Summary: Researchers demonstrated that multiple quantum patterns of twisted light can be transmitted across a conventional fiber link that, paradoxically, supports only one pattern.
Original author and publication date: University of Witwatersrand – January 24, 2020
Futurizonte Editor’s Note: Even if the tool we use is onedimensional, we can have a multidimensional conversation at the quantum level. It seems to me there is a practical lesson to be learned there.
From the article:
New research done at the University of the Witwatersrand in Johannesburg, South Africa, and Huazhang University of Science and Technology in Wuhan, China, has exciting implications for secure data transfer across optical fibre networks. The team have demonstrated that multiple quantum patterns of twisted light can be transmitted across a conventional fibre link that, paradoxically, supports only one pattern. The implication is a new approach to realising a future quantum network, harnessing multiple dimensions of entangled quantum light.
Science Advances today, published online the research by a team led by Professor Andrew Forbes from the School of Physics at Wits University in collaboration with a team lead by Professor Jian Wang at HUST. In their paper titled: Multi-dimensional entanglement transport through single mode fiber, the researchers demonstrate a new paradigm for realising a future quantum network. The team showed that multiple patterns of light are accessible after a communication link of conventional optical fibre, that paradoxically can only support a single pattern. The team achieved this quantum trick by engineering entanglement in two degrees of freedom of light, polarisation and pattern, passing the polarised photon down the fibre and accessing the many patterns with the other photon.
“In essence, the research introduces the concept of communicating across legacy fibre networks with multi-dimensional entangled states, bringing together the benefits of existing quantum communication with polarised photons with that of high-dimension communication using patterns of light,” says Forbes.
A new twist, a new paradigm
Present communication systems are very fast, but not fundamentally secure. To make them secure researchers use the laws of Nature for encoding by exploiting the quirky properties of the quantum world, such as in the case of the use of Quantum Key Distribution (QKD) for secure communication.
“Quantum” here refers to the spooky action at a distance so abhorred by Einstein: quantum entanglement. In the last few decades, quantum entanglement has been extensively explored for a variety of quantum information protocols, notably making communication more secure through QKD. Using so-called “qubits” (2D quantum states) the information capacity is limited but it is easy to get such states across fibre links using polarisation as a degree of freedom for the encoding. The spatial pattern of light, its pattern, is another degree of freedom that has the benefit of high-dimensional encoding. There are many patterns to use, but unfortunately this requires custom fibre optical cable and so unsuitable to already existing networks. In the present work, the team have found a new way to balance these two extremes, by combining polarisation qubits with high-dimensional spatial modes to create multi-dimensional hybrid quantum states.