While quantum computing has made great gains in recent years in terms of transistors and logic gates and reprogrammable chips, the technology still lacks one vital component: data transfer. This is a fundamental part of normal microprocessor operation; it involves the routing of information from one location to another. An international team of researchers has successfully trialled a "quantum data bus" that does just that, however, thanks to a technique called perfect state transfer.

The technique, which has been theorized for years but only now proven experimentally, involves moving one qubit, encoded in a single particle of light, to a (relatively) distant location without losing any quantum information. The researchers accomplished this with a one-dimensional lattice that they made from a series of 11 structures called waveguides. These are hollow tubes that they coupled together by injecting horizontally and vertically polarized laser light. The effect is akin to an optimized quantum tunneling.

They were able to transfer quantum information – preserving the encoded quantum state as the photonic qubit moved – across this array with an average fidelity of 97.1 percent.

Transferring quantum information between locations is essential to quantum processing of all kinds, as without it quantum processors could not communicate or store data in memory. The researchers believe this experimental showing of perfect state transfer of an entangled (photonic) qubit is a big breakthrough in the pursuit of quantum computing, though we should caution that even if this does prove to be a critical development it is but one of many steps still needed to reach that goal.

The researchers, who come from RMIT University, Politecnino di Milano, and the South University of Science and Technology of China, have demonstrated that the theory works. Now scientists need to work toward a more faithful and robust system for quantum state relocation that could stand up to the needs of functional quantum computing.

A paper describing the research was published in the journal Nature Communications.

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