Toshiba Europe’s Cambridge Research Laboratory has broken the long distance record for quantum communication over optical fibers exceeding 600km in length.
This breakthrough should advance long distance quantum-secured information transfer between metropolitan areas and is expected to allow the ultrafast solution of complex optimization problems in the cloud, ultimately ushering in the much talked about ‘Quantum Internet’.
One of the most difficult technological challenges in building the quantum internet is on how to transmit quantum bits over long optical fibers.
This is important as small changes in the ambient conditions – such as temperature fluctuations – can cause the fibers to expand and contract.
This in turn scrambles the fragile qubits which are encoded as a phase delay of a weak optical pulse in the fiber.
Toshiba has now demonstrated a novel ‘dual band’ stabilization technique which sends two optical reference signals at different wavelengths, thereby minimizing the phase fluctuations on long fibers.
The first wavelength is used to cancel the rapidly varying fluctuations, while the second wavelength, at the same wavelength as the optical qubits, is used for fine adjustment of the phase.
Upon deploying these new techniques, Toshiba found that it was possible to hold the optical phase of a quantum signal constant to within a fraction of a wavelength, with a precision of 10s of nanometers – even after propagation through 100s of km of fiber.
The scientists also noticed that the fiber can expand and contract with temperature changes, scrambling the quantum information without cancelling these fluctuations in real time.
According to Toshiba, the first application for dual band stabilization will be for long distance Quantum Key Distribution (QKD).
As of now, commercial QKD systems are limited to around 100-200km of fiber.
By introducing the dual band stabilization technique, Toshiba has implemented Twin Field QKD on long fibers and demonstrated QKD over 600km.
Image and content: Toshiba Corporation via Eurekalert