Efficient distribution of high-dimensional entanglement through 11 km fiber

Abstract

High-dimensional entanglement enriches our understanding of entanglement and shows many advantages in quantum communications tasks, so its long-distance distribution is a key technology. Here, we use multicore fiber to distribute four-dimensional (4D) entanglement over 11 km. The observed fidelity is <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi>F</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0.921</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.001</mml:mn> </mml:math> , which is feasible for high-dimensional quantum networks. We observed the violation of high-dimensional Bell inequality ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mi>I</mml:mi> <mml:mn>4</mml:mn> </mml:msub> </mml:mrow> <mml:mo>=</mml:mo> <mml:mn>2.635</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.014</mml:mn> </mml:math> ) and steering inequality ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mi>S</mml:mi> <mml:mn>4</mml:mn> </mml:msub> </mml:mrow> <mml:mo>=</mml:mo> <mml:mn>1.900</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.003</mml:mn> </mml:math> ) for a 4D system over a distance of 11 km and finally demonstrated 4D quantum key distribution based on entanglement in proof of principle. Our work provides an experimental platform for high-dimensional quantum technologies and enables the intracity high-dimensional quantum network.