Unscrambling entanglement through a complex medium

Photonic high-dimensional entanglement has recently emerged as a practical way to enhance the capacity of quantum information systems, as well as increase their robustness to noise. However, the transport and control of high dimensional quantum states of light remains a challenge due to the complexity of the channel, which encompasses effects like mode-mixing in multimode waveguides and free-space turbulence. In this work, we show six-dimensional spatial-mode entanglement distribution through a 2m long commercial multi-mode fibre with 84% fidelity. Contrary to classical techniques, we determine the complex transmission matrix of the fibre and reverse its effect on the correlations of the quantum state by only performing measurements after the photon has gone through the complex media. Even more, using a unique property of entangled states, the medium is rendered transparent to entanglement by carefully "scrambling" the photon that did not enter it, rather than the photon that did. These results are a significant step towards the controlled and efficient transport of high-dimensional entanglement, paving the way for practical implementations of long-distance quantum communications.

Link of the publication: Nature Physics

Contact author:

Mr. Suraj Goel (B.Tech graduating student, internship research work under the supervision of Prof. Mehul Malik, Heriot-Watt University Edinburgh)