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UID:DSC-14284
DTSTART;TZID=Europe/Berlin:20180412T133000
SEQUENCE:1523518828
TRANSP:OPAQUE
DTEND;TZID=Europe/Berlin:20180412T143000
URL:https://www.dresden-science-calendar.de/calendar/de/detail/14284
LOCATION:IFW\, Helmholtzstraße 2001069 Dresden
SUMMARY:Keil: Advanced semiconductor entangled photon sources for quantum c
 ommunication applications
CLASS:PUBLIC
DESCRIPTION:Speaker: Robert Keil\nInstitute of Speaker: IFW Dresden\, Insti
 tut für Integrative Nanowissenschaften\nTopics:\nMaterialien\, Physik\n L
 ocation:\n  Name: IFW (B3E.26\, IIN)\n  Street: Helmholtzstraße 20\n  Cit
 y: 01069 Dresden\n  Phone: \n  Fax: \nDescription: Future quantum communic
 ation networks involve the exchange of information between separate nodes 
 using single photons [1]. These flying qubits suffer from transmission los
 ses due to absorption and decoherence\, demanding the development of new c
 oncepts to relay quantum states efficiently. Emitters of polarization-enta
 ngled photons play a key role in this regard\, enabling robust qubit trans
 fer using the so called quantum repeater scheme [2]. So far\, photons gene
 rated from spontaneous parametric down conversion [3] have been used to de
 monstrate such entanglement-based concepts. This process is characterized 
 by Poissonian statistics\, i.e. a tradeoff has to be made between source b
 rightness and multi-photon emission probability. This fundamentally limits
  its applicability for scalable networks.  Semiconductor quantum dots are 
 the most promising candidates for the deterministic generation of polariza
 tion-entangled photons. However\, for practical applications\, these sourc
 es have to fulfill a demanding set of requirements: High degree of entangl
 ement\, high coherence\, high brightness and precise wavelength control. D
 espite various studied material systems and architectures\, so far the inv
 estigated quantum dot species lack the ability to meet these specification
 s.  In this talk\, I present the progress in addressing these challenges b
 y improved quantum dot growth and device implementation. The fabrication o
 f ultra-symmetric and homogeneous quantum dots is demonstrated\, exhibitin
 g entanglement fidelities up to 0.91 and a yield of almost 100% entangled 
 photon emitters without any post-growth tuning [4]. The quantum dots show 
 unprecedented wavelength control and can be matched to the rubidium optica
 l transitions. In order to enhance the source brightness\, quantum dot con
 taining nano-membranes with a rear gold mirror have been attached to a GaP
  solid immersion lens\, leading to record high entangled photon pair extra
 ction rates [5]. Furthermore\, optimizations in the growth process led to 
 4-fold improved coherence times\, allowing the demonstration of two-photon
  interference between remote quantum dots as a core process of a quantum r
 epeater. In order to improve the long-term stability of this interference\
 , active frequency feedback was applied to the QDs\, using a rubidium-base
 d Faraday anomalous dispersion optical filter as frequency reference [6]. 
  In conclusion\, two ongoing projects towards an ideal entangled photon so
 urce are presented. The first work utilizes planar-ring cavities to achiev
 e Purcell-reduced radiative lifetimes. In the second approach\, quantum do
 ts are embedded in a PIN diode to suppress perturbations induced by trappe
 d charge carriers surrounding the quantum dot.  [1] H. J. Kimble\, Nature 
 453\, 1023-1030 (2008) [2] R. Jin et al.\, Sci. Rep. 5\, 9333 (2015) [3] Y
 . H. Shih et al.\, Phys. Rev. Lett. 61\, 2921 (1988) [4] R. Keil and M. Zo
 pf et al.\, Nat. Commun. 8\, 15501 (2017) [5] Y. Chen et al.\, under revie
 w at Nat. Commun. [6] M. Zopf and T. Macha et al.\, under review at Phys. 
 Rev. Lett.
DTSTAMP:20260523T154425Z
CREATED:20180410T075836Z
LAST-MODIFIED:20180412T074028Z
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