Quantum dot-based broadband optical antenna for efficient extraction of single photons in the telecom O-band
Jingzhong Yang, Cornelius Nawrath, Robert Keil, Raphael Joos, Xi Zhang, Bianca Höfer, Yan Chen, Michael Zopf, Michael Jetter, Simone Luca Portalupi, Fei Ding, Peter Michler, Oliver G. Schmidt
Abstract
Long-distance fiber-based quantum communication relies on efficient non-classical light sources operating at telecommunication wavelengths. Semiconductor quantum dots are promising candidates for on-demand generation of single photons and entangled photon pairs for such applications. However, their brightness is strongly limited due to total internal reflection at the semiconductor/vacuum interface. Here we overcome this limitation using a dielectric antenna structure. The non-classical light source consists of a gallium phosphide solid immersion lens in combination with a quantum dot nanomembrane emitting single photons in the telecom O-band. With this device, the photon extraction is strongly increased in a broad spectral range. A brightness of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mn>17</mml:mn> <mml:mspace width="thinmathspace"/> <mml:mi mathvariant="normal">%</mml:mi> </mml:math> (numerical aperture of 0.6) is obtained experimentally, with a single photon purity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msup> <mml:mi>g</mml:mi> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo stretchy="false">(</mml:mo> <mml:mn>2</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:msup> <mml:mo stretchy="false">(</mml:mo> <mml:mn>0</mml:mn> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:mn>0.049</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.02</mml:mn> </mml:math> at saturation power. This brings the practical implementation of quantum communication networks one step closer.