rydberg atoms.<br>
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