Toshiba 600km quantum communications distribution breaks long distance record

The Cambridge Research Laboratory of Toshiba Europe announced a demonstration of quantum communications over optical fibres, reaching further than 600 kilometres in length, the furthest distance achieved by optical fibres in quantum communications.

The breakthrough marks a major step forward in the development of a future quantum internet, a global network of quantum computers connected by long distance quantum communication links that would allow ultrafast, cloud-based problem solving, improved secure communications and a more accurate global timing system.

Other breakthroughs in the field have been made, including the demonstration of long-distance teleportation of qubits of photons, with a fidelity of more than 90%.

Developing a solution to the transmission of quantum bits over long optical fibres has proven challenging in the past, with small changes to ambient conditions, such as temperature fluctuations, can cause the fibres to expand and contract, scrambling the encoded qubits.

Toshiba’s breakthrough was made possible by using a ‘dual band’ stabilisation technique, sending two optical reference signals at different wavelengths to minimise phase fluctuations on long fibres.

The first wavelength is used to cancel the fluctuations, with the second wavelength operating at the same wavelength as the optical qubits used for precise adjustment of the phase.

This method allowed Toshiba to hold the optical phase of a quantum signal constant to within a fraction of a wavelength, with a precision of 10s of nanometres even after travelling through hundreds of kilometres of fibre.

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