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VERSION:2.0
PRODID:Icfo
X-PUBLISHED-TTL:P1W
BEGIN:VEVENT
UID:69f27be27851e
DTSTART:20210408T090000Z
SEQUENCE:0
TRANSP:OPAQUE
LOCATION:ICFO Auditorium and Online (Teams)
SUMMARY:ICFO | MARIA AUXILIADORA PADRÓN BRITO
CLASS:PUBLIC
DESCRIPTION:Photons are good candidates for carrying quantum information be
 cause they are very stable particles: they interact weakly with the medium
  and barely with each other. However\, this has drawbacks when you want to
  process the information because\, in this case\, it is preferable to have
  photon-photon interactions. For example\, for applications in quantum rep
 eaters\, such interactions would allow deterministic Bell state measuremen
 ts\, increasing the entanglement distribution rate between two remote node
 s. Getting two photons to interact with each other efficiently requires ma
 pping them into a nonlinear medium at the single-photon level\, that is\, 
 a medium that reacts differently when it interacts with a single photon th
 an when it does with two. Such strong nonlinearity has been demonstrated w
 ith Rydberg atoms\, which are atoms excited to a state with a high princip
 al quantum number.\nIn this thesis we have performed nonlinear quantum opt
 ics experiments using an ensemble of cold Rydberg atoms\, where we have st
 udied the properties of the quantum light emitted by these atoms. First\, 
 we demonstrated nonlinearities at the single-photon level. To reach this s
 tage\, we made several improvements to the previous experimental setup ava
 ilable in the group\, of which the implementation of a dipole trap was esp
 ecially relevant. We evidence quantum nonlinearity by measuring photon ant
 ibunching for the transmitted light after interacting with the Rydberg sta
 te under electromagnetically induced transparency (EIT). We also showed th
 e generation of single photons on-demand after storing weak coherent state
 s of light pulses as collective Rydberg excitations. Then\, we studied the
  variation of the light statistic throughout the output pulse after propag
 ating through the medium as Rydberg polaritons\, which are superposition s
 tates of light and Rydberg excitations. We showed that the properties at t
 he beginning and the end of the pulse were different from those of the ste
 ady state. In particular\, the light detected after the input pulse was ab
 ruptly turned off gave much stronger suppression of two-photon events. The
 n\, we investigated how to exploit this effect to generate single photons 
 on demand. To do this\, we analyzed the quality of the single photons dete
 cted at the end of the pulse as a function of the detection probability an
 d compared the results with those obtained by storing the input pulse as c
 ollective Rydberg excitations. We showed that the photons were generated m
 ore efficiently when increasing the detection window at the cost of deteri
 orating the single photons statistics.\nFinally\, we investigated the indi
 stinguishability of the photons emitted by our Rydberg atomic ensemble\, a
  crucial property for using Rydberg atoms as nodes in quantum networks. We
  also compared the single photons generated after storage under EIT condit
 ions with those obtained using a two-photon Raman excitation to the Rydber
 g state. We measured the indistinguishability by making them interfere wit
 h weak coherent states of light in a Hong-Ou-Mandel experiment. And we sho
 wed that\, although we obtained better photon statistics under EIT conditi
 ons\, the indistinguishability from those obtained with Raman excitation w
 as significantly higher.
DTSTAMP:20260429T214506Z
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