Distribution of high-dimensional orbital angular momentum entanglement over a 1 km few-mode fiber

Abstract

High-dimensional entanglement has demonstrated its potential for increasing channel capacity and resistance to noise in quantum information processing. However, distributing it is a challenging task, imposing severe restrictions on its application. Here we report the first distribution of three-dimensional orbital angular momentum (OAM) entanglement via a 1-km-long few-mode optical fiber. Using an actively stabilizing phase precompensation technique, we successfully transport one photon of a three-dimensional OAM entangled photon pair through the fiber. The distributed OAM entangled state still shows a fidelity up to 71% with respect to the three-dimensional maximally entangled state (MES). In addition, we certify that the high-dimensional quantum entanglement survives the transportation by violating a generalized Bell inequality, obtaining a violation of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mo>∼</mml:mo> <mml:mn>3</mml:mn> </mml:math> standard deviations from the classical limit with <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>3</mml:mn> </mml:msub> </mml:mrow> <mml:mo>=</mml:mo> <mml:mn>2.12</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.04</mml:mn> </mml:math> . The method we developed can be extended to a higher OAM dimension and larger distances in principle. Our results make a significant step towards future OAM-based high-dimensional long-distance quantum communication.