Einstein termed quantum entanglement a spooky phenomenon, something that seems to go against the very basic law—nothing travels faster than light. An eminent group of Chinese scientists recently just shattered Einstein’s belief. They proved entanglement is a very real phenomenon and that it can be used for quantum communication. They achieved something unprecedented in the quantum world— quantum entanglement across three ground stations in China separated by more than 1200 km. Such distances have been unheard of so far, with the maximum achievable distance so far around 100 km. Among the three cities, Delingha, Ürümqi, and Lijiang, the distance between Delingha and Lijiang is 1203 kms.
Quantum entanglement is the phenomenon for transmitting encrypted information. This encrypted information lays the groundwork for building highly secure, unhackable quantum networks. So, the current achievement by scientists is highly significant and could well pave the way to build such quantum networks.
Why is Quantum Communication Highly Secure?
What makes quantum communication so secure? This is because only the entangled particles know the information being transmitted. Measurement of any one of the particle of the entangled pair results in immediate breakdown of the entanglement. Hacking such system means measuring the quantum state of a particle, which instantly destroys the entanglement. Accordingly, cryptography based on entanglement of quantum particles can help instantly detect any mala fide interception to the transmission. Conventional method of encrypting messages using a public-private key pair, but it’s prone to hacking. Quantum communication, on the other hand, provides exponentially high security because the keys themselves are encoded in the quantum states of the particles. The moment someone tries to eavesdrop, the entanglement breaks down, revealing an intrusion.
Ground-based vs. Space-based Quantum Communication
Ground-based quantum entanglement experiments are on for many years and require either the air or optic fiber as the transmission medium. With air, quantum particles collide with atoms and other particles quickly losing their entangled state. Therefore, transmissions distances are extremely short. Even when using fibre optic, the transmission distances don’t go beyond a couple of hundred kilometres. Consequently, repeaters must be used, but even they are not very practical, making the system extremely complex to build. This is because the repeaters must store the photons received from two distinct sources and entangle them without measuring anything. Therefore, the solution is to make the photons travel the maximum distance in empty space where they find little disturbance.
The Experiment
This successful quantum communication experiment was led by Professor Jian-Wei Pan of Hefei University in China. China had already started preparing for the experimenting by launching a satellite named Micius into low Earth orbit in 2016. Micius uses special crystals and lasers for generating entangled photons. The crystal and laser system on Micius can generate 6-million pairs of photons at any given time. However, the ground-based stations for which these photons are destined can detect only one pair out of these 6 million. All the other pairs lose their entanglement when traveling through the Earth’s atmosphere.
The satellite then transmitted the entangled photons to different ground stations spread across the three cities. The distance achieved in this experiment is almost ten times more than the previous record for entanglement. The ability of ground stations to receive photons is a major challenge in such communication. For this, they must dynamically track the satellite moving at a very fast pace and establish optical links with it.
This clearly shows how challenging it is to work with entangled particles. However, in spite of such low rate, Jian-Wei Pan, a Chinese physicist, is all praise for such a system. He says Micius’s performance is a trillion times better than the best optical fiber-based communication for quantum particles. China has plans to further launch more satellites for use in quantum communication.
China Takes the Lead
According to Nicolas Gisin, a physicist at the University of Geneva, China has taken the leadership in the field of quantum communication. China has shown the world that global quantum communication is definitely possible and is achievable in the time to come.
A number of researchers and institutes have been trying to build something similar. However, they have always faced shortage of funds. The success of Chinese scientists’ experiment might well prove to be a catalyst to garner more funding for such experiments. Some notable efforts are on at Canadian Space Agency, National University of Singapore, and University of Illinois. Scientists are also developing quantum communication protocols at Max Planck Institute for the Science of Light, Germany.
Building a Globally Secure Network
Quantum communication forms the core of the idea of a universal unhackable Internet. The very idea of a highly secure, virtually impenetrable Internet sounds exciting and opens doors to many future possibilities. The path to achieve such a quantum-communication-based network is a long one and requires immense hard work and investments. However, the success of Chinese scientists surely paves the way to such a secure global network.
