快猫短视频

A city-wide quantum communications network in Hefei, China, that has been running for almost three years is the largest demonstration to date of how a future quantum internet might work.

The network, created by Teng-Yun Chen at the University of Science and Technology of China (USTC) and his colleagues, uses commercial fibre optics hardware to connect 40听computers at government buildings, banks and universities that are clustered into three subnetworks, each separated by around 15 kilometres.

In a traditional computer network, data is sent in small packets that can be intercepted by anyone. With enough time and computing power, even encrypted messages can be cracked open. On the other hand, quantum key distribution offers the promise of completely secure encrypted communications by sending photons in particular quantum states. Any attempt to observe or copy a quantum state will alter it, thanks to the strange properties of quantum physics, making it impossible to eavesdrop on a quantum connection without raising the alarm.

The most robust way to build a quantum network is to have a link between each and every user, but this becomes prohibitively expensive for all but the smallest networks 鈥� imagine a version of the internet in which you needed a direct connection to every other computer. To get around this, the USTC team used smaller subnetworks and switches that can create routes between different users as needed, like a telephone operator patching wires together.

The network also includes three devices known as trusted relays, which are used to simplify the network architecture. These relays have a downside because they could, in theory, be used to intercept data being transmitted between two users. Another disadvantage is that the network only transmits at 49.5 kilobits per second 鈥� slower than the telephone modems used in the 1990s 鈥� and establishing a secure quantum link takes up to five minutes because of the precise calibration required to detect individual photons.

In their paper, the researchers say that their network has been operating for 31 months, and it can be connected to other similar set-ups via long-distance quantum links and satellite relays, paving the way for a global quantum network. The team wasn鈥檛 available for interview about the work when contacted by 快猫短视频.

at the University of Bristol, UK, says the experiment can be considered a large-scale demonstration of a first-generation quantum network. In a second-generation network 鈥� also referred to as the 鈥渜uantum internet鈥� 鈥� users would be able to share photons directly and avoid the need for trusted relays.

鈥淭hink of going from the telegraph to telephone, and then the internet,鈥� says Joshi. 鈥淚n terms of quantum communication, we have done the telegraph, point to point. Now we have the kind of telephone system where you have an operator sitting in front of a switch box, plugging connections in. We want to go on to something far more seamless in the future.鈥�

at the University of Cambridge says that the approach borrows architecture from classical communications and that this is the largest metropolitan quantum communications network yet demonstrated 鈥� even if it isn鈥檛 yet fast enough to be used for everyday use.

鈥淚t鈥檚 showing how people are starting to deploy things that are getting towards real-world applications,鈥� says Penty. 鈥淚 wouldn鈥檛 call this a real-world application yet, but it鈥檚 heading in that direction.鈥� 听

听