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UID:69d4b769d656d
DTSTART:20250929T083000Z
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TRANSP:OPAQUE
LOCATION:ICFO Auditorium and Online (Teams)
SUMMARY:ICFO | TERESA DIMITRA KARANIKOLAOU
CLASS:PUBLIC
DESCRIPTION:Cold atom platforms have become central to quantum technologies
  such as information processing\, simulation\, and metrology. Their versat
 ility and high degree of control make them especially powerful. A key brea
 kthrough in the field was the ability to trap individual atoms using light
 . Far-off-resonant optical dipole traps&mdash\;like optical tweezers and l
 attices&mdash\;enable precise positioning of atoms in diverse geometries\,
  from simple 2D arrays to complex 3D structures.\nAnother major advantage 
 of cold atoms is their ability to mediate interactions between photons\, w
 hich do not naturally interact in free space. Cold atomic ensembles act as
  a nonlinear medium\, enabling strong interactions even at the two-photon 
 level. Using collective atom-photon coupling and Rydberg-state excitations
 \, they allow for photon-photon gates and the creation of non-classical st
 ates of light. These two features&mdash\;strong optical nonlinearities and
  precise atomic positioning&mdash\;make cold atoms a leading platform for 
 quantum networks\, quantum simulations\, and studies of light-matter inter
 action.\nA phenomenon common to both platforms is photon scattering\, whic
 h can either be of an intended or unintended nature. Up until recently\, s
 imple theories of scattering were sufficient for the community. However\, 
 the advance of atomic platforms now requires more nuanced and sophisticate
 d theories to understand scattering and their consequences on applications
 . This constitutes the main theme of the thesis.\nIn the application of at
 om trapping\, in many practical situations atoms may experience state-depe
 ndent potentials. The potential mismatch can lead to excess heating and re
 duced elastic scattering of light\, as compared to well-known limits like 
 an atom in &ldquo\;magic-wavelength&rdquo\; traps or a trapped ion. In the
  first part of the thesis\, we develop a model to analyze these effects\, 
 which can have important consequences in quantum optics or in atom imaging
 .\nIn the second part of the thesis\, we investigate how Rydberg spin wave
 s decohere in the presence of light scattering\, within the context of Ryd
 berg Electromagnetically Induced Transparency (EIT). Within Rydberg EIT\, 
 an initial photon is stored as a coherent\, extended superposition across 
 atoms. This initial photon can strongly modify the propagation of subseque
 nt photons\, leading to large nonlinearities\, but the scattering of subse
 quent photons can reveal information about where the first photon was stor
 ed\, leading to decoherence of the initial superposition state. This in tu
 rn can lead to decreased utility or ability to retrieve the first photon. 
 Here\, we elucidate the nature of decoherence\, and in particular for the 
 first time we take fully into account the three-dimensional nature of the 
 ensemble and its multiple scattering of light. We find regimes in which mu
 ltiple scattering might offer additional protection from decoherence\, as 
 compared to previous simplified theories.\nOverall\, this thesis makes new
  advances in understanding the nature of microscopic atom-light interactio
 ns and scattering\, and connects this fundamental physics to key consequen
 ces in real-life applications.\n&nbsp\;\nMonday September 29\, 10:30h. ICF
 O Auditorium \nThesis Director: Prof. Dr. Darrick Chang
DTSTAMP:20260407T075105Z
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