On the night of September 27, an extraordinary event that would have stunned hackers and cyber criminals across the world took place in the Gujarat capital of Gandhinagar.
That night, quantum signals carrying the key to unlock secret information was successfully passed through open air from Bhaskaracharya National Institute for Space Applications and Geo‑informatics (BISAG‑N) and IIT Gandhinagar, a distance of 5.56 km. A huge improvement from 2021, when the Indian Space Research Organisation (ISRO) demonstrated quantum communication over a distance of 300 metres.
The Union Ministry of Electronics & IT billed it “India’s First 5.56 km Free‑Space Quantum Key Distribution Link.”
This quantum mechanics application, which allows the security key to pass from one point to the other with absolute safety, has been made possible by the work of three physicists who won the Nobel Prize in Physics in 2022 for their experiments with entangled photons: French physicist Alain Aspect, American theoretical physicist John F Clauser and Austrian quantum physicist Anton Zeilinger.
In quantum mechanics, two or more particles, say photons, can exist in an entangled state, in a ’till death do us apart’ commitment. Even when separated, what happens in one will be quickly, like in a mirror, reflected in the other. In quantum physics terms, the quantum state of one will instantly correlate with the measurement of the other.
The great Albert Einstein, who theorised that nothing can travel faster than light, was highly sceptical of this instant change in one photon when something happens to its separated pair. He ridiculed it as “spooky action at a distance”. Aspect, Clauser and Zeilinger not just proved Einstein wrong but also exploited this instant synchronicity to develop secure communication.
This synchronisation of entangled quantum states, like in the case of starlings that fly in a synchronised fashion, is its biggest security cover. If a hacker or cybercriminal attempts to intercept a photon in transit, the very act will immediately change the property of the photon (wave function collapse, in physics jargon).
Meaning, to even observe is to scramble the nature of the photon. This in quantum physics is called the ‘No-Cloning Theorem’. A cyber criminal just cannot take a copy of the photon, as the very act alters its shape and alerts the owners. It is a kind of hacker’s curse. The moment he snatches gold, it not just turns into stone but also flashes ‘Hacker Fooled’ in vivid colours at the offices of both the sender and the recipient.
Quantum Key Distribution merely hands over the security key. With this key, whose measurements cannot be looted even by future supercomputers, standard symmetric encryption techniques can be used to encrypt and transmit actual data over normal classical networks like the internet.
If the Quantum Bit Error Rate (QBER) is below 11 per cent, it is a sign that no hacking has taken place. “The field trial, conducted on the night of September 27–28, established a secure quantum communication channel between BISAG‑N and IIT Gandhinagar. Using QNu Labs’ Pointing, Acquisition and Tracking system, the trial achieved a stable Quantum Bit Error Rate below 5 per cent,” an official release said.
Minor errors are attributed to weather conditions like fog or rain, atmospheric turbulence, and even daylight interference.
Quantum states can be transported through fibre optic channels like glass optical fibres, too. This suits ground-based networks connecting fixed locations like data centres, banks, and government offices over city-to-city distances. The problem is that the glass absorbs light and scatters it inside over long distances. Therefore, its range is limited to just a few hundred kilometres.
When communication is done through free space, satellites can be used to cover considerably larger distances.
