Advanced semiconductor entangled photon sources for quantum communication applications

Date

Apr 12, 2018

Time

1:30 PM - 2:30 PM

Speaker

Robert Keil

Affiliation

IFW Dresden, Institut für Integrative Nanowissenschaften

Language

en

Main Topic

Materialien

Other Topics

Materialien, Physik

Host

Kristina Krummer-Meier

Description

Future quantum communication networks involve the exchange of information between separate nodes using single photons [1]. These flying qubits suffer from transmission losses due to absorption and decoherence, demanding the development of new concepts to relay quantum states efficiently. Emitters of polarization-entangled photons play a key role in this regard, enabling robust qubit transfer using the so called quantum repeater scheme [2]. So far, photons generated from spontaneous parametric down conversion [3] have been used to demonstrate such entanglement-based concepts. This process is characterized by Poissonian statistics, i.e. a tradeoff has to be made between source brightness 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 polarization-entangled photons. However, for practical applications, these sources have to fulfill a demanding set of requirements: High degree of entanglement, high coherence, high brightness and precise wavelength control. Despite various studied material systems and architectures, so far the investigated quantum dot species lack the ability to meet these specifications. In this talk, I present the progress in addressing these challenges by improved quantum dot growth and device implementation. The fabrication of ultra-symmetric and homogeneous quantum dots is demonstrated, exhibiting 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 optical transitions. In order to enhance the source brightness, quantum dot containing nano-membranes with a rear gold mirror have been attached to a GaP solid immersion lens, leading to record high entangled photon pair extraction 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 repeater. In order to improve the long-term stability of this interference, active frequency feedback was applied to the QDs, using a rubidium-based Faraday anomalous dispersion optical filter as frequency reference [6]. In conclusion, two ongoing projects towards an ideal entangled photon source are presented. The first work utilizes planar-ring cavities to achieve Purcell-reduced radiative lifetimes. In the second approach, quantum dots are embedded in a PIN diode to suppress perturbations induced by trapped 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. Zopf et al., Nat. Commun. 8, 15501 (2017) [5] Y. Chen et al., under review at Nat. Commun. [6] M. Zopf and T. Macha et al., under review at Phys. Rev. Lett.

Links

• Seminars at the IFW

Last modified: Apr 12, 2018, 9:40:28 AM